> /p ^- CORNELL UNIVERSITY MEDICAL LIBRARY ITHACA. DIVISION. FROM SIMON HENRY GAGE, OnASS OB- 1877. Cornell University Library The original of tiiis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924084820426 THE SYDENHAM SOCIETY INSTITUTED MDCCCXLIU. LONDON MDCCCLIII. MANUAL iiMvVi' HUMAN HISTOLOGY. BY A. KOLLIKER, PR0FE9S0E OF ANATOMY AHD fHTSlOLOOT IN WURZBUEQ. TEANSLATED AND EDITED GEORGE BySK, F.R.S., and THOMAS HUXLEY, F.R.S. ME I. LONDON: PRINTED FOR THE SYDENHAM SOCIETY. MDCCCLIII. T PRINTED BY C, AND J. APr/ARD, BAHTHOLnMKW Cf.OSK, -cc AUTHOR'S PREFACE. Medicine has reached a pointy at which Microscopical '' Anatomy appears to constitute its foundation, quite as much as the Anatomy of the Organs and Systems ; and when a profound study of Physiology and Pathological Anatomy is impossible, without an accurate acquaintance also, with the most minute , structural conditions. ! It seems, therefore, to be the task of the cultivators of this branch of science, to communicate the results of their researches, not only to their fellow inquirers, and to those who have, in other ways, gone more deeply into medical science, but to all who are devoted to the study of Man in general, and especially to render them easily available by students and practitioners. The attainment of this object is sought, in the present work, by giving a view, as condensed as possible, of the relations of the elementary parts of the body, and of the more intiinate structure of the organs. In the execution of this plan, with the exception of some important, but still doubtful questions, all polemical disquisition is avoided, and the History of the Science also left altogether in the background ; whilst as constant vi AUTHOR'S PREFACE. reference a8~eo«l€l--i»~€iM3P''weyHb&'-ad«Mtted^has been made to Physiology and Pathological Anatomy, as well as to Com- parative Histology. For further information, the Author refers to more detailed Anatomical works, and particularly to his 'Microscopical Anatomy,' in which the data for all that is here only briefly expressed, will be found. WuBZBfRG; August 1st, 1852. TRANSLATORS' PREFACE. The Translators feel that an English edition of a book, which has justly taken so high a position as Professor KoUiker's 'Manual of Human Histology/ needs no lengthened intro- duction to the members of the Sydenham Society. In the rendering of the work they have endeavoured to follow faithfully the text of the 'Handbuch der G-ewebelehre/ with the occasional incorporation, however, of a few sentences from the larger 'Mikroskopische Anatomic,^ by the same Author, where it appeared to them that the more condensed style of the present work had rendered the sense less clear than was desirable. They have also added, in the shape of notes (distinguished by a smaller type), whatever comments of their own seemed to be called for. But the short time allowed by circumstances for the publication of the present volume (which includes the first half of the original), having prevented their making these notes so full, or so numerous, as might have been desired upon several subjects, and particularly on the general doctrine of the Cell, the Translators propose to viii TRANSLATOR'S PREFACE. add such additional Commentary as they may have to offer, in a " General Appendix" at the end of the work. No alteration has been made in the expression of the measurements, for which the Paris line, equal to about ith (00888138) of an English inch (and now very generally adopted on the continent), is taken as the \init; nor in the signs '" for 'of a line,' and " for 'of an inch,' the great con- venience of which will probably lead to their more general acceptance. London; August 1st, 1853. CONTENTS. INTRODUCTION. § 1. Historical Introduction .... § 2. Present position of the Science .... § 3. Aids to the Study (Literature, Microscope, Preparations) PAGE 1 3 GENERAL HISTOLOGY. I.— OF THE ELEMENTARY PARTS, pp. 9, 10. § 4. Simple and compound elementary parts § 5. Plastic fluid, fundamental substance 9 10 A. Simple Elementary Parts, pp. 1 1 — 46. (1) Elementary Granules, — vesicles, nuclei — §6 . . . . ,(2) Of the Cells:— § 7. Composition .... I 8. Form, chemical relations, nucleus, nucleolus . § 9. Cell-formation .... § 10. Free cell-formation .... §11. Endogenous cell-formation § 12. Multiplication of cells by division 5 13. Theory of cell-formation . § 14. Vital phenomena of cells, growth § 15. Processes in the interior of the cells — Absorption § 16. Excretive processes ... § 17. Contractility of the cells . § 18. Metamorphosis of the cells, kinds of cells B. Higher Elementary Parts, pp. 48 — 50. 11 14 15 19 20 22 28 30 34 37 44 45 46 §19. 48 CONTENTS. II.— OF THE TISSUES, ORGANS, AND SYSTEMS, pp. 50—106. § 20. Enumeration of them § 21. Epidermic tissue § 22. Cartilaginous tissue § 23. Elastic tissue . § 24. Connective tissue . § 25. Osseous tissue § 26. Tissue of the smooth muscles § 27. Tissue of the striped muscles § 28. Nerve-tissue § 29. Tissue of the true glands § 30. Tissue of the Wood-vascular PAGE 50 53 58 60 70 83 86 90 95 99 103 SPECIAL HISTOLOGY. OP THE EXTERNAL INTE&UMENT, pp. 106— 233. I OF THE SKIN IN THE MORE RESTRICTED SENSE, pp. 106—153. A. Cutis, Derma, pp. 106—130. § 31. Parts of the common integument . § 32. Subcutaneous cellular tissue . § 33. Parts of the corium, tactile papillae § 34. Connective tissue, elastic fibres, and muscles of the § 35. Fat-cells ..... § 36. Vessels of the Skin .... § 37. Nerves ..... § 38. Development of the Cutis § 39. Physiological remarks B. Cuticle, or Epidermis, pp. 131 — 153. § 40. Parts of the Epidermis § 41. Mucous layer . . § 42. Horny layer . . • . § 43. Colour of the Epidermis § 44. Thickness of the Epidermis § 45. Physical and Chemical relations § 46. Growth and regeneration . § 47. Development ..... 106 107 108 110 113 116 118 125 126 131 132 133 136 138 139 143 147 CONTENTS. XI II.— OF THE NAILS, pp. 153—168. PAGE § 48. Parts of the NaU . . . . . . .153 § 49. Structure of the Nail . . . . . . . 157 § 50. Kelation of the Nail to the epidermis .... 160 § 51. Growth of the Nails . . . . . . . 162 § 52. Development of the Nails . . . . . .166 III.— OF THE HAIRS, pp. 168—203. Of the Hairs in the more restricted sense. § 53. Parts of the Hair ....... 168 § 54. Disposition and size of the Hairs . . . . . 169 § 55. External peculiarities, and chemical composition of the Hairs . 170 § 56. Structure of the Hairs, cortical substance . . . .172 §57. Medullary substance . . , . . . . 176 § 58. Cuticular covering ...... 180 § 59. Hair-foUicles . . . . . . . . 183 §60. Hair-follicle in the more restricted sense . . . .183 § 61. Root-sheaths . . . . . . . . 185 § 62. Development of the Hair . . . . . .188 § 63. Shedding of the Hair . . . . . . 193 § 64. Physiological remarks ...... 197 IV.— OF THE CUTANEOUS GLANDS, pp. 203—233. A. Of the Sudoriparous Glands, pp. 203 — 215. § 65. Disposition . . . . . .203 § 66. Structure . . . . . . . . 204 § 67. More intimate structure of the glandular coil . . . 205 § 68. Secretion of the sudoriparous glands . . . . . 207 § 69. Sweat-ducts . . . . . . .210 § 70. Development of the sudoriparous glands . . . . 211 B. Of the Ceruminous Glands, pp. 216 — 220. § 71. Structure ........ 216 § 72. Secretion and development . . . . . . 218 C. Of the Sebaceous Glands, pp. 220—233. § 73. Structure, form, and disposition ..... 220 § 74. More intimate structure . . . . . . 224 § 75. Development ....... 225 X'l CONTENTS. 1 *»"*' OF THE MUSCULAR SYSTEM, pp. 233—289. § 76. Definition of it . § 77. Structure of the muscular fibres $ 78. The mode in which they are associated . § 79. Connection with other parts . § 80. Structure of the tendons . J 8]. Connection of the tendons with other parts . § 82. Accessory organs of the muscles and tendons § 83. Vessels of the muscles and accessory organs . § 84. Nerves of the muscles § 85. Chemical and physical relations of the muscles § 86. Development of the muscles and tendons . § 87. Physiological remarks PAGE 233 233 240 244 245 248 252 259 261 268 272 280 OF THE OSSEOUS SYSTEM, pp. 289—388. § 88. Definition, form, occurrence ..... 289 $ 89. Intimate structure of the osseous tissue . . . . 290 § 90. Matrix of bone . . . . . .294 $ 91. Lacunae and canaliculi . . . . . . 300 § 92. Periosteum ....... 307 § 93. Marrow . . . . . . . . 309 § 94. Articulations of the bones: {ji.) Synarthrosis . . . 311 § 95. (B.) Moveable articulation, Diarthrosis . . . . 320 i 96. Articular capsules ...... 324 § 97. Physical and chemical properties of the bones, and their accessory organs . . . . . . . . 329 § 98. Vessels of the bones, &c. . . . . . . 332 § 99. Nerves of the osseous system . . . . . . 334 § 100. Development of the bones ..... 338 § 101. Primordial cartilaginous skeleton . . . . . 339 § 102. Metamorphoses of the primordial cartilaginous skeleton . . 344 § 103. Changes in the ossifying cartilage . . . . . 348 $ 104. Ossification of the cartilage ..... 352 § 105. Elementary processes in the layers formed from the periosteum . 361 § 106. Bones, not primarily cartilaginous . . , . . 369 § 107. Growth of the secondary cranial bones .... 370 § 108. Vital phenomena in the mature bones . . . . 377 OF THE NERVOUS SYSTEM, pp. 382—498. § 109. Definition, division .... Elements of the Nervous System, pp. 382 — 406. §110. Nerve-tubes or fibres . . . . $111. Nerve-cells ..... 388 . 389 . 403 CONTENTS. xiu Central Nervous System, p. 406. § 112. Spinal cord ...... § 1 13. Conjectural course of the fibres in the spinal cord § 114. Medulla oblongata and Pons Varolii . $ 115. Cerebellum ..... §116. Ganglia of the cerebrum . . . . §117. Hemispheres of the cerebrum § 118. Membranes and vessels of the central nervous system PAGE . 406 . 418 . 422 . 430 . 434 . 439 . 447 Peripheral Nervous System, pp. 459—493. § 119. Spinal nerves ..... § 120. Structure of the spinal ganglia § 121. Further course of the spinal nerves § 122. Cerebral nerves .... § 123. Ganglionic nerves .... § 124. Main trunk of the ganglionic nerves $ 125. Peripheral distribution of the ganglionic nerves . § 126. Development of the elements of the nervous system § 127. Functions of the nervous system . 459 461 467 473 476 477 482 487 493 INTRODUCTION. r The doctrine of the elementary structure of Plants and Animals^ belongs to the last two centuries, originating with Marcellus Malpighi (1638-94), and Anton van Leeuwenhoek (1632-1733), at the period when the assistance of magnifying glasses, powerful, though of very simple form, was first ofiered to observers. The ultimate constituents in respect of form, of organisms, were unknown to antiquity and to the middle ages, for although Aristotle and Galen speak of the homogeneous and heterogeneous parts of the body (partes similares et dis- similares), and Fallopius (1523-62) defined still more exactly the idea of " Tissues," and even attempted to classify them, ('Tractatus quinque de partibus similaribus,' opera, tom. ii, Prancof. 1600), yet the minuter structures were completely hidden from these investigators. Brilliant as were the first efforts of young science under the guidance of these men and afterwards of a Ruysch, Swammerdam and others, yet they were not adequate to acquire a safe footing for it, since, on the one hand, the philosophers were far too little masters of microscopic investigation to strive at once, with clear insight, towards the true goal; while, on the other, the development of other branches of study, as of the grosser Anatomy, of Physiology, of Embryology and of Comparative Anatomy, claimed too large a share of their attention. It thus happened that, with the exception of a few to some extent important works I. 1 2 INTRODUCTION. (Fontana, Muys, Lieberkiihn, Hewson, Prochaska), Histology made no considerable progress during the whole of the 18th century, and acquired no importance greater than that due to a disjointed collection of isolated observations. It was in the year 1801 that it first acquired a rank co-equal with that of its sister anatomical sciences, by the genius of a man to whom indeed, Histology owes no great discoveries, but who under- stood, as no one before him had done, so to arrange existing materials and so to connect them with Physiology and Medicine, that for the future its independence was assured. In fact, Bichat's 'Anatomie Generale' (Paris, 1801), was the first attempt to treat Histology scientifically, and on this account merely, it constitutes an epoch; but besides this, its importance was still greater, inasmuch as the tissues were not merely clearly defined and fully and logically treated of, but full account was taken of their physiological functions and morbid alterations. To this great internal progress, the present century has added an ever-increasing perfection of the external aids of the microscope, and a steadily increasing zeal in the investigation of nature, so that it is not to be wondered at, that in its five decades, it has left far behind aU that was done in the century and a half of its earlier existence. In the last thirty years particularly, discoveries have so trodden upon one another's heels, that it must be considered truly fortunate that a bond of connection has arisen, and that Microscopical Anatomy has thus escaped the danger of becoming, as in earlier days, lost in minutiae. In the year 1838, in fact, the demonstration by Dr. Th. Schwann, of the originally perfectly identical cellular composition of all animal organisms, and of the origin of their higher structures from these elements, afi'orded the appropriate conception which united all previous obser- vations, and aflPorded a clue for further investigations. If Bichat founded histology more theoretically by constructing a system and carrying it out logically, Schwann has, by his inves- tigations, aflForded a basis of fact, and has thus won the second laurels in this field. What has been done in this science since Schwann, has been indeed of great importance to physiology and medicine, and in part of great value in a purely scientific point of view, inasmuch as a great deal which Schwann only indicated, or sliortly adverted to, as the genesis of the cell, the INTRODUCTION. 3 import of the nucleus, the development of the higher tissues, their chemical relations, &c., has received a further development; but all this has not amounted to a step so greatly in advance as to constitute a new epoch. If, without pretensions to prescience, it be permitted to speak of the future, this con- dition of histology will last as long as no essential advance is made towards penetrating more deeply into organic structure, and becoming acquainted with those elements of which that which we at present hold to be simple, is composed. If it be possible that the molecules which constitute cell-membranes, muscular fibrils, axile fibre of nerves, &c., should be discovered, and the laws of their apposition, and of the alterations which they undergo in the course of the origin, the growth, and the i activity of the present so-called elementary parts, should be made out, then a new era will commence for Histology, and the discoverer of the law of cell genesis, or of a molecular I theory, will be as much or more celebrated than the originator of the doctrine of the composition of all animal tissues out of cells. § 2. In characterising the present position of Histology and of its objects, we must by no means forget that, properly speaking, it considers only one of the three aspects which the elementary parts present to observation, namely, their form. Microscopical ' anatomy is concerned with the understanding of the micro- scopic forms, and with the laws of their structure and deve- lopment, not with any general doctrine of the elementary parts. Composition and function are only involved, so far as they relate to the origin of forms and to their variety. Whatever else respecting the activity of the perfect elements and their chemical relations is to be found in Histology, is there either on practical grounds in order to give some useful application of the morphological conditions, or to complete them ; or from its intimate alliance with the subject, it is added only because physiology proper does not afl'ord a due place for the functions of the elementary parts. If Histology is to attain the rank of a science, its first need is to have as broad and certain an objective basis as possible. To this end, the minuter structural characters of animal organisms 4 INTRODUCTION. are to be examined on all sides and not only in fiilly-fonned structures, but in aU the earlier periods from their first develop- ment. When the morphojogical elements have been perfectly made out, the next object is to discover the laws according to which they arise, wherein one must not fail to have regard also to their relations of composition and function. In dis- covering these laws, here as in the experimental sciences generally, continual observation separates more and more, among the collective mass of scattered facts and observations, the occasional from the constant, the accidental from the essential, till at last a series of more and more general ex- pressions of the facts arises, — from which, in the end, mathe- matical expressions or formulae proceed, and thus the laws are enunciated. If we inquire how far Histology has satisfied these require- ments, and what ai-e its prospects in the immediate future, the answer must be a modest one. Not only does it not possess a single law, but the materials at hand from which such should be deduced, are as yet relatively so scanty, that not even any considerable number of general propositions appear well founded. Not to speak of a complete knowledge of the minuter structure of animals in general, we are not acquainted with the structure of a single creature throughout, not even of man, although he has been so frequently the object of investi- gation, — and therefore it has hitherto been impossible to bring the science essentially any nearer its goal. It would, however, be unjust to overlook and depreciate what we do possess ; and it may at any rate be said, that we have acquired a rich store of facts and a few more trustworthy general propositions. To indicate only the more important of the former, it may be mentioned, that we have a very sufficient acquaintance with the perfect elementary parts of the higher animals and that we also understand their development, with the exception of the elastic tissue, and of the elements of the teeth and bones. The mode in which these are united into organs has been less examined, yet on this head also, much has been added of late, especially in man, whose individual organs with the exception of the nervous system, the higher organs of sense and a few glands (the liver, blood-vascular glands), have been almost exhaustively investigated. If the like progress continue to INTRODUCTION. 5 be made, the structure of the human body will in a few years be so clearly made out, that, except perhaps in the nervous system, nothing more of importance will remain to be done with our present modes of investigation. With comparative ^ Histology it is otherwise; hardly commenced, not years but i decades will be needed to carry out the necessary investigations. Whoever will do good work in this field must, by monographs of typical forms embracing their whole structure from the earliest periods of development,^ obtain a general view of all the divisions of the animal kingdom, and then, by the methods above described, strive to develop their laws. As regards the general propositions of Histology, the science has made no important progress since Schwann, however much has been attained by the confirmation of the broad outlines of his doctrines. The position that all the higher animals at one time consist wholly of cells and develop from these their higher elementary parts, stands firm, though it must not be understood as if cells, or their derivatives, were the sole possible or existing elements of animals. In the same way, Schwann's conception of the genesis of cells, though con- siderably modified and extended, has not been essentially changed, since the cell nucleus still remains as the principal factor of cell development and of cell multiplication. Least advance has been made in the laws which regulate the origin of cells and of the higher elements, and our acquaintance with the elementary processes which take place during the formation of organs must be regarded as very slight. Yet the right track in clearing up these points has been entered upon; and a logical investigation of the chemical relations of the elementary parts and of their molecular forces, after the manner of Donders, Dubois, Ludwig, and others, combined with a more profound microscopical examination of them, such as has already taken place with regard to the muscles and nerves, — further, a his- tological treatment of embryology, such as has been attempted by Reichert, Vogt and myself, will assuredly raise the veil, and bring us, step by step, nearer to the desired though perhaps never to be reached, end. [' See a very praiseworthy monograph of this kind by Leydig, Beitrage zur Mikroskopischen Anatomie und Entwickelungs-geschichte der Rochenu. Haie, 1852- (Microscopic Anatomy and Development of the Rays and Sharks.) — Eds.J 6 INTRODUCTION. §3. The aids in studying histology may here be best shortly adverted to. With respect to the literature of the subjectj the more important monographic works are cited under their ap- propriate section^ and here only those large independent works will be noticedj in which further instruction is to be found. It is right to head the list with Schwann's ' Mikroskopische Untersuchimgen iiber die Uebereinstimmung in der Struktur und dem Wachsthum der Thiere und Pflanzen' (Berlin, 1839),' abstracted in Froriep's ' Neue Notizen' (1838), as the most fitting introduction to Histology. Beside this, we may name X.Bichat, 'Anatomie Generale,' Tom. iv (Paris, 1801); E. H. Weber, ' Handbuch der Anatomie des Menschen von Hilde- brandt,' Bd. 1, 'AUgemeine Anatomie' (Braunschweig, 1830), a work distinguished in its day, and even now indispensably necessary, as a store of old literature, [or Ed. 4 (Stuttgart, 1833)] ; Brun's ' Lehrbuch der Allgemeinen Anatomie des Menschen' (Braunschweig, 1841), very clear, concise and good; Henle, 'Allgemeine Anatomie' (Leipzig, 1841), containing a classical account of Histology in the year 1840, many original statements, and physiological, pathological, and historical re- marks; G. Valentin, article 'Gewebe,' in R.Wagner's 'Hand- worterbuch d. Physiologie,' Bd. i (1843); R. B. Todd and W. Bowman, ' The Physiological Anatomy and Physiology of Man,' Parts i, ii (London, 1845-47), mostly based upon original observations, very comprehensive and good, [also Parts iii, iv (1847-52)] ; Bendz, 'Haandbog i den almindelige Anatomie* (Kiobenhavn, 1846-47), with industriously collected historical data; A. Kolliker, 'Mikroskopische Anatomie oder Gewebelehre . des Menschen, Band II, Specielle Gewebelehre, 1. Halfte. u. 2. Halfte, 1. Abtheilung' (Leipzig, 1850-52), containing an expo- sition, as complete as possible, of the minute structure of the organs and systems of man. With these are to be compared the yearly Reports of Henle, in Cannstatt's ' Jahresbericht,' and those of Reichert, in Miiller's 'Archiv,' in the latter of which, more objective views and an earlier appearance would be desirable. Useful figures are found in all the works above cited, with ' Translated for the Sydenham Society, 1847. INTRODUCTION. 7 the exception of those of Bichat, Weber, and Bruns ; further- morej the figures of injections in Berres' 'Anatomic der Mikroskopischen Gebilde des menschlichen Korpers/ Heft 1-12 (Wien, 1836-42), are for the most part excellent, as are the representations of tissues in R. Wagner's 'Icones Physiologicse,' second edition, by A. Ecker. Those of Langenbeck, ' Mikro- skopisch-anatomische Abbildungen/ Lief. 1-4, (Gottingen, 1846-51) ; of A. H. Hassall, 'The Microscopic Anatomy of the Human Body" (London, 1846-49) ; and Mandl, ' Anatomie Microscopique' (Paris, 1838-48), are middling; while, on the other hand, those given by Quekett, ' Catalogue of the Histo- logical Series in the Museum of the Royal College of Surgeons of England^ (London, 1850), are admirable. As regards Microscopes, I may express my opinion that of the more easily accessible, those of Plossl, Oberhauser and Schick, take the first rank. In Italy Amici, in England Ross, Powell and others, produce instruments quite equal to the above, but out of the question for Germany; among small, cheap, but not particularly useful instruments for students and physicians, for 115 to 150 francs, George Oberhauser (Rue Dauphine, 19, Paris,) furnishes the best. The much-famed instruments of Nachet are good, but inferior to those of Oberhauser ; on the other hand, the small ones of Schick for 40 thalers, and those of Plossl for 70 to 100 Fl., would be very serviceable if these artists were as productive as Oberhauser. For the use of the microscope I refer to J. Vogel, ' Anleitung zum Gebrauche des Mikroskops' (Leipzig, 1841) ; H. von Mohl, ' Mikrographie' (Tiibingen, 1846); Harting, 'Het Mi- kroskoop deszelfs gebruik, geschiedenis en tegenwoordige toestand' (Utrecht, 1848-50), 3 Theile; Purkinje, article 'Mikroskop,' in Wagner's 'Handworterbuch der Physiologic,' Bd. 2, 1844; in which works, as well as in that of Quekett, 'A Practical Treatise on the Use of the Microscope' (London, 1848, translated by Hartmann, Weimar, 1850, [also Ed. 2, London, 1852)] ; and Robin, 'Du Microscope et des Injections dans leurs applications k 1' Anatomie et h, la Pathologic' (Paris, 1848), the preparation of microscopical objects is in part very elaborately treated of. A collection of microscopical preparations is indispensably necessary for a more exact study of Histology, especially 8 INTRODUCTION. sections of bones and teeth and injections. Every one may with a little trouble, form a moderate collection for himself, hints towards which he will find in the paragraphs standing at the end of each section of the special part, as well as in the works just cited. Microscopical preparations may also be ex- changed with or purchased of Hyrtl, in Vienna ; Dr. Oschatz, in Berlin j Topping, Smith and Beck, Hett and others, in London j and also in Paris. The largest private and public collections of microscopical preparations exist in Vienna, with Hyrtl (injections) ; in Utrecht, with Harting and Schroder van der Kolk (injections, sections, muscles, nerves) j in London, in the College of Surgeons (animal and vegetable tissues of all kinds) ; with Tomes (sections of bones and teeth) ; and with Carpenter (hard tissues of the lower animals). THE GENERAL ANATOMY OF THE TISSUES. I.— OF THE ELEMENTARY PARTS. §4. If the solid and fluid constituents of the human body be examined with the aid of strong magnifying powers, it appears at once that the smallest parts which they exhibit to the naked eye, as granules, fibres, tubes, membranes, &c., are not the ultimate elements in respect of form, but on the contrary, that all, in conjunction with an universally distributed, fluid, semifluid or even solid, homogeneous, uniting substance, contain minute particles which diflfer in different organs but in the same organs have always a similar appearance. There are various kinds of these so-called elementary parts, simple and compound. The simplest are quite homogeneous, without any trace of their being composed of heterogeneous portions and are nearly allied to the inorganic forms, the crystalline granules and crystals, which also occur in the animal organism. Others already show that they have sufiered a difl'erentiation into an investment and determinate, though homogeneous contents : in others again, the contents present difierences. The most important among all these forms, which may be comprehended under the general title of "simple elementary parts," are the cells, which not only form the starting-point of every animal and vegetable organism, but also, either as cells or after having undergone manifold metamorphoses, make up the body of the perfect animal, and in the simplest animal and vegetable formations (unicellular animals and plants), eveh enjoy an independent existence. Compared with cells, all other simple elementary parts have quite a subordinate 10 GENERAL ANATOMY OF THE TISSUES. importancej so far as their direct participation in the formation of the tissues and organs is concerned; while, from their being almost all contained in the interior of cells and from their being concerned in many and most important ways in the vital processes of these cells, their importance in other respects is very great. The simple elementary parts, which at first wholly comprise the commencing animal (or plant), often unite in the course of development in such a manner that they lose their inde- pendence and cease to exist as isolated elements. In this manner compound forms arise, each of which answers geneti- cally to a whole series of simple ones and which may most fittingly be called the " higher elementary parts." Such a coalescence has hitherto been observed with certainty only in cells, and from these most of the tubular and fibrous elements of the body are produced. § 5. Formative and nutritive fluid — Interstitial substance or matrix. — While in plants the elementary parts in by far the majority of cases, unite directly with one another, in animals there is a very wide difference ; a peculiar interstitial substance which combines them, and is ultimately derived from the blood, is always in a lower or more distant relation therewith. If this take a direct share in the formation of the elementary parts it is called "formative fluid," Cytoblastema (Schleiden), from KVTOQ, a vesicle, and fSXaaTrifia, germ substance ; if it be ^ present for their maintenance, it is called "nutritive fluid;" if it have nothing to do with either the one or the other of these functions, it is called the matrix or connecting substance. The cytoblastema is usually quite fluid, as in the blood, in the' chyle, in many glandular secretions, in the contents of glan- dular follicles and in many embryonic organs; more rarely, viscid and like mucus, as in the gelatinous cellular tissue of embryos {vide infra), still more rarely solid, as the blastema from which the villi of the chorion arise and grow. The " nutritive fluid " takes the place of the formative fluid in all perfect organs; and except when it is contained in special canals and cavities, as in bones, teeth and perhaps in some cellular organs, is present in so small a quantity that it cannot ELEMENTARY GRANULES. 11 be directly observed. A matrix lastly, is found in cartilages and bones as a solid, homogeneous, granular, or even fibrous substance connecting the cellular elements and for the most part arising from the blood, independently of them, [The occurrence of a solid blastema, growing independently, in the villi of the chorion and of a solid matrix deposited directly out of the blood, demonstrates that all parts of the body are not, as Schwann was disposed to believe, without ex- ception developed from cells or in dependence upon cells. A few more recent authors, as Reichert, Bonders, and Virchow, also consider that the connective tissue, excepting its elastic element, is to be reckoned among those tissues which are not at all, or not wholly, derived from cells ; but, as we shall see below, incorrectly. On the other hand, it is certain that in pathological formations such masses very frequently occur, fibrinous exudations becoming changed in great measure, with- out previous organisation, i. e. cell formation, into permanent tissues.] ' A. SIMPLE ELEMENTARY PARTS. I.— ELEMENTARY GRANULES, ELEMENTARY VESICLES, NUCLEL §6. In almost all animal fluids, whether contained in canals, or inclosed in cells, as well as in many more solid tissues, there are found and often in immense quantities, roundish corpuscles of very small, hardly measurable dimensions. Henle has called them elementary granules, and has expressed the opinion that they are vesicular. This, however, is not always true, since it is demonstrable that many of these corpuscles possess no in- vestment. Such is the case with the fatty particles which occur in many cells and glandular secretions, with the granules of [' The Enamel and the Dentine of the teeth, and the so-called Cuticle of the hair, (see §§ on Hair and Teeth, and ' Quarterly Journal of Microscopical Science' for April, 1853,) must certainly be regarded as structures which are not derived directly from the metamorphosis of cells. We are inclined also to believe, that the opinion of Reichert, Donders and Virchow, as to the nature of the connective tissue, deserves much more attention than Professor KoUiker seems disposed to bestow on it. See §§ on Connective and Elastic Tissues, and General Appendix. — Eds.] 12 GENERAL ANATOMY OF THE TISSUES. the black pigment of the eye and of other coloured cells, the granular precipitates of biliary colouring matter, of dififerent salts in the kidneys and in the urine; lastly, the protein granules (albuminous granules) which are found free in certain portions of the grey substance of the central nervous system and of the retina. Among pathological but very common formations, we must enumerate here amorphous deposits, the colloid granules in the thyroid and elsewhere, and the corpuscula amylacea of the central, nervous system, although these sometimes attain a very considerable size. All these granules want the properties observed in the higher elementary parts, such as endogenous growth, multiplication, assimilation, and excretion, and so far incline towards the purely inorganic forms — crystals ; which are also found, though less commonly, in the organism, as for example in the spleen, in the lungs (black columns), in the ear, in the cells of the prseputial glands of the rat, in the blood-corpuscles of the dog and of fishes, in the fat-cells of man, and in the cells of the chorion of the embryo of sheep. Elementary vesicles also occur very frequently, and are for the most part allied, physiologically, with the elementary granules, since, once formed they do not increase, and neither multiply by division nor by endogenous development. The milk-globules may with tolerable certainty be arranged among these; at first included within the -cells of the nascent milk, they are subsequently found free, in enormous numbers, in the perfect secretion and, as Henle first stated, consist of the fatty matter of the milk, with an investment of casein. The immeasurably small molecules of the chyle and of the blood, are also, according to H. Miiller's investigation, fat globules with a protein envelope, and similar vesicles may be found in most other fluids containing fat and albumen in abundance. In fact, since the discovery of Ascherson (Miiller's 'Archiv,' 1840, p. 49), that whenever fluid fat and fluid albumen are shaken together, the fat globules which are formed always become surrounded by an albuminous coat, it is more than pro- bable that whenever, in the body, fat and albumen in the fluid condition come into contact, similar vesicles are produced. A peculiar class of elementary vesicles is formed by the elements which occur in the yelk of certain animals. We are ELEMENTARY VESICLES, AND NUCLEI. 13 best acquainted with them in the yelk of the hen's egg,^ in whose proper yelk-substance and yelk-cavity the globules which have been so long known are all vesicular, but have not the nature of cells. The membranes of these yelk-vesicles are excessively delicate and consist of a protein compound; the contents are fluid albumen, and, in the globules of the yelk-cavity, there is usually a large parietal fat globule, while in the others there are many smaller and larger ones. The development of these vesicles proceeds, in all probability, from the fat globules as in other elementary vesicles, from which, however, they are distinguished by the fact that they distinctly possess the power of growth, during which their contents undergo metamorphosis, since in many the number of fat globules increases with age. Similar vesicles exist, also/ in the yelk of fishes, Crustacea and spiders, and here, as in birds, they have only a temporary importance, since they are not directly applied to the formation of the embryo, but only serve to nourish it. Lastly, free nuclei occur in many localities, either tempo- rarily, where cells are formed immediately round nuclei, as in the chyle, the blood-vascular glands, the Peyerian patches ; or permanently, as proper elements of the tissue, in the wall of the thymus vesicles, in the rust-coloured layer of the cerebellum, and in the granular layer of the retina.^ [Von Wittich (' De Hymenogonia albuminis.' Regimontanii. 1850), has lately given some information upon the formation of the so-called Aschersonian vesicles. According to Wittich, whenever oil and albumen come in contact, a portion of the oil is saponified by uniting with the alkali of the layer of albumen in contact with it, and this layer being thus rendered insoluble by the deprivation of its alkali becomes precipitated, and thus forms the Aschersonian so-called haptogen membrane. According to this explanation the process would be purely [' It is, however, by no means certain that the yelk-corpuscles of the hen's egg are elementary granules. According to Dr. H. Meckel (Die Bildung der fur partielle Furchung bestimmten Eier der Vogel, &c., Siebold and Kcilliker's 'Zeitschrift,' 1852), they are altered cells. — Eds.] [' The blood corpuscles of man and the mammaUa should be added to this list. See Wharton Jones, 'Phil. Transactions,' 1846.— Eds.] 14 GENERAL ANATOMY OF THE TISSUES. chemical and not physical, and still less vital. In opposition to this view, however, Harting ('Ned. Lane' Sept. 1851), observed, not long ago, the formation of pseudo-cells by the agi- tation of albumen with mercury, in which case the albumen must be solidified, in the same way as by the mere shaking with water or otherwise, (Melsens, in 'Bull, de I'Acad. deBelgique,' 1850, Harting, &c.). Again, if by the bringing together of albumen and chloroform, serum-casein and fat,chondrinand chloroform, — albuminous, casein, and «chondrin membranes are formed, as Panum observed (see in part, 'Archiv f. Path. Anatomie,' iv, 2), it can hai'dly be permissible to assume any chemical action.] II.— OF THE CELLS. § 7. The cells, cellulce, called also elementary cells, or nucleated cells, are perfectly closed vesicles of O'OOS — O'Ol'" in mean diameter, in which we may dis- tinguish a special investment, the cell membrane, and contents. The latter are always composed of a fluid, containing formed particles of various kinds, and a peculiar rounded body, the cell-nucleus, which again con- tains in its interior a fluid and a still smaller corpuscle, the nucleolus. These cells, which must be considered to be endowed with peculiar vital powers, and to be capable of absorption and assimilation, of growth and of multiplication, not only at the earliest period, entirely compose the body of the higher and that of most of the lower animals, but almost wholly generate the higher elementary parts of the fully-developed body. In fact, even in adult animals, we find in very many places that the elements are simply in the condition of cells, and that as such they take a more or less marked share in the performance of the organic functions. Fig. 1. Nerve-cells of the Thalamus opticus of man, — three of them having their processes torn off. x 350. CELLS. 15 [It is not yet quite decided what part cells play in the composition of the simplest animals. Siehold and I have expressed the opinion that the Protozoa, like the simplest plants, are unicellular organisms, but it is granted that no demonstration of this has been given in many, especially the Rhizopods. In all creatures above the Protozoa, it would seem to be certain that their body proceeds from a mass of cells, although in the fully-formed animals, as for example the Hydra, according to Ecker,^ this is not always clearly de- monstrable.] §8. A more exact consideration of the relations of cells gives us the following results. Their fundamental form is globular or lenticular J it is such in all cells during their earliest state, and is permanent in those which occur in the fluids, (blood- corpuscles, &c.). Less common forms are: 1. Polygonal (pavement epithelium). 2. Conical or pyramidal (ciliated epithelium). 3. Cylindrical (cylinder epithelium). 4. Spindle- shaped (contractile fibre cells). 5. Squamous (epidermic scales). 6. Stellate (nerve-cells). The size of cells descends upon the one hand, as in many young cells, blood-cells, &c., as low as 0'002 — O'OOS'", and upon the other attains, as in the cysts of the semen and the nerve-cells, that of 0-02 — 0'04"'. The largest animal cells are the yelk-cells or ova, especially those of birds and amphibia, and a few of those animals which consist of single cells, these, in certain Gregarinse, attaining 0'7"'. The membrane of the cells is generally very delicate, smooth, hardly separable, and marked by a single contour, rarely of any considerable density or measurable thickness ; with our present optical instruments it exhibits no structure of any kind. In the interior of the cells there are invariably found, at a certain time, one or many nuclei, besides fluid and granules of various proportions and of different natures. Cells which contain only [' The tissue of the Hydra presents no essential features of difference from that of the higher animals, and closely resembles the most superficial layer of the dermis in the latter. In its outer part the so-called nuclei are almost wholly converted into thread-cells; hut they may be very readily demonstrated in their ordinary condition in the deeper portions. The resemblance of the gelatinous tissue of the disk of the Medusae to Professor Kolliker's " reticulated connective-tissue" is still more striking. — Ens.] 16 GENERAL ANATOMY OF THE TISSUES. fluid are rare, (fat-cells, blood-cells, cells of the chorda dorsalis), and it is colourless or reddish; in general they contain, in addition, corpuscles in greater or less number, (elementary granules, elementary vesicles, perhaps crystals), and in fact, as a rule, young cells possess few, while older ones contain many, which are very often more densely grouped round the nucleus, or occupy only a single spot (coloured nerve-cells). The chemical composition of the cells is as yet very obscure. The contents in most cells present certain generally disseminated substancesy which occur dissolved in the nutritive fluid or cytoblastema, as water, albumen, fat, extractive matter, salts; a nitrogenous substance, which is precipitated by water and by dilute acids thus resembling mucus, is very extensively dis- tributed and considerably impedes the microscopical analysis of the cells and tissues, inasmuch as it causes them to be obscure and granular, instead of clear and transparent. Many cells contain yet other compounds, as those of the liver, of the kidneys, of the blood, &c. The cell membrane consists of a nitrogenous substance, which is unquestionably a protein compound in young cells, as we may conclude from its solubility in acetic acid (partly even in the cold) and in dilute caustic alkalies. Subsequently the membrane in many cells, yet by no means in all, (e. ff. not in the blood-corpuscles, in the deepest cells of the epidermis and epithelium, nor in the cells of the glandular follicles), becomes less soluble, and here and there more or less approximates the substance of the elastic tissue. .^ The cell-nucleus is a globular or lenticular, clear, or yellowish body, which in the mean measures 0-003 — 0-004'", and rarely, as in the ganglion-globules and ova, attains a diameter of O'Ol — 0"04"'. All nuclei are vesicles, as Schwann supposed and as I have recognised to be their original and universal structure in embryos and adult animals. The mem- . brane is very delicate in the smaller ones, appearing as a simple, fine, dark line ; in the larger it is more marked, even of measurable thickness and limited by a double contour, as in the nuclei of the ganglion-globules, of ova and of many embryos. The contents of the nuclear vesicle consist, ex- cepting the nucleolus, almost invariably of a pellucid or slightly CELLS. 17 yellowish — never more darkly tinged — fluid, in which water and acetic acid precipitate the same dark granules as in the cells, for which reason the nuclei never preserve their natural homogeneous clear appearance, when examined ac- cording to the ordinary methods. More rarely the nuclei have formed contents, as the spermatic filament in the semen; in ova peculiar granules, the so-called germinal spots; also in the fat cells of Piscicola (Leydig). In respect of their chemical composition, only this much can be said of the nuclei, that their membranes are nitrogenous, and in general but little different from the substance forming the younger cell-mem- branes ; they are, however, dissolved more slowly in alkalies, and are but slightly attacked by dilute acetic and mineral acids. In the latter circumstance they approximate the elastic tissue, from which, however, they are most essentially distin- guished by their easy solubility in alkalies. The nuclei are found, so far as I have observed, in all cells of embryos without exception, and in those of adults, so long as the cells are still young. In general only a single nucleus exists in each cell, except when it is multiplying ; in the latter case, however, two or more nuclei arise, according to the number of the developing cells. In certain cells we meet with more numerous nuclei; thus, in those of the semen, 4, 10, 20, and more ; also in the substantia grisea centralis of the spinal cord, of the supra-renal capsules, of the pituitary body, in the hepatic cells of embryos, in the foetal medullary cells of bone, and elsewhere. That nuclei also occur free, and take part in the formation of certain tissues, has already been stated. The nucleoli are round, sharply-defined, generally dark, fat- . like granules, which, on the average, measure 0-001— 0-0015'", are often almost immeasurably small, and in embryos, in the germinal vesicles of ova as the germinal spots, and in the ganglion-globules attain the size of 0-003 — Q-Ol'". In all probability they are always vesicular, as may be surmised from their sharply-circumscribed form, their similarity to elementary vesicles, and also from the circumstance that in certain cells, especially in ova and ganglion-globules, a larger or smaller cavity filled with fluid frequently becomes deve- loped in them. The chemical composition of the nucleoli I. / 2 18 GENERAL ANATOMY OF THE TISSUES. is unknown, their external appearance, their similarity to the elementary vesicles, their disappearance in caustic al- kalies, and their insolubility in acetic acid, would lead us to suppose them to be fat ; the membranes may, as in the elementary vesicles, be a protein compound. Nucleoli are found in the great majority of nuclei, so long as these are still young, and in many during their whole existence ; but nuclei also exist, in which nucleoli cannot be recognised with certainty, or at least become obvious only at a later period; and therefore, at present, the nucleolus cannot be so unconditionally recognised to be an essential constituent of the cell, as the nuclens. Generally, a nucleus contains only one nucleolus, frequently there are two, rarely three, and, in solitary cases, four or five may be present, which are then either eccentric or lie free in the nucleus. [A short time since, Bonders, in a very remarkable work (vide infra), expressed the opinion, that all cell-membranes consist of one and the same, or at least of very nearly allied substances, which agree in their characters with the elastic tissue. For my own part, I believe that all animal cell-mem- branes consist originally of the same substance — of a protein compound, in fact ; that, however, in consequence of its sub- sequent metamorphoses, it may acquire differences' of compo- sition and of reaction. Many membranes in this manner become more resistant with time and, as Bonders justly states, approach elastic tissue ; others change into collagenous tissue, as those of the formative cells of the connective tissue, and of the cartilage cells during ossification; others into syntonin, as in the smooth muscles ; into the so-called horn, and so on. If we assume the primitive cell-membrane to be a protein compound, and from the reaction of young cells and of embryonic parenchyma it can hardly be otherwise, we obtain a correspondence with the vegetable cell, since in this case the primordial utricle, consisting of a protein compound, can be considered as the analogue of the animal cell-membrane, whilst the cellulose membrane appears as a secondary product, as an excretion. Such may be the true condition also in those auiiual structures of the Tunicata which are formed of cellulose, in which case my assertion that here the cell-membranes are composed CELLS. 19 of woody fibre, and that of Schacht (Miiller's 'Archiv/ 1851), that they are nitrogenous, would coincide. If future investi- gation justify this comparison of the animal cell with the primordial utricle of plants, the further question would arise in animals, whether perhaps all the so-called metamorphoses of the cell-membrane are not to be laid to the account of depodts which are thrown down upon the outer side of it, similarly to the cellulose in plants, so that, perhaps, together with the original protein membrane, other secondary collagenous or elastic membranes, &c., might be distinguished, and even the most considerable thickenings of the animal cell be produced, in a manner analogous to that which occurs in the ligneous tissues of plants on the outer side of the protein membrane ; so that, for example, within ossified cartilage-cells the original ceU- membrane might perhaps still exist. in all normal cells of the higher animals, the nuclei can be readily shown to be vesicles, and most beautifully so in em- bryos ; only in those cells which arise directly round nuclei, are the nuclei at first more homogeneous, and subsequently exhibit a distinct membrane. In pathological formations, this cha- racter of the nucleus, which may be called an undeveloped form, is very frequent, and the nucleus-like structures in the Protozoa are also for the most part homogeneous bodies.] k 9. Development of Cells. — With regard to the development of cells, we have to distinguish between their y»*ee origin and their production by the intermediation of other cells. In the former case the cells are developed, independently of others, in a plastic fluid, the cytoblastema of Schleiden, containing chiefly fat, protein, and salts in solution; in the other, or in cell- multiplication, the existent cells either produce the so-called daughter or secondary cells within themselves, or multiply by division; endogenous cell-formation and fissiparous cell- formation. Both kinds of cell-formation agree in this, that the cell-nuclei play a very important part, and appear to be the proper centres of development (bildungs-punkte) of the young cells. 20 GENERAL ANATOMY OF THE TISSUES. § 10. Free cell-development is, in man and the higher animals, far less common than has been hitherto assumed, and under this category we can enumerate, so far as is at present known, only the development of the chyle and lymph corpuscles, of the cells of certain glandular secretions (spermatic cells, ova), and gland-like organs (closed follicles of the intestine, lymph glands, splenic corpuscles and pulp, thymus); lastly, of the cellular elements in the pregnant uterus, in the corpus luteum, in the medulla of foetal bones, and in the soft ossifying blastemata. The separate steps of the process in this mode of cell^development have as yet been traced principally in the first-named cells, but much is yet wanting to complete our knowledge of it. This much is certain, that the origin of the cells is always preceded by the development of cell-nuclei, while it is doubtful, on the other hand, how these are formed. In the chyle and in the spleen we see as the first indication of cell-formation, rounded homogeneous-looking corpuscles of O'OOl — 'OOS'", which, increasing somewhat in size, soon clearly appear to be vesicles, and often, upon the addition of water, exhibit in their interior, together with small granules, a large granule, like a nucleolus. Whether this last, as is certainly the case in the dependent mode of cell-develop- ment, arises before the nucleus and is the condition of the deve- lopment of the latter, or whether it is formed subsequently therein; how, again, the nuclei themselves are developed, whether as originally homogeneous corpuscles, which subse- quently exhibit a difierentiation into inner and outer parts, — envelope and contents, or whether they are not, from the first, vesicular, cannot at present be decided. The nuclei being once formed, the cell-membranes are developed around them, though not always in the same way. In the first place, they may be applied directly around the nucleus, so that the nascent cell is but little larger than its Fig. 2. Contents of a Malpighian corpuscle of the ox, x- 550: n, small; b, larger cells ; c, tees nuclei. CELLS. 21 nucleus; or, in the second place, the latter may become sur- rounded by a greater or smaller quantity of solidifying cyto- blastema, and it is only round this enveloping mass, which I have called an i nvesting gl obule, that a membrane forms. This last occurrence in the free cell-formation has hitherto been observed only in the ovum, in which the germinal vesicle, i, e. the nucleus of the egg-cell, being first formed, surrounds itself with some yelk liefore the vitellary membrane appears. On the other hand, cell-development directly round the nucleus takes place in all the other localities which have been men- tioned above, and is demonstrated by the occurrence, among free nuclei and large cells, of very small c ells, which closely invest the nucleus or are but little separated from it. It may, however, be remarked, that perhaps in these cases also, the cell-membranes at their origin are separated from the nuclei by a very small quantity of cytoblastema, so small as to be incapable of detection. [Free cell-formation is exceedingly frequent in pathological productions, and the cells in pus and in exudations of all kinds arise in this manner; in fact, all pathological cell-formation properly comes under this head. Usually the cell-membranes here arise directly round the nucleus, less commonly as it would seem round investing globules. "With regard to phy- siological processes, as has been already shown, free cell-deve- lopment has been much too readily taken for granted; and especially as regards the epithelial and horny tissues, as well as in many glandular secretions, it has been assumed without any sufficient grounds. Botany knows no free cell- development.P ' [There cannot be said to be any evidence of the occurrence of free cell-development in animals, so long as in any case cited it is not shown that the first-formed particles which make their appearance cannot have derived their origin from pre-existing formed particles, either by the detachment or fission of the latter. Not only does this condition remain unfulfilled for all the instances cited, but it has not been attempted, and would seem to be impossible. In pathological exudations, for instance, who shall determine that the first structural elements which appear, granules, free " nuclei," exudation corpuscles, &c., are not directly derived either from the blood, or from the tissue into which the exudation has taken place ? — Eds.] 33 GENERAL ANATOMY OF THE TISSUES, Fig. 3. § 11. The development of cells within other cellsj or their endogencms origin, is of very frequent occurrence, and easy to be observed in embryos. The commonest form of this cell genesis is, that a so-called parent cell produces two secondary cells, which from the first wholly fill it. The first thing to be observed in this case, in the parent cell, is a metamorphosis of its nucleus, which grows, acquires two nucleoli, becomes elongated, and divides into two. When this has once taken place, , the nuclei become somewhat divari- catedi and then a wall of separation arises between the cells, which divides the parent cell into two perfectly dis- tinct spaces, each of which contains a single nucleus and one half of the contents. The mode in which the multiplication of the nucleus takes place, has not yet been made out with exactness. This much, however, is certain, that where clear observation is possible, it is always the nucleoli, which first divide into two and then diverge a little. In the nuclei, which have at the- same time slightly elongated, there then usually appears, marking the first trace of their division, a median partition, which in favorable cases may be recognised as composed of two secondary nuclei applied to one another by their flat sides, and completely filling the parent nucleus. Very frequently we see, in the course of this process of multiplication of the nuclei, nothing more than, first an elongated nucleus, with a partition and two nucleoli, and then two hemispherical nuclei applied by their plane faces to one another, without its being possible to demonstrate with certainty any endogenous development of nuclei ; so much the Kg. 3. From the cephalic cartilage of an advanced tadpole. Parent cells, with 1 and 2 nuclei, or 2 — 4 secondary cells, and some interstitial suhstance, x 350. Fig. 4. An elongated nucleus, and one containing two secondary nuclei, from the ovum of an Ascaris dentata, x 350. Fig. 4. CELLS. 23 lesSj as it is not to be doubted that, together with the latter process, a multiplication of nuclei by division takes place, in which an elongated parent nucleus, with two nucleoli, breaks up into two by the formation of a constriction which gradually deepens in the middle. The further destiny of the parent cells, with a partition and two nuclei, is not always the same. As a rule, it appears that in each, two perfect secondary cells afterwards become evident, which may serve as a demonstration that the partition is double from the very first. At other times, distinct secondary cells are not recognisable, which however does not imply that there exists a mode of cell-development by the mere formation of partitions, but only that in such cases the secondary cells do not become distinctly separated from the parent cells. Whether the one process or the other take place, it rarely stops at one performance, but is generally repeated a certain, often very considerable number of times; in fact, as long as the organism grows. The parent cells either remain, or they cease earlier or later to be histologically distinct structures, and coalesce with the substance which unites the cells as a matrix. The occurrence of this endogenous cell-development, which may be called cell-development around the collective contents, and which agrees in all essential points with free cell- development around investing masses, has been made out with certainty in the young cartilage of all animals, and probably occurs in embryonic organs in general, in which, from the moment when they consist of actual cells, the total growth essentially depends upon a self-multiplication of the cells without free cell-development. Since, however, it is as yet undecided, whether perhaps cell- development by division, to which attention has been very lately drawn, does not play a part in the one case or in the other, our judgment, so far as regards the latter, must as yet be suspended, until more particular investigations have been undertaken; and the same holds good for many organs of the adult, as the horny tissues and certain glandular secretions. Only, when secondary cells are observed in parent cells, as especially in the pituitary body and in the supra-renal capsules, there can of course be no doubt as to the existence of endogenous cell- development. 34 GENERAL ANATOMY OF THE TISSUES. Fig. 5. Besides these most usual forms of cell-development, there exist yet a few others : 1. In the ova of most animals a peculiar process, the so-called cleavage of the yelk, occurs at the earliest period of develop- ment, which is to be regarded as the introduction to the formation of the first cells of the embryo ; and since the ovum has the nature of a simple cell, it is a case of endogenous cell- development. This cleavage takes place as foUows. After the original nucleus of the egg-cell, the germinal vesicle, has disappeared with the ^ occurrence of fecundation, the granules of the yelk no longer form a compact mass as before, but become dispersed and fill the whole egg-cell. Then, as the earliest sign of commencing development, there arises in the midst of the yelk, around a new nucleolus, a new nucleus, the primary nucleus of the embryo, which operates as a centre of attraction upon the yelk and unites it again into a globular mass, the first "cleavage mass" (Furchungs-kugel). In the further course of development two new nuclei are formed by endogenous development from the first nucleus, and these, as soon as they have become freed by the solution of the parent nucleus, separate from one another for a short distance, act as new centres upon the yelk, and thus break up the first cleavage mass into two. In this way the multiplication of nuclei and of cleavage masses proceeds, — the former always taking the lead, until a very great number of small globules are pro- duced, which fill the whole cavity of the yelk-cell j it is only in exceptional cases that the cleavage-masses break up after the development of three or four nuclei within them ; so that then, instead of two, three or four cleavage-masses imme- diately proceed from one. This process is called total cleavage, because here the whole yelk is disposed around the newly- developed nuclei : partial cleavage is essentially similar, dif- Fig. 5. The ova aiAacaris nigrovmosa, — 1 from the second, 2 from the third, and 3 from the fifth stage of division, with 2, 4, and 16 division-masses : a, chorion ; *, cleavage-masses. In 1 the nucleus of the lower mass contains two nucleoli, in 2 the lowest contains two nuclei. CELLS. 35 fering only in the circumstance that it is not the whole yelk, but a greater or lesser portion, according to the animal, which invests the nascent nuclei. When the process has attained a certain stage, the cleavage- masses all together, or in successive layers, surround them- selves with membranes, and become actual cells, whence we are justified in considering this to be a process of endoge- nous cell-development. In fact, it is nothing else than an introduction to cell- development in the egg-cell, and differs from the ordinary phenomena of that class only in this, that firstly, the nucleus of the parent cell or the germinal vesicle, in most cases (Miiller saw a division of it occur in the Mol- luscs which are developed within Synapta digitated) has nothing to do with it ; secondly, that the parent cell itself persists ; and thirdly, that the investing globules developed by the successive multiplication of nuclei become cells only in the latest generations. This view is the more justifiable, as the cells which have arisen in consequence of the metamorphosis of the last cleavage-masses long continue to multiply by endo- genous development; and the whole process of division may be regarded as a kind of endogenous cell-development, in which, on account of the rapidity with which the nuclei mul- tiply, no formation of cell-membrane takes place in the early generations of "cleavage-masses."^ 2. Closely allied, in some respects, to the cleavage process, are those forms of endogenous cell-development, in which a greater or smaller number of secondary cells are developed within persistent parent cells, as we see here and there in the cartilages, in the supra-renal capsules, and in the pituitary body. In this case there either arise in the ordinary manner, in a cell, two secondary cells, which wholly or partially fill it, and from these, by a continued multiplication, other generations, ' [Dr. Nelson (Phil. Trans., 1852, p. 580), has observed the same thing in jiscarU myatax. — Eds.] ' [We must altogether demur to the notion that the " nuclei" of the dividing yelk exercise any attraction upon the yelk substance. The careful observations of Reichert (Der Fnrchungs prozess und die aogenannte Zellenbildung um Inhaltsportionen, MUller's Archiv, 1846), of Remak (Ueber den Furchnngs-prozess im Froschen-Eie, Miill. Archiv, 1851), and of Nelson, 1. c, appear to furnish demonstrative evidence that no such attraction exists.— Eds.] 26 GENERAL ANATOMY OF THE TISSUES. which sometimes lie quite free, and sometimes are wholly or Fig. 6. partially included in the parent cells of the second gene- ration; or a more free development of a secondary cell within a parent cell occurs^ from which cell - development then takes place in one mode or in the other. In connection with the process of endogenous cell-de- velopment, we may very properly speak of the formation of a great number of nuclei within cells, a process which is frequently the pre- cursor of cell-deve- lopment, but which may also continue alone. Even in the common endogenous cell-development (and also in the cleavage process) we not unfrequently observe three and four nuclei in a parent cell, so that then, instead of two secondary cells, many arise at once, e. g. in the hepatic cells of embryos. In certaiii animals (Cucullanus, Ascaris dentata, Distoma, Cestoidea), instead of cleavage-masses, nuclei alone are developed in the first stages of development, and it is only later, when by successive endogenous multiplication these have increased to a great bulk, that they become surrounded by Fig. 6. Cartilage cells from a fibrous, velvety, articular cartilage of the condyle of the femur of man, x 350, all lying in a fibrous matrix, and readily isolated : a, simple cells, with or without a thickened wall, with 1 or 2 nuclei; b, secondary cells, or cells of the first generation, with 1 or 2 nuclei; 1, 2 — D, or more, in parent cells; b', c, cells of the second generation, 1 — 3 in number, in cells of the first ; d, freed groups of secondary cells. CELLS. 27 cell membranes. SometHing similar appears to take place in the cells of the germ in the Crustacea, in which 10 — 20 nuclei are often found (Rathke, 'De Anim. Crustac. gen./ Regim. 1844). On the other hand, the numerous nuclei in the spermatic cells of most animals are, in general, in no way connected with cell- deve- lopment, since the spermatic filaments are developed in them ; and the like holds good of those cells of the lower animals, whose multi- tudinous nuclei are changed into thread-cells. The im- port of the number of nuclei in certain nerve-cells, and in the large cells of the bone- medulla, which Robin and I have observed, is doubtful; in the latter, I think it is -not improbable that the multiplication of thenuclei is preliminary to theirbreaking up into smaller cells. In all these cases, it may be easily demonstrated that the nuclei multiply spontaneously, but, it is generally doubtful whether this happens by division or by endogenous development. [Cell-development round a mass of blastema containing a nucleus in its interior, which may take place either freely or in an endogenous manner (cell-development round portions of contents), had long ago been seen by von Siebold in the ova of Distoma globiporum, and by Bergmann in the cleavage-masses of Rana, but no further importance was attached to it. Vogt and Nageli were the first who regarded this cell- development, as a deviation from the theory of Schleiden and Schwann, whereupon, supported by observations upon embryos, I (in 1844, ' Entwick, d. Cephalopoden') placed this as a second kind of cell- development, under the name of " cell- development round in- vesting masses," beside that which takes place immediately round nuclei, and pointed out its very extensive occurrence, especially in embryos, where at first it is the sole mode. Later Fig. 7. a. Peculiar granulated cells with many nuclei, from the youngest medullary cavities of the flat bones of the skull in man, x 350. 28 GENERAL ANATOMY OF THE TISSUES. observations upon normal and pathological products have sup- ported this view^ and at the present time the formation of a cell-membrane immediately around the nucleus requires de- monstration, rather than the opposite method. Endogenous cell-development occurs in many pathological products, — most frequently in cancer, yet the steps of the process have not yet been exactly made out. In plants this mode of multiplication of cells is the most extensive, and it occurs commonly as " cell development around portions of contents," more rarely (in the embryo sac) by free development within parent cells.] ^ § 13. A multiplication of cells by division certainly takes place in the red blood-corptiscles of the embryos of Birds and Mammalia, Fig. 8. and in the first colourless blood-cor- puscles of the Tadpole (Remak). It takes place also, in all probability, in the colourless blood-corpuscles of em- bryos, and in the chyle-corpuscles of adult Mammalia under certain cir- cumstances. In all these cases, we see, in elongating cells, the production of two nuclei from the originally simple nucleus, apparently by division; the cells then suffer con- striction in the middle, and contract more and more around the nuclei as they recede from each other, and at last separate into two cells, each of which contains a nucleus. In the chick we see blood-corpuscles in all conceivable stages of separation, so that at length they are connected only by a delicate thread, and there can here be no doubt whatever as to the actual occurrence of this process. Fig. 8. Dividing blood-corpuscles of the chick, x 350. ■ [The endogenous development of secondary " nuclei" seems to us to be ex- tremely doubtful, even upon tbe evidence adduced, and we have been unable to observe anything indicating that regularity of occurrence and importance of function attributed to the nucleolus by Professor Kolliker. In cartilage, in the tooth-pulp, in the homogeneous layers of tbe cutis, and in other localities in which unaltered "nuclei" occur, tbe presence and number of the granules which might be called nucleoli is in the highest degree variable and uncertain. The same irregularity as to the presence of nucleoli occurs in tbe plant {vide Von Mohl, 1. c, and Schacht, ' Die Pflanzenzelle,' p. 30). Upon this subject consult Ihe valuable memoir of Remak (' Ueber extra-cellulare CELLS. 29 Whether division ever take place in other cells than these is not yet determined. If it be allowable to explain, by this process of division, the occurrence jj- g_ of constricted cells with two nuclei, we may suppose it to take place in the nerve-cells, which, in young M mammalia, are not unfrequently more or less divided or even united merely by a narrow isthmus, and also in the ciliated epithelium cells, which, although rarely, present two or three enlargements lying one behind the other, each with a nu- cleus. A peculiar kind of celU development, which is very closely related to division, occurs in the formative cells of the ivory, which as they go on growing, multiply their nuclei and become con- stricted from time to time, so that whilst the portion next the ivory ossifies, the other serves in a manner as a reserve for the subsequent formation of fresh ossifying tissue. [Schwann knew nothing of the occurrence of cell-division. The first who observed it in the blood- corpuscles of embryos was Remak ('Med. Verein.' 1841, No. 27; Schmidt, 'Jahr- biicher,' 1841, p. 145; Canstatt, 'Jahresb.,' 1841), yet he subsequently retracted his opinion ('Diagn. und Pathol. Untersuchungen,' p. 100), and only now, since I have con- firmed it and declared it to be true (Wiegm. 'Archiv,' Jahrg. 13, Bd. 1, p. 19), has he again advocated it [' Entwick. d. Wirbel- thiere,' I). It is extremely probable that' this mode of cell- development occurs very extensively, and it may perhaps turn out that in many embryos and adult tissues, in which a self- multiplication of the cells is certain, and yet in which no parent cells with secondary cells can be demonstrated, cell- development by division may occur instead of endogenous Fig. 9. Dentine cells from the dog, x 350. Enstehung Thierischen Zellen,' &c., Miill. Archiv, 1852), which by no means deserves the epithet of " no longer available ;'' in fact, Remak's views seem to be essentially correct. — Eds.] 30 GENEKAL ANATOMY OF THE TISSUES. cell-development. It is certain that the transverse and longitu- dinal division of the Protozoa is to be placed here, since these animals have the structure of simple cells, and the nucleus-like body they contain takes a share in the process of cell division, like that of the cell nucleus in common cells. In pathological formations cell-division has not yet been observed. In the vegetable kingdom it is rare, and has been seen only in the lower organisms; unless, indeed, we are to reckon here the constriction of the primordial utricle observed by von Mohl, in the course of endogenous cell-development.] ' • [There can, we think, be little doubt that Von Mohl is quite correct in the view he takes of the multiplication of cells in plants by division, and therefore we are by no means inclined to agree with Professor Kblliker, as to the rarity of this form of cell-multiplication in the vegetable kingdom, nor, consequently, in what he says at the conclusion of the preceding note. All botanists of any note (Nilgeli, Von Mohl, Hoffmeister, Alex. Braun, Schacht, Henfrey) maintain at the present time, that the process of cell-division so far from being " rare," is that which occurs in by far the great majority of cases in plants. " That the formation of cells, in all organs of plants (excepting the cells originating in the embryo sac), depends upon the division of older cells, is an opinion which could not for a long time past be opposed by any careful observer, imless he were misled by preconceived notions." (Von Mohl, Anatomy and Physiology of the Vegetable Cell,' 1851, Henfrey's translation). Nor can we agree with Professor KoUiker's estimate of the relative frequency of occur- rence and importance of endogenous cell-development and cell-division in the animal world. In young cartilage, which is cited by our author as a locality in which endo- genous cell-development takes place, we must affirm, on the contrary, that the process is as much one of cell-division as it is in any plant. At this period, the so-called " nuclei" of the cartilage completely fill their cavities (e. g. nasal cartilage of four- months' foetus), and may be seen in all stages of division. The walls of the cavities grow 'm,pari passu, and eventually form a partition between the two nuclei, or rather primordial utricles, which have been thus developed from one. Remak, who, in a very valuable paper (Ueber die Entstehung der Bindegewebes und Knorpels, Mlill. Archiv, 1852), has advocated this view so far as cartilage and connective-tissue are concerned, does not appear to have seen the necessity of extending it to the other tissues. As Reichert, however, long since pointed out (see note, § on Connective Tissue), whatever determines the nature of the cartilage corpuscle and of its matrix, determines that of all the other tissues whose anatomical continuity with cartilage can be traced directly or indirectly. Thus a direct ana- tomical continuity may be shown to exist between the matrix of cartilage, the apparent fibrillse of connective tissue, the fibrillee of muscle, the homogeneous matrix of the cutis and of its papillee, and the so-called walls of the epithelial cells ; while a per- fect identity in size, structure and relation, may be traced between the corpuscles of cartilage, the " nuclei" of connective tissue, those of muscle, of the papillae and of the epithelial cells. — Eds.] CELLS. 31 § 13. Theory of Cell-development. — ^Among the few hypotheses which have, up to the present time, been proposed in expla- nation of the development of cells, that of Schwann, who com- pares it with the formation of crystals, is certainly the most attractive. Without overlooking the differences between a crystal and a cell, which chiefly consist in the former being solid and homogeneous, in its growing by apposition, and in its being bounded by plane surfaces and angles, Schwann endeavours to explain cell-development as a crystallisation of organic matter, and to deduce from the permeability of the latter the differences in the phenomena presented by the two. In a fluid containing organic matters dissolved in con- siderable proportions, a granule, the nucleolus, is precipitated. Once formed, this attracts nutriment from the cytoblastema, and thus becomes the nucleus, which Schwann considers to be solid. This still goes on attracting to itself a substance, which, becoming more and more condensed, at last forms a membrane; which, allowing the passage of fluid cytoblastema through its pores, becomes detached from the nucleus, and we have a cell. In this exposition, we must admire not only the skilful, acute working out of the fundamental idea which the original treatise manifests, but also the assumption of a molecular attraction in cell-development, analogous to that which occurs in the for- mation of crystals, for the existence of which there is, in fact, decisive evidence (only in part, however, known to Schwann), such as the action of the nuclei in the cleavage process, in cell- division, in cell-development round portions of contents, in the cyclosis, and in the formation of granular precipitates in cells.^ On the other hand, it is evidently going too far to call cell- development simply a crystallisation of permeable organic sub- stances, since in this case important differences are overlooked, and non-essentials are made unduly prominent. For it must not be forgotten, that organic permeable substances also crystal- hse; that, in fact, if Reichert have observed correctly (Miiller's 'Archiv,' 1849), and I see no reason for doubt, histogenetic substances capable of forming tissues, as albumen for instance, assume a crystalline form. Hence the molecular attraction ' [See note, p. 25. — Eds.] 32 GENERAL ANATOMY OF THE TISSUES. concerned in the formation of cells is so far peculiar, that — 1, it never produces geometrical solids, but even in the nucleus and nucleolus determines the globular form ; 2, that it aggre- gates, not homogeneous but chemically diflferent substances, as those which constitute the nucleus and the cell-membrane ; 3, lastly, that without exception, in the development of the cell-membrane it limits itself, and does not, like the crystal- lising force, repeatedly apply layer upon layer. Of these differences, the two latter might perhaps be set aside, if with regard to the second point, it were assumed that the nuclei at first consist of the same substance as the cell-membranes, or are almost identical with them in chemical composition ; or if we referred to the fact that in crystallisation also, different substances may unite into one crystal, or that a substance, b, may crystallise around a substance a. In order to diminish the force of the third fact adduced (this objection, indeed, does not hold with regard to endogenous deve- lopment, and therefore in almost all plants, since it is impossible here that the cells should produce any more layers around them- selves), it might be urged that the permeability of the organic membranes, the exchange of constituents which takes place between the juices of the cell and the cytoblastema, and the ap- plication of the molecules attracted from the cytoblastema to the growth of the membrane, and to precipitates within the interior, are perhaps the reasons why the cells develope no new circum- ferential layers. It is not necessary to carry out this last possibility any further, nor to bring forward the difficulties which are opposed to this view also, — among which not the smallest is, that the organic development of vesicles does not stop at the formation of nuclei, but is only finished with the completion of the cell membrane ; since in any case the facts brought forward are more than enough to demonstrate the insufficiency of Schwann's hypothesis. I do not see, however, anything better or more positive to substitute in its place, and I therefore think it will be most expedient simply to group together the ascertained facts into a few general propositions, which may, perhaps, be done as follows. 1. The nucleus of the cell arises in the first place, as a precipitate in an orgaiiisable fluid, and afterwards becomes consolidated in such a manner, that a special investment and CELLS. 33 contents with a nucleolus appear. Its development may in this case be compared to that of inorganic precipitates, yet the constantly globular figure, and the size of nuclei which are just formed, indicate some essential though not yet re- cognised condition peculiar to them. Secondly, cell-nuclei are produced endogenously in nuclei, or by their division under the influence of a nucleolus, which also divides. Here is one condition which is never presented by crystals, — the division from an internal cause ; while the other, the influence of the nucleoli upon the nucleus, can hardly be comprehended in any but a physical way, as a molecular attraction proceeding from the nucleoli, of an indefinable nature, which at last draws the entire half of the parent nucleus within its influence. 3. In the development of cells by division, the cell-nucleus plays exactly the same part which was previously ascribed to the nucleolus, and the occurrence of the formation of cells in this manner demonstrates that chemical conditions are not necessarily concerned therein. 3. In cell-development around portions of contents, and in the cleavage process, the nuclei also operate as simple centres of attraction (einfach attrahirend) upon a certain mass of blastema, and then follows the formation of a membrane upon the surface of this mass, which is most simply understood as a conden- sation of the blastema. 4. In cell-development directly around the nucleus, the investment with blastema is wanting, and the nucleus deve- lopes the membrane immediately around itself. This pro- cess admits of both a physical and a chemical explanation. In the first place, we may with Schwann assume that the nucleus attracts molecules, which, when they have reached a certain amount, condense into a membrane, and, by growing, become detached from the nucleus. Or secondly, it is con- ceivable, that the nucleus in some manner initiates chemical processes, which terminate with the formation of a membrane around it. In this way a coagulable substance might be pro- duced within and excreted from it ; or, like rennet upon casein, it might act upon the protein combinations in the cytoblastema, in such a manner that, they should coagulate where in contact with it ; or lastly, by the extraction of the alkali it might render an albuminous substance insoluble, as is the case in I. 3 34 GENERAL ANATOMY OF THE TISSUES. the development of Ascherson's vesicles. Whicli of these various possibilities really obtains, must at present remain unde- termined, yet, for my own part, I should prefer the first view, in order to retain one and the same condition, a physical one, for all the different modes of cell-development. I do not think it necessary to enter at greater length, in the present place, into this very obscure subject, and I will therefore only once more express my opinion, that I hold the physical processes in cell-development, which may pass under the general name of molecular attraction, to be something quite different from those which attend crystallisation. Although in both, solids arise out of fluids, and grow by the further agglo- meration of molecules, yet in cell-development different sub- stances are as a rule superimposed, plane gepmetrical solids are never formed, and the process is always limited in the same way, after the formation of the cell-membrane. Since organic and even histogenetic substances are crystallisable, the reason of cell-development is not to be found in permeability nor in any of the other properties of organic compounds, which in fact, even if these substances did not crys1;allise, would not suffice to explain all the peculiarities of cells in question, nor their power of self-division and multiplication ; but in those peculiar, as yet unknown combinations of the powers of nature which are con- cerned in organic development. To discover these is the further and difficult task of Histology, which to this end must be wholly directed to the so-called molecular forces of organic forms, especially to those electrical phermmena which must indubitably occur in the cells as well as in their derivative structures, the nerve-tubes and muscular fibres.^ ' [The essential distinction between living organised matter (the cell) and mere inorganic formed matter (the crystal) appears to us to be here overlooked. If some inorganic substance should be discovered crystallising, in the form of nucleated cells, it would not the more approximate to an animal or vegetable cell ; for the essential character of the latter, which is its passage through a definite succession of states and not its form merely, would still be absent. It is this characteristic peculiarity of organised living beings, which has been exhibited with so much force by Alex. Braun, in the plant, under the somewhat fanciful title of ' Verjiingung' (rejuvenescence), but which equally obtains in the animal. The crystal tends to attain a permanent condition, the cell towards its own disappearance, either by death or division. The crystal tends towards an equilibrium with the forces around it, the cell inces- santly disturbs that equilibrium, — life and change being one. — Eds.] CELLS. 35 § 14. Vital phenomena of the perfect cells. Growth The cells, when once completed, perform a considerable number of functions, which relate as well to the form of the whole cell and of its contents, as to their chemical composition, and are called growth and change of substance. As to growth, it occurs perhaps in all cells, though not in all to the same extent. It is clearly manifested in all those cells which are formed directly round a nucleus, since in this case the membranes which at first closely invest the nucleus, in time become more and more separated, whilst the cells which arise around portions of contents or investing masses, and are from the first providedjwith contents, often increase in size but very slightly. Growth is either in surface or in thickness. The former appears very usually to be general, p. ^q when cells increase without altering their form, e. g. the ova, many nerve^cells, &c. ; frequently however it is partial, as in all cells which depart from the primitive globuli i form, in such a manner that the cell-mem branes only add new substance and extend at two or more points. Growth in thickness also occurs, to a certain extent, in all cells, since all cell- membranes become somewhat thicker with age; and it pro- duces in some localities a very considerable thickening of the membrane, occasionally with evident lamination (as in the cartilage cells), and even gives rise to certain structures which have the greatest similarity to the sclerogenous cells of plants (bone-cells). The nuclei and nucleoli also take part, to a certain extent, in the growth of the cells. In the former, a general growth is easily demonstrable in all growing cells; in many, as in those of the smooth muscles, of the epithelium of the vessels, of the formative cells of elastic tissue, and others, there is also a partial growth, in consequence of which they often assume the form of long slender rods. The nucleoli also not unfre- Fig. 10. Cartilage cells of man, x 350. Two cells with thickened walls, from the cartilage of the great cornu of the hyoid bone, containing a clear drop of fat beside their nucleus. 36 GENERAL ANATOMY OF THE TISSUES. quently grow with their cellsj (nerve-cells, ova) ; but except when dividing they never assume any but the globular form. Schwann has given an explanation of the Fig- Jii- ^^ growth, as well of the cell as of the nucleus. He considers that the molecules of the cell-membrane exert an attractive influence upon the fluid which surrounds them, and deposit its newly-formed particles among themselves; if the deposition take place between the molecules already present in the substance of the membrane, the cell becomes distended; if it take place only in the direction of the radius of the cell, the membrane becomes thickened. The nucleus grows less than the cell, because as soon as the latter is formed it no longer comes into direct contact with the concentrated cytoblastema. General growth takes place when the moleculfes of the membranes all attract equally; partial growth, when this happens only or especially at particular spots, where the apposition of new matter takes place to a greater extent. With reference to the mode of formation of precipi- tates and of crystals, this theory appears to me to explain very well the phenomena of general growth, supposing that we ascribe to the cell-membrane the faculty of readUy taking up molecules and applying them to its increase. Such, however, must be the case, for the relations of the nuclei, which even when free, never grow very considerably, and particularly never in one direction^ show that the power of growth is not simply innate in every organic membrane, manifesting itself when sufficient formative material is oflfered, but requires peculiar conditions which are realised only in the cell-membrane. To account for partial growth, Schwann's view must be somewhat extended ; for only those modes of growth in which the cells, during their increase in certain directions, lose nothing of their original dimensions in others, can be interpreted in Fig. 11. Six developing bone-cells from a rickety bone as yet sharply defined from the interstitial substance : — a, simple hone-cells ; b, a compound one, answering to a parent cell with two secondary cells ; c, similar ones with three cells, x 350. ' [This is surely incorrect. The " nuclei" in the hair-pulp, in the tooth-pulp, in conneciiTe tissue, in organic muscle, grow in one direction to a yery considerable extent. — Eds.] CELLS. 37 Schwann's way, but not those in which the cells become narrower as they elongate; here we must assume that whilst new substance is deposited in the one direction, in the other an absorption takes place, for we can in nowise consider the process to be a mechanical one. For the rest, it may be re- marked, that partial growth may depend upon the occurrence of assimilation, in particular cells, only in certain directions, as in the thickened vegetable cells with pore-canals, which is possibly connected with a one-sided direction of the currents in the cell-contents. § 15. Processes in the interior of the Cells. — In order to obtain a clear conception of the processes which go on in the interior of cells, it would before all things be necessary to have a more exact acquaintance with the chemical composition of the cell- contents than we at present possess. Only two kinds of cells, the ovum and the blood-globule, have been investigated with care (see Eemarks) ; but these have such peculiar relations that they can hardly be regarded as types of cells in general. However, we may from these analyses draw certain inferences with regard to other cells, arid bearing in mind what micro- chemical investigation teaches us, it may be permissible to regard the cell contents in general, as a moderately concen- trated solution of protein with alkaline and earthy salts, and dissolved or suspended fatty particles. From these common characters, presented without doubt by all cells, at least in their young condition, many cells differ very widely, insomuch as either some of these constituents greatly predominate or altogether new substances occur. Thus, there exist cells with much protein, as the nerve-cells ; and with much fat, as the fat-cells, the cells of the sebaceous follicles, of the milk-glands,. &c. ; — then such as contain hsematin, pigment, biliary and urinary constituents, mucus (epithelium cells), milk, sugar, &c. &c. The phenomena manifested by these, so variously constituted cell-contents, during life, may be best enumerated as — absorp- tion, assimilation, and excretion. These depend principally upon chemical and physical conditions, and are to a great extent capable of microscopic investigation, since very fre- quently the changes of form in the cell and the changes of its 38 GENERAL ANATOMY OF THE TISSUES. contents go hand in hand. Absorption is manifested in all cells, but to far the greatest extent in those which at first have little or no contents save the nucleus. In these, the primary cause of the absorption is not to be sought in endosmose, but, as Schwann has indicated, in this — that while the mem- branes grow by the attraction of material from the sur- rounding fluid, by virtue of their porosity they allow substances to penetrate into the interior. This filling, however, does not take place by the cells admitting every kind of matter indiscriminately, but they exhibit peculiar relations to the cytoblastema, varying with the period and with the locality; so that they take up one constituent and reject another ; and the like occurs with the absorptive powers of those cells which possess contents from their earliest existence. That this is actually the case, is demonstrated, for instance, by the fact, that in embryos, notwithstanding the identity of the formative material in all cells, i. e. the plasma of the blood, some take up more of one substance, some more of another ; and it is still more clearly evidenced by the fact, that the cell-contents of probably all cells are chemically different from the cytoblastema out of which they are formed and by which they are nourished, as has been clearly shown lately, in the ova and blood-corpuscles, which for example contain far more potass than the blood. The reason of this phenomenon may be generally stated to be, that the cell-membranes do not act as mere filters, but allow one substance or another to per- meate them, according to their chemical composition, the con- stitution of the fluid which imbues them, their condition of aggregation, and their thickness, Endosmose must also be taken into account as a condition in the absorptive actions of cells, though hitherto it has been too freely appealed to, and cells have been too often considered as vesicles provided with merely indifierent porous membranes. That endosmose operates is not to be denied, when it is ob- served how the addition of concentrated or diluted solutions, causes cells to dilate or to collapse, yet it is not easy to deter- mine what influence such conditions have during life, nor what results are produced by the combined operation of the cell- membranes and their contents. From a few facts in vegetable physiology (growth of plants in arsenical and cupreous solu- CELLS. 39 tions, without the admission of these substances), it might be believed that the membranes exercised the more important influence in determining absorption. It is an important question, whether the substances received by the cells and composing them become modified by their vital processes. Schwann has answered it in the affirmative, and has denominated metabolic processes of cells, all those chemical metamorphoses which go on in them and in their separate parts ; and justly so, for the occurrence of such che- mical changes is not only very probable a priori, since in plants all such metamorphoses (and these of the most various kinds) take place in the cells, but may very easily be demonstrated by observation. These changes affect, firstly, the cell-mem- brane, and secondly the cell-contents. As regards the former, this much is certain, that the membranes of most cells not only become denser and more solid with age, but also that they take on a different chemical constitution, though it is impossible in particular cases to say on what the change depends. In the horny tissues, the membranes of the young cells are easily soluble in alkalies and acids, whilst subsequently they sometimes offer extreme resistance to their action : the same takes place in a few of the higher elementary parts, as the nervous tubules, the aniiaal muscles, and the capillaries, in which the sarcolemma, [the sheath of the nerve fibre,] the capillary membranes, which are metamorphosed cell-membranes, react in a very different manner from the original formative cells. In the cartilage cells also, the membrane becomes more resistant with age, and in the course of ossification not only thickens, but is for the most part changed into collagenous tissue, which is subsequently impregnated with calcareous salts. These examples, which might be multiplied, may suffice to demonstrate the occurrence of a metamorphosis of the cell-membranes; further investi- gations will be needed to show upon what it depends, whether, as it would seem, the original animal cell-membrane actually alters in composition in course of time, or whether the change in the reaction depends upon the addition of foreign substances, on the incrustation of the membranes with salts, and so forth, such as botanists are inclined to assume for the vegetable cell- membranes, or whether it depends upon secondary deposits on the exterior of the original membranes. 40 GENERAL ANATOMY OF THE TISSUES. The changes of the cell-contents are of two kinds, formative and resolvent. Both processes are easily followed in the embryos of diflFerent animals, in which, in the first place, the primary formative cells, which at the beginning are distended with the elements of the yelk, especially with oil, acquire by degrees more fluid and homogeneous contents, the yelk granules dissolving, sometimes from the cell-membrane towards the. nucleus, sometimes from within outwards ; and secondly, in cells thus formed, the most various new formations take place, among which that of heematin, of difl'erent kinds of pigment, and of fat, are the most obvious. But metamorphoses of the cell-contents are very common in adult animals also, and are at the same time very important, since in many places, on account of the great number of cells which are affected in the same way at the same time, unexpectedly great results are produced, as one of the most important of which we may name the biliary secretion, which is brought about, so to say, only by the activity of the many millions of cells which form the liver. A pretty series of changes may also be traced in the fat cells, which, according to the deficiency or superfluity of nutritive fluid, in the one case lose their proper contents, and may even become cells containing mere serum, in others are filled to bursting with drops of oilj again, in the cells of the fat- secreting glands, which at first contain but little fat, and finally become crammed with it; and also in the lymph- corpuscles, which develope the colouring matter of the blood within themselves, and thus become blood-corpuscles.^ The formation of mucus, again, must probably be assigned to the epithelial cells of the mucous glands and mucous membranes ; that of the so-called pepsin to the cells of the gastric glands j and that of semen to the spermatic cells. A multiplicity of con- firmatory evidence is afibrded by comparative anatomy, and I will here only advert to the development of the concretions of uric acid in the renal cells of the moUusca, that of sepia in the cells of the ink bag of the Cephalopod, of crystals and concretions of different kinds, in the cells of the invertebrata, and of certain pigments in those of the moUusca. Pathological anatomy affords us the pigment formations, the metamorphoses of cells contain- ing blood-corpuscles and the fatty deposits in cells of all kinds. ' [In the oviparous vertebrata. — Eds.] CELLS. 41 Manifold morphological phenomena go hand in hand with these changes, such as the thickenings of the cell-membrane, which have been already adverted to, with laminated depositions upon their inner surface, and even with the formation of pore- canalsj as the precipitation in the cell-contents of granules of different sorts, as of pigment, albumen, casein (in the yelk, perhaps in the hepatic cells) ; and as the formation of fat drops, of elementary vesicles, of concretions, crystals, and nuclei. Even movements resembling the cyclosis of plants appear to occur in the cells of the lower animals (seen by me in the cells of the arms of a minute Medusa, a new jEginopsis from the Mediterranean, and of Polyclinum stellatum), and in Protozoa (currents in Loxodes bursaria, contractile vesicles in different genera) ; while, on the other hand, the Brownian molecular movements, i. e. a more or less active tremulous motion of granules without further change of place, which may be observed in many cells under the microscope, most beautifully in the pigment cells of the eye, are also, perhaps, hardly to be reckoned among vital phenomena. The nuclei also occasionally, though upon the whole rarely, take part in the changes of the cells. The commonest of these appearances is their becoming clear, as a consequence of the liquefaction of the at first more viscid contents, upon which circumstance it depends that in young cells they are homogeneous, while in the larger they evidently appear to be vesicles. A formation of granules in the nuclei is very rare (see above) ; concretions, colouring matters, and crystals, are also not found here in animals ; on the other hand, the development of the urticating threads in certain animals and that of the spermatozoa, takes place in nuclei. In endeavouring to explain the metabolic processes of cells, we must in all cases especially regard the cell-nucleus ; for just as it excites the development of the cell, so is it the centre of the currents of the contents, and of the deposits and solu- tions ; but it is not to be regarded as the sole agent, for, firstly, it does not appear why the ceU contents should not, like the cytoblastema, become changed of themselves ; and, secondly, the changes of the cell-membrane are, at all events, more independent, and probably also have a certain influence upon the cell- contents, as the depositions which take place upon it. 42 GENERAL ANATOMY OF THE TISSUES. and the solution of the solid contents which often occurs in its neighhourhood, demonstrate. To assume with Schwann a special metabolic force is incorrect, for, in the first place, the causes of the metabolic phenomena are certainly very various ; and, secondly, there is every reason to reduce them to known molecular forces. Thus, for instance, even the action of the nucleus^ may not unfittingly be compared with the so-called catalytic, or contact action, inasmuch as it is hardly at all altered during the changes of the cells, and consists of a nitrogenous substance, which like pepsin, (which is also nothing but cell-contents), very readily produces a chemical alteration in other substances. The relation of the cell-mem- brane to absorption also, may even now be referred to the general laws of imbibition and diffusion. [I here give two analyses as examples of the chemical com- position of the cell- contents. The yelk of the hen^s egg contains: water, 4855; casein, 13'93; albumen, mixed with casein, 0892 j albumen, 2*841 j membranes of the yelk vesicles, 0-459; fats, 3M46 (30-46 according to Gobley), consisting of olein and margarin, 21-304; cholesterine, 0-438; lecithin (containing phosphoric acid), 8-426; and cerebrin; salts, 1-523; a hundred parts of the ash yielded, potass, 8-60 — 8-93; chloride of sodium, 9- 12; phosphatic salts, 66-7 — 67-8; lime, 12-21 ; magnesia, 2-07 ; oxide of iron, 1-45 ; silica, 0-055. The blood-corpuscles contain : water, 68-88; hsematin, 1-67; globulin and membranes, 28-22 ; fat, 023 ; extractive matters, 0-26 mineral substances (without iron), 0-81; of which, chlorine, 016 sulphuric acid, 0-006; phosphoric acid, 0-4; potassium, 033 sodium, 0-10; oxygen, 0-06 ; phosphate of lime, 001 ; phosphate of magnesia, 0-007. To these must also be added, free oxygen and carbonic acid, which likewise occur in the yelk. We have here instances of cells containing much protein, and especially fat, and may consider them to be fair examples of this kind of cell. The comparison of the contents of these cells with the plasma of the blood, out of which those of the ' [This " action of the nucleus" is a wholly hypothetical though a very general assumption. It is important to bear in mind, on the contrary, that there is every reason to believe that the molecular and chemical changes of the cell-membrane and the nucleus are independent of one another. — Eds.] CELLS. 43 one kind are formed, while the others live in it, is very interesting. In the blood-globules there is a considerable preponderance of solid constituents, since the blood-plasma only contains about 10 per cent, of solids, which is evidence^ that there are cells whose contents do not attain an equilibrium with the cytoblastema by which they are supported. With regard to particular substances, the blood-corpuscles contain more fat ; hsematin, which is not found in the plasma ; more potass and phosphoric acid; less chlorine, extractive matters, soda, and earths. The yelk of the hen's egg contains also considerably more solid constituents than the blood, which however is here less surprising than in the blood-corpuscles which swim in the blood-plasma. It is interesting, that the relative proportions of the different substances are quite diffe- rent in this case from the other. We have, namely, an exceed- ingly large quantity of fat, more protein and salts; and among the latter, again, more potass, and also more earthy salts. Even these facts indicate a considerable independence of action in the cells; but those which have been lately made known by Liidwig, tend still more forcibly in the same direction ; for the influence of the nerves upon the salivary glands discovered by this observer must, I believe, be so inter- preted, that it is not only the membrance proprice of the vesicles of the salivary glands, which are so altered in their molecular relations by the nervous influence that they directly exercise an energetic attraction upon the blood-plasma which surrounds them, but the epithelial cells which line them also. If this really be the case, we have an insight into an altogether new condition regulating the absorptive powers of cells, and at the same time cell-life is brought into such connection with the activity of the nervous system, that it no longer appears out of reason to speak of the positive functions of the latter. Such relations are in nowise opposed to analogy, since in the contractile elements we have already a connection between nervous activity and the modification of cell-contents, which perhaps upon further investigation may come under the same general category as the foregoing. In any case, these considerations lead anew to an exact investigation of the ' [This would be true only if the major part of the solid constituents of the blood- corpuscle were its contents ; this, however, is not the case. — Eds.] 44 GENERAL ANATOMY OF THE TISSUES. molecular forces of cells, especially of those electrical phe- nomena which will certainly he found in them. [Very recently Bonders (Nederlandsch. Lancet,) has justly brought forward a character which until now had received no attention, viz. the elasticity of the cell-membranes and the pressure consequently exercised upon the cell-contents. It is an ascertained fact that the cell-membranes are elastic; and it thence naturally follows that, according to the greater or less amount of the contents of the cells, so will these suffer a greater or a less pressure. This, however, reacts again upon the absorptive and excretive processes, so that under a more considerable pressure the latter, under a less, the former prevails, and in certain cir- cumstances it may conduce to the maintaining of a regular interchange of substances. Bonders believes, that the greater density of the cell-contents may be derived from their always being under greater pressure than the cytoblastema.] §16. Excretive processes, — The vegetative functions of animal cells are not limited to mere absorption and metamorphosis, but substances are excreted as a result of their operation. This may take place in two ways.' 1. The cells give out unaltered, the substances which they have received from without. — This occurs in the epithelium cells of those glands which, like the kidneys, lachrymal glands, lungs, &c., simply permit of the discharge of substances from the blood, also in those cells which line the serous membranes, and probably many others. 3. The cells excrete substances which they have prepared within themselves. — Thus the blood-cells give up their hsematin in dilute blood-plasma; the fat cells their fat in emaciated persons ; the hepatic cells, bile ; those of the gastric glands, gastric juice; those of the mucous glands and membranes, mucus. The occurrence of these excretions, of which, in fact, there are assuredly very many with which we are still unacquainted, may in some cases be explained by exosmose ; in others how- ever, as in the secretions of the glands, this cannot take place. Here the exit of the contents is a consequence of the pressure CELLS. 45 to which they are exposed, which pressure is to be referred upon the one hand to the force of the blood, on the other to an attractive force exercised by the cells themselves in absorbing the substances, and to the elasticity of the cell-membranes. The excreted matters in general no longer continue in the organism, but are completely removed as in the glands; in a few localities they remain, taking a solid form, as extra- cellular substance, outside the cells, and form the genuine membraruB proprm of the glands (e. g. of the renal canals), the proper envelope of the chorda dorsalis, and probably also the so-called vitreous membranes (capsule of the lens, membrana Demoursii). An intercellular substance is rare in animals, for the matrix of the cartilages and bones, which for the most part is not excreted by the cells, but is deposited from the blood- plasma or is even formed out of the cells, does not come under this head. It may be said to be present in a smaller quantity and more fluid, however, not only in the cellular tissues, but also in the higher structures, among which there everywhere exists a small quantity of connecting substance. Inter- cellular spaces developed by the excretions of cells between one another, have not been demonstrated with certainty in animals, yet it is probable that most glandular cavities and those of the heart and of the great vessels are of this nature, since they appear to arise by the excretion of fluid in the interior of originally compact masses of cells. [My view, that the genuine membrana propria and the vitreous membranes are formed as excretions, is founded par- ticularly upon the examination of the chorda dorsalis and of the renal canals, in which it may be readily shown that the structureless membranes are secondary formations, arise in in- timate union with the cells of this part, and from the very first appear perfectly homogeneous. The supposition of many authors, especially of Reichert, that these membranes belong to the homogeneous connective tissue, is readily refuted by chemical examination, since they yield no gelatine, but consist of a substance which most closely approximates to the sarcolemma and elastic tissue (comp. Mensonides in 'Nederl. Lancet.' d. iv, 694, and Bonders, ibid., August, 1851, p. 73). To what extent homogeneous membranes formed by excretions from 46 GENERAL ANATOMY OF THE TISSUES. cells, occur among animals is not yet determined^ but the homogeneous chitin-investments of the intestine, and of the external surface in the Articulata, appear to be of this nature.] § 17. Contractility of the Cells. — Among the vital phenomena of cells must be enumerated those contractions which are mani- fested by cell-membranes and also by cell-contents. Contractile cell-membranes are possessed by many if not all Protozoa j and among subordinate cells, by the yelk-cells of the Planarise, the heart-cells of many embryos {Alytes, Sepia, Limax), the cells of the tail of embryo Botrylli. The cilia also, as processes of the cell-membrane, may be mentioned here. Contractile cell-con- tents are found in the fibre-cells of the smooth muscles, in the stellate cells of the skin of the embryo of Limax, and in the animal muscular fibres ; which last, as they consist of a number of united cells, may be here enumerated. Here also I place the contractile phenomena exhibited by the contents of the Protozoa (contractile vesicles) and by the Rhizopoda.'' [Bonders has recently promulgated the view that it is only the cell-contents which are contractile, not the cell-membranes. Although it must be granted, that it is difficult, in the cases in question, to decide what part of the cell contracts, yet it seems very hazardous to endeavour to refer the movements of the cilia in plants and animals, in free and combined cells, to indemonstrable contents in these cilia communicating with the cell. In the cells of the Planarise and in the Protozoa, any one who has actually seen the movements will hardly refer them to anything but the cell-membranes. In the transversely ' [To this list of contractile cells must be added the colourless corpuscle of the blood of man, the Frog and the Skate, and probably that of other Vertebrata (Wharton Jones, /. c), the cells which lie io the meshes of the areolar tissue of the disc of the Medusse (Cyancea), and the young epithelium cells (mucus-corpuscles) of the mucous membranes, in which most distinct protean movements, like those of the colourless corpuscle, may be observed. It is certainly the membrane which contracts in these cases, for it pushes out processes which are only subsequently filled by the granular contents. In the lower plants (/fjyffl) the occurrence of contractile processes in the shape of cilia is universal, and the contractility of the cell substance In the zoospores of Volvox is evinced by the occurrence of a rhythmically contracting space in them. {See Busk on Volvox ghhator, ' Quarterly Journ. of Micr. Sc.,' No. 2, 1853.) — Eds.] CELLS. 47 striated muscular fibres on the other hand, it is evidently the fibrillse or the contents which are contractile, and the sarco- lemma, as an elastic yielding body, only moves with them : the same appears to hold good with the muscular fibre-cells, in which a special membrane cannot be demonstrated.] §18. Metamorphoses of Cells — Kinds of Cells. — The destination of the cells which are found at an early period in the organism is very various. A very considerable portion of them remain but for a short time in their primitive condition, and subsequently coalesce with others to form the higher elementary parts. Another portion, while they enter into no such combinations, change more or less their previous nature ; as the homy plates of the epidermis and nails. Many cells, lastly, never become metamorphosed at all, but remain as cells, until sooner or later, often not before the decay of the organism, they dis- appear accidentally or typically, as the epithelia, glandular parenchymata, &c. The permanent cells may be most conveniently arranged under the following heads : 1. True cells, which have in no essential respect altered their cellular nature. These occur in the epidermis {stratum Malpighii) and the epithelia; in the blood, chyle, lymph; in the glandular secretions, in the fatty tissue, in the grey nervous substance, the red bone-medulla; in the glands (liver, spleen, suprarenal capsules, closed glandular follicles), and the carti- lages. According to their form, these cells may be divided into round, discoid, cylindrical, conical with cilia, and stellate ; according to their contents, they may be distinguished as con- taining fat, protein or serum, hsematin, bilin, pepsin, mucus, or pigment ; and as to their modes of occurrence, some are either isolated in fluids or in solid tissues, others are united into a simple cellular parenchyma, while others are conjoined by an intercellular substance of one kind or another. 3. Metamorphosed cells, which have more or less altered their original structure. To these belong : a. The horny scales : flattened, polygonal, or fusiform ; their membrane being fused into one mass with the contents. In the epidermis, the laminated pavement epithelium,the hairs and nails. 48 GENERAL ANATOMY OF THE TISSUES. b. The contractile fibre cells : fusiform, slightly flattened, considerably elongated cells, whose membrane, together with its soft, solid contents, is changed into a contractile substance. In the smooth muscles. c. The tubules of the lens: very much elongated cells, with viscid, albuminous contents. d. The prisms of the enamel ; greatly elongated, prismatic, and strongly calcified cells.^ e. The bone cells : thickened cells with- pore canals which have coalesced with the homogeneous matrix of the bones and anastomose by means of excavations in it. /. The transversely striated muscular cells : large polygonal cells, whose contents have become metamorphosed into a trans- versely striated tissue, such as is found in the transversely striated muscular fibre. In the endocardium of ruminants. B. HIGHER ELEMENTAHY PARTS. §19. The higher elementary parts correspond, genetically, to a whole series of the simple ones, and it is the cells only, so far as we know, which possess the faculty of producing them. The manner in which this takes place varies. Either the cells while they coalesce retain their cellular nature, and to a certain extent their independence, in which case we have, according as they are fusiform or stellate cells, cell-fibres or cell-reticulations ; or the cells in uniting totally surrender their independence, in which case they form, if they are arranged in lines, elongated elementary parts ; or are united by many offsets, — networks ; or are fused together upon all sides, — membranes. The two former of these again, according to the kind of modification undergone by the contents of the united cells, appear either as fibres, bundles of fibrillce and tubes, or as fibre-networks and tubular plexuses. Since all these elementary parts will be spoken of at length afterwards, among the tissues, we may here simply enumerate them as follows. They are : a. The cell-fibres and cell-networks. — To these belong a part of the nuclear fibres of authors, the cartilage cells of certain ' [Vide infra, § on the Teeth. — Eds.] CELLS. 49 Plagiostome fishes (see Leydig, 'Beitrage zur mikr. Anat. u. Entwickel. d. Rocheu u. Haie./ Leipzig, 1853), the pigment cells of the lamina fusca, pia mater, and of Batrachian larvse, the networks of the nerve cells in the brain of the Torpedo (R. Wagner), the fatty substance of the Lepidoptera (H. Meyer, ' Zeitschrift fiir wiss. Zool.,' Bd. i, st. 178). b. The elastic fibres, fibrous networks, and fibres. c. The fibres of connective tissue, the networks of connective tissue (reticulated connective tissue), and the membranes com-, posed of connective tissue (homogeneous connective tissue). d. The transversely striated muscular fibres and muscular- fibre networks. e. The nerve-fibres and nerve-fibre networks. f. The capillary plexuses of the blood-vessels and lymphatics. g. The trachea and tracheal plexuses of the invertebrata. All these higher elementary parts possess essentially the same properties as cells, especially growth in length and thickness, absorption, metamorphosis, and excretion, and to some extent contractility ; together with other functions which may perhaps also be demonstrated in cells. Their growth is manifested by the fact, that all, without exception, are much shorter and narrower immediately after their formation than subsequently; their absorptive powers, by the dependence of their functions upon the circulation, by the phenomena of resorption in the lymphatics and blood-vascular capillaries, and by the above- mentioned growth, which can only take place by the reception of substances into their interior. A metamorphic and an excre- tive power must be assumed to exist in them ; it is testified by the well-known peculiar products of decomposition of the muscles, and also by the continual transmission of blood-plasma through the walls of the capillaries. The muscular fibrils possess contractility, and the processes in the nerve-fibres, though very peculiar, and at present not to be defined more nearly, may nevertheless in some respects be compared to the functions of the nerve-cells. [With regard to the tracheae, which are placed here only for completeness' sake, I long since found that their terminations are formed by the coalescence of stellate cells into tubes, in which the original cell-contents either remain or become de- 4> 50 GENERAL ANATOMY OF THE TISSUES. veloped into a spiral fibre ; and I published a concise notice of the fact in the year 1849 (' Zeitschrift fiir wiss. Zool./ Bd. i, p. 215, Anmerkung), a view which has since been confirmed by H. Meyer (Ibid., Bd. i), and more recently by Leydig (Ibid., Bd. iii, Heft 4). Literature of the Elementary parts. — In addition to Schwann's work quoted above, may be named: Kolliker, 'die Lehre von der thierischen Zelle,' in Schleiden u. Nageli's 'Zeitschrift fiir wiss. Botanik.,' Heft ii, 1845 ; Eemak, ' Ueber extracellulare Entstehung thierischen Zellen und die Vermehrung derselben durch Theilung u. iiber Entstehung des Bindegewebes u. d. Knorpel,' in Miiller's 'Archiv,' 1853, i. (No longer available. Remak assumes quite confidently, what I only indicated, that animal cells have a primordial utricle, without giving any demonstration of the fact; he describes the multiplication of cells by division to be widely extended through embryonic tissues J finds (what others wiU not easily succeed in doing) two membranes in the later cleavage-masses, and wrongly, denies altogether the occurrence of free cell-development) ; also the treatise of Bonders, cited below under the head of elastic tissue J and the embryological monographs of Reichert, BischofF, Vogt, Remak, and myself. Inasmuch also, as the doctrine of the vegetable cell is important for zoologists, I call attention to Schleiden's first treatise (' Abhandlung iiber die Bildung d. Pflanzenzelle,' Miill. 'Arch.,' 1837) j to his 'Elements of Botany/ to Nageli's Essay ' Ueber die Pflanzenzelle,' in the ' Zeitschrift fiir wissenschaftlich. Botanik,' Heft ii; and to Mohl's Mono- graph upon this subject, in Wagner's 'Handworterbuch' ('Mohl on the Vegetable Cell,' translated by A. Henfrey, Lon- don, 1852) . [To these should be added the more recent works of Dr. H. Schacht, ' Die Pflanzenzelle, &c.,' Berlin, 1852 ; and of Alex. Braun, ' Ueber verjiingung,' Leipzig, 1851. — Eds.] III.— OF THE TISSUES, ORGANS, AND SYSTEMS. § 20. The elementary parts of both the simpler and the higher kinds, are not dispersed irregularly in the body, but are united according to determinate laws, into the so-called tissues and TISSUES. 51 organs. Under the first denomination comes every constant arrangement of the elementary parts always recurring in similar modes in the same parts; under that of an organ, on the other hand, a certain sum of elementary parts having a definite form and function. When several or many organs of a similar or different kind are united into a higher unity, this is called a system. The tissues are of different kinds, according as structural elements of one kind only occur in them, or as various elements and even organs take part in their formation. We can thence distinguish simple and complex tissues, which, however, cannot be sharply separated from one another, and which may be most fittingly arranged in the following series ; (a.) Simple tissues. 1. Epidermic tissue. 2. Cartilaginous tissue. 3. Elastic tissue. 4. Connective tissue. (b.) Complex tissues. 5. Osseous tissue. 6. Smooth muscular tissue. 7. Transversely striated muscular tissue. 8. Nervous tissue. 9. The tissue of the blood-vascular glands, r ~ (. 10. The tissue of the true glands. \\ ^J (►^^'^ The organs may be divided like the tissues, into simple and complex. To the simple belong : (a.) Horny tissue, as the epidermis, the epithelia, hairs, nails, and the lens, which consist solely and wholly of epithelial cells of one kind or another. (b.) The true cartilages and the elastic cartilages, which in their interior, with few exceptions, consist only of cartilaginous tissue, though externally they possess a vascular and nervous coat, the perichondrium. (c.) The elastic ligaments, consisting of elastic fibres, with some connective tissue, and containing only at the surface a few vessels and nerves. {d.) The tendons, ligaments, true fibrous membranes, and fibro- cartilages, containing a preponderance of connective tissue, 52 GENERAL ANATOMY OF THE TISSUES. intermixed with fine elastic fibres, and sometimes cartilage cells in small quantities, and almost entirely devoid of vessels and nerves. Complex organs are : (e.) The smooth muscles and muscular membranes; and — (/.) The transversely striated muscles and muscular mem- branes, both of which, besides their contractile elements, are abundantly intermingled with connective tissue, nerves, and blood-vessels. (^.) The nerves, ganglia, and higher central organs of the nervous system, contain besides grey and white nervous sub- stance, many blood-vessels, and special fibrous investments. (A.) The vessels are composed of connective and elastic tissue, muscles and epithelium in various proportions^ and are provided with vessels and nerves, only in their outermost layers. (i.) The bones and teeth, which, together with their charac- teristic tissues, have peculiar soft structures, containing many vessels and nerves, and the former medulla also. (A.) The blood-vascular glands, composed of a peculiar glan- dular element, in the form of closed follicles of different kinds, and many blood-vessels; with nerves also, and with abundant but generally non-contractile fibrous tissue. (/.) The true glands; glandular follicles, vesicles or tubes with many vessels, nerves, and investing fibrous tissue. {m.) The vascular membranes, as the skin, the mucous, serous, and proper vascular membranes, which in a matrix composed of connective and elastic tissue, generally contain very numerous blood-vessels and lymphatics, in part also simple glands and nerves, and are invested by special epithelial layers. {n.) The separate organs of the tractus intestinalis, as the tongue, the oral cavity, the pharynx, the oesophagus, the stomach, and so forth, into the constitution of which, mucous, muscular and serous membranes, grouped in various ways, enter. (o.) The higher organs of sense, into which almost all the tissues and many more simple organs enter. Lastly, the organs enter into the formation of peculiar systems, of which we may distinguish the following : TISSUES, ORGANS, AND SYSTEMS. 53 1. The external cutaneous system, consisting of the corium, the epidermis, the horny tissues, and the larger (lacteal gland) and smaller glands of the skin. 3. The osseous system, consisting of the bones, cartilages, ligaments, and articular capsules. 3. The muscular system, consisting of the muscles of the trunk and of the extremities, the tendons, fasciae, tendinous ligaments, and bursoe mucosa. 4. The nervous system, composed of the larger and smaller central organs, the nerves and the higher organs of sense. 5. The vascular system, consisting of the heart, the blood- and lymph-vessels, and the lymphatic glands. 6. The intestinal system, composed of the intestinal canal, the organs of respiration, with the thymus and thyroid, the salivary glands, the liver, and the spleen. 7. The urinary and sexual systems. As the separate organs and systems are particularly con- sidered in the special part- of this work, it is not necessary to speak at greater length of them here, and it is only requisite to define the tissues somewhat more closely — staking occasion at the same time to refer to some generalities concerning the organs. § 2]. Epidermic Tissue. — The morphological character of the epidermis is, that it is wholly constituted by independent cells intimately united together without any visible matrix, which are generally nucleated and in part are true vesicles, while in part they are metamorphosed into solid scales. In its chemical characters this tissue is but little known, though this much has been made out, that its cells contain chiefly an albuminous sub- stance, in part also mucous ; and at first all possess easily soluble protein membranes, which however, subsequently, become partially changed into a substance which more or less resists acids and alkalies, — the so-called horn. The physiological im- port of the epidermic tissue is to serve as a defensive covering to those parts of the organism which abound in vessels and nerves, and by the activity of its elements to take part in secretion and absorption. All epidermic tissues are non- vas- cular, and support themselves from a plasma which is yielded 54 GENERAL ANATOMY OF THE TISSUES. by the deeper-seated vessels. They are very easily regenerated when their superficial portions are removed, and in this case they grow chiefly by the development of new elements in the deeper layers ; .even when wholly lost they are readily reproduced. The epidermic tissue takes the following forms ; 1. Corneous tissue. — This always consists of compact masses of cells, which are soft in the neighbourhood of their vascular basis, but at a greater distance become more or less solid and hard (corneous), and frequently lose their originally vesicular constitution and nucleus, and become the so-called horny scales. The following organs are formed by this tissue : a. The Epidermis ; which invests the exterior of the body, and is continuous at the great aper- tures of the internal cavities with the epithelium. It consists of two tolerably distinct layers ; the mucous layer (re^e mucosum), with soft, rounded polygonal cells, which, under certain circumstances, contain colouring mat- ter. This layer applies itself accu- rately to all the inequalities of the co'rium (which nourishes the epidermis), and externally passes into the polygonal scales of the horny layer. d. The Nails. — These may be regarded as a modification of the epidermis, whose horny layer has attained a still greater density; and, with its rete mucosum, lies upon a special depressed surface of the cutis, — the bed of the nail; and is partly sunk in a peculiar cleft, — the fold of the nail. • c. The Hairs. — Filiform epidermic' structures, seated upon a viscular papilla, in a peculiar sac, the hair sac, which is a process of the corium, and is lined by a continuation of the epidermis. The structural elements in the region of the papilla are soft and vesicular ; the more distant are meta- morphosed into three kinds of cells — plates, flat fibres, and more or less rounded irregular cells. Fig. 12. Plates of the horny layer in man, x 350; 1, without addition, viewed from the surface, one with, a nucleus ; 2, from the side. ' [It is to be questioned if the liaiis arej truly epidermic structures, vide infra, § Hair.— Eds.] Al SSUES, ORGANS, AND SYSTEMS. 55 2. Epimelium. — Soft nucleated cells, nowhere densely corneous ,' rounded, polygonal, fusiform, cylindrical or conical in shape; sometimes possessing cilia, sometimes not, and occurring in one or many layers. Hence we have the fol- lowing forms : a. Epithelium in a single stratum. / (1) With rounded, polygonal cells (pave- ment epithelium in: a single layer). J This exists as an investment of tj{e true serous membranes, of most synovial mem- branes, of the cerebral ventricles {ephndyma) of the membrane of Demours, of the back of the iris, and of the inner surfacfe of the choroid (pigment layer), of the tPapsule of the lens and of the retina, of l^he internal ear, of the > endocardium, of the veins, of manySglandular vesicles 3»a canals (racemose glands, kidneys, sudortpi|rouS"--ft»ir^6rumi- nous glands, lungs), and of the ductus interlomlares of the liver. (3) With fusiform, superficially united cells (fusiform epithelium). Epithelium of the arteries, and of many veins. (3) With cylindrical cells (cylinder- epi- thelium). In the intestine from the cardia to the anus, in Lieberkiihn's glands, in the ex- cretory ducts of the gastric glands, as well Kg. 14. Fig. 15. as of aU the other glands which open into the intestine; also of the lacteal and lachrymal glands; in the male urethra, the vas deferens, the vesicuke seminales, the excretory ducts of the prostate, of Cowper's, Fig. 13. Epidermis of a two months' human embryo, still soft, like epithe- lium, X 350. Fig. 14. Epithelial cells of the vessels, the longer ones from the arteries, the shorter from the veins. Fig. 15. Epithelium of the intestinal villi of the rabhit, x 300. 56 GENERAL ANATOMY OF THE TISSUES. Fig. 16. Fig. X7. Bartholini's, and the uterine glands. ^ (4) With cylindrical or coni- cal ciliated cells (simple, cili- ated cylinder-epithelium). Epithelium of the finest bronchise, of the nasal cavities, of the inner surface ofihemembrana tympani,o{the Eustachian tube, of the uterus, from the middle of the cervix, up the Fallopian tubes, as far as the outer surface of the fimbrue. (5) With rounded ciliated cells (simple, ciliated pavement- epithelium). Epithelium of the cerebral cavities of embryos. b. Epithelium in many layers — (1) With cylindrical or rounded cells below, rounded, polygonal, more or less flattened cells above (laminated pavement- epithelium) . Epithelium of the oral cavity, of the lower half of the pharynx, of the oeso- phagus, of the lachrymal canals, of the conjunctiva, of the tympanic cavity, of the vagina and female urethra, of the urinary bladder, of the ureters and pelves of the kidneys, and of certain synovial membranes. (2) With rounded cells below, more elongated ones in the middle, and ciliated conical ones above (lami- nated ciliary epithelium.) Epithelium of the larynx, trachea, and larger bronchise; of the nasal cavity, with exception of the regio olfactoria ; of the lachrymal sac and duct ; of the upper half of the pharynx. Fig. 16. Ciliated cells from the finer bronchiae, x 350. Fig. 17. A simple papilla with manifold vessels and epithelium, from the gums of a child, X 250. TISSUES, ORGANS, AND SYSTEMS. 57 Among the epidermic tissues Pi- ig_ we may also enumerate the crystalline lens and the ena- mel.^ The former consists of long tubular cells filled with albumen, which, as the study of development teaches, are formed by the metamorphosis of a part of the epidermis. The latter contains prismatic, densely-ossified long fibres, which, in all probability, are also nothing more than excessively elongated epithelial cells of the enamel organ of the em- bryonic tooth sac. [The epidermic tissue is found through almost the whole animal kingdom, and as regards its elements, it exhibits no very considerable deviations in animals. One of its kinds, the horny tissue, appears to occur more generally, and to some extent in peculiar forms. To it belong (a), among structures which appertain to the skin : claws, hoofe, horns, spines, plates, and discs, bristles, feathers, and penis-spines, {b), Among appen- dages of the mucous membranes : the horny sheaths of the beaks of birds, of Chelonia, of the Siren and Ornithorhynchus ; the hqrny teeth of the Cyclostome fishes ; of the Ornithorhynchus, of the giU rays of fishes, and of Batrachian larvae ; the whale bohe, the spines and plates of the tongue of Birds, Mammalia, and some Amphibia ; the spines of the oesophagus of Chelonia; the jaws of Cephalopoda and other Invertebrata ; the gastric teeth of many mollusks ; the horny plates of the bird's stomach. In all these structures, but often only by the aid of caustic alkalies, horny plates of one kind or another, as in the corneous structures of man, are discoverable. On the other hand, the hard tissues of the Articulata diifer not only morphologically but also chemically from them, consisting as they do. of a peculiar substance, chitin, and exhibiting no cellular structure.] Fig. J 8. Ciliated epithelium from the trachea of a man, x.350 : a. outermost part of the elastic longitudinal fibres ; b, homogeneous outermost layer of the mucous membranes; c, deepest round cells) d, median long cells; e, outermost ciliated cells. ' [ Vide infra, note § on the Teeth.] ». 58 GENERAL ANATOMY OF THE TISSUES. Literature. — Purkinje et Valentin, 'Dephsenomeno general! et fundamentali motus vibratorii contimii/ Vratisl. 1835, (Discovery of ciliary movement in the higher animals) ; Henle^ 'Symbolse ad anatom. vill. int./ Berol. 1837; 'On the distri-i bution of the epithelium in the human body/ Berlin, 1838j and upon the development of mucus and pus, and their relation to the epidermis (first exact description of the different epidermic cells) ; Valentin, art. Ciliary Motion, in Wagner's 'Handworterbuch/ Jasche, 'De telis epithelialibus in specie et de iis vasorum in genere,' Dorp. 1847. § 33. Cartilage. — Cartilage consists of a solid, but elastic, bluish, milk-white or yellowish substance, which presents two morpho- logical conditions; appearing, firstly, as a simple parenchyma composed of cells; and secondly, as a cellular tissue, with an intermediate substance or matrix between the elements. The cartilage cells present little peculiarity in respect of form; they are generally round or elongated, frequently flattened or fusiform, very rarely stellate (in Cuttle-fishes and Sharks, and in enchondroma). Their membrane is ordinarily thick, frequently invested by concentric laminae; the contents are clear and more fluid with a single nucleus, and, though not constantly, with one or many fat globules. The interstitial substance is either homogeneous or finely granulated or fibrous, even with clear separable fibres. The chemical characters of cartilage are in some respects but little known. It is ascertained, however, that the cells and the intermediate substance are composed of different substances. The membranes of the cartilage cells, in fact, are not dissolved by boiling, and offer a lengthened resistance to alkalies and acids, peculiarities which distinguish them from the substances which yield gelatine, but approximate them to elastic tissue. The contents of the cells coagulate in water and dilute acids, and are readily dissolved by alkalies. The interstitial substance is, in most cartilages, chondrin, and only in the reticulated cartilages is it a substance closely allied to that of the elastic tissue. Consequently the cartilages, which consist only of cartilage- cells, yield no gelatine upon boiling, and its occurrence is no essential character of cartilage. Physiologically, the solidity and elasticity of the cartilages are TISSUES, ORGANS, AND SYSTEMS. 59 particularly to be noted, as by these properties it is fitted for its various uses. In growing cartilages the change of material is very energetic ; they constantly contain, in certain localities, numerous blood-vessels in peculiar canals j and, as I have demonstrated in the nasal cartilage of the calf, even nerves. Their growth takes place, firstly, by endogenous multiplication of cells, traces of which are always clearly to be observed in perfect cartilages; and secondly, by the deposition between the cells, which originally exist alone in all cartilages, of an interstitial substance from the blood plasma, which, accord- ing to Schwann, at first yields no chondrin even in the true cartilages, and subsequently gradually increases in quan- tity. In perfect cartilages the nutrition is by no means energetic; and it has, apart from the vessels of the peri- chondrium which invests many cartilages, and those of the neighbouring bone, no particular agent, except in the cartilages (septum of the nose) of a few mammalia, and in the plagiostome fishes, in some of which last, according to Leydig, even in old individuals, vascular canals exist {Raja), in others anastomosing, fusiform, or stellate corpuscles (Sharks). With age, the intermediate substance of certain true cartilages readily becomes fibrous, and very similar in its chemical characters to that of the reticulated cartilages, which demonstrates that these two kinds of cartilage are not widely separated ; the true cartilages also not uncommonly ossify, vessels, cartilage, and medulla being formed in them at the same time. Cartilage possesses no power of regeneration, nor do _. .„ wounds in cartilage unite by cartilage ; on the ^ other ha,nd, an adventitious development of cartilage is not uncommon. The different kinds of cartilage are : a. Cartilage witfiouf interstitial substance, or parenchymatous cartilage. To this belong the chorda dorsalis of the embryo and of many adult fish ; many foetal cartilages ; the carti- lages of the gill laminae of fishes in part ; and those of the external ear of many mammalia. b. Cartilage with interstitial substance. Fig. 19. Portion of the chorda dorsalis of an embryo sheep, 6'" long; a, shealli ; *, cells, with clear vesicular spaces. 60 GENERAL ANATOMY OF THE TISSUES. Fig. 20. Fig. 21. I. With a more homogeneous, chondrin-yielding substance: true cartilage, hyaline cartilage : it is found in the larger cartilages of the respiratory organs, those of the articulations, of the ribs, and of the nose ; also in all symphyses and synchondroses im- mediately in con- tact with the bones j in the talus ossis cuboidei, and in the so-called ossifying cartilages of the fcetus. 2. With a fibrous inter- stitial substance, yielding no chondrin, or but very little : reticulated cartilage, yellow cartilage, fibro-cartilage in part; epiglottis, cartilagines Santoriniance, WrisbergiancB, cartilage of the ear and of the Eustachian tube ; liga- menta intervertebraliamTpart. [In the Invertebrata many tissues of a similar consistence to cartilage are found, but true cartilage has hitherto been dis- covered only in the Cuttle-fishes.] Literature. — Meckauer, ' De penitiori cartilaginum structure Diss.,' Vratisl., 1836 ; J. Miiller, in ' Poggendorf 's Annalen,' 1836, p. 293 ; Rathke, in Froriep's ' Notizen,' 1847, p. 306 ; A. Bergmann, 'De cartilaginibus Disq. micr.,' Mitavise, 1850. § 23. Elastic Tissue, — The elements of elastic tissue are cylindrical or band-like fibres, with dark contours, which vary in their Fig. 20. Cartilage cells from the white layer of the cricoid cartilage, < 350. From man. Fig. 21. Portion of a human epiglottis, x 350. TISSUES, ORGANS, AND SYSTEMS. 61 diameter from immeasurable fineness up to - a thickness of 0-003'", and even 0005'" (in ^' animals even to as much as 0008'"), and when they are present in quantity, exhibit a yellowish colour. These so-called elastic fibres are, when perfectly formed, quite solid, but may subsequently acquire little cavities in particular spots; and these, in one animal, the Giraffe (Quekett, ' Histo- logical Catalogue,' i), are so regular, that the fibres present a pretty transversely striated appearance. The margins of the elastic fibres are in general quite rectilinear, but in sonje rare cases appear to be notched and even, asVirchow saw them, in newly-developed tissues, beset with a great number of shorter and longer pointed processes. Hitherto the elastic fibres have been separated from the nucleus fibres: since, however, the latter are distinguished from the former in nothing but their diameter; furthermore, as all elastic fibres are originally as fine as nucleus-fibres ; and since, finally, the latter are not formed of nuclei alone, it will be better wholly to suppress the name of nucleus-fibres, and to divide the elastic fibres simply into finer and coarser. The elastic fibres are found either isolated as longer or shorter fibres, which may be straight or wind spirally round other parts (bundles of con- nective tissue, nerves), and in this case they are commonly of the finer kind ; or by the anastomosis of fibres of different sizes, a so-called fibrous elastic network is formed, which is sometimes expanded in a membranous form, and sometimes penetrates other tissues to various depths. A modification of this fibrous elastic network is formed by the elastic membranes, in which the fibres are so closely interwoven, that a connected membrane arises, which in the most extreme cases no longer exhibits any indication of its previous nature, and appears as a perfectly homogeneous membrane with smaller gaps (the fenestrated membrane of Henle). Chemically, elastic tissue presents very decided reactions, but the composition of its substance is not yet exactly known. In cold concentrated acetic acid, the elastic fibres, except that Fig. 22. Elastic network from the tunica media of the pulmonary artery of a horse, with lacunae in the fibre, x 350. 62 GENERAL ANATOMY OF THE TISSUES. they swell a little, are not affected ; if boiled for a whole day, however, they are gradually dissolved : nitric acid colours them yellow J Millon's test for protein tinges them red ; whilst sul- phuric acid and sugar have no action (red coloration) upon Fig. 24. Rg. 23. Fig. 25. them. In a moderately diluted solution of potass, elastic tissue remains, for a long time, unaltered in the cold, except that it swells up and becomes somewhat paler. Heated for a day with it, it becomes converted into a gelatinous mass. In water this tissue does not alter, even after sixty hours' boiling, but changes by boiling for thirty hours in Papin's digester into a brownish substance, smelling like glue, but not gelatinizing, which is precipitated by tannic acid, tincture of iodine, and corrosive sublimate, but not by the other tests for chondrin. Fig. 23. Two secondary buudles of connective tissue from the arachnoid of man, with coiled and straight (interstitial) fine elastic fibres, x 350, and acetic acid added. Fig. 24. Network of fine elastic fibre from the peritoneum of a child, x 350. Fig. 25. Elastic membrane from the tunica media of the carotid of the horse, x350. TISSUES, ORGANS, AND SYSTEMS. 63 Kg. 26. Fig. 27. Physiologically, the prominent characteristic of this tissue is its elasticity, in consequence of which it forms a most essential support to the motor organs, and also plays an important part in other situations, e. g. in the vocal ligaments. With respect to its development, the supposition of Schwann, that this tissue pro- ceeds from cells, receives increas- ing support from modern investiv gations; in fact, in all those organs which subsequently contain elastic tissue, there may be discovered in embryos, peculiar fusiform or stellate, sharply-pointed cells, which by their coalescence pro- duce long fibres or reticulations, in which at first, those localities where the bodies of the cells pre- viously existed may still be recog- nised as enlargements containing elongated nuclei in their interior. In this condition the fibres not unfrequently remain, and they then form a modification of what were formerly called nucleus-fibres, or every trace of their pre- vious composition disappears, so that quite homogeneous fibres or fibrous reticulations are produced. These may then either remain through life as fine elastic fibres and networks, or by increasing in thickness they may pass into the coarser form of the tissue. The more homogeneous elastic membranes are nothing but close elastic networks, whose fibres have so much increased in diameter, that only narrow spaces remain between them. The perfect elastic tissue appears to undergo very little change of substance — at least it is, so to speak, non-vascular, even when it occurs in large masses; on Fig. 26. Formative cells of the elastic fibres, x 350, from the tendo-achillis : a, of a four months' embryo ; b, from a seven months' fcetus, — a few cells free, with one and two processes, others united by twos and threes. Fig. 27. Stellate formative cells of the nucleus fibres out of the tendo-Achillis of a new-born infant, x 350. 64 GENERAL ANATOMY OF THE TISSUES. the other handj in those forms which still present indications of the original cells, a certain movement of the juices may still take place. Elastic tissue is not known to be regenerated, but new formations of it are not rare. The elastic tissue is rarely found in large masses, but it is very frequently mixed with connective tissue, either in the form of isolated fibres or of networks of various kinds. As true elastic organs we may mention : a. The elastic ligaments, in which the tissue, with only a slight admixture of connective tissue and hardly any vessels and nerves, exists, so to speak, in a pure form. As such we have the ligamenta subflava of the vertebrae, the ligamentum nuchee, certain ligaments of the larynx, the stylo-hyoid liga- ment, and the ligamentum suspensorium penis. b. The elastic membranes, which appear in the form either of fibrous networks or of fenestrated membranes, and are found in the walls of the vessels, especially in those of the arteries, in the trachea and bronchia, and in the fascia superficialis, [In all the vertebrate classes the elastic tissue is found in the same localities as in man, and in a few particular situations besides, as in the ligaments of the cat's claw, in the alary membrane of mammals, in the folds of the alary membrane and in the lung sacs of birds. In the Invertebrata this tissue appears to be rare, and it is not even certain that the elastic ligaments which occur in them (as, for example, in bivalves), agree anatomically and chemically with the elastic tissues of the higher animals. Of the different parts belonging to the elastic tissues, the so-called nucleus-fibres of Gerber are almost alone those whose development has been examined. With regard to these, Henle's view, that they arise by the coalescence of elongated nuclei, was almost universally received, until lately Virchow and Bonders nearly contemporaneously brought forward another conception. Both these authors proceed from the invest!-, gation of the connective tissue, and show that what in it have been held to be elongated, isolated, or more or less coalesced nuclei, are nothing more than fusiform or stellate cells, with fine processes, which closely surround a generally elongated nucleus, and are partly united into fibres or networks. With TISSUES, ORGANS, AND SYSTEMS. 65 regard to the development of these cells, Virchow deduces from Schwaun's observations, and Bonders from his own investi- gations, the result that the well-known fusiform cells in the rudimentary areolar tissue of embryos are nothing more than the formative cells of the so-called nucleus-fibres ; to which, then, as a consequence, it is added that the proper connective tissue does not proceed from cells, but is nothing else than J fibrillated c ytobks tema. Hence both these authors agree in placing connective tissue and cartUage side by side and, in comparing the formative cells of the so-called nucleus fibres, which Virchow calls "connective-tissue corpuscles," (Binde- gewebskorperchen,) with the cartilage-ceUs j the interstitial substance of the cartilage, with the fibrous part of the con- nective tissue. Virchow goes still further, and compares even the bone substance to connective tissue j especially that which is developed by the ossification of what I have called soft blastema, in which the bone cavities, he supposes, proceed from stellate anastomosing "connective-tissue corpuscles," a view which seems chiefly to have led him to declare that the nucleus-fibres are hollow, and form a great system of tubules and cavities through the connective tissue, thus probably subserving nutrition. It could be imagined that the nutritious fluid might thus be quickly conducted for considerable distances, and uniformly distributed through the tissue, in which case the nuclei must be considered to be the special regulative portions of the apparatus, while the cells are simply conductors. If we submit these different views to the test of observation, it results that much is quite correct, but that some points are untenable. It is true, that the so-called nucleus-fibres are developed from cells ; and the fact is, indeed, noted in certain earlier statements and figures of Valentin, Hassall, Quekett, and others. In the tissues of full-grown animals, it is in many localities unquestionably impossible, in others very diflficult, to attain to certainty upon these points, because here, even when the nucleus-fibres still present indications of cells, the cell-membrane so closely embraces the elongated and by no means vanished nucleus, that it is often quite out of the question to decide whether we have a cell with two or more slender processes, or a fusiform or stellate nucleus ; on the other I. 5 66 GENERAL ANATOMY OF THE TISSUES. hand in young animals, in which also Virchow made his first observations, and especially in embryos, it is easy to come to a clear decision upon the matter. In man, I find the tendons, ligaments, and the aponeurosis palmaris and plantaris, to be especially serviceable objects ; but in all the places in which elastic tissue is mixed with connective tissue, I was able to follow their development. The observation is most successful in the foetus of three to four months. Here, in all the more solid organs composed of connective tissue, — tendons, ligaments, fascise, corium, — the proper connective-tissue fibrils are already quite well developed, while of nuclear fibres, so to speak, there are no traces. Instead of these, however, we find between the often very distinct bundle^ of connective tissue, a great number of fusiform cells of 0-01'" — -015'" in length, which in their middle (of 0003'" — 0003'" in breadth) inclose an elongated roundish clear nucleus with a nucleolus, which completely fills them, and are pi'olonged at their ends into fine dark threads. If we trace these cells, among which are always scattered many round and elongated cells out of which they are formed, and in older embryos a few stellate ones, with from 3 to 5 processes, it is found that they gradually become longer and narrower, and from the sixth month begin to coalesce with one another into elongated fibres or networks ; up to a late period, however (even 7 to 8 months), these formative cells of the elastic tissue may be easily isolated in abundance from all forms of connective ' tissue, either singly or combined by twos and threes. In the foetus at birth this can no longer be done; but here the complete nucleus fibres, at least in the more solid forms of connective tissue, still clearly exhibit their composition out of fusiform and stellate cells with nuclei; which, as we have already seen, is occasionally in some localities even the case in the adult. What holds good of the nucleus fibres may be asserted also of the elastic fibres, which are not further treated of by Bonders and Virchow. Valentin (Wagner's 'Handw. d. Phys.,' I, p. 668) found that the elastic fibres of the ligamentum nucha of the calf are considerably finer than those of the ox, and I stated ('Zeitschrift fiir Wiss- Zool.,' I, p. 11, Anm.) that all the thick elastic fibres of the adult have at one time been common nucleus-fibres. In fact, we find in the new-born TISSUES, ORGANS, AND SYSTEMS. 67 child not a single true elastic fibre, since even those of the ligt. nuchcB, of the ligt. flava, and of the aorta, when largest, do not measure more than 0*0008 — •001"'. This circumstance alone, might, if we take into account the cloSe resemblance of the elastic and so-called nucleus-fibres in other respects, be considered as a demonstration that the former are also deve- loped out of cells, but we have in addition direct evidence that this is their mode of development. In the aorta, in the ligt, nucha, and in the fascia super- ficialis abdominis of human embryos of the fourth and fifth months, we find the same short fusiform ceUs as in the common connective tissue; and their coalescence into originally finer fibres, though perhaps not quite so readily demonstrable as in the former localities, may yet be made out with certainty, so that the agreement in their genesis of the finer with the coarser elastic fibres, may be considered to be established. Not, however, to the same extent, as with regard to the genesis of the finer elastic fibres, can I agree with the authors mentioned in other points. In the first place, concerning the physiological import of the so-called nucleus fibres, I grant to Virchow that even in the adult, in some places, they appear to retain more their original character of a system of canals ; yet I can by no means allow, that these nucleus-fibres are to be regarded as a system of tubules subserving nutrition. In my opinion, all fine elastic fibres, which no longer pre- sent any trace of the original cell, i. e. those of the areolar . connective tissue of the coriwm, fascia, of the perimysium, of the periosteum, of the dura mater, of the serous membranes, of the walls of the vessels, and of mucous membranes, are solid fibres, and only of service to the organism so far as they are elastic. A relation to nutrition can only be supposed of those elastic elements of the tendons, ligaments, and of the cornea, which present conditions more nearly embryonic j but even with respect to these it does not appear so evident that it can be decidedly afllrmed. In the tendons and ligaments, for in- stance, it is plain that a part only of the elastic elements are not quite fully developed, so that possibly cavities may still exist in them; while the rest, much more considerable, are as completely developed as elsewhere, and offer no trace of a cavity. 68 GENERAL ANATOMY OF THE TISSUES. If, nowj it were assumed that the former have a determinate relation to the conduction of the nutritive fluid, it would yet remain unexplained why, in certain regions, these organs were more favoured than in others. If it be further considered, that in the tendons and ligaments, as in the connective tissue in general, vegetative molecular changes and nutrition are assuredly at their lowest stage, — furthermore, that the arrange- ment of the nucleus-fibres (their more longitudinal course, the want of anastomosis of the nucleus-fibres of the different secondary bundles in tendons) appears very little fitted to conduct nutritious fluids from the surfaces of these organs, where oidy the vessels are found, into their interior, — there wiU appear no great necessity for entering further into this hypothesis. For the cornea alone, where the elastic tissue remains in a quite embryonic stage, should I be inclined to adopt Virchow's hypothesis; and, as respects the other tissues, I can only grant that, when the elastic elements are in such an imperfectly developed condition that they still contain canals for greater or less distances, they may have a share in the distribution of the nutritive fluid which naturally inter- penetrates these organs, and, therefore, in their nutrition, but that this must rather be regarded as a secondary function, and will not justify their approximation to the fine canals of the teeth and bones, which exist specially for the purpose of nutrition. Such a function might much rather be ascribed to the undeveloped nucleus-fibres and their formative cells in the immature (pathological or normal) connective tissue ; for here, at least, the anatomical and physiological relations of the tissu6 are not opposed to such an assumption j it would amount to little more, however, than what may be asserted of every undeveloped fibrous tissue. A second and much more important point in which I differ from Bonders and Virchow is the general mode of looking at the connective tissue. Both these writers hold that it is not composed of cells, but is developed by the fibrillation of a homogeneous cytoblastema; and they believe that all the fusiform embryonic cells, which since Schwann's time have been regarded as its formative cells, belong not to it, but to the elastic tissue. I can by no means admit such a view, and it TISSUES, OKGANS, AND SYSTEMS. 69 seems to me to be comprehensible, only when we recollect that these authors arrived at it more upon theoretical grounds, than by direct observation. With Virchow, a passage in Schwann appears to have been conclusive, where he describes the embryonic connective tissue as a gelatinous homogeneous mass, which dissolves upon boiling, and contains cells dis- tributed through it which are not affected by the boiling. Virchow does not hesitate to extend this to all connective tissue, and to assume that the substance soluble in water answers to the subsequently fibrous connective tissue, while the insoluble cells are the formative cells of the so-called nucleus- fibres. Here, however, he has omitted to notice, that Schwann speaks only of a determinate form of tissue, the lax or areolated, and describes in a totally different manner the formation of the more solid connective tissue, e. g. of a tendon. In this case we find, in direct contrast to the former, no trace of cyto- blastema, which can in no way be directly observed, the tendon consisting throughout of fibre-cells, either isolated or united into bundles of connective tissue. To observe this, however, the examination must be made at a very early period, since, as Schwann has justly remarked, the elements of the fibrous tissue are very early developed ; a circumstance from neglecting to observe which, it seems that Donders has been led to adopt the same view as Virchow. For my own part I have found Schwann's statements confirmed in aU essential points, with the single exception that he was unac- quainted with the formative cells of the elastic fibres, and con- founds them with those of the connective tissue. My obser- vations upon these points are to be found in the following section. Hence I cannot admit that cartilage and connective tissue are nearly allied, inasmuch as the fundamental sub- stances of both, even if chemically agreeing, yet, genetically, are very different. Literature. — A. Eulenberg, ' de tela elastica,' 1836; Virchow, ' die Identitat von Knochen, Knorpel und Bindegewebskor- perchen, sowie ueber Schleimgewebe,' in the 'Verhandlungen der,Phys. Med. GeseUschaft in Wiirzburg,' Bd. II, 1851, p. 150 ; and ' Weitere Beitrage z. Kenntniss d. Structur der Gewebe der Bindesubstanz.' Ebend. II, p. 314; Donders in the Nederlansch Lancet.,' 1851, July and August; and in the 70 GENERAL ANATOMY OF THE TISSUES. 'Zeitschrift fiir wissen. Zool./ Bd. HI, p. 348; Kolliker, 'Ueber die Entwicklung der sogenannten Kernfasern, der elastischen Fasern und des Bindegewebes j' in 'Verb. d. Pbys. Med. Ges. in Wurzburg,' Bd. Ill, H. 1. § 34. Fig. 28. Connective Tissue. — Tbe elementary parts which are found in connective tissue may be divided into the essential, never- failing components, and those which are met with only in cer- tain localities. To the former belongs the fasciculated as weU as the more homogeneous connective tissue; to the latter, elastic fibres in their different forms and conditions of development, fat cells, cartilage cells, and pigment cells of different kinds. Besides these, connective tissue contains also no inconsiderable quantity of a gelatinous interme- diate substance. The bimdles of the connective tissue are, among the essential elements,- those which occur most frequently; each of them consists of a certain number of very fine fibrils, the connective fibrils, which are distinguished from their nearest allies, the finest elastic fibres and muscular fibrils, by their smaller diameter (O'OOOS'" — 0-0005'"), their pale colour, their homogeneous appearance, and the complete absence of striation. They are united by means of a small quantity of a clear connect- ing substance, and thus form, the bundles in question, which in many respects resemble those of Fig. 28, Lax connective tissue with fat-cells from man, x350. TISSUES, ORGANS, AND SYSTEMS. 71 the transversely striated muscles, but differ from them in the absence of any special investment comparable to the sarco- lemma, and in their smaller mean diameter (0"004"' — 0*005"'). They are either long, shghtly wavy cords, of uniform thick- ness throughout, which are not directly connected together, but arranged in different ways near and above one another, forming great lamellse and bundles ; or they coalesce like the elastic networks into meshes, and thus form what I have called the reticulated connective tissue. In rare cases the bundles appear not to be composed of fibrils, but are more homogene- ous, as in the neurilemma, where they are known as Remak's fibres. Besides this form of connective tissue, there exists a second, rarer kind, in which neither bundles nor fibrils can be clearly distinguished, but only a membranous or more or less solid, finely granulated, or slightly striated, even per- fectly homogeneous, clear tissue ; homogeneous (or Reichert's) connective tissue. The other elements which occur in con- nective tissue present nothing remarkable, and will be more particularly treated of in their proper places in the special part. The chemical relations of connective tissue are well known : proper connective substance when boiled yields common gela- tine, and contains besides a fluid, whose nature, on account of its generally minute quantity, cannot be investigated. Only where it exists in considerable proportion, as in the gela- tinous connective tissue of embryos, can the presence of much albumen and mucus be easily demonstrated in it. The che- mical qualities of the other constituents of the connective tissue will be spoken of in their place. Connective tissue is of utility to the organism according to its composition, — sometimes as a solid unyielding substance; sometimes as a soft support for vessels, nerves, and glands ; sometimes, finally, as a yielding tissue, filling up spaces and facilitating changes of position. Where elastic elements are present in it in great quantities, its nature alters ; and a great abundance of fat or cartilage cells gives it an unusual softness or resistance. The connective tissue is invariably developed from cells, and, in fact, from fusiform or stellate vesicles, which become united into long fibres or networks, and often break up into fibrils before their union. The mode 72 GENERAL ANATOMY OF THE TISSUES. Kg. 29. Kg. 30. .in which this takes place is not yet quite made out, hut it is most proba- ble that the cells, as they elongate, change, with their membrane and con- tents, into a ho- mogeneous softish mass, which subse- quently breaks up into a bundle of fine fibrils and some intermediate sub- stance. The de- velopment of the homogeneous connective tissue has as yet been little investi- gated, but it would seem, like the other, to proceed from a fusion of rounded or elongated cells, which are perhaps united by an intermediate substance, in which the metamorphic pro- cess has only gone so far as the development of a homogeneous mass, but has not attained the stage of fibrillation. The bun- dles of the connective tissue, when once formed, grow in length and thickness hke the elastic fibres, until they have attained the size which they possess in the adult ; however, there arise subsequently, in many places, additional elements, which are combined with the original ones. The perfect connective tissue, when unmixed, is almost non-vascular, and with regard to nutrition, is certainly very low in the scale, whence it undergoes hardly any morbid changes. The vascular connective tissue is an exception to this rule, but the changes in this case depend not upon any peculiarity in the connective tissue itself, but are determined by the vessels, fat-cells, &c. contained in it. The bundles of fibrils of the connective tissue and the Kg. 29. Formative cells of the connective tissue from the skin of the trunk in a sheep's embryo, f" long, x 350 : a, cell without any indication of fibrils ; *, with commencing ; c, with distinct fibrils. Kg. 30. Three formative cells of the areolated connective tissue from the allau- tois of a sheep's embryo, 7'" long, x 350. TISSUES, ORGANS, AND SYSTEMS. 73 elastic fibres stand, at the bottom of the series of the higher elementary parts, and thence most readily adapt themselves to the regeneration of lost substance, or to the increase of parts which already exist. The union of the different elements of the connective tissue is effected in many ways, but the following forms are most worthy of distinction : 1. Solid connective tissue (formed connective tissue, Henle). In this the elements are intimately united, and in such a manner, that simple organs of well-marked form proceed from them. To this belong : a. The tendons and ligaments, with parallel bundles, united by loose connective tissue, into larger cords, between which a relatively very small number only of fine elastic fibres, and fibrous networks, penetrate. b. The fibro-cartilages have the same structure as the ten- dons and ligaments, but with numerous scattered cartilage cells, and without finer elastic fibres. They exist either as special organs, such as the cartilagines interarticulares and the cotyloid ligaments, or in particular parts of other organs com- posed of connective tissue, especially in the tendons, the ten- dinous sheaths, and the ligaments, c. The fibrous membranes are distinguished from a, only by the frequent interweaving of the bundles, and generally by the more considerable number of the elastic fibres. Here may be enumerated : 1. The muscular fascia, which have more the structure of tendons. 3. The periosteal membranes and the perichondrial mem- branes, containing sometimes a great number of elastic elements. 3. The white dense tunics of many soft organs, as the dura mater, the neurilemma, the sclerotic and cornea, the fibrous coat of the spleen and kidneys, the tunica albuginea of the ovaries and testes, penis and clitoris. In the last-mentioned parts, and in the spleen, these coats, which consist of a solid connective tissue and numerous fine elastic fibres, are continued into the interior, where mixed to some extent with smooth muscles, they constitute a more or less complete frame-work, which appears in the form of partitions, or of a stroma, or of a 74 GENEBAL ANATOMY OF THE TISSUES. trabecular network. In the cornea we find a modification, inasmuch as the connective tissue is transparent, contains fine elastic tissue in a more embryonic state, and when boiled in water yields chondrin, and not gelatine. d. The serous membranes consist of a connective tissue, rich in fine elastic fibres, whose bundles anastomose, or are inter- woven in different modes j and sometimes also, especially at the surface of these membranes, appear more homogeneous. The serous membranes, which never possess glands, and upon the whole but few vessels and nerves, line the cavities which con- tain the viscera, and present an inner surface, which is smooth and shining from the presence of an epithelial investment. They do not necessarily form closed sacs, as was formerly believed, but may have apertures in certain localities (abdo- minal aperture of the Fallopian tubes), or may be whoUy wanting, as upon the articular cartilages j or the areolar foundation may be absent, as in the so-called external lamina of the arachnoidea cerebri. To these membranes belong, 1, the true serous membranes, as the arachnoidea, the pleura, the pericardium, the peritonaeum, and the tunica vaginalis propria, which all, normally, secrete only a minute quantity of serous fluid; and 3, the synovial membranes or capsules of the joints, bursce mucosa, and tendinous sheaths, which afford a viscid yellow secretion, — the synovia — containing albumen and mucus. e. The corium consists of a dense network of bundles of connective tissue, which at the surface, and in the papillae, gives place to an indistinctly fibrillated, in part even more homogeneous tissue, and contains a great quantity of finer and coarser elastic networks, as well as very numerous vessels and nerves. The corium supports the papillse upon its outer surface, and is here covered by the epidermis, in connection with which it forms the external skin ; from the deeper parts it is separated by a soft tissue, generally very rich in fat, the subcutaneous connective tissue, adipose membrane, or panniculus adiposus. f. The mucous membranes essentially consist of a very vascular basis of connective tissue, well supplied with nerves, — the proper mucous membrane — of an epithelial layer covering it, and of a submucous areolar tissue, which TISSUES, ORGANS, AND SYSTEMS. 75 in the intestine is also called the tunica nervea. The for- mer is of the same structure as the corium, only softer, and not unfrequently poor in elastic tissue. The mucous mem- branes are distinguished from the serous, in general by their greater vascularity, their more considerable thickness, their numerous glands, and the mucous secretion, which may be especially ascribed to their soft epithelium; though there are mucous membranes which are as delicate and glandless as serous membranes; and, on the other hand, the synovial capsules may approximate the mucous membranes in their vascularity and the nature of their secretion. The mucous membranes and the external skin are analogous in all their principal components, whence the transitions between the two, such as exist upon the lips, eyelids, and elsewhere, are not surprising. To the mucous membranes belong the innermost coat of the tractus intestinalis ; the lining of the nasal passages, and of their secondary cavities ; the Eustachian tube, the tympanum and mastoid cells, and the conjunctiva. Among the glands, all the larger, present in their excretory ducts, a distinct mucous membrane, as the lungs from the glottis to the finest bronchieBj the liver in the larger gall- ducts and in the gall-bladder; the pancreas in the ductus pancreaticus ; the urinary and sexual organs ; in the urethra, bladder, ureters, pelvis of the kidneys, vagina, uterus, and oviducts; and in the ducts and follicles of the mammary gland ; in the seminal vesicles and in the vas deferens. In all these glands the coats of the mucous membrane pass imme- diately into the walls of the glandular tubes and vesicles, which might thus be regarded as composed of a more delicate mucous membrane. The same might be said of the smaller glands, as those of the intestine, which are directly connected with the larger mucous expansions, only in that case the smaller glands of the skin must be regarded as attenuated processes of it. Inasmuch as both physiology and develop- ment support this view, it would seem to be at any rate justifiable; yet every one is free, notwithstanding, to look more to the difierences which certainly do exist between the parts in question, and to consider them as distinct structures. g. The membranes of the veins, lymphatics, the adoen- 76 GENERAL ANATOMY OF THE TISSUES. titious coat of the arteries, and tJie endocardium, consist of a loose connective tissue not altogether dissimilar to that of the fibrous membranes, and of finer or coarser elastic fibrous networks, with which in the veins smooth muscles are also partly mixed. h. The so-called vascular membranes {tunica vasculosis), to which belong the pia mater, with the plexus choroidei, the choroid coat and the iris, all contain very numerous vessels, which, however, appear to have less reference to the membranes themselves than to the nutrition of other organs. Supporting these vessels we have either a common connective tissue, in which there are no elastic fibres (iris, pia mater), with parallel, matted, and anastomosing bundles, or a homogeneous con- nective tissue [plexus choroidei, choroidea), to which, as in the choroid, peculiar elements, namely, anastomosing cells, gene- rally filled with more or less pigment, may be added. i. The homogeneous connective tissue. — In many organs we find membranes whose chemical nature agrees with that of connective tissue, but which contain neither distinct bundles nor fibres, and appear to be more homogeneous. Such is the homogeneous tissue which often invests the bundles of the arachnoid singly, or in a number together ; the coats of the Malpighian corpuscles of the spleen, and of the glandular follicles of the intestine (tonsils, lingual-foUicles, the solitary and Peyerian glands), certain of the so-called membrants propriee of the glands appear to come under this head also; yet, since some of them do not belong here, and consist of a very diflferent substance from connective tissue, as, for example, that of the kidneys, and since we have no thorough investigation of these structures, for the present nothing decided can be said upon the subject. >>\/v'Vc|- i^^-^^b\av K. Loose or areolated connective tissue {" amorphous con- nective tissue'' of Henle), consists of a soft meshwork of reticulated, or variously interwoven bundles of connective tissue, which in larger or smaller quantity constitute a' filling up and imiting mass between the organs and their parts, and appear under two forms : 1. As adipose tissue, when numerous fat-cells are contained in the meshes of an areolated tissue which is usually very poor in elastic fibres. 2. As common lax connective tissue, when the latter are TISSUES, ORGANS, AND SYSTEMS. 77 few or wanting. The adipose tissue occurs principally in the skin, forming the panniculus adiposus ; in the larger cylindrical bones, as yellow bone-medulla; in the orbit; around the kidneys ; in the mesentery and the omentum ; around the spinal marrow; in nerves and vessels, and in muscles. The areolated connective tissue is widely distributed between the separate organs and viscera of the neck, thorax, abdomen, and pelvis, and everywhere along the course of the vessels and nerves, and in the interior of the muscles, nerves, and glands. [The connective tissue is found in all the four classes of the vertebrata, in about the same condition as in man ; while, on the other hand, in the invertebrata it is very rare, and when present is more homogeneous, or consists of isolated cells and intermediate substance, rarely more fibrous, as in Cephalopoda, in the mantle of bivalves, in the peduncle of the Lingulse, and of the Cirripeds. Fat-ceUs also do not occur among the lower animals to the same extent as among the higher. The firm connective tissue is here replaced by a chitinous substance, or by one consisting of cellulose, and by calcareous or horny tissues. Opinions are stiU divided as to the structure and develop- ment of the connective tissue. Whilst the majority ascribe a distinctly fibrous structure to it, and suppose it to consist of bundles, and these again of fibrils, Reichert considers this tissue to be more homogeneous, and regards the fibrillation partly as artificial, partly as the expression of a folding, a view to which Bidder and Yirchow are also inclined. For my own part, I find a certain amount of truth in Reichert's conception, insomuch as it is not to be denied that there also exists a non- fibrillated, more homogeneous connective tissue, which had previously been little investigated ; but I am nevertheless of opinion, that, as applied to the great mass of the organs com- posed of connective tissue, it is incorrect. The possibility of making out fibrils in delicate membranes, even without pre- paration, the ease with which these may be isolated in tendons and ligaments, and lastly, the circumstance that the fibrils may be demonstrated upon transverse sections of the tendons, and of the more solid connective tissue in general, are for me suffi- cient reasons for retaining the old view. With respect to the development of the connective tissue, I 78 GENERAL ANATOMY OF THE TISSUES. distinguish two types which corresJ)ond with its two principal forms, the solid and the areolated. The former is developed out of masses of cells without any demonstrable matrix, by the elongation of the cells, their breaking up into fibrils, and their coalescence. This is most obvious in the tendons and liga- ments, which, as observations upon Batrachian larvae and upon mammalian embryos show, at first consist entirely of com- mon, rounded, formative cells, which about the same time as the transversely striated muscles are formed, (in mammalia in the second month) become fusiform. The further develop- ment demonstrates (what had escaped Schwann) that only one portion of these fusiform cells, and in fact cells which are re- markable for their size and paler contours, become bundles of connective tissue, while the others, which Schwann in part depicts rightly (Tab. Ill, fig. 11 ; the smallest cell, fig. 6, from connective tissue, the cell b, and the lowest cell upon the right side), remain for a time as fusiform elements, and only subsequently become fused into elastic fibres. There arises, at last, out of ceUs alone, with no distinguishable matrix, a compact tissue composed of two chemically quite distinct fibres. The areo lated connective tissue diflers from 1^ the former in the circumstance that, if not from the beginning yet from the time at which the cells become elongated, an abundant gelatinous intermediate substance is developed be- tween them, which does not yield gelatine, and never becomes converted into it, but contains albumen and a substance similar to mucus; Schwann, indeed, found a substance resembling pyin, in this tissue. Although all embryologists know that the areolated connective tissue is at first of a gelatinous consistence, as, for example, under the skin, in the neck, in the omentum, behind the peritoneum, in the orbit, and in the bones, no one has yet drawn attention to the general occurrence of that inter- mediate substance which was observed by Schwann in a single locality. I originally became acquainted with this tissue be- tween the chorion and amnion, and at first paid more attention to its reticulated anastomosing cells. Subsequently, when I examined it more closely in the enamel organ of the em- bryonic tooth sac, I paid attention to the peculiar intermediate substance, and at the same time Virchow described this tissue from the umbilical cord, where the gelatinous tissue of Wharton r TISSUES, ORGANS, AND SYSTEMS. 79 entirely consists of it. Virchow believed that it ought to be distinguished from connective tissue, and proposed the denomi- nation of mucous tissue {tissu muqueux) for it. I considered it from the first to be connective tissue, and I now feel the more inclined to remain of this opinion, because I find that every description of the areolated connective tissue of em- bryos originally commences under this form, and therefore the circumstance that the tissue in the umbilical cord never arrives at perfection, cannot determine its nature. The mode in which the gelatiniform connective tissue is deve- loped is this : one portion of the cells contained in the gelati- nous basis changes into connective tissue by becoming fusiform, and breaking up into common or reticulated, anastomosing connective tissue, which however, as Schwann has already stated, at first yields no gelatine. In this manner a closer or denser network arises, in the interspaces of which the inter- mediate substance or matrix, and a remainder of the previous formative cells, are contained. In the further course of deve- lopment, new cells proceed from the matrix, which hereby diminishes by degrees in quantity, and at the same time the original network consolidates, fresh cells being added to it, a part of which also become elastic Jfibres and vessels. If subse- quently the areolated connective tissue includes no adipose cells, the gelatinous tissue ends by completely disappearing, and nothing remains but a loose fibrous tissue, containing at most somewhat less fluid, and loose cells in its meshes; if, on the other hand, it becomes converted into an adipose tissue, the spaces remain, and a great part of the cells which have arisen at the expense of the gelatinous substance, subsequently pass, by the development of fat in their interior, into fat- cells. In the gelatinous tissue of Wharton, between the chorion and amnion, and in part in the enamel organ, the areolated connective tissue remains more in its foetal condition of a gela- tinous tissue, yet there exists no natural line of demarcation from ordinary connective tissue, so much the less, since in the gelatinous substance of Wharton, in older embryos even fibrils are quite evident, and in the enamel organ the passage of a part of the gelatinous tissue into common con- nective tissue is demonstrable. So much for the two types of development of the connective 80 GENERAL ANATOMY OF THE TISSUES. tissue. We have yet to state how the bundles become chemi- cally and morphologically what they are. In the first place, I may observe that the formative cells of the connective tissue are not originally distinguishable from the other formative cells of the embryo, do not dissolve by boiling in water, and therefore contain no gelatine. Even when the cells have evidently become fusiform, and have already coalesced into bundles and networks, they still, as Schwann has already stated, yield no gelatine. Therefore, in this case, the change of the cells into a collagenous substance, goes on as slowly as in the matrix, of the cartilages, which, according to Schwann, also, at first, yields no gelatine, and therefore it is no objection to the above view of the nature of Wharton's gelatinous tissue, that it yields no gelatine on boiling, as Scherer has found. How the colla- genous matter is formed out of cells, whether the contents only, or the membrane also, takes part therein, it is very difficiilt to say; in any case, from what we know of the con- tents of embryonic cells, it can hardly be any but a protein substance which yields the gelatine, and, from what takes place in the ossification of the cartilage cells, it seems very probable that the cell-membranes and contents together become metamorphosed into a collagenous substance. The morphological change, which the formative cells of the connective tissue undergo, in the course of their passage into bundles of fibrils, is very probably this, that after their mem- branes and contents are fused into a homogeneous semi-solid mass, they then secondarily break up into fibrils ; the latter process taking place in the same manner as we see it occur in the contents of the animal muscular fibres. Herewith, as a rule, the nuclei of the cells eventually disappear, or if they re- main, as we see occasionally in connective tissue, still they never become changed into the so-caJled nucleus fibres. Though in physiological connective tissue, development from cells must be most decidedly affirmed, it does not therefore follow that a substance which chemically and morphologically closely resembles connective tissue, may not arise in a difl'erent manner. We know, in fact, that the collagenous basis of cartilage, when it breaks up into fibres, becomes deceptively similar to connective tissue, and furthermore, that fibrous exudations may become changed^ into a fibrous substance which TISSUES, ORGANS, AND SYSTEMS. 81 is scarcely, perhaps not at all, to be distinguished from genuine connective tissue. There also exists, however, a pathological true connective tissue in cicatrices of all kinds, and perhaps else- where, which is developed from cells ; and for my own part, therefore, I am opposed to the classing together of all connec- tive tissues. We must in our classifications not only distinguish similarity or identity in structure and chemical composition, but embrace all the conditions, and especially the genesis; and thence we must distinguish both the collagenous fibrous cartilage and the collagenous organised fibrine, from true connective tissue, — ^just as we separate the true elastic fibre, from the chemically and morphologically, very similar fibres of the reticulated cartilages and from certain forms of metamorphosed fibrine. On the other hand, the connective tissue which has not been developed from cells may justly and properly be arranged with cartilage.^ ' [The arguments brought forward by Professor KoUiker in support of his views with regard to the nature and mode of development of connective tissue, appear to us not to preponderate against those of Reichert, Vircliow, and Remak, and to be opposed to our own observations, which agree in all essential points with those of 'the last-named authors. There are two questions in dispute. The first, the structure of the connective tissue; the second, the homology of its various constituents with those of other tissues, and of cells in general. With respect to the first question, it is admitted on all hands that ordinary con- nective tissue (e. g. of the tendons) is composed of two elements : a, a network of elastic tissue, which is not acted upon by cold acetic acid ; i, a substance which is swollen up by acetic acid, and has a more or less fibrillated appearance, contained in the meshes of the elastic tissue. Now it has been demonstrated by Virchow, and the fact is admitted by both Kolliker {supra) and Reichert (Zur Streitfrage iiber die Gebilde der Binde-substanz, iiber die Spiralfaser, &c., Miiller's 'Archiv,' 1852), that the elastic fibres are originally cells, and therefore that they are homologous vrith the cartilage-cell, i. e. the cartilage-cavity with its wall plus the cartilage- corpuscle or nucleus. That this is the case is very evident, upon examining in a young animal (e. g. kitten) the insertion of the tendo-Achillis into the cartila- ginous extremity of the os calcis. It is here easy enough to -see that the oval or rounded ceUs of the true cartilage pass in the most gradual manner into the elongated elastic fibres of the true tendon. The cells retain their cavities for a considerable time, but eventually the nuclei and the thin layer of substance which immediately forms the wall of the cavity, become fused into one mass and altered in chemical composition. A like alteration affects the matrix in various irregular directions, so that the dehcate elastic connecting fibres are formed, and constitute a network through the whole tendon. These connecting fibres are often branched, and even appear fibrillated at the ends, especially if torn out from their connection with one another, and in this condition they exactly resemble the bodies figured by Professor KoUiker as the "fusiform formative cells" (fig. 29). That they have nothing to do I. 6 82 GENERAL ANATOMY OF THE TISSUES. Literature. — C. B. Reichert, ' Vergleichende Beobachtungen iiber das Bindegewebe und die verwandten Gebilde/ Dorpat, 1845; Luschka, 'Die Structur der serosen Haute.' Besides which, consult the works of Virchow, Bonders, Remak, and myself, cited above. with the development of the " fibrUlated" collagenous substance is, however, obvious, from this very simple circumstance — that the latter lies between them, and in part re- places the rest of the matrix of the cartilage, into which it can be directly traced. It wUl not be said in this case, that the "fibrillated" tissue of the tendo-AchUlis is only " decep- tively similar" to true connective tissue — and yet the transition of true cartilage into true connective tissue, is not less certainly demonstrable in the intervertebral cartilages, &c. As Reichert, then, long since indicated, in illustrating his "law of continuity,'' (a law whose full importance, it may be observed, has yet to be developed), and as he and Virchow have since demonstrated, the elastic element of fully-formed con- nective tissue represents the cartilage-cells, while the collagenous element repre- sents the matrix of the cartilage, and is not developed from distinct cells. With regard to the structure of the latter element, Reichert, in his last communi- cation, after considering Kblliker's arguments, denies the truth of his statement, that the ends of the fibrils may be seen in transverse sections of the tendons (§ Tendon, infra), and retains his opinion that it is not truly fibrillated in the uninjured state, but that it is simply plaited. Some remarkable observations upon the behaviour of the " connective fibril bundles" with acids and alkalies, to which Reichert first drew attention in 1846, and which have been since extended by Dr. Paulsen (Bericht., MuUer's 'Archiv,' 1849), are, as the former points out, of the greatest importance in determining the nature of this tissue, and remind one somewhat of the equally puzzling structure of the starch-corpuscle. Dr. Paulsen states, that if a piece of tendon be kept for twenty-four hours in a solution of caustic potass of 10 per cent, strength, it changes into a viscid hyaline mass, so transparent that it can hardly be distinguished from the surrounding fluid. This substance can be torn with equal ease in any direction, and no fibrous structure can in any way be detected in it. Under the microscope the mass is quite transparent, and shows no trace of the well- known striation. However, the connective tissue is at this time by no means dis- solved, nor is its texture destroyed. If the potass be removed by acetic acid, and this if it be in excess, by washing, the original texture returns. The author justly remarks, that if the connective tissue consisted of separate fibrils the impossibility of isolating them in the distended condition would be quite inexplicable. It is however intelligible, that in consequence of such an alteration in the connective tissue its cleavability may be diminished or destroyed, which does away with the necessity of supposing a fibrous structure. On the other hand, if a piece of tendon be hardened by a strong solution of caustic potass, or by nitric or hydrochloric acids, no fibres can be demonstrated in it (Bericht, pp. 40, 41). It is easy enough to verify the truth of these statements, by treating a piece of tendinous tissue with acetic acid, when, as is well known, the fibrillated appearance disappears ; then keeping in view one of the distended and transparent " bundles," slowly add a solution of caustic ammonia, the transparent mass will be seen gradually to shrink, and eventually to resume, what appears to be, a most distinctly fibrous appearance. The gelatinous or rather gelatiniform areolated connective tissue of Professor TISSUES, ORGANS, AND SYSTEMS. 83 § 25. Osseous Tissue. — Morphologically, the osseous tissue consists Fig. 31. The former, of a^ white colour, is essentially of a ma- trix, and, scattered through it, of a mul- titude of microsco- pic cavities, the bone _ . corpuscles, OTclacuruB, Jsg;***^ of 0006 — 0-014'" '^fS.. in length, 0-003 — 0-006'" breadth, and 0-002— 0-004'" thickness Fig. 31. A portion of a perpendicular section of a parietal bone, x 350 : a, lacunae with pale only partially visible canaliculi, filled as in the natural condition with fluid ; b, granulated matrix. The striated parts indicate the boundaries of the lamellae. Kiilliker Is simply ordinary connective tissue, in which the collagenous element is not yet or but little formed. Its development may be readily traced in the most super- ficial layer of the skin and mucous membranes, or in the tooth-pulp, or the so-called actinenchyma of the enamel organ in the calf, &c. The epiglottis of the kitten is particularly to be recommended, as this tissue can be observed passing on the one side into the homogeneous layer of the corium next to the epithelium, and on the other into the so-called fibro-cartilage of the epiglottis. .In all these cases, the mode of development of the areolated connective tissue is essentially similar to that observed by Semak (Ueber die Entstehung des Binde- gewebes, &c., MiiU. ' Arohiv,' 1852, 1,) in the Frog. The layer of the tissue next the epidermis or epithelium, is composed of a nearly. homogeneous substance (matrix), in which lie corpuscles (so-called nuclei), the whole in fact corresponding exactly with embryonic cartilage. Internal to this, vacuolar cavities have been formed in the matrix between the corpuscles, the substance of the matrix appearing as bands or fibres between these vaeuoltB. The latter enlarging, the substance of the matrix is more and more broken up into bands, in which dilatations remain where the "nuclei" are situated, so that the bands often resemble fusiform or stellate cells. A structure of this kind which undergoes no further chemical or morphological alteration, consti- tutes the gelatiniform connective tissue; and it is unquestionable, that its subsequent conversion into perfect areolated connective tissue is effected, as Professor KoUiker states, by the direct passage of these fusiform bodies into the pseudo-fibrillated bundles of the collagenous substance. But it is their outer portion only, that therefore which corresponds with the matrix of cartilage, which becomes thus changed — the elastic element being developed as before, not from separate cells, but by the chemical metamorphosis of the matrix immediately around the cavity which contains the " nucleus," and in various other directions. That the pseudo-filirillated portion of the connective tissue corresponds with the matrix of the cartilages is then, we think, certain. Whether with Remak we are to regard both these as cell-walls, or with Reichert as intercellular substances, must be discussed hereafter. {See General Appendix.) — Eds.] 8i GENERAL ANATOMY OF THE TISSUES, sometimes more homogeneous, sometimes finely granular, very frequently lamellated, and hard and brittle from its being inti- mately combined with calcareous salts; the lacuna are for the most part lenticular, and are united by very numerous fine pro- cesses, the canaliculi ; by which some of them also open upon the outer surface of the bones and into the larger and smaller medullary and vascular spaces in the interior. The lacuna and canaliculi contain a clear substance which may be regarded as the nutritive fluid of the bones, and besides, a cell-nucleus ap- pears in many cases, perhaps constantly, to be inclosed within the lacunse. Besides these two most essential elements, which exist in all bones, numerous vessels and nerves occur in most, as well as, frequently, a peculiar substance, the medulla, which supports them, and consists either of common fatty tissue, or of a loose, scanty, connective tissue, with few fat cells and many peculiar, so- called medulla-cells. These soft parts fill up the larger cavities in the interior of thebones and in the spongysubstance; but are to be found also, at least partially, in narrow canals which penetrate the compact substance, the vascular or Haversian canals, which open in all directions upon the outer and inner surfaces of the bones. The matrix of the osseous tissue is composed of an intimate combination of an organic substance, which perfectly agrees with that of the connective tissue, and of inorganic compounds, among which the phosphate and carbonate of lime are the prin- cipal constituents. The fluid contained in the cavities and canals is not thoroughly understood, but it probably presents a prepon- derance of albumen, fat, and salts, like the serum. The bones, from their solidity and inflexibility, serve as supports to the _. softer organs or for their more secure in- closurej and also perform special func- tions ; as, for example, the auditory ossicles and the parts of the labyrinth which con- duct the sonorous vibrations. The de- velopment of the bones takes place in two modes; firstly, by the metamorphosis of genuine cartilage, and secondly, by that of a soft blastema composed of indifferent cells and of a fibrous Kg. 32. Six developing bone-cells from a rickety bone, as yet sharply defined from the interstitial substance : a, simple bone-cells ; 6, compound ones running to a parent cell, with two secondary cells ; c, such arising from three cells, x 300. TISSUES, ORGANS, AND SYSTEMS. 85 substance similar to connective tissue. In both cases it is the cells — in the one the cartilage cells, in the other, cells without any defined character — which forna the lacuna au&canaliculi by the thickening of their walls, with a contemporaneous develop- ment of pore canals, which subsequently grow into the matrix and unite with' one anotherj whilst the matrix of the cartilage and the fibrous substance harden into the matrix of the bone by the deposition of calcareous salts, which likewise infiltrate the thickened cell-walls. The nutrition of the bones is very energetic, and is effected by the vessels of the investiiig peri- osteum, and, if they be present, by those of the medulla and the Haversian canals also. The bones have a great capacity of re- generation, and readily unite ; in fact, very great losses of sub- stance are repaired, or even whole bones, if the periosteum be left : adventitious development of bone is also very common. The osseous tissue is found, firstly, in the bones of the skeleton, to which also the auditory ossicles and the hyoid bone belong ; secondly, in the bones of the muscular system, as the sesamoid bones and the ossifications of tendons ; thirdly, in the substantia osteoidea, or tooth cement. Many cartilages ossify with tolerable regularity as they grow older ; as the costal-carti- lages, and those of the larynx. Dentine may be regarded as a modification of osseous sub- stance, which, instead of solitary lacurus, presents long canals, — the dental canals; besides which, it exhibits some chemical modifications. The development of the dentine leads to the conclusion that it is an osseous structure, whose cells, in the course of their ossification and thickening, become united into tubes, and have very little or no intermediate substance ; a view which gains additional support from the numerous tran- sitional forms, to be observed in animals, between typical den- tine and osseous tissue. [In the Vertebrata, bone is found more extensively distributed than in man. It exists in the skin (Armadillo, Tortoises, Lizards, Fishes), in the heart (the cardiac bone of the Ruminants and Pachydermata), in the muscular system (diaphragmatic bone of the Camel, Lama, and Porcupine, ossified tendons of birds), in the eye (sclerotic ring of Birds, Chelonians and Saurians, bony scales of the sclerotic of many Fishes), in the external portion of 86 GENERAL ANATOMY OF THE TISSUES. the nose (proboscis of the Pig and Mole, os prtenasale of the Sloth), in the tongue (ps enttglossum of Fishes and Birds), in the respiratory organs (laryngeal, tracheal, and bronchial bones of many Birds), in the sexual organs {penis-bone of Mammalia), in the osseous system {pssa sterno-costalia of birds and some mammals). In the Invertebrata true bones are never found, being, in them, replaced by the so-called calcareous skeletons, which principally consist of carbonate of lime, and arise in different structures as incrustations of homogeneous tissues and of cellular parenchymata, as solidifying excretions of calcareous matter, or as deposits of calcareous concretions. The teeth are limited to the three well-known classes of vertebrata. In the Plagiostomata, structures precisely similar to the teeth occur as cutaneous spines.] Literature. — Deutsch, ' De penitiori ossium structure Obser- vationeSj' Diss. Vrat., 1834; Miescher, 'De inflammatione ossium eorumque anatome general!.' Accedunt observat. auct. J. Miiller, BeroL, 1836; Schwann, article 'Knochengewebe,' in ' Berl. encyclop. Worterbuch der med. Wiss.,' Bd. xx, p. 102 ; Tomes, article Osseous Tissue, in ' Cyclop, of Anatomy,' vol. iii.^ § 26. Structure of the Smooth Muscles. — The smooth muscles consist essentially of microscopic, usually fusiform, more rarely shorter and broader fibres, to which T have given the name of ''contractile or muscular fibre-cells." Each of these elements, in the mean from 002— 004'" long, 0-002— 0-003'" broad, is an elongated cell, wherein, however, no difference between contents and membrane can be distinguished ; but which consists of an apparently homogeneous, often finely granulated or slightly striated, soft substance, in which without exception in the middle of the fibre a generally columnar elongated nucleus ' [While perfectly agreeing with Professor Kolliker's general view of the relations between dentine and bone, namely, that the canals in the former represent the cavities and canalicuU which exist in the latter structure, we do not think that his statement of the mode in which the process of calcification of the dentine takes place i§ correct. So far as we have seen, the dentine is never developed by the immediate ossification of cells, nor do the latter take any direct share in its formation. {^See Quarterly Journal of Micros. Sc, April, 1852.) It may be said that dentine is bone, in which, in consequence of the early disappearance of the " nuclei" from the ossifying blastema, the lacunee are not formed, the dentinal tubes presenting only the canalicuU. — Eds.] TISSUES, ORGANS, AND SYSTEMS. 87 exists. These fibre cells are united by means of a substance which cannot be directly demonstrated, into flattened or rounded cords, the bundles of the smooth muscles; which are then united, by delicate investments of connective tissue with fine elastic fibres (a kind of perimysium), into more considerable masses, in which numerous vessels and a relatively small num- ber of nerves are distributed. Chemically, the principal con- stituent of smooth muscle is a nitrogenous substance similar to fibrin, the so-called muscular fibrin or syntonin (Lehmann), which, from the observations that have hitherto p; 33 ^ ^ been made, is distinguished from blood fibrin only in this, that it is not dissolved by solution of nitre, nor by carbonate of potass, but very easily by dilute hydrochloric acid. The physiological importance of the smooth muscles lies in their contractile power; in con- sequence of which they afibrd considerable assist- ance to the functions of the different viscera. The development of their elements takes place simply by the elongation of rounded cells, the membranes and contents uniting into a homo- geneous soft substance. The nutrition of the smooth muscles would seem to go on very ac- tively, according to the later investigations upon the fluid which bathes them, which, according to Lehmann, has most generally a distinctly acid reaction, and together with lactic, acetic, and butyric acid, contains creatin and inosit; and the same conclusion may be deduced from the frequent occurrence of physiological (in the uterus) and pathological hypertrophies and atrophies of them. Whether smooth muscles are regenerated, or whether loss of their sub- stance is replaced by a similar tissue, is un- known ; on the other hand, new formations of them appear to occur in uterine tumours. The smooth muscular fibres never form large Fig. 33. Muscular fibre-cell from the small intestine of man. Fig, 34. Muscular fibre-cell from the fibrous investment of the spleen of the dog, x350. 88 GENERAL ANATOMY OF THE TISSUES. isolated muscles in the human body; as, for example, is the case in the genito-rectal muscles of mammalia, but exist either scattered in the connective tissue, or in the form of muscular membranes. In both cases the bundles are either parallel or interwoven into networks. Their distribution is as follows : 1 . In the Intestinal canal the smooth muscle forms : first, the tunica musculosa from the lower half of the oesophagus, where smooth bundles are still mingled with transversely striated fibres, as far as the sphincter ani internus : secondly, the muscular layers of the mucous membrane, from the oesophagus to the anus: and thirdly, scattered muscular bundles in the villi. 3. In the Respiratory organs, a layer of smooth muscles appears in the posterior wall of the trachea, and accompanies the bronchia, even to their finest ramifications, as a complete, circularly fibrous membrane. 3. In the Salivary glands, this tissue is found solely in Wharton's duct; and here only scantily, aad forming an incom- plete coat. 4. The Liver has a perfect muscular layer in the gall- bladder, and scattered smooth muscles, also in the ductus choledochus. 5. The Spleen has this kind of muscle in many animals in its outer coat, and in the trabecules, mixed with connective tissue and elastic fibres. 6. In the Urinary organs the smooth muscles are found in the calices and pelves oi the kidneys, form a complete mus- cular layer in the ureters and urinary bladder, but are only sparingly to be found in the urethra.'^ 7. The Female sexual organs possess smooth muscles in the oviducts, the uterus, where during pregnancy their elements become excessively developed, and attain a length of \", the vagina, the corpora cavernosa, and in the broad ligaments of the uterus in different places. 8. In the Male sexual organs they are found in the dartos, between the t. vaginalis communis and propria, in the vas ' [Mr. Hancock (On the Anatomy and Physiology of the Male Urethra, London, 1852), who had made out the existence of the organic muscular layer in the urethra independently, attributes to it much more anatomical and physiological importance. (See below, § Urinary Organs.) — Eds.] TISSUES, ORGANS, AND SYSTEMS. 89 deferens, vesiculce seminales, the prostate, around Cowper's glands, and in the corpora cavernosa peni^. 9. In the Vascular system smooth muscles exist in the tunica media of all, especially of the smaller arteries ; also in that of most veins, and of the lymphatics, with the exception of the finest ; furthermore in the lymphatic glands (Heyfelder) ; and lastly in the tunica adventitia of many veins. The elements, in vessels of middle dimensions, are everywhere fusi- form fibre-cells; in the large arteries, on the other hand, shorter plates, which often resemble certain forms of pavement epithelium; and in the smallest arteries they are more elongated, or even round cells, forms which must be considered as less developed. 10. In the Eye, smooth muscles form the sphincter and dilator papilla and the tensor choroidete. 11. In the Skin, lastly, this tissue appears besides in the dartos, in the form of minute pauscles upon the hair sacs, in the areola, and in the nipple, and in many of the sudoriparous and sebaceous follicles. [The elements of the smooth muscles were formerly tiniver- sally regarded as elongated bands containing many nuclei, which were supposed to be developed by the coalescence of numerous mutually applied cells. In 1847 I showed that this is not the case ; that, on the other hand, the elements of these muscles are only modified simple cells ; and at the same time I demon- strated, that these contractile fibre-cells occur wherever con- tractile connective tissue had previously been assumed to exist, and also, that they are to be found in many localities in which their presence had not been suspected. These views, notwith- standing contradiction at first from certain quarters, are now universally confirmed ; a result to which Reichert, by the dis- covery of a reagent, which readily enables even those who are less practised, easily to isolate the contractile fibre-cells, viz.: nitric and hydrochloric acids of 20 per cent. (Miiller, 'Archiv,^ 1849, and Paulsen, ' Obs. Microchem.,' 1849) ; and Lehmann, by his chemical investigations upon this tissue, have contributed their share. Contractile fibre-cells occur in all four classes of the Vertebrata, but appear to be wholly wanting in the Invertebrata, since the smooth fibres of these creatures, which have been 90 GENERAL ANATOMY OF THE TISSUES. thought to be such, are allied genetically to the transversely striated muscles of the higher animals. Their occurrence in the Vertebrata is in some respects peculiar, and I will here mention the following localities in which they are found : In the skin of Birds, as the muscles of the quill-feathers — in this case with tendons of elastic tissue ; in that of the Orang-outan, in the hair-sacs, as in man ; in the iris of the Amphibia ; in the campanula Halleri of the osseous Fishes (Leydig) ; in the swimming bladder of Fishes j in the lungs of the Frog (in Triton they are here wanting) ; in the mesentery of the Plagiostomata, of Psammosaurus and Le- posternon (Leydig u. Briicke) ; in the genito-rectal muscle of Mammals. In the gizzard of birds these muscles are of a bright red colour, and are united with a tendinous membrane.] Literature. — KoUiker, ' Ueber den Bau und die Verbreitung der glatten Muskeln.,' in the ' Mittheilungen der Naturf. Gesellschaft in Ziirich,' 1847, p. 18, and ' Zeitschrift fiir wiss. Zool.,' Bd. I, 1849 ; C. R. Walther, ' Nonnulla de musculis Isevibus.,' Diss. Lips. 1851.^ [Jos. Lister, 'Observations on the Contractile Tissue of the Iris,' Quart. Journ. Mic, Sc, vol. I, p. 8, PI. i. — Eds.] § 37. Transversely Striated Muscular Tissue. — The elements of this tissue consist essentially of the so-called muscular fibres or primitive muscular bundles, each of which, 0'004 — 0'03"' thick, consists of fine fibrils surrounded by a special homoge- neous, delicate, elastic investment, the sarcolemma : the fibrils ' [Reichert (Bericht, 1849, Miiller, 'Archiv.,') states that, according to Paulsen, the. action of a solution of caustic potass of 50 per cent, causes the smooth muscles to become wavy, and thus to assume a transversely striate"d appearance under the microscope. Macerated in such a solution for three days, they hreak up into small globules : striated muscle behaves in a similar manner, and the globules correspond in size to the interval between two striae. Eylandt (Obs. Microscop. de musculis organicis in hominis cute obviis. Diss, inaug., Dorp. 1850, c. Tab. lithog.), denies the existence oi free smooth muscles in the papilla and areola mammee, in the scrotum, in the skin of the penis or of the prepuce, and in the perinaeum. Nor does he find them in the outer layers of the hair-sacs (apart from the arrectores pili), in the glanduhs sudorifertB of the axilla, of the anus, &c., nor in the glandules ceruminosa. The smooth muscles observed in the papilla and areola mamrrue, in the skin of the penis and of the perinaeum, he con- siders to belong to a greatly developed vascular layer. (See, however, the remarks of Prof. Kolliker upon Eylandt's statements, at the end of § 34.) — Eds.] TISSUES, ORGANS, AND SYSTEMS. 91 Fig. 35. Fig. 36. are generally enlarged at regular intervals, so that they appear to consist of a series of many portions, and give a transversely striated aspect to the muscular fibres, or they appear more even, and then the primitive bundles present a longitu- dinal striation. Be- sides these fibrils, the muscular fibres contain nothing but a small quantity of the viscid substance uniting them, and a certain number of rounded or elon- gated cell-nuclei, which generally lie against the inner surface of the sar- colemma. The association of the muscular fibres into muscles and muscular membranes occurs in such a manner that they either apply themselves parallel to one another, or are united into true networks of transversely striated muscles. They then receive an investment of more delicate or firmer connective tissue, the so-called perimysium, with which finer elastic fibres and also fat-cells are frequently mingled; and are, besides, surrounded by numerous blood-vessels and nerves. In chemical characters the principal substance of the trans- versely striated muscular fibres agrees perfectly with the syntonin referred to in the previous section. The sarcolemma is very resistant to acids and alkalies, whilst the nuclei present the common characters of those organs. A fluid with an acid reaction may be expressed from the muscles, in which Liebig and Scherer have discovered an interesting series of non- Fig. 35. Two muscular fibres of man, x 350. In the one the bundle of fibrils, b, is torn, and the sarcolemma, u, is to be seen as a mere empty tube. Fig. 36. Primitive fibiils from a primitive bundle of the Axolotl {Siredon pisciformU) ; a, a small bundle of them j b, an isolated fibril, x 600. 93 GENERAL ANATOMY OF THE TISSUES. nitrogenous and nitrogenous products of the decomposition of the muscular tissue. The transversely striated muscles are in a high degree contractile, and are the chief instruments of the animal motions. Their elements are developed by the coalescence of round or stellate cells, whose contents change into a homoge- neous, semi-fluid substance, and then break up into fibrils. Once formed, the muscular fibres grow by the elongation and thick- ening of their elements, and in their complete condition they enjoy a very energetic nutrition, which is especially manifested by the multiform products of their decomposition, as well as by the circumstance that their powers are exhausted in a short time when the circulation is suspended. Wounds of the muscles never heal by 'transversely striated muscular substance; but an adventitious forniation of this tissue appears to occur sometimes, though rarely. Transversely striated muscular tissue is found in the fol- lowing parts : 1. In the muscles of the trunk and extremities ; of the globe of the eye, and in all those of the ear. 2. In the muscles of many organs ; as the larynx, pharynx, tongue, and oesophagus (upper half), the end of the rectum (sphincter externus, levator ani), the genital organs {bulbo-ischio- cavemosus, urethralis transversus, transversi perineei, cremaster, muscular fibres of the round ligaments of the uterus, in part. 3. In certain parts of the vascular System, e. g. in the heart and in the walls of the great veins which open into it. [The muscular fibres of animals are not all composed of bundles of transversely striated fibrils, but present a series of other forms, which may best be grouped in the following manner : 1. Muscular tubes, with homogeneous, semi-solid, not trans- versely striated contents (most MoUuscs, Worms, and Radiata). 3. Muscular tubes with a membrane, a semi-fluid, homo- geneous, cortical layer in contact with it, and a fluid or gra- nular, frequently transversely striated or nucleated central sub- stance. (Muscles ofPetromyzon in part, certain muscles [of the lateral line and of the spiracles] of the plagiostome and osseous Fishes. Muscles of the Hirudinidee, iMmbricideB, of Paludina in part, and oi Carinaria). TISSUES, OEGANS, AND SYSTEMS. 93 3. Similar muscular tubes with a transversely striated cortical layer without distinct fibrils. (Many muscular fibrils of the Hirudinidee, and of the muscles of Fishes enumerated under 2). 4. Muscular fibres without any internal cavity, with a sarcolemma and transversely striated contents, which do not break up into fibrils, but frequently into discs (Bowman), Salpce, some Badiata, many Articulata. 5. Similar muscular fibres, which readily break up into fibrils. (Most Vertebrata, certain muscles of Insects). 6. Simple isolated cells, whose contents are changed into a transversely striated substance, which either fills the whole cell or forms only a thin layer upon its membrane. Here my observations lead me to place the peculiar cartilaginous striae, which Purkinje (Mikr. neurol. Beobachtungen, in Miill. ' Arch./ 1845) found in the endocardium of Ruminants. They consist of large polygonal cells with beautiful nuclei, which internally^ but as it seems only upon their wall, contain a transversely striated substance, which is not distinguishable from that in the muscular fibres. AU these forms are readily comprehended, if the genesis of the true transversely striated muscular fibres in the higher vertebrata be properly understood (see the special part. Muscles); and I cannot agree with the supposition of Stannius (Gott. Nachr., 1851, p. 17), that the transversely striated mus- cular fibrils are developed according to many, essentially difi'erent types. Even the gap which has hitherto separated the smooth from the transversely striated muscles becomes less, when we remember that the so-called transversely striated muscular fibrils may also have homogeneous non-striated contents, and also that even when transversely striated they may appear as isolated cells} Muscular fibres of the same description as the transversely striated muscles, and in part actually striated, are very widely distributed. In the Vertebrata such muscles are found in the oesophagus of some Mammalia and of the plagiostome fishes, in the intestine of Tinea chrysitis, in the stomach of Cobitis < [The muscles of the Medusae consist of flat, fusiform bands, whose ends are inter- laced like those of smooth muscle, but which present the most distinct transverse strise.-^EDS.] 94 GENERAL ANATOMY OF THE TISSUES. fossilis, around the poison gland of Snakes, and in the contractile organ of the pharynx of the Carp ; in the skin of Mammalia, Birds, Snakes, and tailless Batrachians (so-called cutaneous muscles), in the tactile hairs of mammals, in the lymph hearts of many Birds and Amphibia ; in the auriculo-ventricular valve of the right side in Birds, and the Ornithorhynchus ; upon the vena cava inferior of the Seal, close above the diaphragm ; in the interior of the eye of Birds ; and roimd Cowper's and the anal glands of mammals. In the Invertebrata, as we have men- tioned, all the muscles belong to this category, whether they be transversely striated or not ; and they are found, therefore, in the heart, the intestine, the genitalia, and often clearly striated. The anastomosis of the primitive bundles of the muscles, with which Leeuwenhoek was already acquainted,^ and which I rediscovered in the heart of the frog, has now been seen in many places, and appears to be constant in the hearts of the lymph and blood-vascular systems of all animals, and in the muscles of the Invertebrata, especially those of the vegetative and generative organs (Hessling, Leydig). Simple arborescent branchings of muscular fibres, which Corti and I noticed in the tongue of the frog, are on the other hand rare, and have been seen elsewhere only in Artemia salina, and in the oral and anal discs of Piscicola (Leydig).]^ Literature. — W. Bowman, article Muscle and Muscular Motion, in Todd's 'Cyclopaedia of Anatomy,' and 'On the Minute Structure of Voluntary Muscle,' in ' Phil. Trans.,' 1840, II, 1841, I ; J. Hoist, ' De Structure, Musculorum in genere et annulatorum Musculis in Specie,' Dorp. 1846 ; M. Barry, 'Neue Unters. iiber die schraubenformige Beschaflfenheit der Elementarfasem d. Muskeln, nebst Beobachtungen iiber die musculos. Natur d.Flimmerharchen'(Miill.'Arch.,'1850,p.539). ' [It has been pointed out to us by Professor Sharpey, that Leeuwenhoek was not acquainted with the anastomosis of the primary bundles of the cardiac muscles, but has described and figured only that of the secondary bundles, which is indeed obvious upon reference to Leeuwenhoek's Plate (' EXperimenta et Contem- plationes,' Op. Om. Lugd. Bat., torn, i, p. 409, 1722); the ascription in the text is therefore an error. For other remarks upon the muscular tissue, vide infra, § Muscle. — Ebs.] ' [Such branched muscular fibres may be found beautifully marked in the upper lip of the Kat, and in the tongue of Man and Animals. See article ' Tongue,' by Dr. Hyde Salter, in Todd's ' Cyclopaedia.' — Eds.] TISSUES, ORGANS, AND SYSTEMS. 95 Fig. 37. § 38. Nervous Tissue, — The essential elements of this tissue are of two kinds, the nerve-fibres and nerve-cells [ganglion globules). The primitive fibres or tubules of the nerves have either a dis- tinct medulla or they have none. The former consist of three parts ; of a structureless delicate membrane, the sheath of the primitive tubules; of a central, soft but elastic fibre, the central or axi^tband [axis-cylinder, Purkinje; primitive band of Remak); and of a viscid white layer placed between them, the medullary sheath. In the tubules without medulla, which in man occur only in certain peripheral ex- pansions (retina, olfactory or- gan, cornea, Pacinian corpus- cles), the structureless coat contains nothing hut a homo- geneous or finely granular, clear substance, which appears to be identical with the central band of the other tubules, and at any rate may be considered analogous to it, so that the medullary layer may be sup- posed to be absent in these. The primitive nerve tubules of both kinds, especially of the former, occur of very different dimensions, and may thence be divided into fine ones of 0*0005 — 0002'", those of a medium size of 0-002 — 0004'", and thick ones of 0*004 — 001'". Their course is either isolated, so that one tubule runs from the centre to the periphery ; or they divide, especially in their terminal expansions, into a greater or smaller number of branches ; or, lastly, they form actual anas- tomoses and networks. Besides this, many nerve-tubules are connected with nerve-cells, so that they either arise from them or are interrupted in their course by interposed nerve-cells. These nerve-cells, or as they are called in the ganglia. Fig. 37. Tubular nerve-fibres of man, x 350. Four of them fine,, two of them being varicose, one of a medium thickness with a simple contour, and four thick ones ; two having double contours, and two with granular contents. 96 GENERAL ANATOMY OF THE TISSUES. Fig. 38. i 4* a ganglion-cells or ganglion-globules, are endowed with the common attributes of cells. Their membrane presents no peculiarity, except that, frequently, it is very delicate, and even, as in the great central masses, eventually perhaps wholly disappears. The contents are finely granulated, semi-solid, often con- tain pigment, and without exception in- close a distinct vesicular nucleus with a large nucleolus. In size, the nerve-cells vary from 0*003 — 004'", and as regards their form, they may be distinguished principally into round, fusiform, and stellate. The two latter kinds are produced by the prolongation of many nerve-cells into two, three, to eight and more, processes, which in some cases, after a short course, pass into medullated nerve-fibres, in others, present a more marked independence, since, preserving a complete resemblance to non-meduUated nerves, they often run for a considerable distance, and branch out in manifold ways. In what manner finally these processes end, whether free or in connection with nerve-tubules or by anastomosis with similar processes, is not yet made out ; though, upon the whole, it would seem to be not improbable that all three possibilities may occur in different localities. Nerve-fibres and nerve-cells are combined into two sub- stances, which in extreme cases present very wide differences, the grey and the white substances. The former constitutes the so-called white medulla or medullary substance of the spinal cord and brain, and the nerves ; it consists essentially of nerve- tubules, united into bundles or interwoven into plexuses, with blood-vessels ; added to which, in the peripheral nerves, we have special investments of connective tissue, the so-called Fig. 38. Nerve-cell of the Pike (so-called bipolar), passing at its two ends into dark-bordered nervous tubules, treated with arsenious acid, x 350 : a, membrane of the cell ; h, nerve-sheaths ; c, medulla of the nerve ; d, axis-fibres connected with the contents of the nerve-cell ; e, retracted from the membrane. > TISSUES, ORGANS, AND SYSTEMS, 97 neurilemma. The grey substance contains a great preponderance of nerve-cells, besides which, in certain localities, there is a finely granular matrix and free nuclei j but it is rarely found quite unmixed, being usually mingled more or less with nerve- Fig. 39. fibres. This is more especially the case in most ganglia, in the grey substance of the spinal cord, and in the so-called ganglia of the cerebrum ; while on the other hand, in the grey cortex of the cerebrum and cerebellum, it is found in some localities almost without nervous fibres. This substance possesses vessels even in much greater abundance than the white ; and in the peripheral ganglia there are also dififerent forms of connective tissue, which serve to invest their separate parts. The chemical composition of the nervous substance has hitherto, by no means, been sufficiently investigated. In the white substance, the central bands of the nerve-tubules consist of a protein compound very similar to the fibrin of the muscles ; the medullary sheath, chiefly of fats of different kinds, and the membrane, of a substance similar to the sarcolemma. The grey Rg. 39. Nerve-cells of the mhstantia ferruginea from the floor of the fourth ven- tricle in man, x 350. I. 7 98 GENERAL ANATOMY OF THE TISSUES. substance contains a preponderance of albuminous matter, besides a considerable quantity of fat. The physiological importance of the nervous tissue consists, in tbe first place, in its subserving movement and sensa- tion; secondly, in its exerting a certain influence upon the vegetative functions ; and thirdly, in its serving as a substratum to the psychical activities j in all which capacities, according to what we know at present, the grey substance performs the more important part, the white acting rather as a connecting conductor between it and the organs. The nerve-cells are developed from the common formative cells of the embryo, whilst the nervous tubules proceed from the coalescence of the membrane and contents of many such cells, of a rounded, fusiform, or stellate shape j with this, in the medullary tubules a peculiar modifica- tion of the contents occurs, in consequence of which it is divided into a central solid filament and a softer investment. The nutrition in the nervous tissue must be very active, especially in the grey substance, as the great quantity of blood which flows into it clearly shows, but the products of its decomposition are wholly unknown. The white nervous substance is regene- rated pretty readily in, the peripheral nerves, and as it would seem, in the spinal cord also. The adventitious formation of ner- vous tubules has been observed in pathological, new formations, and according to Virchow's observations, it would even appear that an abnormal development of grey substance may occur. The organs composed of nervous substance are : the peri- pheral nerve-cords, nerve-membranes and nerve-tubules, the ganglia, the spinal cord, and the brain. [MeduUated nerve-fibres are found only in the Vertebrata, and even in that class not in every division, as for example, in Petromyzon (Stannius). Fibres without medulla always occur together with the former, and in general in the same localities as in man ; but in other situations also, as in the skin of the Mammalia, in the electric organs of Fishes, and in the sympa- thetic nerve of the Plagiostomata (Leydig). Where nerves are found in the Invertebrata, they contain only pale fibres without medulla, whose structure often completely resembles that of the embryonic fibres of higher animals, especially as regards the occurrence of great nucleated enlargements in the terminal ex- TISSUES, ORGANS, AND SYSTEMS. 99 pansions, which remains of the original formative cells, have, re- cently, less properly been considered to be ganglion-globules.] Literature, — G. Valentin, 'On the course and termination of the nerves,' in the ' Nov. Act. Natur. Curios.,' vol. xviii, t. i ; R. Remak, ' Observations anatomicse et microscop. de syst. nerv. struct.,' Berol., 1838; A. Hannover, 'Recherches micro- scopiques sur le systeme nerveux,' Copenhague, 1844; R. Wagner, 'Neue Unters. iiber den Bau und die Endigungen der Nerven und die Structur der Ganglien,' Leipzig, 1847 ; and 'Neurologische Untersuchungen,' in 'Gottingen Anzeige,' 1850; Bidder and Reichert, 'Zur Lehre vom Verhaltniss der GangHen- korper zu den Nervenfasern,' Leipzig, 1847; Ch. Robin, in ' I'Institut.,' 1846, Nos. 687—699, and 1848, No. 733 ; KoUiker, ' Neurologische Bemerkungea,' in ' Zeitsch. fiir wiss. Zool.,' i, p. 135. § 39. True Glandular Tissue, — The most essential constituents of the true glands are the secreting elements, which appear as aggregations of cells, as closed glandular vesicles, and as open glandular vesicles and glandular tubes, containing as their most important constituent the so-called gland-cells. These cells are for the most part polygonal or cylindrical, and per- fectly resemble certain epithelial cells, but upon the other hand, they are frequently distinguished and characterised by peculiar contents. The union of these cells into the secreting parts of the glands is effected either directly or with the co- operation of homogeneous membranes, the so-called membrance propria, and of connective tissue. In this manner the secreting glandular elements, different in nature according to the different glands, are formed ; and becoming invested with vessels, nerves, and connective tissue, with which elastic fibres, fat cells, and even muscles, are mingled; they are combined into the larger and smaller divisions of the glands. The principal forms of the secreting glandular elements in man are the following : 1 , Solid networks of cells without investing membrane. In the liver (fig. 40). 3. Closed vesicles with a fibrous membrane and an epithelium. Graafian vesicles, mucous follicles (so-called ovula Nabothi), in the cervix uteri. 100 GENERAL ANATOMY OF THE TISSUES. 3. Rounded or elongated glandular vesicles, with a membrana propria and an epithelium. In the racemose glands (fig. 41). 4. Glandular tubes, with a membrana propria, or a fibrous membrane and an epithelium. Tubular glands (fig. 42). Fig. 40. Fig. 41. To these elements are also added, (except in those glands enumerated under 3, which become emptied of their contents by the occasional bursting of their follicles, and the simplest tubu- lar glands) special excretory ducts, which, after manifold rami- fications, either pass directly into the glandular vesicles and glandular tubes, or, as in the liver, are simply applied to the secreting networks of cells. These ducts are at first similar in their structure to the secreting parts, but they always possess epithelial cells, which have not the specific contents of the proper gland cells, and mostly also exhibit a diflferent form. The wider excretory ducts consist of a fibrous investment and of an epithelium, and often also, possess a muscular layer, and in their ultimate divisions, a fibrous, a muscular and a mucous layer very frequently exist as special structures. Chemically, the glands are, as yet, little known. The glan- dular cells, as the most important structures, are allied in this respect also, to the epithelial structures, only that frequently. Fig. 40. Network of hepatic cells, b; and finest ductus interlobitlarei, a ; of man after nature ; the union of both diagrammatic, x 350 ; c, vascular spaces. Fig. 41. Two of the smallest lobes of the lung, aa; with air-cells. It; and the finest bronchial ramifications, cc ; upon which also air-cells are seated. From a new- born child, X 25 ; semi-diagrammatic figure. TISSUES, ORGANS, AND SYSTEMS. 101 they contain in their interior peculiar substances, — as fat, the constituents of the bile, of the urine, of the ^. ^„ Fig. 42. gastric juice, mucus, &c., and thence assume a specific character. The true glands either separate certain constituents from the blood, or by means of it, elaborate peculiar substances or struc- tural elements, and according as they do the one or the other, is the import of their separate parts different. In the former glands the cells play a more subordinate part, and are at most of importance, so far merely, as they impede the passage of this or that constituent of the blood, and allow only certain of them to pass (kidneys, lachrymal glands, small sudoriparous glands, lungs) ; whilst in others, the cells take a very important share in the formation of the glandular fluid, by producing within them the specific secre- tion, which then either drains out of them (liver, mucous glands, gastric glands, pros- tate, Cowper's glands, salivary glands, pancreas), or becomes free by the gradual dissolution and breaking-up of the cells themselves (lacteal glands, fat-glands, testis, larger sudoriparous and ceruminous glands). In the former case, as in the Graafian follicles, a peculiar cell-development may take place in the .secretion which is formed, whilst in the latter, new elements continually arise in place of those gland-cells which are removed as they attain their full development, in con- sequence of which the character of these cells as a coating of the glandular canals is frequently lost, and they appear simply as a part of the secretion {testis, lacteal gland during lactation). All the glands here mentioned, with the ex- ception of the sexual, are developed from the internal and external epithelial structures of the body, conjoined with the vascvdar membranes which support these epithelia. Some of them originate as involutions of these membranes, and retain the cavities throughout the course of their deve- Fig. 42. Gastric gland from the pylorus of the dog, with cylinder-epithelium : a, larger glandular cavity ; *, tubular appendages of it. 102 GENERAL ANATOMY OF THE TISSUES. lopment (lungs, small intestinal glands), others are at first hoUow, but afterwards increase by the addition of solid out- growths (liver) ; others, again, are solid from the very first, con- tinue to grow in this condition, and only secondarily come to possess cavities (cutaneous glands, racemose glands). The nutrition of the glands goes on with great energy, and they belong to the most vascular organs of the body. Except in the uterine glands, no regeneration of the glandular substance takes place, but hypertrophy occurs in them, and even the accidental formation of minute glands. The true glands of the human body may, according to the form of their ultimate elements, above described, be divided as follows : 1. Glands with closed glandular vesicles, which dehisce periodically. Ovary, follicles of the uterus. 2. Glands whose parenchyma consists of cells united into a network. Liver. 3. Racemose glands, in which, rounded and elongated glandular vesicles are seated upon the ultimate ends of the excretory ducts. a. simple, with one or few glandular lobtiles. Mucous glands, sebaceous glands. Meibomian glands. b. composite, with many glandular lobules. Lachrymal glands, salivary glands, pancreas, prostate, Cowper's and Bartholini's glands, lacteal glands, lungs. 4. Tubular glands, whose secreting elements have the form of canals. a. simple, consisting of only one or a few csecal tubes. Tubular glands of the stomach and intestine, uterine glands, sudoriparous and ceruminous glands. b. composite, with many branched glandular canals, which may also be united into a network. Testis, kidney. [The forms of the glands of animals, notwithstanding their variety, may, with few exceptions, be brought under one of the four categories here established. The following are worthy of par- ticular notice : 1. The glandular cells, with peculiar excretory ducts, to be found in some Articulata, which either, singly, form glands, or are united together in numbers by a membrana pro- pria. 2. The occurrence of a structureless, chitinous membrana intima in many glands of the Articulata, 3. The formation of TISSUES, ORGANS, AND SYSTEMS. 103 certain secretions [Uric acid and bilin in MoUusks, bilin in Crustacea] within special spontaneously enlarging "secreting vesicles" (Nageli, H. Meckel), which may be compared to the yelk vesicles (§ 6). 4. The colossal size (up to 0"1"') of many glandular cells of Insects, and the peculiar ramifications of their nuclei.] Literature. — J. Miiller, *De Glandularum secementium structure penitiori,' Lips. 1830 j H. Meckel, ' Micrographie einiger Driisenapparate niederer Thiere,' in Miill, 'Arch.,' 1846 ; Ft. Leydig's 'Vergleichend-anatomische Abhandlungen,' in 'Zeitschrift fiir wiss. Zool.' § 30. Tissue of the Blood-vascular Glands j—TJj\ier this denomina- tion are most appropriately comprised, a series of organs, which agree in this, that in a peculiar glandular structure, they elabo- rate from the blood or other juices certain substances which are not excreted by special, permanent, or periodically-formed excre- tory ducts, but simply by filtration from the tissue, and are afterwards applied in one way or another to the general pur- poses of the organism. It may be, that this wide definition includes organs, which it will be necessary to separate in future ; but vdth our present slight knowledge of these structures, it is the only one which is possible without enter- _ .„ ing more fully into the subject. The essential glandu- lar tissue of the organs in question appears imder i the following forms : / 1. As a parenchyma of larger and smaller cells, imbedded in a stroma of connective tissue. Su- pra-renal bodies, anterior lobes of the hypophysis cerebri. Some of the cells Kg. 43. A few of the glandular vesicles from the thyroid gland of a child, x 250 : a, connective tissue between them ; b, membrane of the glandular vesicles; <.', their epithelium. '-f ft u :.;r h ;^H . j^^.; m*>t % "' '^jM\ H xVy-^ 1 u <-* ■M- 104 GENERAL ANATOMY OF THE TISSUES. here attain the great size of 004'"; and then contain, together with a granular substance, many nuclei, and perhaps secondary cells. 2. As closed follicles, each of which consists of a membrana propria with an epithelium upon its inner side, and has clear contents : thyroidea. The follicles, which are not enlarged cells, are surrounded by a large quantity of connective tissue, and are united by it into smaller and larger lobules. Z. As closed follicles, with a membrane of connective tissue, and contents consisting of nuclei, cells and some fluid. Among these I enumerate : a. The solitary follicles of the stomach and intestine; and b. The aggregated follicles of the small intestine, or Peyer*s patches (in animals those of the stomach and large intestine also), both of which contain numerous blood-vessels in the interior of the follicles. c. The follicular glands in the root of the tongue, the tonsils, and the pharyngeal follicles, which in the walls of their sacs, contain many closed follicles like those above mentioned, but, so far as we as yet know, without vessels in their interior. d. The lymphatic glands, which appear to consist of follicles like those of the Peyerian patches. 4. As a cellular parenchyma, which contains numerous closed follicles like those just described : Spleen. p- ^^ 5. As racemose, aggregated, glandular vesicles opening into a common closed canal or broad space, whose thick walls are formed of a delicate investment of connective tissue, and of a soft substance consisting of many nuclei and of vessels : Thymus. We know little of the chemical nature of these organs, which are all more or less richly supplied with blood-vessels. Those enumerated under 1, 2, 3, and 5, contain much protein and fat in their tissue, as also do the Fig. 44: A Malpighian corpuscle from the spleen of the ox, x 150 : a, wall of the corpuscle ; *, contents j o, wall of the artery upon which it is seated ; d, sheath of the latter. TISSUES; ORGANS, AND SYSTEMS. 105 follicles of those included under the fourth form, while the remaining parenchyma of the spleen possesses peculiar cor- puscles, not yet completely investigated, which seem to indicate an energetic, retrogressive metamorphosis. We know little of the physiological functions of these glands ; and here it need merely be remarked, that in the spleen, the thyroid, the thymus, the supra-renal capsules, and the pituitary body, it can only be the blood which yields material to them, and only the blood- and lymph- vessels which again receive the sub- stances given off externally or internally (thymus) by them. In the follicular glands of the mouth and pharynx, the secretions are poured into the wider cavities of the glands, and ultimately into those organs, whilst in the intestinal follicles, it is doubtful whether they excrete substances into the intestine, or receive them from thence to give them up again to the vessels. In the lymphatic glands^ the ducts supply the glandular follicles with matters which they take up again when further elaborated. The development of the blood-vascular glands is still very obscure ; although this much appears certain, that most of them are developed without the participation of the intestinal epithe- lium, either from the fibrous wall of the intestine or from the same blastema as that which produces the sexual glands. The thymus and thyroid alone are to be regarded, according to Remak, as diverticula of the intestinal canal. The nutrition of most of these glandular structures is very energetic, as the abundance of the blood they contain and their frequent morbid alterations show : the hypophysis cerebri and the supra-renal capsules alone, in this respect, occupy a lower grade. lAterature, — A. Ecker, art. ' Blood- vascular Glands,' in 'Wagner's Handw. d. Phys.', Bd. IV, 1849. [H. Gray, ' On the Development of the Ductless Glands in the Chick,' Philosoph. Trans., 1853,— Eds.J SPECIAL HISTOLOGY. OF THE EXTERNAL INTEGUMENT. I.— OF THE SKIN IN THE STRICTER SENSE. A. CUTIS. ^ 31. The ecsternal skin, Integumentum commune (fig. 45), consists essentially of an internal layer formed principally of connective tissue, and rich in vessels and Fig. 45. nerves, the true skin, cutis, derma (fig.45,c, rf);and of an external layer composedof cells only, the epidermis (fig. 45, a, b); and it con- tains in addition many peculiar, glandular and horny organs. The cutis may be again subdi- vided into two layers, the sub- cutaneous cellu- lar \ tissue, tela Fig. 45. Perpendicular section through the whole skin of the ball of the thumb, transversely through three ridges of the cutis, x 20 : a, horny layer of the epidermis ; h, its mucous layer ; o, corinm; d, pannicuhu adipoaus (upper part) ; e, papillae of the cutis ; /, fat masses ; g, sudoriparous glands ; h, their canals ; i, sweat-pores. OF THE SKIN, 107 cellulosa subcutanea (fig. 45, d), and the proper corium (fig. 45, c) ; the latter of which, from its rich nervous and vascular supply, forms the most important part of the skin. § 33. The subcutaneous cellular tissue is a tolerably firm mem- brane, constituted chiefly of connective tissue, which in by far the most parts of the body, incloses within its meshes a considerable quantity of fat-cells (fig. 45, /), thus forming the panniculus adiposus ; in some situations, however, as for example in the scrotum, the penis, and the nymphee, &c., it contains but little or even no fat. The innermost layer of the subcutaneous cellular tissue, which upon the trunk and thighs forms a tolerably firm fatless texture, the fascia superficialis, rests upon different organs, as muscular fascia, periosteum and perichondrium, muscles, and the deeper accumulations of fat, and is more or less closely united with them. The union is looser upon the trunk, the two distal divisions of the limbs, the back of the hand and foot, the neck, and especially on the eyelids; the penis, scrotum, and on the extensor side of the articulations, where the subcutaneous mucous bursa, as they are called, are frequently situated, as, for instance, in the knee, elbow, and phalangeal joints. A more close connection sometimes exists, — as where tendinous fibres or • processes {aponeurosis palmaris and plantaris, linea alba), or muscles [palmaris brevis, levator labii superioris alteque nasi, levator labii superioris,&c.), are inserted into the skin; sometimes, — as where the innermost layers of the subcutaneous cellular tissue are blended, as it were, by means of short, strong, filaments of con- nective tissue with the subjacent muscles, /asci^e, tendons, &c. particularly, therefore, on the head, especially on the alee nasi and lips, the forehead and temples, the ear, mouth, and occiput; on the glans penis, beneath the nails, &c. In general, where the fat forms a thick layer, the skin is less moveable than when from any cause it is less abundant or entirely absent. The external surface of the subcutaneous cellular tissue, is connected by means of numerous filamentary processes of connective tissue, with the corium, and is not everywhere clearly distinct from it ; but a separation between the subcu- taneous cellular tissue and the corium may be pretty readily 108 SPECIAL HISTOLOGY. effected, especially when the former contains an abundance of fat, with the exception of certain situations (head, cheeks, chin, &c.), where the follicles of the larger and more closely set hairs penetrate deeply into the panniculus adiposus. The subcutaneous cellular tissue of the penis, scrotum [dartos), &c. passes into the corium without any distinct limitation. The thickness of the subcutaneous cellular tissue varies very considerably, as is well known, according to situation, age, sex, and the individual. The fat-less subcutaneous cel- lular tissue of the eyelids, and of the upper and outer part of the ear, measures, according to Krause |"', on the penis I'", on the scrotum §'". The panniculus adiposus is 1'" thick on the cranium, brow, nose, lobe of the ear, neck, dorsum of the hand and foot, the knee and elbow ; in most other situations it is 3 to 6'", though in fat persons it may exceed 1" in thickness, and in thin ones may sink below 1'". § 33. The proper corium is a tough, slightly-elastic membrane, and is composed principally of connective tissue, which in the thicker parts presents two, though not very well-defined layers, which may be designated the "reticular" and the "papillary" portions (p. reticularis and p. papillaris). The former constitutes the inner layer of the corium, and consists of a white, reticulated membrane, frequently distinctly lami- nated in its deeper portions, and containing in special, narrow or wide, scanty or numerous meshes, the hair follicles and cutaneous glands, together with much fat. The papillary part of the corium is the reddish-grey external superficial layer (fig. 45), which in its dense, firm tissue, contains the upper portion of the hair-follicles and cutaneous glands, and the terminal expansions of the vessels and nerves of the skin. Its most important element consists in the cutaneous or tactile papillae, papilla tactHs (fig. 46) ; small, semi-transparent, flexible, but tolerably solid elevations of the external surface of the corium, which are ordinarily conical or clavate in form, but in certain places present numerous points (compound papilla). With regard to their number and position, the papilla of the bed of the nail, of the palm of the hand, and of the sole of the foot, are very numerous (E. H. Weber enumerates upon OF THE SKIN. 109 Kg. 47. 1'" square of the vola Kg- 46. manuSy 81 compound, ^ or 150 to 200 smaller papillte), and disposed ^ with tolerable regu- larity in two principal series, each of which has 2 to 5 papillae in the transverse direction, placed upon linear elevations, ^ to s " broad, by ^ to f high,— the ridges of the corium. The course of these ridges is visible, even ex- ternally in the epidermis, and therefore needs no further de- scription. Elsewhere the papilla are more irregularly scattered, either very close together, as in the labia minm-a, the clitoris, the penis,and the nipple, or somewhat more widely apart, as upon the extremities, with the exception of the places named, on the scrotum, the neck, chest, abdomen, and back. The size of the papill [Mr. Dalzell, in a communication read before the Edinburgh Physiological Society, January, 1853 ('Monthly Journal of Medical Science,' March, 1853), con- firms KoUiker's account of the corpuseula tacHa in all essential points.— rE ds.] 126 SPECIAL HISTOLOGY. below 7 years of age, for example, the cutis is, according to Krause, only half as thick as in the adult, until at last, though at a time which is as yet undetermined, the new development of cells ceases, as at a later period, perhaps, does the extension of those elements, cells, fibres, &c., which are already formed. The fat-cells of adults, in which the process of growth is especially obvious, according to Harting, are in the orbit twice, in the palm three times as large as in the new-born infant; whence it results, that they increase in size in proportion to the parts of the body to which they belong. [In embryos of two months the skin is 0006 — O'Ol'" thick, and wholly composed of cells. At the third month it is about 0'06"', and already presents tolerably distinct connective tissue. In the fourth month the first lobules of fat appear, and the ridges of the hand and sole of the foot. From the seventh month onwards the panniculus adiposus is rapidly developed, and at birth it is relatively thicker than in the adult.] § 39. Physiological Remarks. — If we attempt to harmonise the anatomical data here brought together, with the phenomena of .sensation exhibited by the skin, we meet with considerable difficulties. The more intimate anatomy of the skin, as it is here detailed, fails to demonstrate nerves in all the papillae, or even in the majority of them ; and yet experiment teaches that though all points of the skin may not feel with the same deli- cacy, they are all nevertheless sensitive. I hoped to be able to submit Wagner's doctrine of the absence of nerves in many papillae to experiments^l proof, by examining the sensitiveness of various parts of the body with the finest possible English sewing needle. At first I really thought that I had found some places which were quite insensible, whilst in others the slightest touch produced sensation; but on carrying the investigation further, it appeared that the very same place was often sometimes sensible, sometimes not; so that, finally, I came to the conclusion that the very smallest portions of the skin are sensitive. But since even in the palm of the hand the papillae containing nerves are widely dispersed, and in other places occur but rarely or even not at all, it only remains OF THE SKIN. 137 either to assume the existence of non-medullated nerve-fibres in all the papillse, or to have recourse to the nervous plexus at the base of the papillae. I should unhesitatingly prefer the latter explanation, were it not : (1 ) that these plexuses are in many places so very scanty, and (2) that the slightest touch of the epidermis produces sensation ; for the present, therefore, I believe this must remain an open question. If we are not in a condition to understand how it is that every point of the skin is sensitive, still less are we competent to explain the different kinds of sensations. In this respect the following very general statement may be made. The excitement of the terminations of the nerves in the outermost parts of the cutis and the papillae is either direct or indirect. The former as it is produced, for example, when the cutis is laid bare, by penetrating instruments and by fluids, is much more intense than that which takes place through the me- diation of the epidermis, one of the functions of the latter being to act as a defence against too violent impressions, and to blunt them according to its greater or less thickness. It can now be partly explained on anatomical grounds, why the delicacy and vivacity of the sense of touch are not every- where equal, why they are less upon the hairy scalp, the back, the two upper divisions of the extremities, than on the face, on the genitalia, the hand and foot, the chest and abdomen. In the first place, where the tactile sense is delicate, the epi- dermis is in itself thin, as upon the eyelids and face, or has, at least, a thin horny layer, as upon the penis and clitoris, whilst upon the back and extremities it is considerably thicker. Yet this circumstance is not a sufficient explanation, for parts with a thicker epidermis, as the palm of the hand and the sole of the foot are delicately sensitive, more so, in fact, than others with a thinner covering, as the back of the hand and foot. Another condition must here obviously come into play, and it is, I think, that the skin is not equally well provided with nerves in all its parts. Simple inspection teaches that the nerves upon the palm of the hand and the sole of the foot are more numerous than upon the back of the hand and foot ; upon the glans penis and clitoridis, the nipple, the face, they are more abundant than upon the abdomen, badk, and thigh, &c. &c. ; and this is to some extent confirmed by my 128 SPECIAL HISTOLOGY. measurements of the sensitive roots of the spinal nerves {vide ' Mic. Anat./ p. 433). With the number of the nerves, is con- nected that of the actually demonstrable dark-contoured nerves in the papillae and the superficial nervous plexus, for nowhere is this more considerable than in the points of the fingers, the lips, the tip of the tongue, and the glans penis. As to the local sensibility of the skin, it is the province of anatomy, especially, to afibrd information, with regard to these two points: 1, how it is that we do not distinguish with the same clearness and exactness, in all parts of the body, the point at which a single irritation is applied : and, 3, why two stimuli operating at the same time, under certain circum- stances, appear double, under others single (Weber's experi- ment). I think that Weber's experiment cannot be explained by the mode of distribution of the peripheral nerves, but depends very probably upon their central relations. It seems to me to be simplest to assume, that every peripheral end of a nerve is capable, when irritated, of producing a conscious sensation, but that, on account of the small number of nervous fibres (in the cerebrum) which unite these with the seat of consciousness, if many contiguous, or even more distant,, cutaneous nerves are excited, only a single conscious sensation results. In this case, the nerves of acutely sensitive parts must be connected with the seat of consciousness by more numerous intermediate fibres than those of other localities, and at the ends of these fibres, also, we must suppose a sort of interlace- ment to take place. Upon this hypothesis, the former of the two points might be explained. A local irritation is, indeed, felt locally; but, according as the nerves implicated are united with the brain by more or fewer conductors in the spinal cord, are we able to assign, more or less exactly, the precise spot ; so that, in some cases, the limits of error will not exceed s"' — I'", while, in others, they may extend to l" — Ij" and more. E. H. Weber has endeavoured to demonstrate, in his last able Treatise upon the sense of touch, that it is only the ter- mination of the nerves in the skin, not the fibres in the nervous trunks, which are the mediators of the sensations of pressure, warmth, and cold; and he has expressed a suppo- sition, that tactile organs as yet unknown may exist in the OF THE SKIN. 129 skin. R. Wagner believes that he has, in fact, found these organs in his so-called corpuscula tacMs, and he supposes that, composed as they are, according to him, of superimposed membranes, in the interspaces of which a very minute quantity of fluid is lodged, like elastic cushions, or a bladder filled with water, they are specially fitted to receive impressions from the epidermis at the extremity which is directed towards it, and to transmit them to the ends of the nerves which lie in and upon them. In my opinion, Weber's view of the greater sensibility of the terminations of the nerves in the skin, can hardly be doubted; but, on the other hand, there is no obvious rea- son, a priori, why peculiar hitherto unknown organs should exist to that end; nor why the condition to which I have already referred, the more isolated course of the fibres of the nervous tubules in the papillae and terminal plexuses, their fineness, superficial position, and the delicacy or ab- ' sence of the neurilemma, may not abundantly suffice as an explanation. That Wagner's so-called corpuscula tactus, my axile corpuscles, are not tactile organs in the sense intended by Weber, is easily demonstrable. Independently of the erro- neousness of his views of their structure, and of the fact that the nerves are not distributed in them, but only proceed along them, outside, in order, in many cases, to terminate even beyond them — we find that all the essential functions of the skin are also performed without such corpuscles. The feeling of warmth and cold, of orgasm, of tickling, of pressure, of prick- ing, of burning, of pain, are found partly over the whole surface of skin, partly in places where these corpuscles are certainly absent, which sufficiently shows that they have not in the remotest degree the signification ascribed to them by Wagner. However, it is not likely that they exist for nothing in those particular localities, in which the sensibility to pressure is the greatest, and which we use especially as tactile organs, as the ends of the fingers, the point of the tongue, and the border of the lips; and I consider them as parts, which, in consequence of their being composed principally of dense, imperfectly -formed elastic tissue, confer a certain solidity upon the points of the papillm, and serve as a firm support for the nerves, in consequence of which, a pressure, which in other situations is not sufficient to I. 9 130 SPECIAL HISTOLOGY. affect the nervej here takes effect. They would, in fact, be organs, like the nails and phalangeal bones, not essential and indispensable to the sense of touch, but only conferring upon it a greater acuteness than elsewhere. If, in this sense, they are to be called tactile corpuscles, I have nothing to say against the term, but then the phalanges and the nails, the " whiskers" of animals, &c., equally deserve the name of tactile organs.^ The contractility of the skin is exhibited in the wrinkling of the scrotum and of the skin of the penis, the erection of the nipple, and the occurrence of the so-called cutis anserina. It depends upon the smooth muscles of the skin already de- scribed, which, as Froriep and subsequently Brown- Sequard and I have found, contract by electricity, inasmuch as by this means, even in the living subject, the cutis anserina, the erection of the nipple, and, in recently-executed persons, a wrinkling of the scrotum can be produced. In the erection of the nipple by gentle mechanical irritation, the whole areola becomes diminished by the contraction of its circular fibres, and thus protrudes the nipple whose muscular fibres, in this case, seem to be relaxed. Cold causes the areola and the nipple to contract, both becoming small and firm. The cutis anserina, which consists in wholly local contractions of the portions of the skiu around the hair sacs by which their apertures are protruded conically, is explained simply by the existence of the muscles which I discovered, and which pass obliquely from the superficial part of the cutis down to the hair sacs, and when they act, extrude the sacs, and retract those portions of the skin whence they arise. The assumption of a contractile connective tissue in the skin, as well as in other parts, I must repudiate here, as I have already done (Mittheil. der Ziiricher Gesellschaft, 1 847, p. 27), because the smooth muscles, which can be microscopically demonstrated in the skin, and whose contraction by galvanism may be experi- mentally shown, sufficiently account for all the contractile phenomena which it exhibits. ' [See, however, Wagner's reply to Kiilliker, 'Ueber die Tastkorperchen,' in Miiller's 'Archiv,' August, 1852.— Eds.] OF THE SKIN. 131 B. EPIDEBMIS. § 40. The corium is everywhere covered by a semitransparent membrane formed wholly of cells, and containing neither vessels nor nerves, — the epidermis, which applies itself exactly to all the elevations and depressions, and which accordingly upon Fig. 55 A. its inner surface presents an exact cast of the outer surface of the corium, the convexities and concavities of course being reversed. Upon its outer surface, also, the epidermis, to some extent, represents the form of the corium, since the more marked elevations and depressions, such as the ridges of the palm of the hand and of the sole of the foot, the folds at the joints, muscular insertions, &c. are expressed in it, — the latter even Fig. fAA. Surface of the palm, from within: a, ridge answering to the groove between the ridges of the cutis ; *, a similar one corresponding with the cleft between the rows of papillae ; c, sweat ducts ; d, broader points of insertion of these into the epidermis ; e, depressions for the simple and compound papillae. 132 SPECIAL HISTOLOGY. more strongly ; on the other hand, the papillae produce either no perceptible projection, or hardly any. The epidermis consists of two layers, chemically and morpho- logically distinct, and which are separated by a tolerably sharp line of demarcation, viz., the mucous layer and the horny layer. § 41. The mucous layer, stratum Malpiffhii, rete or mucus Mal- piffhii {rete mucosum), of many authors, is that part of the epidermis which lies immediately upon the corium, and almost everywhere appears undulated; in many places it is distin- guishable even to the naked eye by its colour, which is whitish or variously tinged with brown, and it is further charac- terized by its small, soft, easily destroyed, peculiarly dis- posed cells. The form of these cells and their disposition are not the same in all localities. The innermost of them (fig. 55 6), which, without interspersed free nuclei or semi-fluid substance, form a single layer resting im- mediately upon the free surface of the corium, are elongated, and not unfrequently resemble the cells of cylinder-epithelium ; they are placed perpendicularly upon the corium; their length is about from 00033—0006'", their breadth 00035— 0003'". Upon these immediately follow, in most places, elongated or even round cells of O'OOS — 0004'" in many layers; but in a few localities, as in the hand and foot, at the free margin of the eyelids, in the mucous layer of the nails and hairs {vide infra), there are interposed here and Fig. 55 B. Perpendicular section of the skin of the Negro (from the leg), x 250 : aa, cutis-papillse ; b, deepest intensely-coloured layer of perpendicularly elongated cells of the stratum mucosum; c, upper layer of the stratum mucosum; d, horny layer. Kg. 55 B. OF THE SKIN. 133 there, between the rounded and elongated cells, one, two, or even three layers of similarly elongated and perpendicularly disposed elements, so that the mucous layer, on account of the numerous strata of perpendicular cells, has a striated appearance in its deepest part, under a low power. This character is the more striking, since the other elements of the mucous layer, the further they are followed from the first, round cells outwards, become thinner in another direction, i. e., become horizontally flattened (fig. 55 c), and finally in the uppermost layers are transformed into thick vesicles, 0-006— 0-016'" broad, and 0002— 0008'" thick. At the same time, from their mutual pressure, they acquire a polygonal form, which may even be recognised in isolated cells. All the cells of the mucous layer agree, in essential points, in their structure, and are nucleated vesicles distended with fluid. Their membrane is pale, often diflScult of demonstration in the smallest, frequently quite distinct, always delicate, thicker in the larger ones, yet by no means to be compared to that of the cells in the horny layer. The contents are never quite fluid; but also, excepting in the coloured epidermis {vide infra), never normally contain larger particles, granules or fat-drops for example ; but are finely granulated, with more or less clearly-defined granules, which invariably diminish in number in the more external cells. The nucleus, lastly, is small in the smallest cells (0-0015 — 00025'"), in the large, of greater size (0003 — 0-005"'); globular or lenticular, in the round and flattened cells; elongated, in the elongated cells. In the larger cells it appears obviously, vesicular, often with a nucleolus, and lies centrally in the midst of the contents; in the smaller it is apparently more homogeneous, without any visible nucleolus, and so disposed that it is not unfrequently in contact with one part or other of the cell- walls. $ 42. The horny layer {stratum corneum), forms the external semi- transparent part of the epidermis, which in white people is colourless, and is composed almost wholly of uniform cells metamorphosed into plates. The deepest plates are still very similar to the uppermost cells of the stratum mucosum; but even in the second or third layer we find the widely different 134 SPECIAL HISTOLOGY. epidermic or fiorny plates. They (fig. 56. 1, 3, 3) are, in fact, j^ 5g plates of moderate thickness, which in the lower and middle parts of the horny layer retain tolerably regular polygonal (4-5-6 sided) and smooth surfaces ; in the upper layers, on the other hand, they present more irre- gular outlines, are variously crooked and curved, and thence often appear to be wrinkled and folded. These plates must be regarded as cells, completely flattened, and containing a very minute quantity of viscid fluid ; and not, as might at first be imagined, as homogeneous lamellae, composed throughout of the same substance; for by the addition of various reagents, especially of acetic acid and of potass, they swell up and assume the form of vesicles (fig. 57) J at the same time, a rudimen- tary nucleus becomes obvious in a few, particularly in those from the middle and inner layers, but by no means in the majority of them, in the , form of a flat, homogeneous, rounded or elongated corpuscle, 0003 — 0-004'" in length, and 0002— 0003'" in breadth, which, especially when seen from the side, is easily recognised by the dark contours which it then presents. The size of the plates of the ordinary horny layer varies from 0*008 — 0016'", and in the outer layer it is commonly somewhat greater than in the inner. Upon the body of the penis the cells measure 0-008'" — 0-013'" ; upon the fflans, the largest are 0-016 — 0-03'"; upon the outer side of the ladia minora 012 — 003"'; on the labia majora 001 — 0-016'". These last, larger Fig. 56. Horny plates of man, x 350 : 1, without addition, viewed from the surface one with a nucleus ; 2, from the side ; 3, treated with water, granular and dark ; 4, nucleated plate, such as occur on the outer surface of the labia minora and on the glans penis. OF THE SKIN. 135 cells, all possess distinct nuclei, and are almost identical with the epithelial plates, e. g., of the cavity of the mouth and of the vagina (fig. 56. 4.) Whilst the stratum Malpighii, except in its upper layer, is but indistinctly laminated, a clear lamination is obvious in the horny layer, inasmuch as its plates applied together horizontally, form strata in number proportionate to the thickness of the horny layer (fig. 55). It must not be imagined that these strata are distinctly defined from one another ; they are con- nected by their surfaces, and can only be detached and demon- strated adhering together in numbers, by dissection, which is much facilitated by boiling or macerating the epidermis. The innermost, like the stratum Malpighii, taken altogether, exhibit a wavy course wherever papillae exist, projecting out- wards over the points of the papillae and following the depres- sions between them. This takes place in the most striking manner where very much developed papillae coexist with a mo- derately thick rete Malpighii, especially in the palm and in the sole of the foot, in which (see the figure in the section on the sudoriparous glands) the horny layer penetrates so deeply between the papillae, that its deepest cells are on a level with half their height : where the papillae are smaller, the horny layer sinks less deeply between them, or even lies quite flat upon the stratum Malpighii, as is the case where the pa- pillae are absent. From this cause the boundary line between the horny layer and the stratum mucosum in perpendicular sections, is sometimes straight, sometimes wavy, with smaller or greater elevations and depressions. The other parts of the horny layer take a more even course the further they are from the mucous layer; yet not merely in the hand and foot, where, as is well known, the ridges of the corium are marked ex- ternally upon the epidermis, but in many other localities a slightly wavy course of the uppermost layers may be perceived in perpendicular sections, and slight elevations indicate ex- ternally the points beneath which the papillae are seated. In the separate lamellae the plates are sometimes irregular, some- times arranged circularly, as around the excretory ducts of the glands and hair-follicles, and also round the papillae on the palm of the hand and sole of the foot, as may be seen most readily at the apertures of the sudoriparous glands. 136 SPECIAL HISTOLOGY. § 43. As regards the colour of the epidermis, in the white races, as has been said, the homy layer is colourless and transparent, or slightly yellowish, the mucous layer yellowish white, or brownish. The colour is deepest in the areola and in the nipple, passing even into blackish-brown, especially in women during pregnancy and after they have borne children: it is less intense in the labia majora, the scrotum, and the penis, where for the rest it varies greatly, being sometimes almost entirely absent, sometimes very distinct, and is least considerable in the axilla and round the anus. Besides these situations, which in most in- dividuals are more or less tinged, in the dark-complexioned more than in the fair, a lighter or more deeply coloured, frequently very dark pigment is deposited in various other localities in the stratum Malpighii ; in pregnant women in the linea alba, and in the face (rhubarb-coloured spots) ; in persons who are exposed to the sun, in the face, especially the brow, chin, and cheeks; in the neck, the thorax, the back of the hands, the fore- arm ; and in dark persons over almost the whole body. These tints are not produced by special pigment-cells, but are seated in the common cells of the mucous layer, round whose nuclei a finely granular or more homogeneous colouring matter or actual pigment granules are deposited. When the skin is only slightly coloured, it is mostly only the neighbourhood of the nuclei and in fact, only of the lowermost layers of cells which is impli- cated, so that in perpendicular sections the papillae are seen to be surrounded by a yellowish fringe; darker shades are produced by the extension of the colour to two, three, four, and more layers of cells, and over the whole cell contents ; some- times by a darker coloration of the deepest layer of cells ; the two conditions commonly coexisting. The horny layer also of the coloured places of the skin, has according to BLrause, its cell- walls slightly tinged ; this appears, however, only upon com- paring them Tfvith those of uncoloured parts of the skin, and only in the more deeply-tinged parts. In the Negro, and the other coloured human races, it is also only the epidermis which is coloured, whilst the corium completely resembles that of Europeans. The pigment, however, is far darker and more abundant. In the Negro (fig. 55), in whom, as regards the OF THE SKIN. 137 arrangement and size of the cells, the epidermis is precisely like that of the European, it is the perpendicular cells of the deepest part of the mucous layer which are darkest (dark brown or blackish-brown), and they form a sharply-marked fringe con- trasted against the clear corium. To thesd succeed clearer but still brown cells, which are accumulated particularly in the depressions between the papillae, but are also found on their points and lateral portions in many layers; finally at the boundary close to the horny layer there follow brownish-yellow or yellow, often rather pale, more transparent layers. AH these cells are coloured throughout, with the exception of their membranes, and especially the parts round the nuclei, which, in the internal layers, are by far the darkest portions of the cells. The horny layer of the negro alsainclines to yellow or brownish. In the yellowish skin of a Malay head in the anatomical col- lection at Wiirzburg, I find the same appearance as in a dark- coloured European scrotum. It follows, then, that the epidermis of the coloured races is, in no essential point, distinguishable from the coloured regions in the white man, and it even agrees in nearly all respects with that of certain localities (the areola of the nipple, for instance). [.Pathological coloration of the epidermis (freckles, mothers' marks, Sec.) according to Simon, Krause, Barensprung, and my own observations, is produced exactly as the more in- tensely-coloured spots in the white man, and as the colour of the negro's skin. Pigment deposits in the corium and in the papillae, such as may be seen in cicatrices, after chronic inflam- mation of the skin, and frequently as in ichthyosis and many iKEvi, associated with a coloured epidermis, iu which the pig- ment is developed directly from the blood-corpuscles and their colouring matter, must be carefully distinguished from the fore- going. Numerous instances of partially or entirely white Negroes and of black Europeans, not as a consequence of change of climate, but as a congenital or subsequently arising abnormal condition of the skin, have been noticed (see Hilde- brandt. — Weber, II, fig. 526 j Flourens, Compt. rendus XVH). But, for the future, it will have to be remembered, so far as the dark coloration of Europeans is concerned, that it may also arise from a deposition of the colouring matter of the bile.] 1'" 138 SPECIAL HISTOLOGY. § 44. The thickness of the epidermis as a whole, varies exceedingly, depending especially upon that of the horny layer. It measures : ji — ^ "' upon the chin, the cheeks, and brow, in the external auditory passages, and upon the eyelids: upon the bridge of the nose, on the breast and nipple in the female, on the back of the toes and fingers, upon the neck and back, on the inner and outer side of the thigh, on the scrotum and the labia minora: 4 — Ts" oil t^6 edge of the eyelids, on the male chest and nipple, the hairy scalp, the chin, penis, prepuce, and glans penis: ra — tc" ^^ t^^ r^d external parts of the lips, on the back of the hand : ra — ?'" on the flexor side of the fingers and toes: I — Y" on the palm : and — I — 1 j'" on the sole of the foot, in which two latter localities the variations are greatest, independently of the circumstance, that in the furrows and at the joints the skin is thinner than elsewhere. With regard to the proportionate thickness of the horny and mucous layers I find, in some localities, that the latter is constantly thicker than the former ; i. e., in all parts of the face, in the hairy scalp, in the penis, the glans, the scrotum, the nipple, and the skin of the thorax in man ; in the labia majora and minora, on the back and neck. Here the mucous layer is 3 — 6 times, or 2 — 3 times as thick as the horny layer, according as its thickness is measured from the bases or from the points of the papilla; in a few of the localities mentioned, however, the stratum Malpighii is, in" its thinnest parts, of the same thickness as the epidermis, as in the glans. In the rest of the body, both layers are either equal in thickness, as in the external auditory passage, and here and there upon the flexor side of the first two sections of the extremities, or the horny layer is 2 to 5 times thicker than the mucous, and in the thickest places even 10 to 12 times as thick. OF THE SKIN. 139 The absolute thickness of the stratum Malpighii varies (at the base of the papillce) between 0007 and 0'16"'; where it is thicker than the horny layer, it measures in the mean OO^'"; where it is thinner, O'Ol — 0'02"'. The horny layer by itself measures in many places only 0'005"', in others 1'" or more; when its thickness exceeds that of the stratum Malpighii, it is generally about O'l — 0-4'", when it is less, 0-01'". § 45. Physical and vital Properties. — The epidermis is but little elastic, flexible in the living condition and not easily frangible, softer in the deeper than in the superficial layers. The cells con- tain, neither in their membranes nor between them, any demon- strable pores (apart from the sudoriparous ducts and hair-sacs, which, in a manner, have their outermost portion hollowed out in the epidermis), and form a very solid, hardly permeable substance. Many experiments, especially those of Krause, show, that the horny layer of the epidermis permits no fluids, except those which act chemically upon it, as the mineral acids and the caustic alkalies, to pass through it, either by pores, or by imbibition, or by endosmose and exosmose, while it readily takes up gaseous matters, or easily vaporizable substances (alcohol, ether, acetic acid, ammonia, solutions of chloride of iron in ether, of acetate of lead in alcohol), and gives them off (cuta- neous evaporation). This conclusion is not invalidated by the undeniable passage of water, liquid substances, ointments, and even solid matters (sulphur, cinnabar), through the uninjured epidermis, since in these cases a mechanical intrusion of the substances, in and through the sudoriparous ducts and hair-sacs, or their penetration into the sweat-ducts, and mingling with the sweat, explains their absorption. The mucous layer, at any rate, is easily penetrated by liquids, as is sufficiently shown by pathological anatomy (exudations which penetrate the mucous and raise up the horny layer into a vesicle, the ready occurrence of absorption after the separation of the homy and the super- ficial portion of the mucous layer, by the action of vesicants.) In their chemical relations, it is indeed well known how the cells and plates of the epidermis behave with regard to certain reagents, but there exists, at present, no perfectly satisfactory 140 SPECIAL HISTOLOGY. total analysis of the epidermis^ with regard to its two layers which difiFer so widely; and the organic combinations, also, which occur in it, are not sufficiently known. The so-called horn, which forms the membranes of the homy-plates, is insoluble in water, easily soluble in concentrated alkalies and concentrated sulphuric acid, whence the skin, if wetted with these substances, feels slippery and greasy; there remains, however, a small residue insoluble in alkalies; con- centrated acetic acid, also, dissolves it, first rendering it gelatinous, by which it is distinguished from the protein compound of the hair. It contains less sulphur than the hair and nails, which is perhaps the reason why salts of lead, mercury, and bismuth, colour the hair but not the epidermis. Besides these, Mulder finds in the horny layer a gelatinous matter, which is obtained by long boiling in water, and which would appear to be of a collagenous nature. The epidermis does not, putrefy — it melts in the fire without bending or swelling up, and bums with a clear flame. [The behaviour of the epidermis towards reagents is particularly of importance for the microscopist, on whose behoof I add the following account. After long maceration in water, the epidermis becomes detached in portions, and under moderate pressure is resolved into a white powder, consisting of the isolated horny plates, and the uppermost cells of the rete Malpighii. Boiled in water, pieces of the horny layer break up into their elements much more readily. Boiled in concentrated acetic acid for 15 to 25 minutes, all the horny plates become perfectly isolated, forming a cloudy, whitish deposit in the test tube; they are exceedingly pale, so that they are often hardly visible under a full illumination; and are completely swollen up and changed into globular or elongated, distended, but always more or less flattened vesicles of 002 — 0032"' breadth, and 0-006 — OOl'" thickness, the nuclei when they are present being also pale and hardly to be perceived. The Malpighian layer becomes pale under the action of cold, con- centrated acetic acid, the cells and nuclei being rendered more distinct. The cell-contents are partially dissolved : by longer action the contours of the deepest layers of cells become OF THE SKIN. 141 invisible. The same thing occurs after boiling for four minutes. Caustic potass and soda act differently, according as the solutions used are concentrated or diluted. In the latter case, immediately after the addition of the reagent, the horny layer is rendered more clear, it swells up and changes in a short time into a beautiful tissue of peUucid, globular vesicles, without nucleus or granules, and with sharp, moderately- thick contours, 0-02 — -032'" in breadth, and 0016 — 002'" in thickness. If concentrated, solutions of the caustic alkalies render the plates at first smaller, so that they measure only 0*012 — 0'016"', and are at the same time more wrinkled and pale, but with defined, dark contours ; in the course of an hour they swell up so as to appear as cells, but it takes two or three hours to give them the aspect of the plates which have been heated with dilute solutions. Boiled with these fluids, even the dry horny layer swells up, in an instant, into the most beautiful tissue of cells, without either granules or nuclei (fig. 57), and at the same time the dissolving cell-contents, mixed with the alkali, are col- j^» 57_ lected in the cells, into greater and smaller granular masses; after the action of the heat for five hours, all the cells disap- pear without leaving a trace, and yellowish and pale fat- drops in no great number, swim in the liquid. The cells of the Malpighian layer are still more acted upon by alkalies than those of the horny stratum : they swell up at once, and appear distinctly as delicate vesicles; these then dissolve, all but the uppermost two or three layers, which require a longer time, like those of the homy stratum, though less than the latter. The nuclei of all the cells with- stand the operation of this reagent even less than the cells; whilst, when the latter are dissolved, a granular or striated sub- stance remains behind, which is, probably, partly fat. Concen- Kg. 57. Horny plates boUed with caustic potassa and distended; the contents partially and vrholly distended, x 350. 143 SPECIAL HISTOLOGY. trated sulphuric acid, in five minutes, causes the horny layer to swell up so much, that its elements, although still remaining flattened and irregular, appear quite distinctly to be vesicles; after half an hour they are somewhat more distended, and easily separable from one another. By boiling with this acid the plates swell up even in a minute, without exhibiting nuclei, and in two minutes they disappear without leaving any trace. Boiling in dilute sulphuric acid renders the horny layer hard and transparent, and dissolves it wholly in 4—5 hours. The cells of the stratum Malpighii are little altered by cold sulphuric acid: on boiling, their contours and nuclei at first become more distinct, but in about two minutes the whole is dissolved. Nitric add colours the epidermis yellow, softens and changes it into xantho-proteic acid. The cells of the homy layers swell up somewhat, after a time, in the cold, and become granular ; the stratum Malpighii is rendered granular and indistinct, and sharply defined from the horny layer. Upon boiling, the whole epidermis is entirely dissolved in half a minute. Hydro- chloric acid does not tinge the epidermis, and in the cold renders the cells of the horny layer somewhat more distinct than nitric acid. After boiHng for a minute the horny layer becomes a beautiful cellular tissue, exactly as after the addition of dilute solution of potass. In carbonate of potass the epi- dermis is hardly changed at all. After seventeen weeks it is hardened and easily cut with a knife. Nitrate of silver colours it violet or brownish-black, by the formation of oxide of silver, of chloride of silver, and of black sulphuret of silver, ia. consequence of the chloride of sodium and sulphur which it contains. Investigated microscopically with the help of acetic acid, the tissue of the epidermis is seen to remain quite unchanged, and minute dark granules are visible between its elements. Nitrate of mercury gives the epidermis a reddish- brown hue, sulphurets of the alkalies render it brown and black: many vegetable colours unite with it. In alcohol and ether it is insoluble, with the exception of the small quantity of fat which it contains. From all this, it results, with regard to the elementary parts of the epidermis, that they are cells, which, however, as the alkalies show, do not everywhere present the same characters. In the stratum mucosum they are actual vesicles and easily OF THE SKIN. 143 soluble — in the homy layer, scarcely so; and here, in fact, a distinction must be drawn between the resisting cell-mem- brane and the cell-contents, which swell up and disappear more readily; these, in the natural condition, form an apparently ho- mogeneous simple plate, but the difference between them may be readily exhibited by reagents. In what parts the small quantity of collagenous substance, which has been noticed, has its seat, is not clear; perhaps it forms a portion of the contents, especially of the cells of the mucous layer, or belongs, it may be, to an intermediate substance between the cells, which, however, is not microscopically demonstrable. If the fat of the epidermis is not merely accidental, arising from the cutaneous secretions, it is most probably contained within the Malpighian cells. Bruns, Todd and Bowman, Valentin and Bruch, recom- mend the use of alkalies for the investigation of the epidermic tissues, but their full importance was first shown by Donders (Mulder's 'Phys. Chemie,' p. 257, et seq., and ' Hollandische Beitrage,' I u. II). They are now generally recognised as quite indispensable reagents for the investigation of the horny tissues ; but, as Paulsen ('Obs. Microchem.,' &c. Dorpat, 1848) and Reichert (Miill. 'Arch,' 1847, Jahresbericht.) advise, it is well always to use only definite solutions. I may add, that a great saving of time is effected by the heating of the tissues to be investigated, in test tubes, with these and other reagents, as I have already done in examining those tissues of animals which contain cellulose ('Annales d. Sc. Nat.,' 1846).] § 46. Growth and Regeneration. — The epidermis possesses no power of continually active growth depending upon intrinsic causes and founded upon the vital relations of its cells, or those which it has with the corium; it is essentially a stable tissue, which does not change in its elementary parts, but, somewhat like a cartilage,^ has all its vital energies directed to its unchanged self-maintenance as a whole (thickness of the whole epidermis, proportion of the rete Malpighii to the horny layer), and in its separate parts. However, since a throwing- off of the external layers, if not necessarily, yet accidentally, takes place almost continually over the whole body to a greater ' [See, however, the note upon the desquamation of cartilage, infra. — Eds.] 144 SPECIAL HISTOLOGY. or less extent, the epidermis is, so to speak, continually occu- pied in replacing what is lost, or in growing, and thus ex- hibits its vegetative life in a more remarkable manner. Which- ever takes place, it is the corium and its vessels from which the fluids required by the epidermis are derived. In every locality, we may suppose, that a certain determinate quantity of plasma, corresponding with the anatomical and physiological relations of the vessels of the corium and the thickness of the epidermis, permeates the latter, and, when it is not growing, simply fills its cells and plates (independently of that more watery fluid which subserves the cutaneous evaporation), maintaining their vital activity, and at the most causing temporary deposits of pigment in the rete Malpighii. If, on the other hand, its outer layers be removed, a certain amount of plasma becomes free and disposable, and then regeneration takes place, which, if it pro- ceed continuously, may even be called growth. It is in this process that the vegetative life of the epidermis-cells is most dis- tinctly evidenced, particularly in the rete Malpighii, where it is unquestionably most intense, exhibiting itself especially, in the multiplication and growth of the cells, and in their chemical changes. In the horny stratum the phenomena are less strik- ing, though it must not be considered to be inactive even in the uppermost layer; being by no means dead matter, as we evidently see, when under certain conditions, especially under abnormal states of the corium — the source of its nutrition — ^it sometimes becomes hyper trophied, sometimes completely dies away. We have not as yet, however, attained to an exact insight into the vital manifestations of the epidermic cells, and are therefore not in a condition to decide which of the phenomena presented by them are to be ascribed to their own activity, and which to the nature of the plasma which nourishes them. The latter is certainly of the greatest importance for the epidermis, and it is more than probable that most of its peculiarities, as, for instance, its typically different thickness in different parts of the body, the difl'erent relations of the stratum Malpighii to the horny layer, and its pathological states, depend upon qualitative and quantitative differences in the plasma. Upon what condition, furthermore, it depends, that in the Malpighian layer, the changes of the cells are far more considerable than in the horny layer, whose elements all closely OF THE SKIN. 145 resemble one another^ is as little obvious as the cause of the somewhat defined line of demarcation between the two layers, a condition which appears still more strikingly in the nails, and would lead one to suppose that, at the first formation and in the course of the development of the epidermis and nails, a very considerable alteration suddenly takes place at one point in their cells, thus determining their separation into two layers. [In the deep fold of the skin which surrounds the glans penis and clitoridis, a continual desquamation and reproduction of the epidermic scales, which are here soft and nucleated, takes place, in consequence of which a peculiar secretion, the smegma preputii, is produced. Hitherto this secretion has been erroneously, but almost universally, supposed to be a sebaceous matter secreted by the preputial glands. 'The microscope shows: 1, that in the female, where the presence oi smegma preputii is constant, neither sebaceous nor any other glands exist upon the prepuce or glans clitoridis ; 2, that in the male, in whom such glands are indeed found, they are commonly but insignificant in relation to the quantity of smegma, and are often very few and scattered ; 3, finally, that the smegma, in both sexes, consists principally of cells of the same form as those of the prepuce and glans penis and clitoridis ; whence, taking also into account the fact, that in the male it is generally distinctly composed of superimposed layers covering the whole prepuce continuously, whilst the sebaceous glands occur only isolated, it naturally follows that the smegma is principally constituted of desquamated epidermis. However, this does not exclude the preputial sebaceous matter in the male from also taking a share in proportion to the number and size of Tyson's glands, in the formation of what goes under the common name of smegma. There would in this locality then, really be a constant desquamation of the external, and a new development of the internal layers of the epidermis, but here there are special purposes in view which elsewhere do not enter into consideration. The preputial fold, in fact, is to be compared to a gland; and as the secretions of these are very often formed only by the continual casting off of the cells which line them (e. g. sebaceous glands), so is that of the prepuce. We must recollect that in many animals e.g., the Weasel, the Beaver (E. H. Weber), without essentially I. 10 146 SPECIAL HISTOLOGY. changing the character which it possesses in man, the prepuce takes on a highly glandular nature, and that even in man it yields a secretion which differs considerably from common epidermis. According to Lehmann, the yellow, fatty, strongly- odorous preputial smegma of man contains, when dried, in 100 parts : Ethereal extract, 52'8 ; alcoholic extract, 7*4 ; aqueous extract, 6-1 ; earthy salts, 9*7 ; albuminous substances soluble in dilute acetic acid, 5"6 j insoluble residuum, 18-5. The ethereal extract contained saponifiable fat, cholesterin, a non- saponifiable and uncrystallisable fat and bihn (GallenstoflF). The smegma of the horse possessed nearly the same con- stituentsj and among the salts, oxalate of limej while in man, ammonio-phosphate of magnesia occurred. The watery extract contained neither albumen nor casein. An extensire" desquamation of the entire horny layer of the epidermis, such as takes place in the embryo and in many animals, does not occur in man except in certain morbid states. On the other hand, its power of regeneration is exhibited in other modes than those which have been mentioned. Excised portions of the epidermis, for instance, are very readily replaced, and with tolerable rapidity, so long as the corium is not injured ; and, in fact, not by the immediate deposition of epidermis in the wound, but only by the growing up of the whole epidermis from below. If the corium be injured as well, an epidermis is, indeed, formed upon the substance of the cicatrix, but without any of the previous elevations and de- pressions of the internal and external surface, because the new corium has neither papillae nor ridges. If the epidermis be raised up into a vesicle by acrid substances, e. g., Tartar emetic, a slight burn, fee, the wall of the vesicle, which con- sists of the homy layer and some few layers of cells of the mucous layer, never again becomes adherent; but from the main substance of the mucous layer, which mostly remains lying upon the papillae, a new horny layer is by degrees developed. If we inquire more minutely into the mode of regeneration of the epidermis, there can, in the first place, be no doubt that it takes place in the Malpighian layer, inasmuch as losses of substance of the homy layer, e. g., a piece cut out, are restored not by the formation of a new portion in the gap, but by the growth outwards of a horny layer from below (the wound OF THE SKIN. 147 remaining wholly unchanged), which gradually raises the bottom of the wound, and brings it to a level with the surrounding epidermis, the latter, in consequence of the pressure that it suffers from the growing portion, becoming everted and exfoliating. The reason of this phenomenon is to be sought, simply in this, that the non- vascular epidermis draws the materials which it requires for its nutrition and regeneration from the superficial vessels of the corium. It is more difficult to ascertain from what portion of the Malpighian layer the regeneration proceeds. If a layer of cyto-blastema and of free nuclei existed upon the surface of the corium, as many authors suppose, we might acquiesce in the view, that the epidermis grows by free cell-development in those innermost layers which rest immediately upon itj but such a cyto-blastema, as we have seen, does not exist, the stratum Malpighii being invariably formed by perfect cells; and thence nothing remains, but to suppose an endogenous cell-development around portions of contents in the deepest round cells, or a multiplication by division, for which latter view the occasional occurrence of two nuclei in some of the softer epidermic cells, seems to speak. It can be more easily made out, how, in the course of the growth of the epidermis, the youngest epidermic cells become changed into homy plates. The small and round vesicles of the deeper layers of the stratum Malpighii become larger and flatter the more they approach the surface, until at last they are completely converted into flatteaed plates. In the meanwhile their nuclei at first grow a little, and then, as a general rule, disappear wholly in the horny layer; whilst the cell-contents, which are granular in the mucous layer, clearly distinct from the cell-membrane, and probably semi-fluid, become more solid and homogeneous in the horny layer, and finally coalesce with the cell-membranes. At the same tim?the latter are chemically altered, becoming less and less soluble in caustic alkalies.] §47. Development of the Epidermis. — The first layers of the epi- dermis are developed, in the Mammalia, by the metamorphosis of the most superficial of the original formative cells which com- pose the young embryo. When the rudiments of the stratum Malpighii and horny layer are once indicated, the former con- 148 SPECIAL HISTOLOGY. tinues to increase in thickness, in consequence of the multipli- cation of its elements, whilst the horny layer, for the increase of its proper substance and to replace what it loses by des- quamation, recruits itself from it exactly as in the adult. How the multiplication of the cells goes on in the rete Malpighii has not been directly observed j but it is certainly not by free cell-development, since in embryos of all ages the mucous layer consists wholly of cells, and free nuclei are altogether absent. As regards the horizontal extension of the epidermis, it appears, as Harting (' Rech. micrometr/ p. 47) justly observes, from the circumstance that the epidermic scales of the foetus and of the adult differ very little in superficial size, that it can only in a very slight degree be ascribed to the growth of its elements. In fact the horny plates of the embryo of fifteen weeks already measure 0"009 — 0013'", in the sixth month 0-01 — 0-013'", in the seventh month 001 — 0-014'", in the new-born infant 0-012 — 0-016'", in the adult 0-008 — 0016'". Since, however, keeping in mind the structure of the horny layer, it cannot well be supposed that new scales are continually intercalated from below between its elements, and since a superficial multiplication of the cells of the rete, which also do not increase in size, must certainly be granted, it seems impossible to admit any other conclusion than that, in agreement with the great superficial growth of the cutis and of the rete, and the small extensibility of the horny layers, a series of desquamations of the latter take place, which, if this view be correct, must likewise obtain after birth. [In an embryo of five weeks I found, in the place of the epidermis, nothing but an external layer of polygonal cells of 0013 — 0-03'" in diameter, and an internal layer of small cells of 0003 — 0-004"'j in embryos of fifteen weeks the epidermis is 0-01 — 0-013'", thick and composed as before, only that the deep layer of cells answering to the stratum mucosum is often already double, and the external cells measure only 0-009—0-013"'. In the fifth month the epidermis in one instance measured on the heel and ball of the hand 0-03 — 0-034'", over the ridges of the cutis 0-036 — 0-04'", in the furrows between them on the back 0-03 — 0034''', of which thickness one third may OF THE SKIN. 149 be regarded as belonging to the horny layer and two thirds to the rete Malpighii. In a somewhat older embryo it was, on the heel 006 — •064'" (mucous layer 0"05, horny layer 0-01 — 0014'"), on the surface of the hand 005'" (mucous layer 004, horny layer O-Ol"'), on the back 0-02— 0-024"' (mucous and horny layers of equal thickness). The mucous layers consisted of many layers of smaller cells, the lowest of which were already elongated, and stood perpendicularly ; the horny layer, of at least two layers of polygonal flattened cells, with round nuclei. In the sixth month the epidermis upon the thorax measures 002— 0-022"', on the palm of the hand 006'", on the sole of the foot 0-07'", and everywhere it consists of many layers of cells. The outermost one or two are composed of horny plates without nuclei 0-01 — 014'" perfectly similar to those of the external horny layer in adults ; then foUow 3 — 4 layers of polygonal cells, the largest 001 — 0-012"', with nuclei 0-004"'; finally a mucous layer, whose thickness equals about one half or two fifths that of the whole epidermis, with at least 3 or 4 layers of rounded cells of 0003 — 0004"', the lowest of which are some- what elongated, and are seated perpendicularly upon the cutis. In the seventh month, I found in one embryo, that the epidermis on the heel measured 0'12"' (mucous layer D072,'" horny layer 0-048'"), upon the back 0-07"' (mucous layer 004'", horny layer 03"') : in another it measured on the heel 012 — 0-14'" (mucous layer 0-05— 0-06'", horny layer 007— 008'"), on the knee 0-046 — 0-064'" (mucous layer 0016 — 0-024'", horny layer 0-03 — 0-04'".) Both layers of the epidermis are as sharply separated from one another as in adults, and their elements similar to those of the perfect epidermis, especially the lowest parts of the stratum Malpighii and the plates of the horny layer, which have no nuclei, and measure 001 — 0-014"' in the uppermost layers. In the new-born infant, apart from the thickness of the epi- dermis, which in one case measured on the heel 0-1 — 0-11" (mucous layer 004 — 0-05'", horny layer 006'") nothing particular is to be observed, except that by maceration, &c., it is much more easily separated from the corium than in the adult. The non-nucleated horny plates measured 0-012^-016"', on the labia minora where they possess nuclei 0-016-0-02"'. 150 SPECIAL HISTOLOGY. During embryonic life a desquamation of the epidermis occurs, which is perhaps repeated several times. Such is the fate, probably, of the layer of polygonal cells which arises first of ail, and which in the second to the fourth months, becomes metamorphosed into an almost structureless membrane, and is then no longer to be found ; perhaps also of the layer of epi- dermis, which covers the points of the hairs which have not yet appeared externally {vide infra § Hairs); and in the second half of the foetal period it may be easily demonstrated as an actively occurring process. From the fifth month onwards, in fact, con- tinually increasing desquamation of the external epidermic cells takes place, and these becoming in most parts mixed up with the sebaceous secretion of the skin, form the so-called vemios caseosa or smegma embryonum. This is a whitish or yellowish, viscid, inodorous material, which, especially from the sixth month onwards, covers the whole surface of the foetus with an often considerably thick and even laminated sub- stance, which is most abundant upon the genitalia, on the flexor side of the joints (axilla, knee, nates), on the sole, the palm, the back, the ear, and on the head in large quantity, and when microscopically examined consists mainly of epidermic cells, but also contains sebaceous cells and fat globules. Ac- cording to Davy (' Lond. Med. Gaz.,' March, 1844) the vernitv caseosa contains in 100 parts, 5*75 elain, 313 margarin (8"88 fat); the rest, 91"13 per cent., must be reckoned as epidermic scales, for since the vernix caseosa contains no free fluid, the 77*87 per cent, water and 13"25 solid substance found by Davy must be laid to the account of epidermic cells. This also holds good of Buck's analysis ('De Vernice caseosa,' Halis, 1844) who found in 100 parts, 10'15 fat, 5'40 epithelium, and 84*45 water (so that there was 89"85 of epithelium); and also in two other cases, in which the water was not exactly determined, he found 1480 and 931 per cent, of fat, and therefore 8620 to 89*69 of moist epithelium. According to Buek, the fat of the verniss caseosa, contains no cholesterin, as had been stated by Fromherz and Gugert, but oleic acid, and either stearic or margaric acid, which are probably not free, but combined with glycerine, — a circumstance which also evidences its origin from the sebaceous glands, in which, normally, no cholesterin is formed. Lehmann found (1. c.) in the Axyvernix caseosa of a OF THE SKIN. 151 nearly full-grown foetus, 47*5 per cent, of ethereal extract, 15*0 of alcoholic extract, 3'3 of watery extract, 4'0 of acetic acid ex- tract (earthy phosphates and albuminous substances), epidermis and lanugo 23-7. In the ethereal extract the reaction of bilin was absent and the fresh vernix contained a large quantity of water, which in all probability had entered its cells from the liquor amnii. The smegma generally appears about the sixth month, varies greatly in quantity, and is, especially in newly- born infants, sometimes very greatly developed (as much as 85 drachms, Buek), sometimes wholly wanting; in which latter case it either becomes mixed with the liquor amnii, which in fact often contains epidermic cells as well as fat (Mark, in Heller's 'Archiv,' 1845, p. 218), or may have been from the first, less developed. After birth the smegma is thrown oflf in the course of from two to three days, and the permanent epi- dermis appears, of whose further changes up to the adult state there is little to be said. In a child four months old the epidermis measured — Bpidermis in toto. On the heel 0-26'" On the back of the foot . . 0-048— 0-06'" On the palm 0-07— O'l'" On the back of the fingers . 0-056— 0-07'" On comparing this with the adult, it is to be observed that the epidermis of the young, child is disproportionately thick, and that this thickness depends especially upon the rete Malpighii, whilst the horny layer exhibits only a slight development. The pigment of the rete Malpighii arises, in the coloured races, only after birth. P. Camper (' Kleinere Schriften,' 1782, Bd. I, p. 24) saw a negro child, which at its birth was reddish, and hardly differed from that of an European, rapidly become tinged black at the edges of the nails and round the nipple. On the third day the genitalia became coloured, and on the fifth and sixth the blackness spread over the whole body. In Europeans also, at birth, the pigment of the areola and of the other places which have been mentioned is not yet present : it is gradually developed in the course of the first year, so that in children of two or three months old it is only indicated. In investigating the skin, perpendicular and horizontal sec- tions of fresh, dried, and boiled preparations are serviceable : Mete Malp. Homy layer. 0-12'" 0-14'" ^ 0-032— 0-04'" 0-016—0-02"' 0-04- 0-07'" 0-03" 0-04- 0-05'" 0-016—0-02"' 152 SPECIAL HISTOLOGY. they may be moistened with an indifferent fluid or with various reagents, the most important points in regard to whose effects have been noticed in the foregoing paragraphs. The epidermis is separated from the corium by maceration, by boiling, and where it is not thick, as on the genitalia, by acetic acid and soda, easily and in large flakes, so that its lower surface and the papillae of the corium become visible in the most beautiful manner, and the latter may be examined singly or in groups. In the fresh skin their position and number are quickly and easily to be recognised in horizontal sections, passing through the papillae and the deep layers of the epidermis. Its vessels are to be studied in thin parts of the skin {genitalia, lips), in the fresh condition, or in injected preparations with those of the rest of the skin ; its nerves in perpendicular sections, in isolated papillae, or in thin portions of the skin (prepuce, glans, eyelids, conjunctiva bulbi) after the addition of acetic acid and dilute solution of caustic soda, or according to Gerber and Krause's method. Gerber boils the skin until it is transparent, lays it a few hours in oil of turpentine until the nerves are white and glistening, and then examines them in fine perpendicular sections made with the double knife. According to Krause, the nerves are seen very well after treating the skin with nitric acid, if the right amount of action is hit upon. The elastic tissue of the skin comes out well under the action of acetic acid, soda, and potass. The smooth muscles may be readily isolated in the tunica dartos — with more difficulty in the penis and in the areola, where it needs familiarity with them, in order in all . cases, to recognise them with the naked eye. On the hair sacs they are rendered visible microscopically, if a sac, with the sebaceous glands which appertain to it, be isolated, especially after the application of acetic acid, as small bundles near and in front of the sebaceous glands, but best and very easily in perpendicular sections of boiled skin (Henle). The examination of the fat cells is especially instructive in thin persons, in whom their membranes and nuclei are readily visible : in other cases their membranes are readily demonstrable by the aid of ether, which extracts the fat j but the nuclei are seen with difficulty, though they may occasionally be discovered here and there even in full cells. The epidermis must, for its Malpighian layer especially, be examined fresh, in fine perpendicular sec- OF THE NAILS. 153 tionsj to which acetic acid and dilute solution of soda may be added ; the horny layer, particularly by the addition of alkalies, in perpendicular and horizontal sections; however, mere mace- ration in water separates its elements from one another, and those who are practised can discover them in fresh preparations, when viewed both laterally and from the surface.] Literature. — Gurlt, ' Vergleichende Unters. iiber die Haut des Menschen u. d. Haus-saugethiere,' &c. in Miill. 'Archiv,' 1835, p. 399 (good figures for the period) j Raschkow, ' Mele- temata circa Mammal, dentium evolutionem,' Vratisl, 1835 (first more complete description of the elements of thfc epider- mis under Purkinje's guidance) ; Simon, ' Ueber die Structur der Warzen u. iiber Pigmentbildung in der Haut,' Miill. ' Arch.,' 1840, p. 167 (pigment-cells in the rete of white per- sons) ; Krause, article ' Haut,' in Wagner's ' Handworterbuch,' II, 1844, p. 137 (a detailed and excellent treatise) ; KoUiker, ' Zur Entwicklungsgeschichte der aussern Haut,' in 'Zeitschrift fiir wiss. Zool.,' Bd. II, p. 67 ; ' Histological Observations,' ibid. II, p. 118; Eylandt, 'De musculis organicis in cute humani obviis,' Dorp. Liv., 1850. Besides these, refer particularly to the works of Simon (' Die Hautkrankheiten durch anatomische Untersuchungen erlautert,' 2 Aufll., Berl., 1851) ; Von Baren- spruug ('Beitrage zur Anat. u. Pathol, der menschUchen Haut,' 1848) ; and Kramer {' Ueber Condylome u. Warzen,' Getting., 1847). Figures are given by E,. Wagner, 'Icon, phys.;' Berres, tab. vi, vii, xxiv (middling, with the exception of what regards the vessels) ; Arnold, ' Icones org. sens.,' tab. xi (very pretty, but drawn with too low magnifying powers) ; HassaU, tab. xxiv, xxvi, xxvii (among others, the skin of the negro also, and the areola of the white from within, coloured) ; and myself, ' Mikr. Anatomic,' Taf. i. II.— OF THE NAILS. § 48. The nails, ungues, are nothing but peculiarly metamorphosed parts of the epidermis, and like it, they consist of two layers, — of a soft mucous-, and a horny layer, or the proper nail. 154 SPECIAL HISTOLOGY. That part of the corium upon which the nail lies, or the bed of the nail, corresponds exactly in form with it, is elongated, quadrangular, arched in the middle, shelving off anteriorly and posteriorly, and especially on the sides. When the nail is removed by maceration in connection with the epidermis, its anterior and middle parts are uncovered, whilst its lateral edges and its posterior segment, on the other hand, are invested by a process of the cutis, the wall of the nail, which is anteriorly depressed and rounded off, posteriorly more acute and longer, and, taken together with the bed, forms a fold, the fold of the nail, which receives the lateral edges and the posterior (3 — 3"') portion of its root (figs. 58, 60). Fig. 58. The bed of the nail presents upon its surface peculiar ridges, similar to those of the palm and of the sole of the foot (fig. 58 a). They begin at the bottom of the fold of the nail, at the posterior border of its bed, and, as Henle (p. 270) justly remarks, they run from the middle of it almost as from a pole. The middle ones pass directly forwards ; the lateral at first describe an arc, which is the more convex the further out the ridges lie, and eventually are directed forwards like the others. At a distance of 3i — Sj" from their origin, they all at once become more prominent, and take on the form of true lamince, of 0'034 — 0"1"' in depth, which run directly, almost to the anterior edge of the bed of the nail, and then end suddenly, as if truncated. The line of transition of the ridges into the lamimB is convex anteriorly, and divides the bed of the nail into two sections, differing both in their extent and in their colour : the posterior smaller one is nearly covered by the Fig. 58. Transverse section through the body and bed of the nail, x 8 : a, bed of the nail, with its ridges (black) ; b, corium of the lateral parts of the wall of the nail ; c, stratum MalpigUi of the nail with its ridges (white) ; e, horny layer on the wall of the nail ; /, horny layer of the nail, or proper nail substance, with short notches upon its under surface. OF THE NAILS. 155 wall of the nail and underlies its root, the anterior and reddish- coloured division underlying its body. The ridges and lamin^ae of the bed of the nail, the number of which varies between 50 and 90, are, at their edges, beset with a series of short papillae of O'OOS — 0"016"'. In addition, I can confirm Henle's statement that the bottom of the fold of the nail exhibits a few transverse ridges with larger papillae directed forwards; further forwards, where the lamina cease, there are also long isolated papillae. On the nail of the little toe, the papillae are frequently not seated upon ridges, but are more dispersed. The wall of the nail has no ridges upon its lower surface, and rarely a papilla here and there. These commence again upon its margin, where they are of some length, and are continued thence upon its upper surface, which is in no respect distin- guishable from the cutis of the back of the fingers and toes. The corium of the wall and of the bed p. gg of the nail is dense, and for a considerable distance contains but little fat; in the ridges and laminae with their papillae, it is abundantly provided with fine elastic fibres. The vessels are particularly nume- rous in the anterior segment of the bed of the nail; behind, where the root of the nail lies, and in the wall they are more scanty; their capillaries, 0-005 — 0008'", form very distinct simple loops in the papillae, and single trunks often pass, even into many papillae. The nerves have the same relations below as in the skin, but I have hitherto been unable to detect either terminal loops or divisions in them. In the nail itself we may distinguish, the root, the body, and the free edge (fig. 60). The soft root (fig. 60 I) corres- ponds in its extent to the posterior ridged segment of the bed of the nail, and is either wholly hidden in the fold, or exposes a small semi-lunar surface, the lunula. The pos- terior edge is attenuated, slightly bent upwards, and is the thinnest and most flexible part of the nail. The hard body, which increases in thickness and breadth from behind for- wards {k), lies for the most part with its upper surface un- l^gi 59. Capillaries of the bed of the nail, after Berres. 1 156 SPECIAL HISTOLOGY. covered; its somewliat sharp thin edges are hidden in the lateral parts of the fold, and its under surface reposes upon Fig. 60. the anterior segment of the bed of the nail : lastly, the free edge (m) is, in cut nails, directed straight forwards, but if un- cut, it curves downwards round the ball of the finger, and with the rest of the nail, attains to a length of as much as two inches. The lower surface of the body and of the root answer in their form exactly to the bed of the nail, and we there- fore find laminae and ridges upon them, as well as furrows, in the same order as on the latter, only here the edges of the laminae are straight and not papillated, whilst the furrows, instead of having an even bottom, as in the nail-bed, are pro- vided with shallow pits for the reception of the papillae. By the mutual inter-locking of the elevations and depressions, the intimate union of the nail with the corium is effected, which becomes still more close by the application of the under surface of the wall of the nail upon its base and edges. The colour of the nail, so long as it remains in its natural condition, is whitish and transparent, at its free edges ; reddish in the body, with the exception of a very narrow clear margin close behind the commencement of the free edge ; in the lunula, whitish ; the colour of the last two portions arising principally from the corium and its iblood-vessels which shine through them. Separated from the corium and epidermis, the Fig. 60. Longitudinal section through the middle of the nail and bed of the nail, X 8 : a, bed of the nail, and cutis of the back and points of the fingers i b, raucous layer of the points of the fingers ; c, of the nail ; d, of the bottom of the fold of the nail ; e, of the back of the finger ; /, homy layer of the points of the fingers ; g, be- ginning of them under the edge of the nail ; h, horny layer of the back of the fingers ; i, ends of it upon the upper surface of the root of the nail ; AJJdy j I, root j m, free edge of the proper substance of the nail. ail;*jady OF THE NAILS, 157 nail is of a tolerably uniform whitish colour, and transparent, though somewhat whiter at the root than in the body. § 49. Structure of the Nail. — The nail consists in its deeper parts of a soft, somewhat pale stratum mucosum, which is distin- guished from the hard external horny layer, or proper nail, still more sharply than Fig. 61. in the common epider- mis. It covers the whole of the lower surface of the root and body of the nail, frequently also a small part of the upper surface of the root, and forms by itself the above- mentioned laminae on the under surface of the nail. Its thickness at the -pos- terior part of the root upon the under side mea- sures 0"12"'5 on the up. per, 0'14"'j close behind the margin of the root * directly from behind forwards, 0'24 — 0-36'"; on the body of the nail on the laminae, more posteriorly and at the edge 004— 0-05"' ; in the middle 0-06'", even 0-08— -096'" and 0-12'" ; between these, 0-032 — 004'". The Malpighian layer of the nail, like that of the epidermis, consists wholly of nucleated cells, and agrees in all essential points with it, except that the deep portion contains many layers of elongated (of 0-004 — 0-007'") perpendicular cells, in conse- quence of which a striated appearance is produced, which has Fig. 61. Transverse section through the body of the nail, x 250. J, cutis of the bed of the nail ; B, mucous layer of the nail ; C, horny layer of it, or proper nail substance : a, layers of the bed of the nail ; i, layers of the stratum Malpighii of the nail ; c, ridges of the proper substance of the nail ; d, deepest perpendicular cells of the mucous layer of the nail ; e, upper flat cells of it ; /, nuclei of the proper sub- stance of the nail. 158 SPECIAL HISTOLOGY. misled Giintlier, and probably Rainey also/ into supposing the existence of peculiar glands under the nail. In the Negro, according to Beclard (Anat. Generale, p. 309), the stratum Malpighii of the nail is black; and according to Krause (1. c, p. 124), its cells would in this case appear to contain dark-brown nuclei, as well as yellowish-brown ones, in dark Europeans. According to Hassall (p. 253), the younger cells of the nail (i. e., those of the stratum mucosum), generally con- tain pigment, which I can confirm, at least in some cases. The horny layer of the nail, or its proper substance (figs. 58 /; 60 k, I, m; 61 c), is that hard brittle portion which forms its upper part and its free edge. The under surface of this layer is quite smooth, posteriorly at the root; further forwards it exhibits sharp ridges separated by broad furrows, which are inserted into the furrows of the mucous layer of the nail. These ridges of the proper nail substance appear in transverse sections (figs. 58, 61), as pointed processes of O'Ol — 0'02"' in length, which, as a rule, are most strongly developed at the edges of the nail, even to 0'04 — 0'06"', and answer precisely in their number to the laminae of the under side of the stratum Malpighii. The upper surface of the sub- stance of the nail is smooth, taken as a whole, yet sometimes even here, very distinct, parallel, longitudinal streaks appear as the last, almost effaced indications, of the inequalities of its bed. Usually, the thickness of this part of the nail continually increases from the root to near the free edge, so that the body of the nail is, anteriorly, at least three times thicker (from 0'3 — 0'4"') than the former ; at the free edge, again, it liecomes somewhat less. In its transverse diameter also, with the excep- tion of the posterior edge of the root, the substance of the nail is not everywhere equally thick ; it thins considerably towards the lateral edges, so that at last the nails, where they lie in the fold, measure not more than 006 — 0'12"', and finally ter- minate quite sharply. ' [With respect to Rainey's observations, Eeichert, in his Report for 1849-50 (' Miill. Arch.,' 1850-51), says that the observation as to the follicles is quite cor- rect, and that with Dr. Ammons, who had studied the growth and regeneration o£ the nails for some jrears, he had seen such capsules containing horny cells, with especial distinctness upon the bed of the nail of the great toe. — Eds.] OF THE NAILS. 159 With regard to the structure of the proper substance of the nail, it can hardly be made out without the action of reagents. In perpendicular sections we see, particularly in the body, noth- ing but horizontal, fine, straight, or curved, closely approximated lines, which one would be inclined to consider as the optical expression of delicate, super-imposed lamellae, and between these, a multitude of elongated, horizontal, opaque or peculiar reddish- transparent striae, evidently nuclei. Only upon the most posterior part of the root, and on the under surface, where it meets the stratum Malpighii, do more or less distinctly flattened cells with nuclei appear disposed in layers. Horizontal sections show even less than the perpendicidar ones ; exhibiting a pale transparent substance, granular here and there, and mostly without indi- cation of any structure whatsoever, occasionally with very indis- tinct contours of plates similar to those of the homy layer of the epidermis. Very different are the appearances presented after treating the nail with alkalies and certain acids. If the substanceof the nail be boiled in dilute caustic soda, it becomes changed upon the first bubbling of the fluid into a beautiful cel- lular tissue (fig. 63, A, B), whose polygonal elements all, without exception, the deep as well as the su- perficial, possess nuclei of 0-0030— 0'0046"' in length and breadth, and 0'002"' in thickness, which, according as they turn their surfaces or their edges to the observer, appear as rounded, very pale, and finely-granulated discs, or as long, narrow, dark contoured rods ; it deserves further to be noted, that together with these, large and very pale nuclei of 0"006 — O-Ol'" and more, occur in considerable numbers, probably owing their existence to the excessive action of the reagent which has Fig. 62. Nail plates boiled with caustic soda, x 350. A, from the side ; B, from the surface : a, membranes of the distended elements of the nail ; b, their nuclei, from the surface j e, from the side. 160 SPECIAL HISTOLOGY. swollen them up. Caustic soda and potass also (which has a similar action upon the whole, though it acts more upon the nuclei) demonstrate the important fact, that the cells of the nail are flatter in the superficial, than in the deeper layers. If, in fact, a fine perpendicular section be moistened with cold, or better, with hot solution of soda, we see the cellular structure of the nail appear almost at the very instant it becomes moistened, without any obvious enlargement of its elements ; and it is observable, at the same time, that its deepest cells are at least as thick again as the most superficial. If the soda solution acts longer, the section gradually swells up, in the under cells first, on account of their greater softness, and only subsequently in the flat and hard upper elements. By treating the nail with cold sulphuric and nitric acids, •and also by boiling with hydrochloric acid, its elements are isolated. Taking these facts, together with what we see in the unaltered nail, it results that its horny layer consists of closely united but not sharply defined lamellsej each lamella being com- posed of one or many layers of nucleated, polygonal, flat scales or plates, which, excepting their nuclei, are very similar to those of the horny layer of the epidermis and in their deepest layers are thicker and somewhat less in circumference than in the upper and uppermost layers. Those of 0'0I2;— 0"016"' may be regarded as of an average size, as may be seen upon the addi- tion of sulphuric acid, which otherwise exerts but little action, and at the commencement of the operation of soda and potass. § 50. With respect to the relation of the nail to the epidermis, I must especially refer to the perpendicular and transverse sections figured in figs. 58 and 60. They show, in the first place, that the epidermis applies itself upon the root, the posterior part of the body, and upon the margins of the nail, and that it meets it under the free edge and on the anterior parts of the lateral edges. This happens in such a manner, that whilst the mucous layer of the epidermis passes con- tinuously and without any line of demarcation, into that of the nail, the horny layer is, properly speaking, never continued directly into the actual substance of the nail, but partly applies OF THE NAILS. 161 itself with its lamellae parallel upon the nail, partly abuts upon it at various oblique angles. At the root, the horny- layer passes more or less deeply into the fold of the nail, and at the same time runs, in a thin layer which becomes very fine anteriorly, upon the upper free part of the nail, as far as the end of the lunula or the beginning of the body. Ante- riorly and posteriorly, in which latter region this layer not uncommonly reaches the posterior margin of the root, its cells lie parallel to the upper surface of the nail; while in the middle, where it is thickest (fig. 60 i), they are oblique or perpendicular to it. At the free edge of the nail the relations of the parts are similar, where the horny layer meeting the end of the under surface of the body of the nail, partly with more horizontal, partly with oblique lamellse, is perhaps also continued upon the commencement of the free edge. On the lateral edges, again, the horny layer passes anteriorly, in hori- zontal strata, under the nail ; more posteriorly it is arranged as upon the root, or simply rests against the edge of the nail. The horny layer thus forms a kind of sheath for the nail, which bears some resemblance to the sheath of the hair, though it is much more imperfect. If we compare the nail with the €pidermis, we find, in the structure of its mucous layer, not the slightest peculiarity of any importance, while the horny layer is distinguished from that of the epidermis by its cells being nucleated, harder, and chemically different ; by their flattening and intimate union. For the rest, the agreement of the two structures is so close, that the proper nail may justly be con- sidered, as it has long been, a modified portion of the horny layer of the last joints of the fingers and toes. [According to the chemical investigations of Scherer and Mulder, the nails agree very closely with the epidermis; and, according to Mulder, they are distinguished from it, only by their somewhat greater proportion of sulphur and carbon. In his last essay, he considers them to be composed of protein + sulphamid (6'8 per cent, of the latter). This agrees with the observed action of reagents, with which the plates of the nail behave almost exactly like horny plates, only they are attacked with more difficulty and possess nuclei. According to Lauth, the nails contain more phosphate of lime I. 11 163 SPECIAL HISTOLOGY. than the epidermis, whence they derive their hardness : this may be correct, although, as Mulder states (' Phys. Chemie,' p. 536), both yield about the same proportion of ash (1 per cent.). As regards the lamellar structure of the proper nail, it is to be regarded in the same light as that of the horny layer of the epidermis; but it is not so distinct, because the plates of the nail are more intimately connected than the elements of the epidermis. Reagents, however, render the lamellar structure very evident, and it is also clear in pathologically thickened and curved nails. § 51. Growth of the Nails. — The nails grow continually, as long as they are cut; on the other hand, if uncut, their growth is limited. In this case, as may be observed in those who are long confined to their bed by sickness, and in the Eastern Asiatics, the nails become 1^ — 3 inches long (in the Chinese, according to Hamilton, 2 inches), and curve round the points of the fingers and toes. During the growth of the nail, the mucous layer does not change its position at all, but its homy layer is constantly being thrust forward. The formation of the latter goes on continually wherever it is in contact with the stratum Maljnghii, in other words upon its whole under surface, with the exception of the free anterior edge ; further, in many nails, upon a very small por- tion of the upper surface of the root, finally, at the posterior edge of the root itself. It is, however, the root portion which grows fastest, whilst the body of the nail is more slowly deve- loped, which is demonstrated especially by the fact that it is not much thinner at the boundary between the root and the body than it is anteriorly upon the body itself, and that the transition of the cells of the stratum Malpighii into nail-cells is easily shown at the root, but with difficulty in the body. By the constant addition of new cells at the edge of the root, the nail grows forwards ; by their addition to its under surface, it is thickened. The longitudinal growth exceeds that in thickness, because the first rounded cells, as they move from behind and below, forwards and upwards, become more and more flattened and elongated. OF THE NAILS. 163 [The mode in which the plates of the nail arise from the cells of the mucous layer, is easily demonstrable at the root of the nail. Here, in fact, the uppermost cells of the mucous layer are constructed very differently from the deeper ones; they are more or less flattened, and closely resemble the cells of the epidermis, but they possess a nucleus, which, however, is only to be discovered by adding caustic soda, and then with difficulty. If we follow these cells, which form a layer of 006 — 0'12"' in thickness, towards the proper substance of the nail, we find that they become more and more flattened, and at last pass without any defined boundary into the latter, uniting together more closely, and taking on a more transparent ap- pearance. In the body of the nail, the formation of nail substance is demonstrated with more difficulty, yet here, in opposition to Reichert, we must assume that it does take place, because the nail almost invariably increases in thickness even in the bodyj from behind forwards. However, there is unquestionably, in this part, a sharper demarcation between the two layers of the nail, than in the root ; but in fine sections it appears by no means so sharp as in those which are commonly examined, and I find, in fact, that the transition of the cells of the mucous layer into the plates upon the body of the nail, is demonstrable with tolerable readiness, particulai'ly on the addition of alkalies, where the ridges of the under surface of the proper nail are well developed. Between the ridges also, though, no direct transition is recog- nisable, yet it may be observed that the plates of the proper nail which border upon the mucous layer are much less flattened than in the interior and on the surface, which also indicates that they are developed upon the spot. In conclusion I must add, in support of my view, that it is only in this way, that it becomes explicable why the under surface of the proper nail substance upon the root of the nail is almost smooth, while on the body of the nail it presents more or less prominent ridges. The origin or increase of these lidges demonstrates clearly that nail-substance is also formed here. Corresponding with these ridges and with the grooves between them, we also find that the lowest layers of the nail plates, which are quite horizontal upon the root, run with an undulating course upon the body (fig. 61). The general result then is, that whilst the formation 164 SPECIAL HISTOLOGY. of the nail goes on especially at its root, yet that plates are added to the body of the nail from below, though more slowly and scantily, thus producing the anterior thickening, or at least preventing the necessary thinning of the nail anteriorly. It is to be remarked further, that the development of nail- substance takes place in all parts of the middle line of the nail more rapidly than in the lateral portions, which, anteriorly, are almost as thin as in the root, though they possess longer processes below. But even there, substance must be added to the body of the nail, because it becomes broader anteriorly. The plates of the substance of the nail once formed, alter in certain respects, as they are pushed forwards and upwards by those which come after them. In the first place, their nature becomes altered in a manner which is little understood, the change consisting partly in the deposition of more phosphate of lime, partly in a solidification (conversion into horn) of their organic elements, particularly of the cell-membranes, in conse- quence of which, from being soft, as at the root and under surface of the nail, they become gradually harder and harder. In the second place, like the horny cells of the epidermis, they are very considerably flattened, and at the same time increase somewhat in their longitudinal and transverse diameters; finally, they coalesce more completely, so that they cannot be separately recognised, without the action of reagents, in the upper and an* terior parts of the nail, which appear to be composed of nothing but a homogeneous substance which tears in all directions j whilst in the lower parts the separate nail-plates are, at least indi- cated, and are occasionally tolerably distinct. On the other hand, the nuclei of the nail-plates do not disappear, and in this lies a characteristic distinction between the horny layer of the nail and that of the epidermis. They are to be seen in perpendicular sections, of fresh nails, and after treatment with caustic soda, and even in the most superficial layers, though somewhat smaller and flatter than in the deep layer. It follows then, that certain metamorphoses go on in the proper substance of the nail, which as in the epidermis, are tp be ascribed to a peculiar growth and vital process in the nail-cells themselves. These seem to occur, however, almost solely in the lower and posterior parts of the nail, for if, as Schwann states (fig. 91), two points be marked upon the posterior portion of the free OF THE NAILS. 165 surface of the nail, oue behind the other, by piercing it with a needle and colouring with nitrate of silver, they in no wise alter their relative position in the course of the two or three months, during which they are moving towards the point of the nail. As to the pathological conditions of the nails, they are readily regenerated when they have been detached, in conse- quence of crushing, burning, freezing, cutaneous disorders (scarlet fever, &c.), inflammations, exudations, suppurations and efi"usions of blood in the bed of the nail ; in fact, as Pechlin ('Obs. Phys. Med.,' p. 315) narrates, this regeneration may take place periodically; in a boy, the nails, every autumn became blueish-black and desquamated, together with the epidermis (the horny layer ?), and were subsequently regene- rated. In such a case, according to Lauth (' Mem. sur divers points d' Anatomic,' in the 'Annales de la Societe d'Histoire na- turelle de Strasbourg,' t. i, 1834), and Hyrtl ('Anatomic' p. 883), the whole bed of the nail becomes covered by soft horny plates, which harden by degrees, grow into a regular nail, and eventually project with their free edges beyond the end of the finger. When the last joint of the finger has been lost, rudimentary nails frequently appear upon the back of the second and even of the first phalanx. The older cases are quoted in Pauli ('De vulneribus sanandis,' Gottingse, 1825, p. 98), more recently Hyrtl (1. c.) saw such a nail 2'" long and 3"' broad on the first phalanx of the thumb. As the formation of nail-substance depends upon the vessels of the bed of the nail, we may, with Henle, assume that varying condi- tions of the latter may frequently produce local thickening, thinning, or even detachment of the nail, and that their deformities in cyanosis and phthisis depend on these causes. The thickening and abnormal development of the nails, however, arise very frequently, as I have observed, from a partial ob- struction of the capillaries of their bed. Thus in the lamellated nails of old people, greatly thickened and curved downwards in front, I find all the capillaries of the anterior segment of the bed of the nail closely fiUed with fat granules of difi^erent sizes, and wholly impermeable to the blood; in such a case the development of nail-substance can take place only in small lamellse in the fold, which then, as may be readily understood, are raised up by those which are growing behind into a con- 166 SPECIAL HISTOLOGY. tinually more and more oblique position ; their posterior extremities forming, on the surface of the nail, transverse streaks one behind another at short intervals. After dividing the nervus ischiadicus, Steinriick ('De nervorum regeneratione/ pp. 45: — 49) observed, in the Rabbit, that the nails and hair fell ofif, which is a result of the influence of the nerves upon the vessels. Finally, the shape of the bed of the nail also in- fluences its formation. It is thus explained, how (see Henle, 1. c), after inflammation and closure of the fold of the nail, the formation of new nail at the posterior edge ceases, the nail no longer growing forwards, but at aU its edges exactly covering its bed. § 52. The development of the nail begins in the third month with the formation of the bed and fold, which are marked off from the surrounding parts by the gradual growth of the skin into the wall of the nail. At first the bed of the nail is lined by the same cells as those which form the other parts of the epider- mis (see § 47), only that even in the third month the cells of the stratum Malpighii are distinguished by their elongated and polygonal form (length 0-004"' j breadth 0-001— 0-0016'"). In the fourth month thiere arises, between the stratum Malpighii and the horny layer of the bed of the nail, which latter is formed by a simple layer of polygonal clearly nucleated cells, a simple lamina of pale, flat, but also quadrangular and nucle- ated cells, 0'009"' in diameter, which are closely united toge- ther, and must be regarded as the first indication of the proper substance of the nail ; at the same time also, the stratum Mal- pighii under these cells becomes thickened so that it is certainly composed of, at least, two layers. The nail is therefore at first wholly included within the epidermis; it is formed over the whole surface of the bed of the nail as a quadrangular plate, and arises between the embryonic mucous layer and the homy layer, without doubt by a metamorphosis of the cells of the mucous layer, as is probable especially from the minute size of the original cells of the nails. In the course of its further development, the nail is thickened by the addition of new cells from below (in the fifth month its thickness is about 0034'", in the sixth 0-04'", of which in the latter 0-025'" must OF THE NAILS. 167 be reckoned as proper nail substance) j it increases by the extension of its elements and by the addition of new ones at its edges ; but it remains even to the end of the fifth month, hidden under the horny layer of the epidermis, until finally it becomes free, and in the seventh month, even begins to grow longitudinally, so that at this period, except in its greater soft- ness and its smaller dimensions, it presents no essential differ- ence from the perfect nail. With regard to the bed of the nail, its ridges are already indicated at the end of the fourth month, and in the fifth they are well marked, 0-02 — 0-024'" deep, 0-004 — 0-005'" broad, and 0-008 — 0-014'" distant ; these measurements also indicate the breadth of the laminae of the stratum Malpighii. At the sixth month they are somewhat larger and further apart. In the new-born infant, the whole nail is 0-3 — 0-34'" thick ; 0-16'" being proper nail substance, 0-14 — 0-18'" stratum Mal- pighii. Its elements are still almost identical with those at the sixth month, and they appear with tolerable distinctness in the nail proper without any reagents, as elongated polygonal nu- cleated plates 002 — 0-028'", as Schwann has already partly re- marked. The free edge, projecting far forwards, which is presented in all nails, is worthy of remark. It is considerably thinner and narrower than the body, and is separated from it by a semilunar line ; it is rounded anteriorly, as much as 2'" long, and is plainly nothing but the nail of an earlier period which has been thrust forward by the longitudinal growth 6f the nail in the course of its development. In fact it nearly corresponds in size with a nail of the sixth month. Soon after birth the long free edge of the nail of the new- born infant is cast off, at least once (according to Weber many times), in all probability in consequence of external mechanical violence, which it is unable, owing to its delicacy, to resist. In the sixth and seventh months after birth, I find that the nails which the child brought into the world, are com- pletely replaced by new ones, and in the second and third years the nail-plates are not distinguishable from those of the adult, whence it follows that the nail increases in thickness, less in consequence of any enlargement of its elements, than by the addition of new ones to its edges and under-surface. 168 SPECIAL HISTOLOGY. [The investigation of the nail-cells and plates is best made in fine sections of recent nails, with and without the addition of reagents, especially caustic soda and sulphuric acid, conceruing whose operation the most important points have already been noted. To examine the relations of the parts of the nail to one another and to the epidermis, the nails must be separated from the cutis by maceration, or by boiling in water. It is then seen, that the nail is detached, with the cuticle, from the finger; and in transverse and longitudinal sections, its mode of connection with the former is perceived. The bed of the nail also, its lamintB and ridges, the fold and the lamime in the stratum Malpighii of the nail, are easily seen, in this way. Since fine sections, in such a nail, are not readily made, precisely in the most important parts — ^the margins and root, — it is neces- sary, for this purpose, to employ fresh nails separated from the bone with the cutis, and dried. These aiford all the informa- tion required, portions of them swelling up readily in water, and exhibiting the structure of the different layers, with acetic acid and caustic soda, in the most distinct manner.] Literature. — A. Lauth, ' Sur la disposition des ongles et des polls,' Mem. de la Societe d'hist. nat. de Strasbourg, 1830-4 ; Gurlt, ' Ueber die hornigen Gebilde des Menschen u. der Haussaugethiere,' Miill. 'Arch.,' 1836, p. 262; Keichert, in Miill. 'Arch,,' 1841, Jahresbericht ; O. Kohlrausch, 'Recension von Henle's allgem. Anat.,' in Gotting. 'Anzeigen,' 1843, p. 24; Rainey, ' On the structure and formation of the nails of the fingers and toes,' in ' Trans, of Microsc. Society,' March, 184& ;' Berthold, 'Beobachtungen iiber das quantitative Verhaltniss der Nagel- u. Haarbildung beim Menschen, in Miill. 'Arch.,' 1850. HI.— OF THE HAIRS. § 53. In every hair we distinguish the free part or shaft, scapus, with its tapering point, from the portion inclosed within the sac, the root, radix. In straight hairs the former is generally straight and rounded ; in the wavy, undulated and somewhat flattened; in the curly and woolly hairs, it is twisted spirally and quite flat or slightly ribbed. The root is always straight, tolerably cylindrical, and softer and thicker than the shaft, at OF THE HAIRS. 169 Fig. 63. least in its lower part ; in living hairs it ends in a still softer knob-like enlargement, li to 3 times thicker than the shaft, — - the " bulb of the hair" (c), which is placed, cap-like, upon a papillary process of the sac, the "hair-papilla" (less properly termed pulpa, or blas- tema pili, hair-germ), or, in other vrords, receives the papiUa in an ex- cavation in its. base. § 54. Disposition and size of the Hairs. — The hairs are distributed over al- most the whole surface of the body,^ but exhibit very considerable differ- ences in size and number, according to their situation, to individual pecu- liarity, age, sex, and race. As regards the former, three varieties may be admitted, besides many transitional forms : (1) long soft hairs, of 1' — 3' and more in length, 0-02 — 0-05'" in thickness ; (2) short stiff thick hairs, of l—y in length, and 0-03— 007'" in thickness ; (3) short, excessively- fine hairs, down (lanugo), of 1 — 6"' in length, and 0-006— 001'" in thickness. The distribution of the first form is well known ; to the second belong the hairs at the entrance of the nostrils {vibrissce), in the external auditory passage, the eyelashes {cilia), and eyebrows; to the third, finally, must be referred Fig. 63. Hair and hair sacs of middling size, x 50 : a, hair shaft ; i, root of the hair ; c, bulb of the hair ; d, epidermis of the hair ; e, inner root-sheath ; /, outer root-sheath ; g, structureless membrane of the hair sac ; h, transversely and longitu- dinal fibrous layer thereof; i, papilla of the hair; *, excretory ducts of the seba- ceous glands, with epithelium and layers of fibres ; I, cutis at the aperture of the hair sac i m, stratum mucosum ; n, homy layer of the epidermis, the latter somewhat re- tracted into the sac ; o, end of the inner root-sheath. ' [No hairs exist upon the upper eyelids, the lips, the palm of the hand, and sole of the foot; nor on the dorsum of the last joints of the fingers and toes, the inner surface of the prepuce, and the glans penis. — Eds.] 170 SPECIAL HISTOLOGY. the hairs on the face, trunk, and extremities, also those of the caruncula lachrymalis, and those (frequently ahsemt) of the labia minora (Henle). The number of hairs upon a given extent of surface varies very much, depending especially upon age, sex, and the colour of the hairs. According to Withof, on a surface of \a'' there were found 147 black, 163 brown, 182 fair hairs. In a moder- ately hairy man, he found on la" 293 upon the scalp, 39 on the chin, 34 on the pubis, 23 on the fore arm, 19 upon the outer margin of the back of the hand, 13 on the anterior surface of the leg. In men, closely set hairs occur not unfre- quently upon the chest, shoulders, and extremities. The hairs are placed either singly, or in twos and threes, even four and five together. The latter is the rule in the foetus, but the same disposition obtains also in adults, especially in the lanugo. As Osiander and especially Eschricht, have shown, the direction of the hairs and haif-sacs is rarely straight, but oblique, and in different degrees in different parts of the body, as may be demonstrated with ease in the hairs of em- bryos, and, though less obviously, in adults also. The regularity depends on this, that the hairs being arranged in curved lines, which converge towards either certain points or certain lines, or diverge from them in two or more directions; there result a multitude of figures, which may with Eschricht be denominated "streams," "whorls," and "crosses." Streams with converging hairs are found, for example, in the median line of the back, chest, and abdomen, in the line which answers to the ridge of the tibia, &c. &c. ; streams with diverging hairs occur on the line between the thorax and abdomen, on the one hand, and the back on the other, &c. ; whorls and crosses with diverging hairs are found in the axilla, on the scalp, at the internal angle of the eye ; with converging hairs, on the elbow. For further details I must refer to Eschricht's figures and descriptions, concerning which, however, it is to be re- marked, that many variations occur with regard to these points, and Bschricht's figures represent only some of them. § 55. External peculiarities and chemical composition of the Hairs, In embryos, the hairs are generally quite colourless and clear j OF THE HAIRS. 171 they very slowly become coloured^ so that in youth they are, in general, paler than in middle age. In the adult the downy hairs, which have remained in a fcEtal condition as it were, are invariably the palest ; the longer ones are always darker, and the darkest are those of the head, beard, and pubis. The hairs are very elastic j according to Weber, they stretch without breaking to nearly a third more than their length, and if they be stretched only a fifth, they contract again so per- fectly, that they remain permanently only ^th longer. They readily imbibe water, and as readily give it out again ; they are therefore sometimes dry and brittle, sometimes moist and soft, according as the skin or the atmosphere contains much or little moisture. They become longer or shorter, according to the amount of moisture which they contain, whence their use in Hygrometry. In spite of their extensibility, their strength is considerable, and hairs of the head will bear at least 6 oimces without breaking. JTie chemical composition of the hairs is not yet sufficiently understood, but they are chiefly composed of a nitrogenous substance, soluble in alkalies with the evolution of ammonia, and insoluble in boiling acetic acid. Scherer and von Laer consider it to be a combination of protein with sulphur, and the latter supposes, in addition, the existence of a small quantity of a substance similar to gelatine, whilst Scherer regards a second nitrogenous matter which he found, to be a product of decomposition. Mulder considers the substance of the hairs to be a protein compound combined with sulphamid, of which he finds 10 per cent. Besides their nitrogenous consti- tuents, the hairs, as even the earlier investigations showed, contain a considerable quantity of dark or clear fatty matter, which may be extracted by boiling in ether and alcohol. From horn and epidermis, the substance of the hair is distinguished, according to Mulder, especially by its insolubility in acetic acid and by the same test, from albumen and fibrin. The hairs withstand putrefaction better than any other part of the body, so that even mummy hairs are found to be quite un- changed; in water they are not dissolved, except in Papin's digester. Metallic oxides colour the hair just as they do the epidermis ; thus, for example, they are blackened by the salts of silver and manganese, sulphurets of these metals being pro- 173 SPECIAL HISTOLOGY. duced. Chlorine bleaches them. The ash amounts to about 1 — 2 per cent., and contains oxide of iron (more in dark hair) j oxide of manganese ; silica (traces) ; phosphate of magnesia and sulphate of alumina were found by Jahn in white hairs ; and according to Laugin, copper occurs in the greenish hairs of those who work in copper and brass. ^§ 56. With regard to their more intimate structurCj two substances may be distinguished in all hairs without exception, and in many there are three : 1, the cortical substance, or better, fibrous substance, which constitutes by far the most considerable portion of the hair and determines its form ; 3, the cuticle, a delicate external investment of the fibrous substance ; 3, lastly, the central medullary substance, which is often absent. The cortical or fibrous substance is longitudinally striated, very often presents dark dots, is streaked or spotted and except in white hairs, in which it is transparent, is more or less deeply coloured; the colour is sometimes distributed through the whole substance with tolerable regularity, sometimes more con- centrated in certain elongated, granular spots. The more in- timate structure of the cortex of the hair, and the signification of its spots and strise, cannot be properly understood without the use of acids and alkalies (which afford important aid in the investigation of the hairs in general) and other manipulations. If a hair be treated with concentrated sulphuric acid at a warm temperature, its fibrous substance is much more readily broken up than, before, into flat elongated fibres of various breadths (commonly 0003 — 0*005"'), which are characterised particularly by their rigidity and brittleness, and by their irregular, even notched, margins and ends: in pale hairs they are clear, and in dark ones have a dark tinge. These so-called hair-fibres are not, however, the ultimate elements of the fibrous substance; each of them, in fact, consisting of an aggregation of flat, mode- rately-long fibre-cells or plates, which may be found isolated among the fibres after the thorough action of sulphuric acid. These (fig. 64), which may best be named the plates of the fibrous substance, or the fibre cells of the cortex,' are flat and generally fusiform, 0-024— 0-033'" long, 0002— 0004'", or even 0005'" broad, 00012- 00016'" thick, with uneven surfaces and OF THE HAIRS. 173 irregular edges ; they do not swell up into vesicles on the addi- tion of caustic alkalies, and they very frequently exhibit a darker streak in their interior, Pi g4_ of which we shall speak imme- diatelyj under certain circum- stances they also contain gra- nular pigment; for the restthey are homogeneous, and present no minuter elements, such as fibrillse or the like. They ap- pear to be more strongly united longitudinally, than in the direction of their breadth, whence it arises that the cor- tical substance easily breaks up into the long fibres above mentioned. The fibres them- selves (which I should not be inclined to consider as com- pound elements of the cortical substance, since their con- stituents are separable, and they themselves are far, too irregular), without constitu- ting distinct lamellae, like the plates of the nail and of the epidermis, form a compact fibrous bundle, and in this manner the cortical substance, V/''' which constitutes the princi- *~ pal bulk of the hair, is produced. The dark spots, dots, and streaks of the cortex, are very various in their nature, and are principally : 1, granular pigment; 3, cavities filled with air or fluid J and 3, nuclei. The action of caustic potass and soda, which soften and swell up the cortical substance without attacking the spots (fig. 67), shows that they are in great measure nothing but aggregations of pigment Fig. 64. Plates or fibre-cells of the cortical substaace of a hair treated with acetic acid, X 350 : A, isolated plates, 1, from the surface (3 single, 2 united) ; 2, from the side. B, a lamella composed of many such plates. A^'4 '/ 174 SPECIAL HISTOLOGY. gi'anules, which are deposited in the plates of the hair, are especially frequent in dark hairs, and vary very much in respect to their size and form. Dark spots of a second kind are very similar to the pigment deposits, but turn out on examination to be little cavities filled with air. They are best studied in white hairs, where they cannot possibly be con- founded with pigment. Here we see dispersed through the whole cortical substance round dots of 0'0004 — 0008"', or longish streaks of 0-004'" in length, 0-0004-- 0-0008'" in breadth, which, sometimes more scattered, sometimes more numerous and arranged in irregular lines, run parallel with the axis of the hair. The dark contours and somewhat clear centre of these> attract attention at once, and call to mind fat granules, which, in fact, for a long time I held them to be ; but they are nothing but excessively minute cavities filled with air, which occur very frequently also in fair, bright-brown> and bright-red hairs, often in very great numbers, while they are wanting in very dark hairs, and in the lower half of the root of all hairs. Thirdly, there occur in the cortex, other tolerably dark strise or lines, which in dark hairs are commonly con- nected with the pigment- I spots, in such a manner that the striae form the ends of the spots, or pass through them axially; in white and pale hairs they appear not unfrequently as prolongations of the air cavities, but in both kinds of hairs they often occur independently, in va- rious numbers and degrees of dis- tinctness. I hold these streaks, which are commonly most distinct in pale or bright-brown hairs without any medulla. Fig. 65. A, a piece of a white hair after treatment with caustic soda, x 350 : a, nucleated cells of the medulla without air ; b, cortical substance with a fine fibril- lation and prominent linear nuclei ; e, epidermis with its plates projecting more than usual ; B, three isolated linear nuclei from the cortex. OF THE HAIRS. 175 to be sometimes the expression of the composition of the hairs by the above-described fibre-cells; in other words, to be the boundary lines of the separate elements of the cortex, and sometimes I consider them to be their nuclei. For, even in the shaft of the hair, the cortical plates all contain fusiform nuclei 0-01--0016'" long, 00005"'— 0-0012'" broad, which may, in fact, be isolated by rubbing down white hairs which have been boiled in caustic soda. Besides these, there appear in the cortical substance, and with especial distinctness in a whitish place immediately above the bulb, certain fine striae, which are produced by inequalities in the surface of the cortical plates and which do not readily disappear, even after the continued action of alkalies^ but eventually give place to a finely fibrous appearance; they cannot be isolated, but are visible in those portions of the cortex which have been separated by sulphuric acid and some- times even are very distinct (fig. 66). The description of the cmtex, which has just been given, holds good especially for the hair-shaft. In the root of the hair, so long as it is still solid and brittle, we find essen- pj gg tiaUy the same conditions; and it is only in its lower half, where it becomes gradually softer, at first finely fibrous and then granular, that the structure of the cortex undergoes a progressive change. Here, in fact, the above-described plates are less rigid, and take on more and more distinctly the form of elongated cells (fig. 66) of 0020— 0-034'" in length, and 0009 — O'Oll'" in breadth, whose cylindrical, straight, or serpentine nuclei of O'OOS — O'Ol'", are very easily rendered visible by the action of acetic acid and may also be readily isolated. The soft and shortened plates then pass into elongated, rounded cells, with short nuclei, the fibrous structure becoming more and more obliterated, and these are finally continued without interruption into the elements of the lowest and thickest part of the hair, the bulb. They (fig. ^l) are nothing more than round cells of 0-003 — 0-006'", which lie closely pressed together ; and like the cells Kg. 66. Two cells from the cortex of the root of the hair (the finely-striated part of it immediately above the root), with distinct nuclei and a striated appearance, X 350. 176 SPECIAL HISTOLOGY. of the raucous layer of the epidermis, sometimes contain only Fig. 67. colourless granules, sometimes are so full of dark pigment-granules, that they become true pigment- cells. It must be added, that the chemical rela- tions of the cortex are altered in the lower half of the root, its elements becoming more sensitive to the action of acetic acid, which does not affect the plates of the shaft at all j they swell up and dissolve in alkalies also, much more quickly than those of the shaft.^ The colour of the cortical substance arises partly from spots of pigment, to some extent from air cavities, and partly from a colouring matter diffused through and combined with the sub- stance of the cortical plates. The first or the granular pigment, exhibits all shades from clear yellow, through red and brown, to black ; the diffused pigment is quite absent in white hairs, and is scanty in clear, fair hairs ; it is most abundant in the more opaque fair hairs and in red as well as in dark hairs, in which it may by itself give rise to an intense red or brown colour. The colour of the cortex depends especially upon that of these two pigments, but sometimes the one, sometimes the other predominates, and it is only in the very light and in the very dark hairs that they are developed in about equal proportions. § 57. The medullary substance is a streak or cord which extends in the axis of the hair, from the neighbourhood of the bulb nearly to the point (figs. 65, 68). It is generally absent in the Fig. 67. Cells from the deepest part of the bulb of the hair, x 350 : a, from a coloured bulb, with pigment granules and somewhat hidden nucleus; b, from a white hair, with a distinct nucleus and but few granules. ' [Keichert (' Bericht' for 1850, Miill. 'Archiv,' 1851) asserts that the cortical substance of the hair is composed of superimposed laminae, and recommends, in order to demonstrate the fact, that a hair should be treated with a solution of caustic potass of 10 per cent., and then submitted to pressure. Under these circumstances, " beautiful lamellae appear. The separate layers exhibit no trace of being composed of fusiform cells ; they appear finely striated, and in places, hyaline ; sometimes elon- gated spots appear, of which it cannot be determined with certainty whether they are nuclei or perforations in the membrane." In some, there was no trace of these to be seen. Seichert considers the fibres of the cortex to be artificial products, and was unable to convince himself of the existence of nuclei in this part of the hair.^EDs.] OF THE HAIRS. 177 lanugo and coloured hairs of the head, but is Usually present in the thick, short hairs, Pi gg and in the stronger long ones, as well as in the white hairs of the head. If white hairs be boiled with caustic soda until they swell and coil up, we can often, by the use of simple pressure,demonstrate without further trou- ble,the cellular struc- ture of the medullary cylinder, which is then transparent for transmitted light (fig. 65 a). If a hair thus treated be carefully teased out, it is easy to isolate the medullary cells, either in aggregate masses, or even completely separate (fig. 69). They are rectangular or quadran- gular, rarely rounded or fusiform of 0007 — 001'" in diameter, occasionally containing dark, fat-like granules, and often when the alkali has not acted too strongly, a rounded clear spot of 0001 6 — O'OOS'", which is plainly the rudiment of a nucleus, and which also seems to swell up somewhat in soda. In fresh hairs, the medulla in the shaft is silvery white or dark, an appearance which, as many more favorable objects show, arises from rounded-angular, granular corpuscles, black (opaque) or of a brilliant white, according to the illumination. Fig. 69. Kg. 68. A portion of the root of a dark hair slightly acted upon by caustic soda, X 250 : a, medulla, still containing air, and with Cells, which appear pretty distinct ; b, cortex with pigment spots ; o, inner layer of the epidermis ; d, outer layer of it ; e, inner layer of the inner root-sheath {Huxley's layer) ; /, outer fenestrated layer {Henle's layer). , Pig. 69. Eight medullary cells, with pale nuclei and fatty granules, from a hair treated with soda, x 350. I. . 12 178 SPECIAL HISTOLOGY. tolerably uniform in size, but varying according to the hairs, from 0-0002 — 0'002"' and occupying the medullary cells in great quantity (fig. 68). These granules are not fat or pigment, as has been hitherto universally supposed, but air-vesicles, as may be readily demonstrated by boiling a white hair in ether or oil of turpentine, in both of which cases the medulla becomes quite clear and transparent. If such a hair, treated with water, be dried between the fingers, it soon, often quite sud- denly and visibly to the naked eye, assumes its previous white colour, and if immediately after drying, it be placed under the microscope, without fluid, or with fluid at one end only, nothing is easier, than to see the re-entrance of the air and the con- sequent darkening of the medulla. Not only in white hairs, but in dark ones also, the medidla contains air in the fresh state, only in this case it does not appear of a pure silvery white, but with a blonde, red or brown tinge; this does not arise from any special pigment, which is only found occasionally in the medulla of dark hairs, but proceeds from its being seen through the coloured cortical substance. A more careful investigation of the medullary cells shows, that while fresh they contain many small cavities in a viscid substance ; in these lie the air vesicles, which communicate to them the granular appearance above described. If we observe the air which has been expelled refilling the medulla of a dried hair, it seems as if all the cavities of one and the same cell communicated with one another, at least the air frequently passes in continuous winding streams from one cavity into the other; indeed from the sudden manner in which the air sometimes fills the medulla, it might almost be believed that the cavities of contiguous cells were connected together. However this may be in certain cases, it is conceivable, that even if the cavities of the different cells are quite closed, and only separated from one another by delicate partitions, the air stiU may quickly fill the medulla under the appearances we have noted. For the rest, the vacuities of the medullary cells, whether they are quite closed or not, are of different sizes, the aeriferous medulla appearing sometimes coarsely, sometimes finely granular. I have also seen cases in which the medullary cells obviously contained only a single, large air-vesicle, and appeared almost like small fat-cells. Very frequently single larger or smaller spots may be OF THE HAIRS. 179 observed in the medulla, which contain no air, and are thence pale and this is constantly the case in the lowermost part of the medulla, close above the bulb. The medulla and the cortex are widely different if we com- pare the extreme forms of their elements; in the one case we have rigid homogeneous elongated plates, almost without contents, in the other rounded vesicles filled with fluid or air. If, however, we take into account all their conditions, we shall find, that the limits are not so marked, and in fact are often hardly distinguishable. On the one hand, for instance, the medullary cells are not unfrequently of an elongated or short fusiform figure, whilst on the other the plates of the cortex present a considerable cavity containing pigment. If such plates contain, instead of pigment or the smaller air vesicles, air in a larger cavity, as occurs sometimes though not frequently, it is still more difficult to distinguish the two kinds of elements from one another, and the more so if, as in red hairs, the medulla and cortex are in places, or for considerable distances, not distinctly defined from one another, the superficial cells of the medulla being scattered and passing quite gradually into the plates of the cortex, which lie very close together and con- tain much air. It is not intended to imply, by this, that the medulla and the cortex are identical, but only that transitions exist, and that the differences which occur are less marked than is commonly supposed. The diameter of the medulla is generally, in proportion to that of the hair itself, as 1 : 3— r-5 ; relatively and absolutely, it is thickest in short thick hairs, thinnest in the down and hairs of the head. In a transverse section it presents a round or flattened figure, and the cells which comprise it are disposed in 1 — 5 or even more longitudinal series. [The medullary substance, the cells in which were first accurately described by G. H. Meyer, varies most of all the constituents of the hair. In tiie down and the hairs of the head, it has been stated, by some, that it is wholly absent, which is to be corrected thus far, that it is certainly generally absent in the former, and frequently in the latter, perhaps more frequently, in certain individuals. In white hairs, even those of the head, of a tolerable length and thickness, I have 180 SPECIAL HISTOLOGY. never failed to find it always beautifully distinct. In rare cases the medullary tract is double throughout (Bruns, figure in Hassall), more frequently divided in places into two tracts^ which soon unite again. In the lower part of the root, the medulla, which is here clear, is often thicker, and exhibits the nuclei of its cells very distinctly, especially after the addition of acetic acid. Steinlin and Eylandt assert of the medullary substance, that it does not belong to the proper hair, but to its papiUa, and originally represents a prolongation of this into the free part of the hair, which then dries up. This is incorrect. The papilla or germ of the hair is a part of the cutis, and has the same structure as the papilla of the latter, whilst the medulla of the hair is composed of isolated cells, which by their resistance to alkalies, are in all respects allied to those of the epidermis. On the other hand, in animals, as has long been known, and as lately Brocker has especially shown, the papilla often projects far, even to the point of the hairs, bristles or spines, subsequently drying up ; but in these instances, ac- cording to Brocker, it never, even after the action of potass, exhibits a cellular texture, whilst this is always obvious in the medullary substance, which is often present at the same time. Such an elongation of the papillae may occasionally be noticed even in man, to a certain extent ; thus Henle found it a few times prolonged into a short point. But any prolongation of this kind must be distinguished as decidedly from the cellular medullary substance, as in animals.] § 58. The cuticle of the Hair {cuticula), is a very thin, transparent pellicle, which completely invests the hair, and is very closely united with the cortical substance. " In its normal position, and observed in an unaltered hair, it is evidenced by hardly anything more than by numerous dark, reticulated, irregular or even jagged lines, which surround the hair at intervals of 0-002 — 0006'" from one another, and occasionally also by small serrations at its apparent edge (fig. 70 A) ; if, on the other hand, a hair be treated with alkalies, the cuticle is raised in smaller or larger lamellae from the fibrous substance, and is even separated into its elements. These are quadrangular or rectangular flat plates without nuclei, generally pale and trans- OF THE HAIRS. 181 parent (fig. 70 B), which do not swell up into vesicles by the action of any reagent, and disposed in an im- bricated manner, form -^ a simple membrane K"'/- which completely sur- t i ^ , rounds the cortex of 1-'. ^' -" the hair, in such a i -' ' way, that the deeper or lower cells cover the upper ones. By sulphuric acid also, the structure of the epider- mis is readily made out ; the hair is, as it were, bristled at the edges with the erected plates and by scraping or rubbing, the cuticle is less easily obtained in large lamellae, but is readily enough reduced to its elementary parts. On the shaft of the hair the cuticle consists only of a single layer of plates 0-002 — 0-003'" thick, which measure 0-024 — 0028'" in the transverse direction of the hair ; 0-016 — 002'" in that of its length ; and are hardly more than 0-0005'" in thickness. The same structure exists also in the upper part of the root of the hair ; at its lower part, on the other hand, so far as the inner root sheath extends, two layers of the epidermis constantly occur. The outer (fig. 68 d) is rendered especially obvious by the action of soda or potass, and with a little pressure frequently comes away from the hair with the inner root sheath, whilst the inner layer becoming undulated, remains lying upon the cortical substance, and may be easily studied, as well in the side view as upon its surface. In hairs that are torn out, this layer is found only where they are covered by the inner root sheath, otherwise it remains behind in the hair- sac. Its elements also, are broad cells without nuclei, covering one another like tiles, which do not swell up in alkalies, and are soluble with great dif&cultyj they are thicker than those of the other layer, and measure only 0-002 — 0-004'" in the direction of the length of the hair. The whole outer layer measures 00016 — 0'002"', whilst the inner layer upon the root Fig. 70. j4, surface of the shaft of a white hair, x 160; the curved lines mark the free edges of the epidermic plates ; B, epidermic plates from the surface, isolated by the action of caustic soda, x 350. One or both of their longer edges are bent round, and so appear dark. 183 SPECIAL HISTOLOGY. has a thickness of 0-0035 — 0-0035"'. Upon the bulb of the hair, the two layers of cuticular plates pass with a tolerably defined margin into soft nucleated cells, which are broad in the transverse direction of the bulb, very short longi- tudinally, and somewhat longer in their third diameter, which stands perpendicularly or obliquely to the longi- tudinal axis of the hair. They are readily attacked by alkalies, or even by acetic acid, possess without excep- tion transverse and longish nuclei, and finally pass, on the bulb, into the already described, round cells of which it is formed.^ > [We cannot agree with Prof. Kolliker that the cuticle of the hair passes into the outer cells of the bulb. It may be worth devoting a little space to this matter, as the whole question of the homology of the hair essentially turns upon it. So far from being able to trace the two layers of the cuticle into the round ceUs of the bulb, we find that they cease somewhat suddenly when the shaft begins to expand, while its substance is fibrous-looking and contains only much-elongated nuclei. Below this point, as Henle has correctly figured in his 'AUgemeine Anatomie,' PI. I, fig. 14, the transverse striations of the cuticle are absent ; and if the cuticular layer be viewed in section, it will be seen to be composed of a more transparent substance, which gradually becomes thinner until it is hardly distinguishable as a distinct layer, and at the same time loses the oblique lamination, which it has above, where it is continuous with the two layers of the cuticle proper. The careful addition of caustic ammonia is particularly fitted to demonstrate the structure of this part. In the first place, it raises up the outer layer of the cuticle from the inner, and shows that the former, at any rate, is not continuous with any cells ; and secondly, it dis- solves and forces out the substance of the lower soft portion of the bulb, so that the lower part of the cuticle may be obtained as a transparent, colourless, and indepen- dent sheath, even from the very darkest hairs ; lastly, under favorable circumstances, this reagent raises up a definite basement membrane from the outer surface of the lowest part of the bulb, in immediate contact with the rounded "nuclei" of this part, and this basement inembrane may be traced upwards into direct continuity with the homogeneous portion of the cuticle above-described. (In the ' Edinburgh Monthly Journal of Medical Science,' for March, 1853, Mr. Dalzell states that the papilla of the hair has a basement membrane. Is it this structure to which he refers .') In all cases in which, in man or in animals, we have isolated the hair-bulb from its sac, it seemed to have a definite limiting outer line down to the narrow neck by which it passes into the hair-sac, though it was not often easy to obtain evidence that this limiting line was the expression of a distinct basement membrane. However, the same difficulty would occur with any dermic papilla ; and it seems to us that there is sufficient evidence to show that the cuticle of the hair is not the product of any direct metamorphosis of cells, but represents a modified basement membrane with a subjacent layer of peculiarly-altered blastema, corresponding precisely with the " Nasmyth's membrane" and the enamel of the teeth. Vide infra, § on Teeth.— Eds.] OF THE HAIRS. 183 § 59. The hair-sacs, folliculi pilorum, are flask-like follicles 1 — 3"' long, which embrace the roots of the hair tolerably closely, and, in the lanugo, are lodged in the substance of the upper layers of the corium, while in the stronger or long hairs, they generally project into its deeper portion, and even extend for a greater or less distance into the subcutaneous cellular tissue. These follicles are simply to be regarded as involutions of the skin, with its two constituents, the corium and the epidermis, and there may be distinguished, therefore, in each of them an external fibrous, vascular part, the proper hair-sac, and a non-vascular, cellular investment lining this, — the epidermis of the hair-sac ; or, since it immediately surrounds the root of the hair, — the "root-sheath" (vagina pili). § 60. The proper hair-sac consists of two fibrous investments, an external and an internal, and of a structureless membrane j it is on an average 0*015 — 0'032"' thick, and contains in its lower part a peculiar structure, the papilla of the hair. The external fibrous membrane (fig. 63 h), the thickest of the three layers of the hair-sac, determines its external form, and by its innermost layer is very closely connected with the corium. It consists of common connective tissue with longi- tudinal fibres, without any intermixture of elastic fibres, but with a considerable number of long fusiform nuclei; it contains a tolerably close plexus of capillaries, and exhibits also a few nervous fibrils with occasional divisions. The internal fibrous membrane (fig. 71 a) is much more delicate than the external; bounded by smooth surfaces, and everywhere of equal thickness, it extiends from the bottom of the hair-sac as far only as the entrance of the sebaceous glands. To all appearance, it contains neither vessels nor nerves, and is composed solely of a simple layer of transverse fibres, with long narrow nuclei, which may be seen particularly well in the empty hair-sacs of both coarse and fine hairs, with or without the addition of acetic acid. They resemble smooth muscular fibres, although they cannot be completely isolated and actually recognised as true fusiform fibres with a single nucleus; 184 SPECIAL HISTOLOGY. Fig. 71. on wMch account, and especially as no contractions of the hair- sacs have in general been observed, I must for the pre- sent refrain from positively deciding upon their nature. The third layer, lastly (fig. 71 b), is a transparent- struc- tureless membrane, which, when the hairs are torn out, invariably remains behind in the hair-sac, and extends from its base, though, as it would seem, without covering the papilla, as far as the in- ner root-sheath, and perhaps higher. In the iminjured hair-sac it appears only as a pale streak 0-001 — 0-0015'", rarely 0-003'" thick between the outer root-sheath and the transversely fibrous layer of the hair-sac ; by preparing an empty hair-sac, however, it can readily be obtained in large shreds, and then appears smooth externally; internally it is covered with very delicate, transverse, often anastomosing lines, which, like the membrane itself, remain unchanged in acids and alkalies. Neither acids nor alkalies bring out cells or nuclei in this membrane, and it therefore probably belongs to the category of true structureless membranes. The papilla of the hair (fig. 63 i) also, less properly termed the hair-germ, pulpa pili, belongs to the sac, and corresponds with a papiUa of the cutis. It is generally seen but indistinctly, especially in dark hairs with a coloured bulb, either appearing, only as a clear indistinctly-defined spot, or after the tearing out of the hair, remaining so covered by the cells of the bulb Fig. 71. A piece of the transverse fibrous layer and of the structureless membrane (vitreous membrane) of a human hair-sac, treated with acetic acid, x 300 : a, trans- versely fibrous layer with elongated transverse nuclei i b, vitreous membrane in ap- parent section ; c, its edges, where the sheath which it forms is torn ; d, fine trans- verse partly anastomosing lines (fibres) on their inner surface. OF THE HAIRS. 185 that nothing can be made out of it. It is only in the hair-sacs of white hairs that its outlines can be more frequently distinguished without wholly isolating it, especially by the help of a little pressure. Eeagents, on the other hand, avaU nothing, for they attack the papilla to about the same extent as the bulb, with the sole exception of a weak solution of caustic soda, in which it retains its outlines, for a time at any rate, whilst the cells of the bulb are freed and may be pressed out of the sac. The papilla is ovate or fungiform, i — ^"' long, ^^ — ^"' broad, and is connected with the layer of connective tissue of the sac, by a pedicle : it has sharp contours and a perfectly smooth surface, and in its structure completely agrees with the papillae of the cutis, consisting of an indistinctly fibrous connective tissue with scattered nuclei and fat-granules, but not of cells. I have taken every pains to discover vessels and nerves in the isolated papillee, but in vainj even acetic acid and dilute solution of caustic soda, which in general do such excellent service in these cases, have failed, and Hassall and Giinther met with the same results. It must not hence be concluded, that the papilla contains no vessels or nerves, for we know that in other places, where vessels do certainly exist, they often com- pletely escape the eye; as, for example, in the dermal papilla and in the villi ; and with respect to the nerves, in the papillae of the cutis. In some animals the vessels may very readily be seen. § 61. The root sheath, or the epidermic investment of the hair- sac, is continuous with the epidermis around the aperture of the follicle, and may be divided into an external and an internal layer, which are distinctly defined from one another. The external root-sheath is the continuation of the stratum Malpighii of the epidermis, and lines the whole hair-sac, resting for its lower half on the transparent membrane above de- scribed; higher up, when this and the transverse fibres are absent, it lies directly upon the longitudinally fibrous layer. Its structure corresponds exactly with that of the stratum Malpighii, even in the having the outermost cells, which in the Negro, according to Krause, are always brown, and in whites are so, at least in the hairs of the labia majora, towards the 186 SPECIAL HISTOLOGY. upper part, arranged perpendicularly. At the bottom of the hair-sac, the outer root-sheath, its cells becoming gradually rounded, passes continuously, and without any sharp line of demarcation, into the round cells of the hair-bulb which cover the papilla. The outer root-sheath is generally about 3 — 5 times as thick as the inner ; but not unfrequently it becomes thinned towards its upper part, and below invariably passes into a very thin lamella. In the coarse hairs it measures in the middle of the root 0-018 — 0-03'", and presents 5 — 12 layers of cells. The inner root-sheath (fig. 68 — e. g.) is a transparent mem- brane which extends from almost the very bottom of the hair- sac, over more than two thirds of it, and then suddenly ceases. It is closely connected externally with the outer root-sheath, internally with the cuticle of the hair (its oiiter layer), so that normally there is no space between it and the hair ; further it is distinguished by its great density and elasticity, and it consists in all but its lowermost part, of two or even three layers of polygonal, elongated, transparent, and somewhat yellowish cells, all of which have their longitudinal axes parallel to that of the hair (fig. 68). The outermost layer (fig. 73, A), which alone was formerly known, the inner root-sheath of Henle, is formed of elongated cells without nuclei, 0*016 — 0'02"' in length, and 0'004! — 0'006"' in breadth, which are intimately connected, and in the ordinary mode of investigation, after the addition of acetic acid, caustic soda or potass, which swell up the hair, or after the hair has been teased out, present elon- gated fissures between them, whence they appear like a fenestrated membrane. In quite recent hairs, however, if all reagents and mechanical injury have been avoided, we see hardly any trace of apertures in the upper half of the layer in question, and in the lower half (from the finely fibrous part of the cortex upwards), at most mere indications of them, in the form of striae, clear or dark, according as they are in or out of focus, and similar to those of the cortex of the shaft. We can hardly avoid supposing, therefore, that the openings as they are commonly seen (0-005 — 0008'" in length, and 0-001 — 003'" in breadth), are produced artificially by the teasing out of the membrane. Secondly, cells also occur in the root-sheath, between which gaps are never visible. These (fig. 72, B) OF THE HAIRS. 187 which form a simple or a double layer (Huxley's layer) are constantly situated internal to the common, and as far as I Kg. 72. ) ' I I 1- : r, ' \ > 1 1 ' ( 1 r '^^:' L have seen, always single, fenestrated layer of cells ; they are shorter and broader than the cells which have already been described (0-014 to 0-018'" long, 0-006 to 0009"' broad), but are also polygonal, and always possess, at least in the lower half of the root-sheath, distinct elongated nuclei often prolonged into points of 0-004—0-006'". The diameter of the whole inner root-sheath is, upon the average, 0-006 — 0-015"', whence it follows, that its cells, of which there are never more than three layers, are at least 0002 — 0-005'" thick. They are recognisable at once in their natural position, and by the teasing out of the root-sheath, and are readily isolated by the use of soda and potass (fig. 73), but without swelling up, a character which no less than their great resistance to alkalies altogether, distin- guishes their cells, in common with the epidermic scales of the hairs, from all others. At the bottom of the hair-Sac the inner root-sheath consists only of a single layer of beautiful, large, polygonal, nucleated Fig. 72. Elements of the inner root-sheath, x 350 : A, from the outer layer, 1, its isolated plates ; 2, the same in connection, from the uppermost parts of the layer in question, after treatment with caustic soda: a, apertures between the cells, i: B, cells of the inner not-perforated layer, with elongated and slightly notched nuclei ; C, nucleated cells of the lowest part (single layer) of the inner sheath. 188 SPECIAL HISTOLOGY. cells, without any intermediate openings (fig. 73, C), which be- coming at last* soft, delicate, and rounded, pass without defined limits into the outer layers of the round cells of the hair bulb. Superiorly, this membrane not unfrequently becomes somewhat separated from the hair, and ends, not far from the apertures of the sebaceous glands in a sharp, notched edge, formed by its separate more or less projecting cells. Thence upwards, it is replaced by a layer of cells, in some cases at first nucleated, but at other times not, which gradually approximates more and more, as it is traced higher up, to the horny layer of the epidermis, into which it passes continuously; it is not, however, any direct continuation of the inner root-sheath. § 63. Development of the hairs. — The first rudiments of the hairs are flask-shaped, solid processes of the mucous layer of the epi- dermis formed by its growth inwards, in which, the internal and external cells subsequently become differentiated in such a manner, that the former, a gradual conversion into horn going on, are, in the axis of the rudiment, metamorphosed, in the first place into a small delicate hair, and secondly, around this into its internal sheath ; while the latter, undergoing less alteration and remaining soft, constitute the outer root-sheath and the soft cells of the hair-bulb. Hence the hairs and their sheaths arise at once in their totality. The former, as minute hairs with root, shaft, and point, and are therefore not developed point first, as the teeth are, with their crown first, and still less as Simon has supposed, from their root first. The elements of the youngest hairs are nothing but elongated cells similar to those of the cortex of the later hairs, which are developed by the lengthening and chemical alteration of the innermost cells of the rudiments of the hairs. MeduUary cells are entirely wanting, but the cuticle is clearly visible. The inner sheath is striated, presents no openings, and consists of elongated cells, which have been developed from those lying between the hair and the outer sheath. The proper hair-sac is formed, in its fibrous layers, essentially in loco, out of the formative cells which surround the rudiment of the hair ; possibly, however, they may be considered as an involution of the cutis, pro- duced by the ingrowing process of the epidermis. Its OF THE HAIRS. 189 structureless membrane, which appears very early, is, not im- probably, closely related to the external cells of the rudiment of the hair, answering to the outer hair-sheath, and formed by an excretion from them like the membraruB propria of the glands ; as to the papilla it is hardly possible to consider it as any- thing but an outgrowth of the fibrous layer of the hair-sac, analogous to the papillae of the cutis in general ; though the circumstance that it appears at a time when the hair-sac is hardly demonstrable as a whole, and that it may always be pulled out together with . the rudiments of the hair and root- sheath, is apparently opposed to this view. [The first rudiments of the downy hairs and of their sheaths, are found in the human embryo at the end of the third or at the beginning ofthe fourth month, upon the forehead and eyebrows. They consist of papilliform masses of cells 0'03"' in diameter (fig. 73), which are visible, even to the naked eye, as minute whitish spots separated by regular intervals. They are con- tinuously connected with the reie Malpighii of the epidermis and are nothing more than per- Fig. 73. fectly solid processes of it, which m »fcTa 8 i«» si' ^#tyH|^ ^^^B penetrateobliquelyintothecormw, *--:ixu5aB3fe?"^^^^ssa^^^^s and here lie in the meshes of a M^mS delicate capillary network; these .^^M' cells are spherical 0003 — 0004"' '" ^^B'- i in diameter, and consist of a fsF^ clear granular substance and «» round nuclei of 0002 — 0-003'". Nothing was to be seen of any dermic investment of these rudiments; in other words the foundation of what I have described as the proper hair-sac was not laid. In the fifteenth week the processes were already larger (0-025— 0-03'" long, 0-013—0-02'" broad), flask-shaped, and surrounded by a thin structureless investment, which was continued into a delicate membrane lying between the cutis and the rete Malpighii, but united more closely with the latter. Besides this investment, which is, probably, only the structureless Fig. 73. Rudiment of the hair from the brow of a human embryo, sixteen weeks old, X 350 : a, horny layer of the epidermis ; 4, its mucous layer ; i, structureless membrane surrounding the rudiment of the hair and continued between the mucous layer and the corium ; m, roundish, partly elongated cells, which especially compose the rudiment of the hair. 190 SPECIAL HISTOLOGY. membrane which I have discovered in the perfect hair (see ^ 60), anotherj external layer of cells occurs on the hair-sacs, which can generally be separated only in shreds with it, from the cutis, rarely altogether : this I regard as the first indication of the fibrous layers of the hair-sacs. In the 16th and 1 7th weeks the processes of the mucous layer, which I will henceforward simply call " hair-rudiments," increase in size up to -004 — 006'" length, and 0'03 — 004'" breadth, and acquire thicker cover- ings, but as yet exhibit no trace of a hair. In the 18th week these first appear in the eyebrows, as hair-rudiments of 0"1 — 0'2"', their central cells becoming somewhat elongated, and arranging themselves with their longitudinal axes parallel to that of the rudiment, whilst the peripheral cells are disposed with their now longer diameter transversely. A variety of shade in the hitherto homogeneous hair-rudiment arises in this manner, and a central substance, broad below, running above into a sharp point, becomes marked off from an outer portion, which is narrow below and thick above. When the rudiment has attained a length of 0'22"', this marking off is still more distinct, the rather longer and especially broader, inner cone having a somewhat clearer appearance (fig. 74). Finally, in rudiments of hair of 0'38"', the inner cone is divided into two structures, a central portion somewhat darker, and an external, perfectly transparent and glassy, — the hair and the inner root- sheath, — whilst the peripheral cells which have remained opaque, constitute unmistakeably the outer root-sheath (fig. 75 A). At the same time the papilla, which was even before (fig. 74) just traceable, becomes more distinct, and the proper hair-sac also more recognisable, as the cells which lie external to its struc- tureless membrane begin to pass into fibres which may, even at this time, be known by their decussation. The hair-sacs and hairs arise, in other places exactly in the same manner as in the eyebrows, except that their development takes place somewhat later. In the 15th week, no rudiments of hairs are visible, except on the forehead and eyebrows; in the 16th and 17th week they appear aU over the head, back, chest, and abdomen; and not till the 20th week on the extremities. The hairs themselves never make their appearance earlier than 3— =-5 weeks after that of the rudiments ; in the 19th week, for example, the commencement of hairs is nowhere to be seen, except on the forehead and OF THE HAIRS. 191 eyebrows ; and in the 24th week they are still absent upon the hand and foot, and partly on the fore-arm and leg. Once formed, the hairs and hair-sacs continue to grow. The former sometimes penetrate the epidermis immediately Fig. 75, Fig. 74. (eyebrows, eyelashes, fig. 75), sometimes their points are insinuated between the horny layer and the stratum Malpighii, or among the elements of the horny layer itself, and grow for a time covered by the epidermis (chest, abdomen, back, extremities [?]), through which they eventually make their passage. Involutions of the skin growing towards the hairs as they pass out, never exist, and the supposition that they do, rests upon a whoUy subjective foundation. Fig. 74. Rudiment of a hair from the eyehrow (0'22"' in length), x 50, its inner cells forming a distinct cone, as yet without any hair, hut with the papilla indicated : a, homy layer of the epidermis ; b, mucous layer ; c, outer root-sheath of the subse- quent sac ; i, structureless membrane upon its outer side ; h, papilla of the hair. Fig, 75. A, rudimental hair from the eyebrows, with just developed but not yet erupted hair, of 0-28'" in length. The inner root-sheath projects beyond the point of the hair somewhat at the upper part, aud laterally at the neck of the sac ; the first rudiments of the sebaceous glands appear in the form of two papillary outgrowths from the outer root-sheath. B, hair-sac from the same, with its hair just erupted ; the inner root-sheath projects through the aperture of the hair-sac ; the rudiments of sebaceous glands are as yet not developed ; the letters u, i, c, h, i, have the same signification as in fig. 74 : e, hair-bulb ; /, hair-shaft ; g, hair-point ; «, rudiments of the sebaceous glands. 192 SPECIAL HISTOLOGY. The downy hairs, lanugo, the eruption of which is com- pleted in the 33d — 25th week, are short fine hairs, whose peculiar arrangement has been noted above. They measure on the bulb O'Ol'", on the shaft 0-006'", at the point 0-0012 — 0"002"'j are pale, or almost colourless, and consist only of cortical substance and a cuticle. In man, the bulb is usually colourless, and often rests upon a very distinct papilla, arising in the ordinary manner from the bottom of the hair- sac. It has the same three layers as in the adult, and pos- sesses a very well-developed epidermic investment, consisting of an external root-sheath of 0"004! — 0'012"', and an inner sheath of 0-006 — 0-008'", without openings. After their eruption, the downy hairs grow slowly to a length of i — J of a line, and in fact to a greater length in the head than elsewhere. Generally they remain to the end of foetal life, gradually acquiring a darker colour, becoming in many cases, as on the head, even blackish; another small portion falls off into the liquor amnii, is swallowed with this by the foetus, and may afterwards be found in the meconium. A proper shedding of the hair does not take place at all in the foetus, so far as I can see, infants being born with the lanugo; as little does any trace of a further formation of hair appear after its complete eruption. The question whether the point of the hair is first formed, or whether the latter is developed at once as a whole, is readily solved. Hairs which are just formed, have a bulb with soft cells, a horny point and an intermediate portion, in which the cells are converted into horn, and are partly found passing into the cells of the root, whence there can be no doubt that we have here a whole hair. That the homy part of this hair subsequently forms the point of a larger hair, is of no im- portance; and as little as the hairs of the head of a newly-born infant can be called points of hairs, because they subsequently become the points of larger hairs, can we so denominate these. Nor can it be said that the first foetal hair subsequently becomes, in totality, the point of a larger hair, since the hairs do not grow by the simple apposition of new elements, like the bones, but by the multiplication of their lowest soft cells, some of which are always retained as a reserve for cells to be newly developed, whilst the others are converted into horn; whence OF THE HAIRS. 193 also it happens, that the cells even of a complete hair-bulb are to be regarded as the successors of those of the foetal hair.]^ § 63. Shedding of the Hair. — After birth, a total shedding of the hairs takes place in consequence of the development of new hairs within the hair-sacs of the lanugo, which gradually force out the old ones. This shedding of the hairs, which I discovered in the eyelashes of a child of one year old, commences by an outgrowth of the soft round cells of the bulb and of the neigh- bouring outer root-sheath, from the bottoms of the sacs of the ' [From what has been said above (see note on the Cuticle) it is clear we do not share Professor KoUiker's view that the hair is an epidermic production. Reichert's view, on the other hand, that the hair results from the cornification of a dermic papilla or matrix, which drying up and becoming filled with air, remains* as the me- dullary portion, seems to us to be nearer the truth. There can be no doubt of these two facts: 1, that no line of demarcation can be traced between the papilla of the hair and its shaft ; and 2, that in many animals the papilla is vascular and nervous for a considerable distance into the shaft, and, therefore, is certainly a dermic structure. Whether Reichert's somewhat mechanical notion of the " drying up" of the matrix to form the medulla is correct, is not of much importance, so long as we keep in view the unquestionable continuity of tissue and homological identity, of the medulla and cortex with the dermic papilla. For us, in fact, the Hair is homologous in all its parts with the Tooth. The sub- stance, of the shaft corresponds with the dentine, offering even rudimentary tubes in its aeriferous cavities ; the inner layer of the cuticle answers to the enamel, the outer to Nasmyth's membrane ; and whoever will compare these structures will be struck by the similarity even in their appearance. The sac answers to the dental capsule; the outer root-sheath to the layer of epithelium (enamel organ) next the capsule; the fenestrated membrane to the stellate tissue; and what Professor Kolliker calls " Huxley's layer," to the columnar epithelial layer of the organon adamantincB. The comparison may seem startling at first, but the examination of the development of the teeth of an osseous fish, for example, vrill suffice, we believe to afford full justification of it. With respect to the not very important question, as to the nature of the first rudi- ment of the hair-shaft, i. e. whether it is the point of a hair or a whole hair, we must confess that we should be tempted to arrive at the opposite conclusion to our author. Inasmuch as the portion of the hair which first appears becomes the point of the fully-grown hair, we should say that the hairs are formed like the teeth, point first. A hair, like a tooth, has a definite form to attain. As the latter has a peculiarly constructed and narrowed root when complete, so has the hair when it has attained its full growth a peculiarly constructed bulb ; and it is not a perfect hair until this peculiar bulb is developed. Until it has attained this form it goes on growing ; but once having reached it, it grows no more, but falls out and is replaced by a new hair (see following §). — Eds.] I. 13 194 SPECIAL HISTOLOGY. 0, into long processes composed of cells, by which the hair is raised from its papilla, whilst at the same time it becomes converted into horn even in its lowermost portion. When these processes have attained a length of 0'25"', a differentiation of their outer and inner cells takes place, similar to that which has been already described as occurring in those processes of the stratum Malpighii, in which the hairs of the lanugo are developed. The outer cells, in fact, remaining round and colourless, as they were before, the inner ones begin to develope pigment in their interior and to elongate, becoming distinguished at the same time from the former, as a conical sub- stance with its point directed upwards. At first (fig. 76 A), this central substance is quite soft, and like the layers of cells which surround it externally, dissolves readily in solution of caustic soda; subsequently, however, when, to- gether with the process which incloses it, it has elongated, its elements harden, and separate into two portions, an internal dark pigmented, and an external clear part, which are nothing else than a young hair, together with its inner sheath (fig. 765). The young hair, whose point at first does not project beyond its inner root-sheath, now grows gradually, forcing its point through the aper- ture of the old sac, while at the same time its root-sheath elongates, and thrusts upwards the bulb of the old hair, until Kg. 76. The eyelashes of a child of one year old pulled out, x 20 : A, one with a process of the bulb or of the outer root-sheath, of 0-25'", in which the central cells are elongated (their pigment is not represented), and are clearly defined as a cone from the external ones ; B, eyelash in whose process, of 0-3'", the inner cone is metamorphosed into a hair and an inner root-sheath ; the old hair is pushed up, and like A and fig. 75, possesses no inner root-sheuth : a, outer; b, inner root-sheath of the young hair ; c, pit for the papilla of the hair ; d, bulb ; e, the shaft of the old hair ; /, bulb ; g, shaft ; h, point of the young hair ; i, sebaceous glands ; k, three sudoriparous canals, which in A open into the upper part of the hair-sac ; I, transition of the outer root-sheath into the rete mucosum of the epidermis. OF THE HAIRS. 195 Fig. 77. at last it passes completely out, and mates its appearance at the same opening with the old one, which is more and more pushed up. When the development of the hair has gone thus far, the last stage may be readily understood. The old hair, which has for a long time ceased to grow, and to be connected with the bottom of the sac, being thus extruded, falls out, while the young hair becomes larger and stronger, and fills the gap left by the old one. The primary cause of the dying away and casting off of the old hair, I consider to be the development of the processes of the hair bulb and outer sheath from the bottom of the sac, which has been described. As the sacs do not elongate to a corresponding extent, they push upwards all those parts which lie above them, and cause a continually increasing space to exist between the papiUa and the proper hair, or the point at which the round cells of the bulb begin to elongate and undergo conversion into horny matter. The hair thus becomes in a manner detached from the source of its nourishment : it receives ^ less and less blastema, at last ceasing to grow, and becoming convprted into horn in its lowest part. The ceUs of the pro- cesses, on the other hand, which are connected with the papilla, are incessantly supplied from it with new formative material, which for the time they apply not to the formation of horny matter, but to their own growth. In this manner the pro- cesses continue to grow, and mechanically elevate the cor- nified root of the old hair, with its sheaths, to the aperture of the sebaceous glands, where to all appearance a partial solution of the old sheaths takes place : this may be observed with certainty in the inner sheath, and must be assumed to occur in the outer. All that has been said, holds good only with respect to the Kg. 77. An eyelash with the root-sheaths from a child one year old, with an old and a growing young hair, x 20 ; the young hair is wholly extruded, and now two hairs appear at one aperture. A sudoriparous canal opens into the hair-sac. The letters have the same signification as in fig. 76. 196 SPECIAL HISTOLOGY. eyelashes. The hairs of the head, and the other hairs of the body of the child (almost a year old) in question, never con- tained more than one hair, though their bulbs presented processes without hairs like those which precede the shedding of the eyelashes ; such processes, in fact, being of very common occurrence in the hairs of children within the first year. I believe I am not wrong, if from the presence of these processes I deduce the universal occurrence of a shedding of the hairs, particularly as it is certain that in many children within the first 2 — 6 months after birth, the hairs of the head fall out and are replaced by new ones. However, further observation is necessary to determine what period is occupied by this first shedding of the hair, in what hairs it occurs, and whether perhaps the process is subsequently repeated. [If we compare the shedding of the hairs with their first development, we find a great resemblance between the two pro- cesses. In both, elongated projections, wholly formed of round soft cells, shoot like buds from the stratum Malpighii, in the one case of the skin itself, in the other of the hair-sacs and hairs. In both, a separation of the inner from the outer cells next takes placej and while the latter arc metamorphosed into the outer root-sheath, the former become the inner root-sheath and the hair. TThe latter arises, as is stUl more clear in the shedding of the hairs than in their first development, Hke the nail, with all its parts at once, as a small hair provided with point, shaft, and root, and which only subsequently begins to grow, in con- sequence of which it enlarges in all its parts, and finally reaches the surface. The differences between the two modes of development are very inconsiderable, and chiefly depend upon the rudimentary hair-processes, in the one case proceeding from the hairs themselves, but not in the other; and upon the circumstance that the young hairs, although in both cases they lie at first in a closed space, reach the surface more readily in the one case, than in the other. In the periodical shedding of the hair of animals, the observations of Heusinger and Kohlrausch, and lately those of Langer, Gegenbaur and Steinlin, show that the new hairs are also developed in the sacs of the old ones ; although, according to the last author, with whom however Langer is not quite in OF THE HAIRS. 197 accord, the process does not appear to be exactly the same as in man. § 64. Physiological Observations. — The hairs have a definite length, dependent upon locality and sex, but if they are cut they grow again, and consequently exhibit the same conditions as the other horny textures. The place from whence the growth of the hair proceeds is unquestionably the bottom of the hair-sac. Here there arise around the papillae, with the co-operation of a blastema formed out of its vessels or those of the hair-sac, new elements, by the continual multiplication of the existing cells, while those which are already present, somewhat higher up pass uninteruptedly, the middle ones into medullary cells, the next into cortical plates, the outermost into epidermic scales, and thus the homy part of the hair is continually forced from below upwards, and elongates. In the latter no formation of elemen- tary parts takes place, but at most a certain metamorphosis of those which are already existent, which produces a gradual thinning of the root from the bulb upwards, until it acquires the thickness of the shaft. Higher up still, these changes of the elementary parts cease, whence cut hairs, for example, do not produce new points. The root-sheaths and the outer layer of the epidermis take no part in the growth of cut hairs. The complete hair, though non-vascular, is not a dead substance. Mthough the processes which go on in it are not at all understood, we may suppose that fluids are diffused through it which subserve its nutrition and maintenance. These fluids are furnished from the vessels of the papilla and sac of the hair, in all probability ascend (particularly from the bulb) without any special canals thrpugh the cortex upwards, and thus reach all parts of the hair. Having served for the nutrition of the hair, they evaporate from its outer surface and are replaced by a fresh supply. Perhaps the hairs also absorb fluids from without, though of course only in the condition of vapour, like a hair used as a hygrometer; on the other hand I cannot believe that, as many authors would seem to suppose, the secretion of the sebaceous glands passes from without into the hairs, since the perfectly closed cuticle is probably impervious to it. In the same way it seems to be in 198 SPECIAL HISTOLOGY. nowise proved that the hairs are pervaded by a peculiar oleaginous fluid (Laer), which might proceed from the medullary substance (Reichert)^ and which keeps it greasy, for such a fluid has not been demonstrated, and the greasiness of the hairs may be more simply explained by the externally adherent sebaceous matter, which is readily visible. The existence of air in the medullary axis and in the cortex can only arise from a dis- proportion between the supply of fluid from the hair-sac and the amount evaporated ; it is owing, as it were, to a drying- up of the hair, which, however, must not be supposed to go so far that the hair contains no fluid in its aeriferous portion. In any case, however, these portions are the most inactive, or relatively dead parts of the hair; the cortex, on the other hand, which is also most readily altered by alkalies and acids, notwithstanding the apparent hardness and density of its elements, is the most rich in juices, and is that in which the nutritive process is most actively going on. Hence it follows, that the hair lives, and is to a certain extent dependent upon the collective organism, particularly on the skin, from whose vessels (i. e, those of the hair-sac) it derives the materials necessary for its maintenance. Therefore, as Henle well says, the condition of the hair is a sort of index of that of the activity of the skin ; if they are soft and shining, the skin is turgescent and transpires ; if they are dry, brittle, and rough, then it may be concluded that the surface of the body is in a collapsed condition. The falling out of the hairs certainly depends, in many cases, — when, for example, it takes place in the course of normal development, — on nothing else than a want of the necessary nutritive material, which in the instance already explained, in speaking of the shedding of the hairs, depends on the detach- ment of the hair from its matrix by the abundant production of cells at the bottom of the hair-sac. In age, perhaps, it arises simply from the obliteration of the vessels of the hair-sacs. The whitening of the hairs, which chiefly depends upon a decoloration of the cortex, and less upon that of the almost colourless medulla, should probably be here considered, for its normal occurrence in old age gives it the significance of a retro- gressive development. The frequent occurrence of cases, in which the hair grows OF THE HAIRS. 199 grey first at its point or in the middle, and the well-esta- blished instances of its rapidly becoming white, are interesting, and strongly testify to the vitality of the hair; but it has not yet been shown, what peculiar processes in the elements of the hair produce the decoloration of its different pigments. As in youth hairs which are shed are replaced by others, so at a later age something similar appears to occur. It is quite certain that during the period of full health and activity, a continual replacement of the numerous hairs which fall out goes on; furthermore that new hairs in great numbers spring up at the time of puberty in certain localities, but the manner in which this takes place is unknown. Inasmuch as even in adults we find hair-sacs with little processes downwards, whose proper hair has an abrupt clavate end, as in the child; since further, in this case it not unfrequently happens that two hairs come out of one aperture, and even exist together in one sac; and, finally, since in hairs which have fallen out spontaneously, we invariably find roots like those' which exist in the extruded hairs of the first shedding, it may be assumed that an actual shedding of the hairs occurs, even at a later period, in such a manner that the old hair-sacs produce new hairs while they throw off the old ones. I do not, however, intend to affirm by this, that an actual new formation of hairs does not occur after birth, but only this much, that in adults they are certainly regenerated from the already existing hair-sacs, especially if it be recollected that, according to Heusinger's observations, the whiskers of dogs, when pulled out, are reproduced from the same sacs in a few days, and also that during the shedding of the hair in adult animals, according to Kohlrausch, the young hairs are pro- duced from the old sacs. Also, when the hairs which have fallen I [Henle (' Allg. Anat.,' p. 303) gives a very excellent description of this state of the hair-bulb : " Instead of the soft cellular hair-bulb, we find an inconsiderable clavate enlargement, which is solid and fibrous, like the substance of the shaft, only more clear. From its outer surface, short and irregular processes project downwards, which are probably the notched lower edges of the outermost layers of the cortical substance ; they look like fibres connecting the hair with the inner wall of the sac. This kind of root is found in hairs which have fallen out spontaneously, and it is, therefore, probable that it belongs to a later stage of development of the hair, or rather marks the conclusion of its development. When the connection with the sac has ceased, which is the case in these clavate roots, the hair grows no longer; probably it is no longer nourished, but falls out." — Eds.] 200 SPECIAL HISTOLOGY. out after a severe illness, are replaced, it is more probable, since, according to E. H. Weber, the sacs of lost hairs remain for a long time, that they arise in the old sacs, than that new ones are developed.^ [The multiplication of the cells of the bulb of the hair during its growth takes place unquestionably, not by free cell- development, since no trace of anything of the kind is to be seen in any bulb, but either by endogenous cell-development round portions of contents, or by division. I do not think that all those hairs which possess a sharply-defined clavate bulb are on that account dead and ready to fall out. It is certainly thus in many cases; but in others this condition indicates nothing more than the normal termination of growth, whence of course, it does not follow that the nutrition also has ceased. In proof of the occurrence of a continual development of the hairs indepen- dently of the old hair-sacs, the hairs which lie spirally curled up under the epidermis and subsequently break through it, upon the forearm, leg, &c., are frequently cited. But I do not know that it would not be more correct to consider this, with many pathologists, rather as an abnormal process. In the first place this formation of the hairs by no means occurs in all persons; and secondly, where it does, there are found together with those coiled-up hairs, which are apparently normally developed, others which are evidently abnormal, in great quantities. These, often in considerable number (up to 9), with thick sheaths, lie in one sac and have rounded points, with irregular bulbs. With respect to their relations, it might for the present be wiser, so long as an actual, normal new develop- ment of hairs has not been demonstrated, not to assume it, and to consider that, even at a later period, the development of new hairs within the old sacs is the normal mode, especially since Dr. Langer has actually observed it to take place in many ' [Berthold (Miill. 'Archiv.,' 1850) has communicated some curious statistics relative to the growth of Hairs. The hairs of the head of a female of from 16 to 24 years of age, grow at the rate of 7 lines a month. The growth of the hairs of the beard is quicker the oftener they are cut; shaved every 12 hours, they would attain a length of from 5J — 12 inches per annum ; every 24 hours, from 5 — 7J inches ; every 36 hours, from 4 — 6^ inches. They grow faster by -fg during the day than during the night; and in 18 days of summer, 0'026 more than in 18 day of winter. — Eds.] OF THE HAIRS. 201 instances in the very same manner as that which I have described in children. The reason why the hairs grow con- tinually, if they are cut, but not otherwise, is the same as I have already adduced, to account for the same occurrence in the nails. The vessels of the papilla excrete a certain quantity of nutritive fluid, just so much as is sufficient to keep the whole hair continually moist and in a state of vitality. If the hair be cut, more nutritive fluid is supplied than the hair can use, and therefore it grows by the aid of the superfluity until it has attained its typical length again, or if it be continually cut, it as continually grows. Dzondi, Tieflenbach ('Nonnulla de regeneratione et trans- plantatione,' Herbip, 1822) and Wiesemann (De coalitu partium. Lips. 1824) have succeeded in transplanting the hairs with their sacs. Hairs are developed also in abnormal places, e. g. on mucous membranes, in encysted tumours, ovarian cysts, and in all these cases, even in the lungs (Mohr's case), possess sacs, root- sheaths, and an otherwise normal structure. No hairs are developed upon cicatrices of the skin. No satisfactory reason can be given for the excessive growth of the hairs, nor for their morbid universal falling out, together with their frequent reproduction in the same way; probably the principal causes are to be found in increased or diminished exudations from the vessels of the papilla and of the hair-sac, and more remotely in the state of the skin and the organism in general. In other cases vegetable productions (funffi) in the interior of the hair itself (in Herpes tonsurans, the " Teigne tondante," Mahon, ac- cording to Gruby ['Gaz. Med.,' 1844, No. 14], and Malmsten, (Miill. 'Arch.,' 1848, 1), or under the epidermis of the hair and around it (in the Porrigo decalvans of Willan according to Gruby), are concerned in the production of baldness, which then is limited {Alopecia circumscripta). The process of becoming grey is also obscure, although grief, excessive intel- lectual activity, and nervous influences are sometimes evidently concerned in it. It is not until physiology and chemistry have approached these latter processes, that we can hope for a scientific pathology and treatment of the hair. Plica polonica, which, according to Bidder (1. c), is a disease of the shaft of the hair, is said by Guensburg and Walther (Miiller's 'Archiv.,' 1844, p. 411, and 1845, p. 34), to arise from a fungus which 203 SPECIAL HISTOLOGY. is developed in the hairs (bulb, shaft), and partly destroys them; whilst Miinter (ibid., 1845, p. 42) could find no such fungus. This disease, as well as peculiar yellowish-white rings upon the human hairs, consisting of epithelial cells without nuclei (Svitzer, in 'Fror. Notizen,' 1848, No. 101), which appear to consist of an altered secretion of the sebaceous glands, are less interesting from a histological point of view, and therefore are but shortly adverted to here. For microscopic investigation, a white hair with its sac should be chosen in the first instance, subsequently coloured ones. Transverse sections may be obtained, either by shaving twice at short intervals (Henle), or by cutting hair on a glass (H. Meyer), or in a bundle between two cards (Bowman), or fixed in a cork (Harting); longitudinal sections, by slicing a finer or splitting a coarser hair. The hair-sacs may be examined, both isolated and with the hair ; their different layers may be separated by preparations, and the nuclei of the external ones may be demonstrated by acetic acid. Concerning the papilla, all that is necessary has been said above; the whole upper part of the root-sheath generally follows the hair when it is torn out, and in the macerated skin it comes out very readily with the hair; its cells may be made out without addition, or by a little acetic acid or caustic soda. The inner root-sheath is often to be found entire in torn out-hairs, and may without further prepa- ration, or by stripping off the outer sheath, be readily recognised in all its parts. Caustic soda and potass acting for a short time, make it still more distinct. The cuticle must particularly be examined with alkalies and sulphuric acid, like the hair itself. The most important details upon this point have already been given, and more may be found in Bonders (1. c). I will only add that in this case also, the apphca- tion of a high temperature (see above, in the section on the nails) saves much time. In investigating foetal hairs, in the very young state it is sufficient to tear off the epidermis, attached to which the rudiments of the hairs will be found. In older embryos fine sections of the skin must be made; or the epidermis, and the corium may be stripped off together, in which' case caustic soda is of assistance. Literature. — Eble, 'Die Lehre von den Haaren in der gesammten organischen Natur.,' 2 Bde., Wien, 1831 ; Esch- OF THE GLANDS OF THE SKIN. 203 richt, 'Ueber die Richtung der Haare am menschlichen Korper/ in Miill. 'Arch./ 1837, p. 37; V. Laer, 'De structure capill. hum. observationibus microscopicis illustr./ 'Dissert. inaug./ Traject. ad Rhenum, 1841, und 'Annelin der Chemie u. Pharmacie/ Bd. 45, No. 147 ; G. Simon, ' Zur Entwicklungs- geschichte der Haare,' Miill. 'Arch.,' 1841, p. 361 ; Krause, article 'Haut.,' in Wagners 'Handworterbuch d. Phys.,' 1844, Bd. II, p. 124 ; Kohlrausch, 'Ueber innere Wurzelscheide und Epithelium des Haares,' Miill. 'Arch.,' 1846, p. 300 ; Jasche, ' De telis epithelialibus in genere et de iis vasorum in specie,' Dorpat, 1847 ; KoUiker, ' Ueber den Bau der Haar- balge und Haare,' in the ' Mittheil d. ziirch., naturf.,' Ges., 1847, p. 177; Hessling, 'Vom Haare und seinen Scheiden in Froriep neue Notizen, 1848, No. 118 ; Langer, 'Ueber den Haar- wechsel, bei Thieren und beim Menschen,' in den ' Denkschr. d. Wien,' Akad., 1850, Bd. I. The comparative anatomy of the hairs is treated of by Heusinger in Meckel's ' Arch.,' 1822, 1 823, und 'System der Histiologiej' Erdl, in 'Abh. d. Miinch.,' Akad., Bd. Ill, ii; Gegenbaur, in 'Verhund. d. pliys. med. Gesellschaft zu Wiirzburg,' 1850 ; Steinlin, in ' Zeit- schrift, fiir rationellen Medizin,' Bd. IX. The allied horny tissues are described in the 'Dorpat. dissertations,' by Brocker, ' De texturel et formatione spinarum,' 1849 ; Hehn, ' De text, et form, barbae Balsense,' 1849 ; Schrenk, ' De formatione pennse,' 1849. IV.— OF THE GLANDS OF THE SKIN. A. OF THE SUDORIPAROUS GLANDS. §65. The sudoriparous Glands consist of a single delicate, more or less convoluted tube, which secretes the sweat. They are formed over the whole surface of the skin, with the exception of the concave side of the concha of the ear, of the external auditory meatus, the glans penis, one lamella of the prepuce, and a few other localities ; and, open upon it by numerous fine apertures. 204 SPECIAL HISTOLOGY. § 66. In every sudoriparous gland (fig. 45, fig. 78), we may distinguish, the glandular coil (fig. 78 a, fig. 75 g), or the „ . proper aland, from the Fig. 78. 4. J X J excretory duct or sudo- riparous canal (fig. 45 h, fig. 78 b). The former is a rounded or elongated corpuscle of a yellowish or transparent yellow- ish-red colour, which in general measures ^ — l'"; but on the eyelids, the integument ofthe^pem*, scrotum, nose, convex side of the concha of the ear, on the other hand, not more than ^ — U"; whilst on the areola of the nipple and in its neighbourhood, at the root of the penis, and between the scrotum and perinseum, it attains as much as i"', and in the hairy parts of the axilla reaches as much as i"' — 1"' — If in thickness, and 1 — 3'" breadth. The sudoriparous glands, in most cases, are lodged in the meshes of the pars reticularis of the corium, sometimes more superficially, sometimes deeper, surrounded by fat and loose connective tissue, together with or among hair-sacs. They occur more rarely in the subcutaneous connective tissue, or at its boundaries, as for example in the axilla, to some extent in the areola mammae, in the eyelids, penis, and scrotum, the palm of the hand and sole of the foot. In the two last-named localities, they are disposed in rows under the ridges of the cutis, and at tolerably equal distances apart ; in other places they are met with, usually in a regular manner, singly or in pairs, in each mesh of the corium, although, according to Krause, spaces of )^ — ^"' Ihie exist, where they are totally absent, or 3r-^< Fig. 78. A sudoriparous coil and its vessels, x 35 : a, glandular coil ; *, excretory duct or sweat duct j c,-, vessels of a glandular coil, according to Todd and Bowman. OF THE GLANDS OF THE SKIN. 305 occur in groups of 3 or 4 close together. In the axilla, the glands form a connected layer under the corium. According to Krause, there occur on a square inch of the skin between 400 and 600 glands on the back of the trunk, the cheeks, and the two superior segments of the lower extremitiesj 924 — 1090 on the anterior part of the trunk, on the neck, brow, the fore-arm, back of the hand and foot ; 2685 on the sole of the foot; and 2736 on the palm of the hand. The total number of the sudoriparous glands, without reckoning those of the axilla, is estimated (somewhat too highly) by Krause at 2,381,248, and their collective volume (with those of the axilla), at 39,653 cubic inches. The vessels of the sudoriparous glands are particularly well seen in those of the axilla (fig. 78) j in others, the vessels may also be seen here and there (best in the penis, where, for example, glands of 0'36"' are supplied by the most delicate ramifications of an artery of 0"06"', in their interior) ; and in successful injections of the skin, the glands appear as reddish corpuscles. Nerves have not hitherto been found in them. § 67. Intimate structure of the glandular Coil. — The sudoriparous glands, in general, consist of a single much convoluted canal (in one case, according to Krause, |"' long), twined into a coil, which retains pretty nearly the same diameter throughout its length, and terminates, either upon the surface of the coil, or in its interior, in a slightly enlarged blind extremity. In the large glands of the axilla alone, the canal is usually divided, dichotomously, into branches, which subdivide, and some- times, though rarely, anastomose ; and after giving off small csecal processes, each separate branch finally terminates in a blind extremity. The glandular canals have either thin or thick walls (fig. 79). The former (fig. 79, A) possess an external fibrous investment, consisting of indistinctly fibrous connective tissue, with scattered elongated nuclei; internally this is sharply limited, perhaps by a membrana propria, and is covered by a single, double, or multiple layer of polygonal cells of 0"005 — 0-007'", which in their chemical relations and other- wise, correspond perfectly with the deep cells of pavement-r epithelium, except that they almost invariably contain a few 206 SPECIAL HISTOLOGY. fatty granules, and still more frequently a small quantity of yellowish or brownish pigment-granules. The thick-coated sudoriparous glandular canals (fig. 79 B) Fig. 79. possess, besides the two layers just described, a middle layer of smooth muscles running longitudinally, whoSe elements are easily separable, as muscular fibre-cells of 0'015 — 0'04"' long, 0-003 — 0-005, or even 0-008'" broad, occasionally, with a few pigment-granules, and each containing a roundish elongated nucleus. Whenever the glandular tubes contain only fluid, the epithelium is a single very distinct layer of polygonal cells of 0-006 — 0-015'"; in the opposite case it can be seen only with difficulty, or not at all. With respect to the occurrence of these two forms of glandular canals, the thick muscular walls are found, especially in the large glands of the axilla, whose cells all possess muscular walls, and thence acquire a very pecuHar striated appearance. I have noticed a precisely similar structure only in the large glands of the root of the^ewi* and of the nipple, although it is true that there is occasionally a muscular development, but slighter and only partial, in the glands of the palm, whose wide canals are distinguished by the thickness of their walls, and exhibit a muscular structure dis- Fig. 79. Sweat ducts, x 350. A, one with tliin walls and a central cavity, with- out a muscular coat, from the hand : a, connective investment ; *, epithelium ; c, cavity. B, a portion of a canal without a cavity, and with a delicate muscular layer, from the scrotum i u, connective tissue ; J, muscular layer ; c, cells, which fill the glandular canal with yellow granules among their contents. OF THE GLANDS OF THE SKIN. 207 tinctly enough, though thinner than elsewhere. The same description applies to certain glands of the scrotum, and even of the back, of the labia majora, of the mons veneris, and of the neighbourhood of the anus; yet with this limitation, that often only a small part of the glandular tube, perhaps merely its csecal extremity, is provided with a muscular coat. The glands of the leg, of the penis, of the thorax (the areola excepted), of the eyelids, and the majority of those of the back and thigh, of the chest and abdomen, as well as of the two prominent segments of the upper extremity, are delicate and without muscles. The diameter of the glandular canals varies, in the smaller glands from 0-022 — 0-04'", and is about 0-03'" on the average; the thickness of the walls, 0-002 — 0-003'" ; of the epithelium, 0-006'"; of the cavity, 0-004 — 0-01'". Among the axillary glands some have canals of 0-07 — O-l'", even 0-15'", with walls 0-006'" in thickness, without the epithelium, the half of which is formed by the muscular layer ; others, and in fact the largest glands, possess canals of 0-03 — 0-06"', with walls of 0-004'"; in the areola and the genitalia, also, the dimensions of the larger glands vary, though within narrower limits. All the coils of the sudoriparous glands are penetrated by connective tissue, interspersed with fat cells, which supports the vessels and unites the separate convolutions of the tubes with one another; some of them have an external fibrous covering investing the whole coil (of common connective tissue with fusiform nuclei), which is particularly well developed in those more isolated coils which are lodged in the subcutaneous cdlular tissue [penis, axilla, &c.) §68. Secretion of the sudoriparous Glands. — All the smaller sudoriparous glands contain, as soon as any cavity is apparent in their canals, which, however, is by no means always the case, nothing but a clear, bright fluid, without any formed contents. In the axillary glands, on the other hand, the contents abound in formed particles, and appear either as a greyish, transparent, semi-fluid substance, with innumerable fine, pale granules, and often with solitary nuclei; or as a whitish-yellow, tolerably viscid matter, with a varying quantity 208 SPECIAL HISTOLOGY. of larger, opaque, colourless or yellow granules, nuclei and cells, similar to the epithelial cells above described. That these contents, which, as I have found, contain much protein and fat, differ considerably from the common sweat, which is fluid and presents no formed elements, and probably rather approximate to the sebaceous secretion of the skin, is evident, on which account we might be induced to remove the glands of the axilla from the class of sudoriparous glands, and to regard their secretion as of a peculiar kind. These glands, however, some- times afford a secretion containing but few granules, or even nothing but fluid; and among the larger axillary glands smaller ones occur, which, so far as regards their contents, exhibit many transitions, on the one hand into the large, and on the other into common small glands. If we further con- sider that, occasionally, the sudoriparous glands in other situations, as, for instance, in the areola of the nipple, contain a fluid abounding in granules, it is clear that it is unadvisable to distinguish the large axillary glands from the common kind, on account of the difference in their secretion; and the more so, indeed, because we by no means know whether the latter, under certain circumstances, may not contain granules. As respects the origin of the granular contents, they must be referred to the cells which are developed in the glandular tubes. For we frequently meet in these with cells containing the same granules, which also occur free within the glandular canals; and frequently may be said to constitute their whole con- tents. It sometimes happens, also, that in one and the same gland the ends of the glandular tubes contain nothing but cells, while the excretory duct exhibits hardly any trace of them, presenting merely granules and scattered free nuclei; and in this case we can easily see that the cells, as they pass further upwards, become broken up to a greater and greater extent, thus setting free their nuclei and the granules in their interior. These cells plainly proceed from the epithelial cells lining the canal of the sudoriparous coil; for, in the first place, the cells of the contents and the epithelium resemble one another in all respects ; and secondly, where cellular or granular contents are found in the glands themselves, the epithelium is for the most part completely absent, so that the former rests immediately OF THE GLANDS OF THE SKIN. 209 upon the muscular membrane. Now, since on the other hand, in those glands which contain only a clear fluid, the epithelium is always easily seen, and often presents many dark (even golden yellow) pigment-granules in its cells, it may perhaps be assumed, that the cells in the contents are nothing but detached epithelium, and that the secretion mainly depends upon a growth and continual casting off of the epithelial cells. [The examination of the secretion of the sudoriparous glands is neither chemically nor microscopically complete. As regards the former, the fact that the axillary glands secrete fat and a nitrogeneous substance in large quantities, appears to me interesting, since from the obvious similarity in structure between these and the other sudoriparous glands, we may perhaps draw some conclusions as to the secretion of the latter. We already know that the ordinary perspiration contains nitrogenous matters (extractive); and as Krause (1. c, p. 146) has clearly shown, fat also ; and it may be asked whether these substances do not perhaps in certain situations (e. ff. hand, foot) occur more abundantly, or under certain conditions (local, adhesive, peculiarly odorous perspiration) increase in quantity. The so-called sweat-corpuscles of Henle (1. c, pp. 915 and 939), that is, structures similar to the mucous corpuscles, I have hitherto found neither in the sweat of man nor in the smaller glands ; but I may remark that almost constantly, even in the smaller sudoriparous glands, certain canals exist which present no cavity, but are wholly filled with epithelial cells. These appeared to me always to be near the bUnd end (fig. 79, B), whilst those which are nearer the excretory duct, almost invariably exhibit a cavity 0'004 — O'l'" in diameter. I con- sider it therefore to be not impossible, that in the common sudoriparous glands, a cellular secretion is at times formed and excreted in the same manner as in the axillary glands; for from what we see in the canals of the latter, it can hardly be doubted that granules, nuclei, and perhaps also remains of cells, occur in the sweat of the axilla. Whether the sweat in different individuals and races of men present notable differences is unknown, for it is not ascertained that the different odour of the cutaneous exhalation in the European and the Negro, for instance, depends on the sweat or the material of the per- I. - 14 210 SPECIAL HISTOLOGY. spiration j nor have its pathological relations been investigated, at all events not microscopically. § 69. Sweat-Ducts. — The excretory ducts glands, the sweat-ducts, Fig. 80. or of the sudoriparous spiral-canals (figs. 45, 80), commence at the upper end of the glandular coil as simple canals, ascend with slight un- dulations vertically through the corium, and then penetrate between the papillce (never through their points), into the epidermis. Here they begin to twist, and according to the thickness of the cuticle they perform from 2 — 16 closer, or more distant spiral turns, until eventually they terminate by small, round, often funnel- shaped apertures, the so-called sweat-pores on the free surface of the epidermis. The length of the sweat- ducts depends on the situa- tion of the glands and the thickness of the skin. The commencement of the duct is invariably narrower than the canal in the coil itself, measuring 0'009 — 0"012"'; it continues narrow up to its entrance into the stratum Malpighii, where it dilates to about double the size, i. e., to 0*024 — 0-028'" (fig. 80) ; retaining this breadth, it traverses the epidermis, and terminates in an aperture of ■i^ — ^"'. In the axillary glands, the excretory duct measured in one case at the level of the sebaceous glands 0'06 — 0"09"', immediately under the epidermis 0"03"', in the epidermis itself Fig. 80. Perpendicular section through the epidermis and outer surface of the corium of the bulb of the thumb, transversely through two ridges, x 50, and treated with acetic acid : a, homy layer of the epidermis ; b, mucous layer ; c, cutis ; d, sim- ple papilla ; e, compound papilla ; /, epithelium of a sweat-duct passing into the mucous layer ; g, cavity of it in the cutis ; h, in the homy layer ; i, sweat-pore. OF THE GLANDS OF THE SKIN. 211 0"06"'. In the corium the sweat-ducts have always a distinct cavity, an external investment of connective tissue, with elon- gated nuclei (in the glands of the axilla, muscles also), at all events inferiorly, and an epithelium composed of at least two layers of polygonal, nucleated cells without pigment granules. Where the ducts enter the epidermis, they lose their investment of connective tissue, which coalesces with the outermost layer of the corium, and henceforward they are bounded by nothing but layers of cells, which in the stratum Malpighii are nucleated, but in the horny-layer are without nuclei. Chemically and morphologically they completely resemble the epidermic cells, with the sole exception that they are disposed more perpendicularly, particularly in the horny-layer. The duct has often a distinct cavity in the epidermis, at other times there is a granular streak in the place of it, which is probably either a secretion or a deposit from the secretion. The sweat-pores, whose disposition, cor- responding with that of the glands, is sometimes very regular, at others more irregular, are distinguishable, even with the naked eye, in the palm of the hand and sole of the foot. In other localities they are visible only with the aid of the microscope; occasionally the excretory ducts of two glands unite into a single canal (Krause). § 70. Development of the sudoriparous Glands. — The sudoriparous Fig. 81. glands first appear in the fifth month of embryonic life, and are originally perfectly solid, slightly flask-shaped, pro- cesses of the stratum Malpighii of the epidermis, and are very similar to the first rudiments of the hair-sacs. In the earliest condition which I have observed, the processes measured in the sole of the foot 0-03— 0-09"' in length, and O'Ol'" in breadth at the neck, at the bottom 0-018— -O-OS'", and even the very longest did not penetrate more Fig. 81. Rudiment of a sudoriparous gland of a human embryo at five months, X 350 : a, horny layer of the epidermis ; b, mucous layer j c, corium ; d, rudimentary gland as yet without any cavity and consisting of small round cells, 212 SPECIAL HISTOLOGY. than half through the cutis, which was 0"25"' thick. They were entirely composed of round cells, perfectly similar to those of the stratum Malpighii of the epidermis; besides which, each process had a delicate investment, which was continuous with the boundary of the inner surface of the epidermis. No trace of sweat-pores or ducts was visible. — At the beginning of the sixth month, the glands in the sole of the foot and palm of the hand extend as far as the middle and inner fourth of the cutis, measure at the clavate extremity 0028 — OO*"' and 0-016 — 002 in the duct which arises from them, are already slightly serpentine, and present a cavity, at all events partially, in their narrow portion ; they do not, however, penetrate the cuticle, or in any way open on the surface. It was not before the seventh month that I per- ceived, in the same situations, the first indications of the sweat-pores and ducts in the ^dermis, though as yet very indistinct, and the latter form, ing only half a spiral turn /' (fig. 82, A) ; at the same time the part of the gland which projected into the corium was more considerably developed, reached as far as the innermost portion of that structure, and at its csecal extremity was bent into a hook or even slightly convoluted, so as to afford the first indication of a glan- dular coil of about 004 to 0-06'". The canal arising from it usually presented several marked undulations and measured in total thickness 0"015 — 0"022"', with a cavity of 0-003 — 0004'", which frequently extended even to the ter- Fig. 82. A, rudiment of a sudoriparous gland 6om a seven-months' fetus, x SO. The letters a, i, , x 300 diam.: a, sarcolemma and interstitial connective tissue; b, transverse section of the muscular fibrils, with the interstitial substance. Fig. 9,1. Portion of a muscular fibre of man, treated with acetic acid, x 450 diam, : a, sarcolemma; I/, simple nucleus ; c, double nucleus, surrounded with fatty molecules. 336 SPECIAL HISTOLOGY. of Du Bois-Reymond, and above all of Bowman. According to the latter, a division of the muscular fibres into "discs" (fig. 92) Fig. 92. is quite as natural, although not so frequent, as that into fibrils, and that they may be con- sidered as columns composed of such discs, quite as correctly as bundles of fibrils. Were jj, 1^ ^ a muscular fibre completely divided in the direction of both the transverse and longitu- dinal striae, rounded, angular, minute particles would be produced, which may be termed primitive particles, or " sarcous elements." In the fibre, these elementary particles are con- nected in both directions, the same particles ,v..^iji4",v ii tbe one case constituting a "disc," and in t.*ii^v^^^ the other a segment or joint of the fibrils. The -^'.■ [The insertion of muscles without the intermediation of tendons, directly into the connective tissue of the skin and mucous membranes, is seen very beautifully in the tongue and in the facial muscles of Mammals. The former case has been well described by Dr. Salter (Todd's ' Cyclopaedia,' article ' Tongue') ; the latter may be examined with great ease in the levator labii superioris of the Rat (fig. 94 yi). Here, the muscular bundles run in the subcutaneous connective tissue, keeping a pretty even diameter until they nearly reach their insertions. They then divide into THE MUSCULAR SYSTEM. 245 § 80. The sinews, tendons, are brilliant, white or yellowish structures, composed almost entirely of connective tissue. They are sub- divided according to their figure into the rounded, cord-like, true tendons, and into membranous aponeuroses {centrum tendineum, galea, tendons of the abdominal muscles, latissimus dorsi, cucullaris, &c.) The two forms, either in their external configuration, or internal constitution, do not admit of definite distinction ; they consist of connective tissue, which is charac. terised by the parallelism of its elementary fibres, its consistence, and its poverty in elastic filaments. The elements of the connective tissue, the fibrillm, may be readily perceived, in fresh tendon, to be, as they are everywhere, extremely minute. In the cord-like tendons, they are slightly wavy in their course, all perfectly uniform in size, parallel to the long axis of the tendon, and in the recent state so closely approximated, that the demonstration of the existence of primitive fasciculi is not easy. Such fasciculi, however, do exist, having a breadth of many branches, each of which, either tapers off to a conical extremity, or divides into a number of delicate pointed pro- cesses. In either case, the ends of the muscular fibre gradually or sud- denly lose their striation, and pass directly into the irregular nucleated bands of the connective tissue. No sarcolemma can be demonstrated in the branched ends of the muscles, and the bands of the connective tis- sue are directly continuous with tlie matrix of the muscle; the change, from the one to the other, being evidenced merely by the appearance of the sarcous elements. Nothing can afford a more complete proof of the homology between the pseudo- fibrillated tissue of muscle and that of connective tissue, than what we find here. — Eds.] Fig. 94 A. Branched muscular fibres from the upper lip of the Eat : a, epidermis and aperture of a sebaceous gland j b, muscular fasciculi dividing at their extremities, the ultimate divisions becoming continuous with the irregular, more or less stellate bands of the subcutaneous areolated connective tissue ; c, " nuclei" of the latter. 246 SPECIAL HISTOLOGY. Fig. 95. 0"006 — 0"008"' and a rounded polygonal figure, as may be seen, especially in transverse sections of dried tendons, par- ticularly on the addition of alkalies. But in the natural state, they are so firmly united that they cannot he isolated. On the other hand, in true tendons, in the recent state, secondary and tertiary fasciculi are very evident (fig. 95). Delicate dissepiments, in fact, of loose connective tissue, penetrate the substance of the tendon, and by their mutual connection form a continuous system of parallel tubes, thus dividing the tendinous fibrils or primitive fasciculi into numerous larger or smaller groups. Secondary fasciculi, mostly of a polygonal, or perhaps rounded or elongated figure, and having a diameter of 003 — 0-06'", may be very readily distin- guished; and tertiary fasciculi, with polygonal contours, of O'l — 0'05"' and more in diameter, and bounded by rather stronger dissepiments; there are, also, general- ly apparent, still larger subdivisions, composed of numerous tertiary fasciculi, and which being closely united in very various numbers and groups, by a com- * men envelope of lax connective tissue, con- stitute the tendon it- self. The aponeuroses are constituted either in the same way as the true tendons, and consist of several layers of parallel, secondary fasciculi, disposed contiguously in the same plane; or, more resemble the fibrous membranes, and present primary and secondary fasciculi decussating in two or more directions (abdominal muscles, diaphragm). Fig. 95. Transverse section of a tendon of the calf, x 20 diam.: a, secondary fasciculus; b, tertiary; o, nuclear fibres not quite in transverse section, but appearing as little streaks in the former ; d, interstitial connective tissue. THE MUSCULAR SYSTEM. 247 Mne elastic fibres (the so-termed nuclear fibres) occur in the secondary fasciculi of all tendons, in various conditions of development : sometimes as a series of slender fusiform cells connected by delicate processes; sometimes as fully-formed fibres of uniform thickness, or as isolated fusiform cells. The arrangement of these elastic elements is uniform throughout, and they run at regular distances, parallel to, and among the fasciculi of connective tissue. Consequently, in the transverse section of a tendon, the dark ends of the elastic fibres are apparent, distributed, at constant distances of 0-007 — 0"008"' apart, over the whole section. But besides these stronger elastic filaments, measuring from 0*0005 — O^OOl'", there exist in most, perhaps in all tendons, extremely delicate fibrils of 0-0002 — 0'0004"', connecting the former in various directions, so that in reality there is, in every ^ gg tendon, an elastic network, pene- trating and entwining the fasci- culi of connective tissue. These fibrils may also be distinguished on a transverse section, as minute dark points, or as lines radiating from the coarser points exhibited in the section (fig. 96) ; and they are still more evident in lon- gitudinal sections, in which more especially, the whole of the fibrous system just described comes very readily into view. In such sections, also, it is evident that, in every case, in which the formative cells of which the fibres are constituted still retain a certain degree of independence, very distinct elongated nuclei exist in them. Besides these elastic fibres, the tendons, in certain situations, contain cartilage-cells {vid. infra), as well as coTaraon fat-cells, particularly in the more lax tendons, as in the tendinous fibres of the intercostal muscles, of the triangularis sterni, masseter, &c. The transversely banded aspect of the tendons, to which their glistening appearance is due, depends simply upon the numerous Fig. 96. Tendon of the tibialis posticus, Man, x 60 diam.: a, secondary fasciculi; i, thicker nuclear fibres ; c, interstitial connective tissue. 248 SPECIAL HISTOLOGY. curves of their fibrils, which correspond with each other throughout the fasciculus ; this appearance is destroyed when the tendon is forcibly stretched, and merely indicates its innate elasticity, which comes into play in the relaxed con- dition. [The primary tendinous fasciculi, according to Bonders and Moleschott, are seen in transverse sections treated with potass ; this reagent, according to them, separates the secondary fasciculi into smaller ones, each of which consists of from 5 to 10 primitive fasciculi. In moistened transverse sections of dried tendon of man and the mammalia, I can very distinctly recognise the primitive fasciculi, although they have extremely delicate outlines. The appearance thus obtained affords an indistinct image of that presented in a transverse section of muscle. Even the very fibrils are, in this way, rendered distinct, a circumstance which appears to me of the greatest importance. When a transverse, not a longitudinal section of tendon moistened with water or acetic acid is examined, there will be observed in all the secondary fasciculi, or in the primary when they can be distinguished, if not in all, yet in most cases, an extremely regular and minute punctation, nearly like that of the muscular fasciculi (fig. 90), only not quite so distinct. The apparent granules are pale, round, of the same diameter as the tendinous fibrils which are obtained in other ways, and can be explained in no other manner than as being the transverse sections of such fibrils. These facts, better than any other, contradict Eeichert's view, according to which, the tendinous tissue is composed of a homogeneous substance. {Vid. § 24, note) .] § 81. Connections of the Tendons with other parts. — The tendons are connected on the one side with the muscles, and on the other with the various parts moved by the muscles. Even by the naked eye, it may be seen, that the former connection is efiected, in the one case, in such a way that the tendon and muscle are continued into each other rectilinearly, and in the other so that the muscular fibres, with rounded extremities, join the borders and surfaces of the tendons and aponeuroses at an acute THE MUSCULAE SYSTEM. 249 Fig. 97. Pl/'ii'I angle, as in the instance of the penniform muscles. The microscopic conditions in these two cases, are widely different. In the former, the muscular fasciculi pass immediately into those of the ten- don, in such a way that no sharply defined limit exists between the two tissues, and the en- tire fasciculus of muscular fibrils is continuous with a nearly equal- sized bundle of tendinous fibrils (fig. 97). Extraordinary as it may sound, I must say, — in order to describe the impression that this sort of conjunction of muscle and tendon gives me, — that it is that of a continuous connection of the muscular and tendinous fibrils. Where the muscular fasciculi join the tendons and aponeuroses at an acute angle, we find, — in complete contrast with the condition just described, — an abrupt limit be- tween the muscle and tendon (fig. 98). For in this case, the fibres of the muscle really end, for the most part, obliquely truncated, with a slightly conical projecting terminal surface, or, more rarely, perceptibly attenuated, though always rounded, and are attached at a more or less acute angle to the surfaces of the tendons and aponeuroses, and on the borders of the former. Notwith- standing this, how- ever, the connection between the two tissues is of the most intimate kind. The extremities of the Fig. 97. A primitive fasciculus : a, from one of the internal intercostal muscles of Man, continuous into a tendinous fasciculus, b, into which it passes without any de- fined limit, A 350 diam. Fig. 98. Disposition of the muscular fibres, at their oblique insertion into the tendon of the gastrocnemius (Man), x 350 diam.: a, a portion of the tendon cut longitudinally; i, muscular fibres with slightly conical or truncated extremities, aflixed in small depressions on the inner aspect of the tendon, to the border of which the perimysium internum, c, is connected. 350 SPECIAL HISTOLOGY. primitive fasciculi are inserted into minute pits in the surface of the tendon, whilst, at the same time, the connective tissue between them, the perimysium internum, is continuous with that on the surface of the tendon. These relations are best observed in muscles which have lain a long time in spirit, or been boiled ; in which also, the sacciforni blind extremity of the sarcolemma may occasionally be clearly seen. The last- described condition occurs whenever muscular fibres and tendons meet obliquely, consequently in all semipenniform and penniform muscles ; in those, whose tendons of insertion com- mence as membranous expansions {soleus, gastrocnemius, &c.), and which arise from the surfaces of fasciae, bones, and car- tilages. Where, on the other hand, aponeuroses or tendons, with their elementary tissues, join muscles in a straight line, a real transition, for the most part, takes place between the tendinous fasciculi and muscular fibres, but not always, for even in such apparently rectilinear transition of muscles into tendons, there is frequently an oblique insertion of the former, with free extremities, though at very acute angles; in such cases, for instance, as where tendons penetrate deeply into the substance of a muscle, and there divide into separate fasciculi. From what I have hitherto observed, there are many muscles, in which all the fasciculi connected with tendons begin or terminate free, and indeed scarcely one in which this is not the case, with a greater or less number of fasciculi; whence it may be deduced, as a general rule, that the tendons have for the most part a less diameter than the muscles. Besides muscles, tendons are connected with bones, carti- lages, fibrous membranes {sclerotica, sheath of the optic nerve, tendinous fascise), ligaments, and synovial membranes (subcru- ralis, &c.) With the first-named textures, the connection is either indirect, with the intervention of the periosteum and perichondrium, into the similarly constituted elements of which, the tendinous fibres, for the most part, are continuous, or to the thickness of which they appear to add, or direct. In the latter case [tendo Achillis, tendons of the quadriceps, pectoralis major, deltoideus, latissimus dor si, ilio-psoas, glutai, &c.) the ten- dinous fasciculi rest, at an acute or right angle, on the surface of the bones, and become attached, without the intervention of the periosteum, which is Avholly wanting in these situations, to THE MUSCULAR SYSTEM. 251 all the elevations and depressions, of the surface (fig. 99). Close to the bones, the tendons frequently contain, throughout Fig. 99. a certain extent, delicate, isolated cartilage cells, which are sometimes, however, contiguous and disposed in small rows. In exceptional cases, I have also seen the tendinous fibrils, at their extremities next the bone, entirely incrusted with cal- careous salts, in the form of granules (ossified). In fibrous membranes, the tendons cease quite imperceptibly, and without any interruption of continuity {tensor fascia, biceps humeri). [In man, I must positively deny that the tendinous fasciculi are ever connected merely with the sarcolemma (Reichert). Nor could I satisfy myself that this is the case in the River- crab, in which, the tendons, it may be remarked, consist of chitine. Whilst other animals have afforded indubitable evi- Pig. 99. Insertion of the tendo Achillis into the calcaneum of a Man 60 years old, X 300 diam. A, bone with lacunae, a; canalli and fat-cells, b : B, tendon with tendinous fibrils and cartilage cells, c. 252 SPECIAL HISTOLOGY. dence of the existence of the. same conditions as iu man, the Frog, in particular, presents evidence of this fact ; in the tadpole of which, owing to the sparing development of pigment in the tail, the transition of the extremities of the muscular fibres, which are frequently divided into 3 and 5 serrations, into the same number of minute tendons, may be very distinctly seen. In the caudal muscles also, of the Cod, I noticed, very distinctly, the continuous connection of the tendons and mus- cles ; in this case, owing to the shortness of the muscles, many muscular fibres were even seen in their entire length, together with the tendinous fasciculi at each end.^] § 82. Accessory organs of the Muscles and Tendons. — A. Tlie muscular envelopes or fascia are fibrous membranes surrounding single muscles or entire groups of muscles, together vrith their tendons. They dififer in structure according to the degree in which they partake of the character of tendons and ligaments, or of simple muscular sheaths ; in the one case presenting that of tendons, and in the other of membranes composed of connective tissue and elastic fibres. In the former case they are white and glistening, and exhibit, in all respects, the struc- ture of tendons and aponeuroses ; in the latter they frequently ' [There can be no doubt that both the modes of connection between muscles and their tendons, described above, exist. Is it not possible, that the gradual transition or the sharp line of demarcation between the muscle and its tendon, may have some connection v?ith the age and completeness of the particular bundle examined ? In the Frog, we have noticed that among neighbouring bundles, some exhibit transitions between the proper muscular tissue and the tendon, while others have the former very sharply defined ; and the examination of the insertion of the triceps extensor eubiii of a seven-months' fcetus has afforded us the most evident transitions from tendon into muscle, although the insertion of the bundles is here very oblique (fig. 106 A, 5). The best way of expressing the mode of connection of muscles with their tendons, perhaps, would be to say, that the matrix of the muscle and the matrix of the connective tissue, into which it is inserted (whether in the form of tendon or otherwise, are invariably continuous ; the appearance of continuity or of discon- tinuity of the two tissues, arising solely from the sudden or gradual cessation of the deposit of the sarcous elements at their point of junction. The nature of the corpuscles which are to be found at the junction of tendons with bones and cartilages — Professor Kolliker's "cartilage corpuscles," — has been adverted to iu the note at p. 81. — Eds.] THE MUSCULAR SYSTEM. 253 contain a larger quantity of fine elastic fibres in their con- nective tissue, and in some places may even assume the structure and dull-yellow aspect of the elastic membranes {vid. fig. 49), and contain a close elastic network of the strongest kind. The fasci(B are always of the tendinous character, where for some mechanical purpose a tough unyielding structure is requisite. They are of this kind, therefore : 1. At their origin from bones. 2. Where muscles arise from them; and they are of the nature of aponeuroses. 3. Where tendons radiate into them and they themselves act as terminal tendons. 4. Where thickened por- tions of them supply the place of ligaments. On the other hand they are more or less elastic, where they constitute a firm envelope to the muscles, but, at the same time, one which does not impede their changes in form. This is their character, especially in the middle of the limbs. [The membrance interosse mencement will be seen extending from one side of an Haversian canal. One side of a space may be becoming the seat of a new system, while the opposite is under- going further enlargement. — Eds.] THE OSSEOUS SYSTEM. 295 The lamelltB of the . Haversian canals (fig. 113 c, 113 b) surround those canals concentrically, in greater or less num- ber. They constitute, as it were, the walls of the canal, and are intimately united to each other, much in the same way that the laminae of the walls of the larger vessels are con- tinuous with each other. The number of lamellae belonging to a canal, and the collective thickness of the system formed by them, varies not inconsidera- bly, and bears no constant re- lation to the size of the canal, as is the case to some extent in the vessels ; small canals, there- fore, are not unfrequently sur- rounded by numerous lameUse, and larger ones by but few.^ In general, it may be said, that the largest canals have thin walls, those of a middle size thick ones,^and the most minute, again walls of little thickness. The thinnest walls I have com- monly noticed, measure 0008 — 0-02'", and the thickest 008 — 0*1"'. The thickness of the lameUse varies between 0002 and 0005"', being on the average 0-003 to 0004'"; in number, there are usually from eight to fifteen ; sometimes. Fig. 112. Segment of a transverse section of a human metacarpal bone, treated with oil of turpentine, x 90 diam.: a, external surface of the bone, with the exterior fundamental lamellae; b, internal surface towards the medullary cavity, with the inner lamellae; e, Haversian canals in transverse section with their lamellar systems ; d, interstitial lamellae ; e, lacunae and processes. ' [The "interstitial laminae" are the remains of Haversian systems, the larger parts of which have been removed by absorption to form new spaces. The irregular outline of the outermost of the laminae of a Haversian canal (see fig. 113) results from its being the first deposition within the pre-formed irregular Haversian space. (Tomes and De Morgan, 1. c.,p. 5.)— Eds.] 396 SPECIAL HISTOLOGY. however, no more than four or G.ve, and occasionally as many as from eighteen to twenty-two. The lamellae of the Haversian Fig. 113. canals, together vrith their canals, extend to the internal and external surfaces of the diaphyses, where they are connected with the general lamellee ahove men- tioned — the funda- mental lamella (fig. 111). The latter con- stitute an external and an internal layer, and penetrate also into the substance of the diaphysis, where they are in- terposed between the separate lamellar sys- tems and the me- dullary canals. The two former layers, or the external and in- ternal fundamental lamellpe, are parallel to the external and internal surfaces of the bone, and vary in thickness appa- rently without any definite rule, from 0"02"' to 0"3"', or even 0*4'". The latter, or interstitial fundamental lamell(B, are seen most clearly where the superficial fundamental laminse are developed, in partial connection and parallel with which they extend from without inwards, and from within outwards, some distance into the substance of the diaphyses, where they are interposed in masses, varying in thickness from 0'03 to 0'12"', Fig. 113. Portion of a transverse section of the shaft of the humerus, x 350 diam., treated with oil of turpentine : a. Haversian canals ; b, their lamellar systems, each lamella presenting a more transparent and more opaque portion, with radiating strise in the latter ; c, darker lines, which probably indicate greater intermissions in the deposition of the osseous substance ; d, lacuna: without visible rays. From a preparation by Dr. H. Miiller. THE OSSEOUS SYSTEM. 29/ between the other lamellae (fig. 112, d). lu the interior of the compact substance, on the other hand, in man, the Haversian systems are so closely crowded, that there can be no qnestion as to the non-existence of lamellar groups between them, and it is evident that those lamellae, which in a transverse section appear in man to be parallel with the surface, almost all belong to horizontal canals j and it is but rarely that distinct inter- stitial masses are seen, as is usually the case in other mam- malia. The thickness of the separate lamellae just described is much the same as that of the lamellae of the Haversian canals, and their number varies from 10 to 100. We have hitherto considered only the diaphyses of the long bones. In their apophyses, the thin cortical layer of compact substance naturally presents only a few systems of Haversian canals, which, however, are constituted as elsewhere. The exterior fundamental lamellae are few in number, and inter- nally, owing to the existence there of the spongy substance, they are wholly wanting. In the latter substance, the very few Haversian canals present lamellar systems as usual, except that they are thin, and the remainder, according to the con- dition of the osseous network, consists of a lamellated and fibrous tissue, which in general follows the contour of the medullary spaces and cells. The flat and short bones present a similar arrangement internally, whilst the cortical substance of these bones differs from that of the cylindrical, only in the circumstance, that the fundamental lamellae, in the flat bones, form layers parallel with both surfaces of the bone. The thickness of the fundamental lamellae in the cranial bones (parietal), is sometimes the same in both aspects, and varies from 0'08"' to 0'16"', sometimes they are wanting in vascular situations, and in places, wholly so, on the external aspect of the bone, in which case the Haversian lamellae reach almost to the surface. With respect to the intimate structure of the osseous lamellae, which is best studied in transverse sections, dried, polished, and sufficiently thin, there is usually evident, besides the bone- cells and canaliculi, in the generally not very distinct lamellae, an extremely fine though very distinct punctated appearance, so that the whole osseous tissue appears granular, and to be composed as it were of separate, densely crowded, pale granules. 298 SPECIAL HISTOLOGY. measuriug O-OOO^"' (fig. 114). If water or weak syrup, or albumen, be applied to a slice of bone, it assumes a condition Fig. 114. probably similar to that which it pos- sesses during life. j^;^pwf»*«^.Uo'^'t'*=M!jSE^^^' i'^„--i The lamellae, for the '■v/.t^"",-jfetoto kag ^Mfc^> ^f-^ "lost part (both in iJHlaBMw»*'^ihJi thB«,a>ffl ^ /^- '.. Tr^P^ < transverse and per- ^SMfe^aj^M^gik4^^^i^^^™*^«^^' pendicular sections), '-i. . ^*^a!SSr«g9^^g§g*^«^ larly from the surfaces, ^ 4^ - ' a great number of very j» ' <— ♦* nne canals, measur- J^ 4^ »»i "^ ^jZ '^ 0-0005 — 0-0008'" #fc* ^\^^'^ ^ I \ T^-wJ in diameter — the bone- ^ , "^77 ^ * j " ing liameter — the bone- w j j» '. ' canaliculi above-men- 1* v *''^ '^^'^ j^ ^ "' * tioned (figs. 115, 116, , -* «-. ^^ and 117). The lacunse **^^n ^ * *''*' * are equally numerous ^ ^ — • 1^ '^ in both of the lamel- ■*- 2"'*' *"'*■'' J 7 ^ lar systems before de- ^^* i» It. '*H. f ff scribed, and are placed so close together, that, according to Harting (1. c, p. 78), from 709 <, 'T^Jik ^ '\^\^ ^ W<^ to 1120, or, on the ' Sfc. •* ** w '\ '^ \ average, 910 of them * ^ *" *"* ''^^ , ' in '•■ •. SB* • occur within the space ,<* .*** ■''^^[f '^ -^ of a square millimeter. ^ *^ ji?^ ^ They lie for the most ^*„ iv"^ part within the lamellae, *"" » *K -Ji* ^^ but also between them, * and are invariably placed with their broad sides parallel with the surfaces of the lamellae. The canaliculi proceeding from them are much branched, and penetrate the osseous substance in all Fig. 115. From a transverse section of the shaft of the humerus, x 300 diam.: a, Haversian canals ; d, lacunse with their canals, in the Haversiah lamellae ; c, lacunse of the interstitial lamellae ; d, lacunae with unilateral canaliculi proceeding to the surface of the Haversian system. 302 SPECIAL HISTOLOGY. Fig. 116. directions, their course being irregular, and often actually curved. They proceed principally, however, in the first place, from both surfaces of the lacunse straight through the lamellae ; and secondly, parallel with the Haversian canals, from the two poles of the lacunse. It is only in certain limited spots that these canaliculi present cacal terminations j everywhere else some of them anastomose in the most various ways with the canaliculi of the neighbouring lacunse, whilst others commu- nicate with the vascular canals, the medullary cavities, and the medullary spaces or cancelli of the spongy substance, or open on the surface of the bone. 7%e entire osseous substance, there- fore, is penetrated by a connected system of cavities and canaliculi, by means of which the nu- tritive juice secreted by the vessels is conveyed into its densest tissue. The lacunse and canaliculi do not exhibit precisely the same conditions in every part of the bones. In the lamellar systems of the Haversian canals, as seen in a transverse section, the elongated lacunse, by reason of their curvature, lie as it were concentric to the canal, and their excessively nume- rous pores or canaliculi ne- cessarUyproduce a very close striation radiating from the vascular canal (fig. 115). The lacunse are sometimes extremely numerous, some- times more scanty; in the former case they are, for the most part, arranged in tolerably regular alternation, or one behind the other in the direction of ,V1 *J+ h\*t. M t * i Fig. 116. Section parallel with the surface from the shaft of a hnma.n femur, X 100 diatu.: a, vascular canals ; 6, lacunae seen from the side, belonging to the lamellae of these canals ; o, lacunse viewed on the flat side, in lamells which are cut horizontally. THE OSSEOUS SYSTEM. 303 the radius of the lamellar system ; but they are also frequently disposed very irregularly, either crowded together (vide the lower part of fig. 115), or separated by wider interspaces. In horizontal and longitudinal sections of Haversian canals (fig. 116), when the section has passed through the middle of a canal, the lacunae appear narrow and elongated, and disposed in rows one behind the other, and in numerous layers, parallel with the canal; and also furnished with numerous canaliculi, which proceed for the most part directly inwards and outwards (consequently transversely through the lamellae), but partly in a direction parallel with the long axis of the canal. If the section strike the surface of a system, the superficial lacunae come into view, presenting very elegant forms, rounded or oval (figs. 115 d, and 117), surrounded in an irregular manner by a Fig. 117. complete tuft of canaliculi, which look directly towards the observer, and consequently appear more or less shortened, and by a smaller number of other canaliculi distributed on the surface of the lamellae. Occasionally, even in the thinnest parts of a section, there occurs a tuft of canaliculi, cut across transversely, and without the lacuna to which they belong, whence these portions of bone exhibit a sievelike aspect. All Kg. 117. Lacunae viewed on the flat side, Trith the canaliculi, from the parietal hone, X 450 diam. The spots on the lacunse or between them belong to canaliculi, which are cut across, or are the openings of canaliculi into the lacunae ; aaa, groups of transverse sections of canaliculi, each gioup belonging to a lacuna which lias been destroyed in the making of the section. 304 SPECIAL HISTOLOGY. the canaliculi arising from the inner aspect of the innermost lacunae of an Haversian system, proceed towards the canal, with which they, hy this means, communicate, as may be clearly seen in thin, perpendicular, and transverse sections of bones filled with air, and in the walls of medullary canals laid open longitudinally. From the borders and external aspect of the same lacunae other canaliculi are given off, which perhaps occasionally terminate in blind extremities, but for the most part communicate with those of the neighbouring, and particu- larly of the outer lacunae. The succeeding rows of lacunae are all mutually connected in a similar way, and thus the network of canaliculi and lacunae extends to the outermost lamellae of the system, where the lacunae either communicate with those of the contiguous systems or of the interstitial lamellae, or terminate independently, in which latter case (fig. 115 e?) all the canaliculi, or at least most, and the longest of them, proceed inwards, that is to say, towards the vascular canal, from which they derive their nutritive fluid. In the interstitial osseous substance between the Haversian systems, when it exists in small quantity, the few lacunae, frequently not more than from 1 to 3 in number, are disposed more irregularly, and also present a rounded form (fig. 115 e); when the interstitial substance is more abundant, and distinctly lamellar, the lacunae are also disposed more regularly, with their sides parallel to those of the lamellae. The canaliculi of these lacunae, in like manner, communicate with each other, and with those of the neighbouring systems. In the outer and inner fundamental lamellae, lastly, the lacunae are all placed with their surfaces parallel with those of the lamellae, and con- sequently looking, for the most part, inwards and outwards, or towards the centre and periphery of the bone. In transverse sections they precisely resemble those of the Haversian systems, only that they are but little or not at all curved, except in the smallest cylindrical bones. In longitudinal sections, whether perpendicular or parallel to the surface, they present the con- ditions above described, with this limitation, however, that a larger number of lacunae, of course, are seen in the same space in the latter case than in the former, and also that the sieve- like aspect described above is more frequently observed, giving the bone considerable resemblance to certain sections of THE OSSEOUS SYSTEM. 305 teeth (fig. 117). The canaliculi of these lamellse communicate, in part as usual with each other, in part open on the ex- ternal and internal surfaces of the bone (fig. 118). At the points of insertion of tendons and ligaments into the bones, 8" the canaliculi of the outer- ^^^"TitSSF^' " ,'*■ 1 ^'~« most lacunae probably ter- ^V^**"*.'^'' 'i."^**?**" ^ " mmate in blind extremities ; ^ ' %^ ~ v , * "^^^ a condition which obtains ^i, ' '^ AAr> * 'SJ. - 1 in every case, in those parts ^^ » ^^ ^^ of bones which are covered ^^, ' 4-*?*^ ^a^— with cartilage (articular ends, p^ K "^ '"^, ' ^^ ribs, surfaces of the bodies i-'jS- , 1ej&.t5 .»•-«• of the vertebrae, &c.) In the rods, fibres, and plates of the spongy substance, the lacunae are disposed in every possible direction, but, for the most part, with their long axis parallel to that of the fibres, bars, &c,, and with their flat surfaces directed towards the cancelli. They anasto- mose also, in these situations, by means of their canaliculi ; and the most superficial lacunae open freely into the cancelli. [The size and shape of the lacunae, in man, upon the whole, vary but little. By far the greater number are melon-seed shaped or lenticular, some, more fusiform or sphericaL In sections of bone well filled with air, in which alone I have made my measurements, I find their average length to be O'Ol — 0-014'", frequently under and above that size, or from 0"006 to 0016'", rarely 0-03 or even 0-034'" (cranial bones, lower jaw). The breadth, measured in horizontal sections, is O'OOS — 0-006'"; in transverse, it is usually somewhat greater, or as much as 0"008"', or even O'Ol'", because the limits between the canaliculi and lacunae cannot always be accurately defined. Their thickness or depth, lastly, in the smallest lacunae, is 0-003 — 0-004'", and in the larger 0002 — 0004'". The diameter of the spherical lacunae is 0-006 — 0-008'". The canaliculi are, on the average, 0*008 — 0-016'" long, seldom less Fig. 118. Portion of the Surface of the tibia of the calf viewed on the external aspect, X 350 diam. The nntnerous points are the openings of the canaliculi ; the dark, larger, indistinct spots indicate the lacunae to which these canaliculi helong, appearing from a greater depth. I. 20 306 SPECIAL HISTOLOGY. or more, up to 0'02"' and 0024'"; in diameter they measure 0-0004'" ; at the finest extremities, 0-0005— 0-0008"'; on the average, 00008 — 0-001'", at their origin from the lacuna. Their true distance apart, in horizontal sections, in which they appear as holes, is 00008 — 0-002'"; in transverse sections, in which they produce the radiating striae, in consequence of their being viewed in several planes, they appear to be somewhat closer together, or at distances varying from 00008'" — 0-0012'". The circumference of a lacuna, together with the radiating canaliculi belonging to it, forms an imperfect sphere, having a diameter of from 0-02"' to 0-034'"; with reference to which, however, it must not be forgotten, that individual canaKculi transgress the usual length of the others, as I have, in fact, measured anastomoses between two lacunae of the length of 004— 0-045'". The contents of the lacuna, according to the later investi- gations of Bonders, Virchow, and myself, appear very closely to resemble those of the cells of cartilage during life; that is to say, they are a clear, probably viscid fluid, with a nucleus. If bone- cartilage be boiled in water or caustic soda for 1 or 2 minutes, these nuclei often show themselves very distinctly; or opaque corpuscles make their appearance, which must be regarded as the contracted cell-contents including the nucleus, and analo- gous to the corpuscles in cartilage. A peculiar phenomenon is seen to occur, when bone is macerated in hydrochloric acid, which was first noticed by Virchow in a diseased, and afterwards J., jjg in healthy bone, and by myself in the J.,^^^ cementum of the horse^s tooth, — the ~\ lacunae become isolated, having longer ^ \ or shorter processes, and appear like ^L \ independent structures, or a sort of -^C \ stellate cells. This phenomenon seems ,.^^ '~ to depend simply upon the circumstance, V'T'^T^^y/' that the tissue immediately surround- V. ^^^ ""* ing the lacunae offers more resistance ^^ to the action of the acid than it does elsewhere. In the cementum of the horse's tooth, cells also enclosing the lacunae, and even Haversian canals, may Fig. 119. A bone spicule from an apophysis, with distinct lacunae and nuclei. Boiled in vrater, and magnified 350 diameters. THE OSSEOUS SYSTEM. 307 be isolated, — the best proof, that everything which thus presents itself in an isolated form, is not necessarily a mor- phological unity.'] § 93. The Periosteum. — Among the soft tissues appertaining to bone, the periosteum is one of the most important. It is a more or less transparent, slightly glistening or whitish yellow, vascular, extensible membrane, investing a great part of the surface of bones, and contributing most importantly to their nutrition, by the numerous vessels which it sends into their substance. ' [It is of very great importance in histology to keep in mind the caution ex- pressed in the last paragraph of the text (see below, note § 101), which applies as well to optical as to chemical distinctness. Tomes and De Morgan assert that both the lacuna and canaliculi have parietes, which are manifested by appearances similar to those observed in the dentinal tubes. They sometimes found the tacuna and canaliculi filled up to a great extent with solid matter, so as to leave only a small space in the centre. An important modification of the lacuncs is described and figured by these authors (1. c, p. 8) in the circumferential laminae. Elongated tubes pass, in bundles or singly, more or less obliquely from the surface towards the interior of the bone. When long, they are sometimes bent once or twice at a sharp angle. They have parietes, and are connected laterally with the canaliculi. They occur irregularly in the cir- cumferential laminae, and in these only. [Similar tubes exist in the cementum of the Teeth.] We can confirm Messrs. Tomes and De Morgan's statement that the nuclei may be found without difficulty in recent bone, and they may always be brought out with great distinctness by the action of dilute hydrochloric or strong acetic acid. This is especially the case in young bone. In old bone we have frequently been unable to discover them. Tomes and De Morgan, however, state that the nuclei are visible in sections of a fossil bone (supposed of a Fterodactyle) in their possession. Another peculiar condition of the " lacunal cells," described by these authors, is their ossification. They found the light and spongy bones of old people to yield, if broken, a white powder, which was composed of large cells detached or united into masses. They are spherical, and contain a dark granular nucleus, which is surrounded by a thick transparent wall. Similar cells may be found adherent to the walls of the Haversian canals and caneelli ; and in this case their nuclei have assumed the form of lacuna, and the canaliculi of adjacent lacuna advance into them. Similar cells may be found in most preparations of adult bone (1. c, p. 12). We must confess that we doubt the assumption of a lacunal form by the "nucleus" in these cases. We have repeatedly examined these bodies, but if the nucleus was visible at all, we found it unchanged, and often adhering to one side of the lacuna. Again, it ie questionable whether they may not rather be compared to the globules of dentine than to cells. — Eds.] 308 SPECIAL HISTOLOGY. The periosteum is not, everywhere, constituted alike. Opaque, thick, and for the most part with the glistening aspect of tendinous structures where it is covered only by the skin, or is connected with fibrous parts, such as ligaments, tendons, /ascite, and the dura mater cerebri, it is, on the other hand, thin and transparent in situations where muscular fibres arise directly from it without the intervention of tendon, and also on the diaphyses, where the muscles merely rest upon the bone, as on the external surface of the cranium {pericranium), in the vertebral canal, and in the orbit {periorbita). "Where mucous membrane rests upon bone, the periosteum is, in most cases, very intimately united to it by the submucous connective tissue, so that the two cannot be separated, and constitute a single membrane, which, as in the palate, alveolar processes, nares, &c. is of greater, or, as in the maxillary sinus, tympanum, ethmoid cells, &c. of less thickness. The connection of the periosteum with the bone itself is either more lax, consisting in simple apposition, and by more delicate vessels which penetrate the bone, or more intimate, taking place by means of larger vessels and nerves, and by numerous tendinous filaments. The former mode of connection is found especially where the periosteum is thin, and the osseous substance more compact, as in the diaphyses, on the inner and outer surfaces, and in the sinuses of the cranium ; the latter, where the periosteum is thicker, and the compact substance thinner, as, for instance, in the apophyses, in the short bones, palate, and at the basis of the cranium. With respect to the intimate structure of the periosteum, it will be found to present, almost universally, excepting where muscles arise directly from it, two layers, which, although closely connected, differ, more or less distinctly, in their struc- ture. The outer layer is composed chiefly of connective tissue, with occasional fat-cells, and is the principal seat of the true periosteal vessels and nerves, whilst in the inner layer, elastic fibres, commonly of the finer sort, constitute continuous, and often, very thick networks — true elastic membranes — super- imposed one upon another, the connective tissue forming the less important element. Nerves and vessels occur in this layer also, but they do little more than merely pass through it, being destined for the bone itself. THE OSSEOUS SYSTEM. 309 [The parts of the surface of bones unprovided with periosteum are: 1. The articular extremities covered with cartilage, and all other places where the bone is covered with cartilage or fibro-cartilage. 2. Where ligaments and tendons are attached to the borders and surfaces of bones at a certain angle, as, for instance, at the insertions of the ligamentaflava, intervertebralia, iliosacra, interossea, teres ossis femoris, patellm, &c. of the tendons of the deltoid, coracobrachialis, popliteus, iliopsoas, triceps suree, quadriceps femoris, glutmi, &c. In all these situations, the tendons, ligaments, and cartilages, are attached directly to the bone, as has been already in part described, and not a trace of periosteum can be detected.] § 93. Marrow of the Bones. — Almost all the larger cavities in the bones are occupied by a soft, transparent, yellowish or reddish, highly vascular substance, the Marrow [medulla ossium). In the cylindrical bones, this substance is found in the medullary canal, and in the cancelli of the apophyses, whilst it is wanting in the compact substance, unless it be in the larger canals; the same is the case in the flat and short bones, the cancelli of which are filled with marrow ; but the diploe of the flat cranial bones, besides the marrow, also contains large veins, of which more will be said afterwards. In accordance with what has been remarked, these venous spaces, the canales nutritii, Haversian canals, and the above-described nerve-canals and air- cavities of the bones, contain no marrow. The marrow appears in two forms, one yellow, the other red. The former, as a semifluid substance, occurs principally in the long bones ; and according to Berzelius, consists, in the humerus of the Ox, of 96'0 fat, 1"0 connective tissue and ves- sels, and 3'0 fluid with extractive matter, such as is found in muscle ; whilst the latter occurs in the apophyses, flat and short bones, above all in the bodies of the vertebrce, the basis cranii, the sternum, &c., and is distinguished not only by its reddish or red colour and less consistence, but also by its chemical composition ; for, according to Berzelius, this substance, in the diploe, contains 75 '0 water, 25*0 solid matters, such as albumen, fibrin, extractive matter, and salts, similar to those of muscle, and merely traces of fat. With respect to its structure, it 310 SPECIAL HISTOLOGY. presents, besides vessels and nerves, connective tissue, fat-cells, free fat, a fluid, together with, lastly, peculiar minute cells, marrow-cells. Connective tissue and fat are universally pre- sent, though in very various quantities. The former, on the surface of the larger medullary masses of the diaphyses, is of rather firmer consistence, but cannot properly be described as a medullary membrane {endosteum, periosteum internum), because it does not admit of being separated as a continuous structure. In the interior of the marrow in the spongy bones, scarcely any connective tissue can be detected except in the larger masses of it, whilst in the diaphyses, this tissue can be readily demonstrated as a very lax and delicate, areolated structure, containing the fat and supporting the vessels and nerves. Its elements correspond with those of the lax con- nective tissue {vid. § 24) ; although, as far as I have seen, it does not contain any elastic filaments. Fat-cells of O'Ol 6 — 0'032"', not unfrequently with a distinct nucleus, occur in large quantities in the yellow, more dense marrow, quite as abundantly as in the panniculus adiposus, but for the most part not aggregated into distinct lobules. In the reddish marrow, when expressed, they are more rare; and in the red pulp of the bodies of the vertebrae and of the flat cranial bones, they occur only in very minute, scanty accumulations, or altogether isolated, to which circumstance, according to Ber- zelius, is owing the small quantity of fat in the diploe. In dropsical marrow these cells are frequently only ^' ' g half filled with fat, or with but one or more ' ^ globules, containing, besides, a large quantity of :.' <» serum ; and in hypersemia of the bones, they appear occasionally to be diminished in size, and occasionally elongated and fusiform. Free fat-globules, and a clear or yellowish fluid, are often met with in the softer kinds of marrow, and frequently in considerable quantity. That the former have not been set free from cells, in the preparation of the specimen may be satisfactorily shown, but it must remain uncertain whether or not they are to be referred to cells that have ceased to exist. Lastly, there occur, together with some Fig. 120. Two fat-cells from the marrow of the human /ef»«r ; a, nucleus j J, cell- membrane ; c, oil ; x 350 diam. THE OSSEOUS SYSTEM. 311 fluid, in all the red, or even only reddish marrow {never in the yellow), minute roundish, nucleated cells, exactly like those of the young medulla {vid. infra, fig. 132). These medulla-cells correspond in every particular with those, which Hasse and I ('Zeitsch. f. ration. Medicin,' Bd. V) found in the hyper- semiated red marrow of the articular extremities of the cylindrical bones, but nevertheless normally exist in the vertebrce, the true cranial bones, in the sternum, and in the ribs, whilst they are wanting in the long and short bones of the extremities, and in the scapula and os innominatum, occurring apparently in variable number in the bones of the face. §94. Connections of the Bones. — A. synarthrosis, connection without articulation. 1. By suture. In this mode of connection, the bones are united by an extremely thin, membranous, whitish streak, to which authors have incorrectly given the name of sutural car- tilage. It is composed merely of connective tissue, which, like that of the ligaments, extends, in short, parallel fasciculi, from the border of one bone to that of the other, and is characterised solely by the presence of numerous, short, unequal-sized, usually elongated nuclei. This sutural ligament, as it may be termed, is very evident as long as the cranial bones are still growing, at the same time, that it is softer and differently constituted {vide infra). As the growth of the cranium ap- proaches its completion, this tissue gradually disappears, be- comes firmer, and, in old age, seems, in many places, especially on the inner part of the sutures, and even before their complete obliteration, to be entirely removed. 2. Connection by ligament, syndesmosis, is eS'ected by means oi fibrous and elastic ligaments. The fibrous ligaments, consti- tuting the majority of the ligaments, are white and glistening^ corresponding in their structure, partly with the aponeuroses and ligaments of the muscles, and partly with the true tendons. Elastic ligaments (fig. 121), are, the ligamenta flava, between the arches of the vertebrae, and tbe Ugamentum nucha, which however, is not nearly so well developed in man, as in some others of the Mammalia. The ligamenta flava are vellowish 312 SPECIAL HISTOLOGY. highly elastic, strong ligaments, the elastic elements of which, in the form of roundish polygonal fibres, 0-0015 — 0004'" thick, united into a dense network, run parallel with the long axis of the vertebral column, and give the longitudinal, fibrillar aspect to the liga- ments. Between these fibres, which are not collected either into fasciculi or lamellce, but are continuously con- nected throughout the en- tire thickness of each yellow ligament, there is interposed some connective tissue, upon / the whole in small quantity,/ but demonstrable in every preparation, and occurring in the form of lax undu- lating fasciculi, which are arranged parallel with the principal direction of the elastic fibres. According to Todd and Bowman (p. 72), the stylorhyoid, and internal lateral ligament of the lower jaw, are, also, chiefly com- posed of strong elastic fibres. 3. By cartilage, synchon- drosis. This mode of con- nection is effected either by cartilage alone, or associated with fibro-cartilaginous and fibrous tissue. The former condition is observed in the adult, only between the ribs and sternum, where, however, properly speaking, a true synchondrosis exists only in the case of the first rib, the rest, from the second to the seventh, being connected with the sternum at the anterior Fig. 121. A, transverse section through a portion of the ligamentum nucTuR of the Ox, X 330 diam., and treated with soda; a, connective tissue, apparently homoge- neous; I, transverse section of the elastic fibres (0'004 — 0-01'" in diameter). B, elastic fibres ; a, from a human lig. subflavum, together with some connective tissue, b, between them ; x 450 diam/ THE OSSEOUS SYSTEM. 313 extremity by articulations; whilst the false ribs are either free at the extremity^ or are incurved one beneath the other. In the symphysis pubis, sacro-iliac synchondrosis, and the junctions of the bodies of the vertebrce, the surfaces of- the bones are covered immediately by a layer of true cartilage, which, in the two former situations, is directly connected with the opposite layer, and in the latter by means of a fibro-cartilaginous tissue, and is externally encircled by fibro- cartilaginous, and fibrous, concentric layers. Tn the two former of these instances, there is, not unfrequently, a cavity in the interior of the connecting substance, so that the sacro-iliac synchondrosis, in particular, may also be regarded as a sort of articulation (Zaglas). [The intervertebral ligaments, or ligamentous discs, of the bodies of the vertebrae, consist, 1, of exterior concentric layers of fibro-cartilage, and whitish connective tissue; 3, of a central, principally fibro-cartilaginous substance; and, 3, of two cartilaginous layers applied immediately upon the bones. The concentric lamelUB consist of alternate layers of con- nective tissue and of fibro-cartilage, which latter, even in fresh transverse sections, may be recognised as dull yellow streaks, which become hard and.:.transparent in water. The fibro-cartilage, on microscopic examination, presents minute, elongated cartilage cells, disposed serially in a fibrous tissue, difiering from connective tissue in its greater rigidity, the absence of distinct fibrils, its great resistance to alkalies and acetic acid, and the total absence of elastic fibres. The whitish layers of the outer laminae, although their fibrils are rather more rigid than those of the common liga- ments and tendons, are less easily separated, and present but few fusiform cells, and frequently no elastic fibres what- ever among them, must nevertheless, at present, be regarded as composed of connective tissue. These laminse are from i to I'" and more in thickness, and form entire circles or segments of such, which, alternating with the somewhat thinner, and also frequently incomplete, rings of fibro-carti- lage, with which they are closely connected, together with the latter constitute the larger half of the intervertebral ligaments. The general direction of the fibres of both sets of laminse is 314 SPECIAL HISTOLOGY. from above to below. They are, however, invariably oblique, so that those of the different layers cross each other. Besides which, it must be remarked, that the individual layers themselves also exhibit a more or less distinctly foliated structure, constituted in such a manner that the fine lamellae, in the portions composed of connective tissue, observe the same direction as the layers themselves, whilst in the fibro-cartilaginous portions they are disposed more in the direction of the radius of the ligamentous disc. The softer central substance of the intervertebral liga- ments, or the gelatinous nucleus of authors, does not differ, essentially, from the portions above described; for, even in this situation, layers of connective tissue occur, although they gradually diminish in proportion to the fibro-cartilage, and are less distinctly defined. The nearer we approach the centre, the less evident is any trace of an alternation of different layers, and of a concentric arrangement of them ; the whole becomes transparent, soft, and, finally, almost homogeneous. The microscope shows the predominance of fibro-cartilage, with large cells (0-012 — 0"024"'), frequently one within the other (fig. 123) ; the uniformly thickened walls of which, composed of J.; J22. concentric layers, often enclose merely a minute cavity, with a shrunken nucleus ; and besides i these, smaller cells fre- quently in process of dis- solution, isolated or ag- gregated together ; and, lastly, an indistinctly fibrous or granular matrix, not un- frequently observed in a state of disintegration, and a con- siderable quantity of fluid contained in larger or smaller areolar spaces in it. The more central portions of this fibrous substance gradually pass into a thin, hard, y el- Fig. 122. Cells from the gelatinous nucleus of the %. interverteiralia : 1, large parent cell, a, with a septum derived from two secondary cells of the first generation, and five secondary cells, *, of the second generation ; with concentrically thickened walls and shrunken nuclei, c, in the small cell cavities : 2, parent cells, u, with two secondary cells, separated by a delicate septum, *, and which, with uniformly thickened walla, contain a minute cavity and shrunken nucleus, k. THE OSSEOUS SYSTEM. 315 lowish lamella of true cartilage, with thickened cells, not unfrequently heset with calcareous particles, which adheres to the bone not unlike an articular cartilage, though less firmly. More externally we find a cartilaginous substance, in the form of isolated minute, discoid, plates or particles, which appear to be in more immediate connection with the fibro-cartilaginous portions, and between these a connective tissue, with scattered cartilage-cells, as in the insertions of the tendons into the bones {vide § 81). The more exterior portions of the surfaces of the bodies of the vertebrae, corresponding to these parts of the discoid-ligaments, are, in contradistinction to the more internal portions, as it were porous, after the removal of the ligamentous layer ; the medullary cavities or cancelli then being exposed. The pores or cancelli are closed only by the carti- laginous substance of the disc, whilst the fibrous tissue, with its vertical fibres, is firmly connected with the interspaces between them. Between the sacrum and coccyx, and the individual coccy- geal vertebrae, are interposed the so-called false inter-vertebral ligaments, consisting of a more uniform fibrous substance, without any gelatinous nucleus. The separate bones of the sacrum, at an early period, have true intervertebral ligaments between them, which afterwards become ossified from without to within, but in such a way, nevertheless, that even in the adult, traces of the ligament may still be perceived in the centre. With respect to the nature of the fibres of the intervertebral ligaments, Bonders is inclined, especially from the consideration of their chemical relations, to regard almost all of them, not as connective tissue, but as analogous to the matrix of true cartilage, as is also H. Meyer (p. 300, et seq., and p. 310). This opinion may be correct, as regards the central, nuclear portion, and the fibro-cartilaginous laminae of the outer portions, but hardly so with respect to the purely fibrous parts of the latter. I believe, moreover, that it is not by chemistry, but by the study of the development of these tissues, that the question will be solved, because, although manifest, visible distinctions exist between the fibrils of con- nective tissue developed from cells, and the fibrous intercellular substance, viewed from a genetic point of view, chemistry probably is not in a condition to distinguish one from the 316 SPECIAL HISTOLOGY. other.^ The intervertebral ligaments are liable to various forms of degeneration J they may become ossified, from their cartilaginous lamellae outwards, the true fibrous substance probably at the same time disappearing ; and in this way anchylosis of two vertebrae frequently takes place. They may become atrophied, easily broken down, and disintegrated, either in the nuclear portion, or elsewhere in circumscribed spots, into a dirty grumous matter. And lastly, it would appear that although in the normal state, they contain no vessels, vessels may, under certain morbid conditions, be de- veloped in them ; at all events, extravasations of blood are not unfrequently met with, most generally close to the bones or in connection with them. In the symphysis pubis, the cartilaginous layer, which is thickest in the centre and anteriorly, and connected with the bones by a very uneven surface, consists, at the sides, where it is from 5 to V" thick, of true cartilage, with a homogeneous, finely granular matrix, and simple cells, measuring 001 — 0-024'". In the centre, the matrix is softer and fibrous, and in this situation, (more particularly, it would appear, in the female sex,) there occasionally exists an irregular narrow cavity, with uneven walls, and containing a somewhat slimy fluid, originating evi- dently in a solution of the innermost .cartilaginous layers, and of which manifest traces may also be perceived in the carti- laginous substance immediately enclosing it. The outer layers of the symphysis, which, as is well known, are most developed anteriorly and superiorly, do not arise, with the exception of the outermost lamellse composed of pure con- nective tissue, directly from the bones, but, properly speaking, unite only the outer portions of the above-described cartila^ ginous layers, and consist principally of a fibrous substance, to all appearance identical with connective tissue, and occasionally containing cartilage cells. ' [In our note on the connective tissue, we have already expressed the views we entertain of the homologies of the elements of cartilage and connective tissue ; and we need merely add that we know of no locality in which the transition of the matrix of cartilage into the pseudo-fibrillated collagenous portion of connective tissue is more unmistakeahly exhibited, than in the intervertebral cartilages of a young animal, e. g., a kitten. We have, in that note, endeavoured to show that the notion of the existence of any real difference in the development of the fibrillated element in the different forms of connective tissue is unfounded. — Eds.] THE OSSEOUS SYSTEM. 317 The formation of the bone-corpuscles, as they are termed, may be traced perhaps more clearly in the symphysis than anywhere else, except in rachitic bone (fig. 124). For at its osseous borders there are always to be found, either half projecting from, or entirely lodged in, the cartilage, isolated, nucleated bone-corpuscles or cells, with homogeneous, and (from ca,lcareous salts) granular walls, measuring 0012 0-016'" with respect to which, from their development and from the consideration of the contiguous cartilage-cells, all of which present more or less thickened walls and rudiments of cal- careous deposits, not the smallest doubt can be entertained. Well characterised, half and wholly ossified parent cells of the same kind, with two secondary cells, and measuring 0-015 Fig. 123. 0-03'", up to some including ten or twenty secondary cells, and having a length of 0-05'", may be distinctly noticed in almost every preparation. The sacro-iliac synchondrosis is effected by means of a flattened layer of cartilage, |_1|"' in thickness, which is closely attached to the auricular surfaces of the corresponding bones, between which it is interposed. The cartilage-cells close to the bone are flattened, with their surfaces directed Fig 123. Cartila^nous border, towards the cartilage of the symphysis in Man, X 350 diam.: u, cartilage cells with thickened waUs; i, the same undergoing ossifi cation ; c, cells nearly ossified, with homogeneous walls free in the matrix of the car- tilage i d, similar cells with calcareous granules ; e, ossified cells at the border of the matrix of the bone containing calcareous granules, and half projecting from it 318 SPECIAL HISTOLOGY. towards it, and present beautiful transitionary forms into half and wholly isolated bone-cells, which exist on the border of the bone. In the interior of this cartilaginous layer, ac- cording to Zaglas, there is always a narrow cavity, which separates the cartilaginous layers of the two bones com- pletely, or almost completely, from each other. It contains a synovia-like fluid, and is bounded by smooth and even walls, which differ from the rest of the cartilaginous substance in their greater hardness, as well as in their structure. The matrix of these cartilaginous layers, in the direction of the sur- face, is finely fibrous ; the cells are all of large size (as much as 0*035"'), with numerous secondary cells and uncommonly thick walls, so that the cavities, even of the secondary cells, often appear extremely contracted ; but they do not exhibit any distinct indication of pore-canals or calcareous deposit. The costal cartilages are invested by a strong perichondrium, composed of connective tissue and numerous elastic elements, which commences at the sternal end in connection with the synovial membrane there existing, and at the other is con- tinuous with the periosteum of the ribs. The cartilage, which is in connection with this membrane by a roughened surface, is of considerable firmness although elastic, pde yellow, or in thin sections, exhibiting a transparent blue tint, internally almost always, in certain spots, of a yellowish-white colour, with a silky lustre. Its matrix in the latter situations pre- sents a fibrous structure, and elsewhere a finely granulated aspect. The outermost cells, to the depth of 006 — 01'", are elongated, flattened, parallel to the surface, most usually small (sometimes not more than 0"006"'), but sometimes larger, and filled with one or even many secondary cells, one placed behind the other; more internally, without entirely losing their flattened figure, they are larger (most of them 0"03 — 0"05"'), oval, and round, and lie with their surfaces towards the ends of the cartilage, and with their long axis for the most part in the direction of the radius of the transverse section of the rib; in many cases, however, they are disposed more irregularly. The largest of these cells (measuring as much as 0-08'", or even Q-l'") are found in the fibrous spots, and they, in common with all the interior cells, contain secondary cells, in varying, frequently in very considerable number (as many THE OSSEOUS SYSTEM. 319 as 60, according to Bonders). The most remarkable charac- teristic of the elementary tissue of the costal cartilage, is the large quantity of fat contained in it. In the adult. Fig. 124. every cell, excepting the most superficial, con- tains, larger or smaller (from 0-0016— 0-008'"), sometimes spherical, sometimes more irregu- lar fat-drops, which fre- quently so surround the nucleus as entirely to conceal it from view (fig. 124, a b), whence it has been assumed, though not quite cor- rectly, that the fat is seated in the latter. The cartilage on the greater cornu of the OS hyoides, and between the body and the greater cornu, and the inconstant cartilaginous appendage to the styloid process, differ in no respect from costal cartilage, only that the cartilage cells in those instances do not always contain large fat-globules. The costal cartilages frequently become ossified in old age ; but this ossificatiouj as well as the fibrillation of the matrix, must not be regarded as a normal process, nor be placed in the same category with the usual kind of ossification. The ossification is sometimes more limited, sometimes more ex- tensive. In the former case, it does not proceed further than to the incrustation of the cartilage-cells, and of the matrix in which they are lodged, which has become fibrous ; in the latter, and frequently also in the former, the ossification is preceded by the formation of hollow spaces in the cartilage, in which is deposited a cartilage-marrow, containing vessels, which are connected, in part with those of the perichondrium, Fig. 124. Cartilage cells of Man, x 350 diam.: a, parent cell with three secondary cells containing oil, from a costal cartilage ; b, two cells &om the same situation, in which the globule of oil is surrounded by a pale border ; c, two cells with thickened walls from the cartilage of the greater cornu of the oa hyoides, which together with the globule of oil also contain a distinct nucleus. 320 SPECIAL HISTOLOGY. in part with those of the ribs ; and the osseous substance is more that of normal bone, though almost always more opaque, less homogeneous, and with imperfectly formed lacunae, which frequently contain a calcareous deposit. Under the name of cartilage-marrow, are understood the medulla-cells, fat-cells, bundles of connective tissue and vessels, which are presented instead of the detritus, afforded by the disintegration of cartilage, and which may be said to correspond in all respects with those of developing foetal bone, and may be readily observed in ossifying costal and laryngeal cartilages. §95. B. Moveable Articulation (Diarthrosis). — The articular ex- tremities of the bones, or any other surfaces entering into the formation of a joint, are invariably invested with a thin layer of cartilage, which in the middle of the surfaces covered by it, is of tolerably uniform thickness, gradually thinning as it extends outwardly, and finally terminating with a very abrupt edge. This articular cartilage is closely applied to the bone with a rough, hollowed or raised surface, but is not united to it by any interposed substance ; and, on the opposite surface, it is in most joints usually quite bare, and directed towards the cavity of the articulation. Sometimes, however, it is in- vested with a special fibrous membrane, a perichondrium, which is an immediate prolongation of the periosteum, and extends most generally only over a small portion of the cartilage, gradually ceasing without any defined margin.^ In some joints (shoidder, hip) the more secure lodgment of the articular head of the bone is ensured by special cartilaginous lips. These are firm, yellowish-white, fibrous rings, attached, at the ' [Relchert, who has paid particular attention to the question of the existence of an epithelium upon the articular cartilages, says, that in the foetal condition of Man and the domestic Mammalia, an epithelium exists over the whole surface of the synovial capsules, and, on the articular cartilage, lies in immediate contact vrith its substance. It resembles the epithelium of the vessels. In adults, on the other hand, he could discover an epithelium only on those parts of the articular capsules which are not subject to friction ; and here it had the same appearance as in the foetal con- dition. It was wanting upon the articular cartilages and their immediate neighbour- hood ; but it was not uncommon to meet with fine desquamated flakes of cartilage in the synovia, which fell readily into folds, and thus resembled a fibro-cartilaginous tissue (Bericht, Miiller's 'Archiv,' 1849, p. 16).— Eds.] THE OSSEOUS SYSTEM. 321 Fig. 125. border of the articular cartilage by a wider basis, immediately to the bone or partly to the cartilage. They thin off to an acute edge, and for the most part free and uncovered by the synovial membrane, or any epithelium, project into the articu- lation, being exteriorly in relation with the periosteum and synovial capsule. As regards the intimate structure of the parts just de- scribed, the articular cartilage, on completely formed bones (fig. 125), and under normal condi- tions, presents throughout, a finely granular, in part almost homo- geneous matrix, in which are lodged delicate cartilage-cells, which to- wards the surface of the cartilage are numerous and flattened, and lie parallel to it ; more deeply they are oval or rounded, more rare, and disposed in various directions; and lastly, close to the bone they are elongated, and placed vertically with respect to the surface of the bone. These cells all have distinct walls, easily distinguished from the matrix by the use of acetic acid, clear, fre- quently granular contents, contain- ing, however, but little fat, and a vesicular nucleus. They occur either isolated or in groups, and present very frequently two, four or even more secondary cells, which in the flat cells are placed close together, and in the elongated are disposed in rows. On the condyle of the lower jaw, as on the corresponding surface of the temporal Fig. 125. Articular cartilage of a human metacarpal bone, cut perpendicularly, X 90 diam.: a, most superficial, flattened cartilage cells ; b, middle rounded cells ; c, innermost cells, disposed perpendicularly in small rows ; d, outermost layer of the bone with ossified fibrous matrix and thick-walled cartilage cells, in this instance ap- pearing dark from their containing air ; e, true bone-substance ; /, ends of the can- celli of the apophysis ; g, one of the cancelli. I. ^ 21 332 SPECIAL HISTOLOGY. bone, until the bone is completely formed, there is a thick layer of very distinctly marked cartilage-cells, covered, towards the cavity of the articulation, by a layer of connective tissue. This cartilaginous layer disappears by degrees, as the bone approaches its completion, and at last there re- mains beneath the layer of connective tissuCj now become both relatively and absolutely thicker, merely an excessively thin and transparent lamina, the elements of which, although morphologically not true bone-cells, nor as yet ossified, still seem to resemble the latter more closely than cartilage- cells. The cartilaginous lips of the joints consist principally of connective tissue, always containing, however, isolated cartilage- cells of a roundish or elongated form, with a moderately thick membrane, distinct nucleus, and occasionally fat-granules. I have not as yet noticed parent cells in this situation, whilst cells of the kind already described in the muscular system (§ 82), arranged in series, are not unfrequently met with, and might perhaps be regarded as cartilage-cells, although their nuclei exhibit the most evident indications of a transition into nuclear fibres. The articular cartilages, moreover, during their development, which will be entered into more particularly afterwards, have no nerves or vessels, as is the case also with the cartilaginous lips. [The condition of the bone beneath the articular cartilages, requires special notice. It consists, in almost all joints, in immediate contiguity with the cartilage, of a layer of in- completely formed bone-suhstance, and, more internally, of that tissue in its usual form (fig. 125). The layer in question, which is 004— 0'16"', or on the average 0-12'" thick, is composed of a yellowish, mostly fibrous, hard, and truly ossified matrix, containing, however, not a trace of Haversian canals or medullary cavities, nor of any perfectly formed lacunsej instead of which it presents roundish or elongated corpuscles, aggregated into little masses or rows, the larger of which are 0-016 — 0-024" in length, and 0-006— 0-008'" in breadth, and the smaller 0-006 — 0-008"' in length, and 0-004 — 0-005'" in breadth, which give thin sections of the bone a perfectly opaque aspect, and consequently might THE OSSEOUS SYSTEM. 333 be regarded as bone-corpuscles (lacunae) filled with calcareous particles, as which they have lately been considered by H. Meyer (1. c, p. 325, 336). By the addition of spirit of tur- pentine, which, however, penetrates with difficulty, this error is dissipated, and it is found, that as in the case of the lacunce of dried bone, the opaque aspect is due only to the air contained in them, and that the bodies in question are nothing more than thick-walled cartilage-cells, retaining their contents (fat, nuclei), presenting occasionally indications of canaliculi, and perhaps also partly calcified; in other words, that they are undeveloped lacunae. The layer in which these cells are lodged, and which, towards the cartilage, is bounded by a straight line, occasionally dark from calcareous particles, and towards the true bone by a sinuous contour, in which the limits, as it were, of the individual lacunae are distinguishable, is not found either exclusively in bones not yet fully formed, as Grerlach believes, nor only at a more advanced age (from 30 upwards, and particularly in old men), as H. Meyer states, but, at all events as far as my observation extends, at all ages, from the complete development of the bone upwards, in- variably in every articulation, except that of the lower jaw and those on the os hyoides} The articular cartilage on the head of ^e femur, in a man 35 years old, measured 1 — Ij " in thickness ; on the condyles in the middle, Ij'"; on the margin, | — V" ; in the fovea patellm, \\ — If'"; in the middle of the condyles of the tibia, 1^"; at the borders, | — |"'; in the middle of the patella, li — 1|"'; in the glenoid cavity of the tibia, i — ^'"; on the body of the astragalus, on the upper side, §'", on the under, j'", on its head, §'"; at the base of the first metatarsal bone, on its head j"; on the inner cuneiform bone, in front, behind, i — |"'. In the foetus, about the middle period of uterine life, the vessels of the synovial membrane, according to Toynbee (' PhU. Transact.,' 1841), extend much further upon the articular cartilage ; of which fact, however, I have been unable to satisfy myself in the humerus of a five or six month foetus, or in new-born infants. In pathological states endo- ' [This peculiarity of the bone beneath the articular cartilages was first pointed out by Dr. Sharpey (Quain and Sharpey, 5th ed., p. clviii) ; and is particularly described by Tomes and De Morgan, 1. c, pp. 10, 11. — Eds.] I'" 324 SPECIAL HISTOLOGY. genous cell-formation is met with in an unusual degree of perfection, and more especially in all kinds of articular cartilages; in whicli the parent cells, frequently, of very considerable size, with one or two generations of secondary cells, and also con- taining fat, lie tolerably free in the fibrous matrix, and admit of being readily isolated, (vide also Ecker in Roser and Wunderlich's 'Archiv,' vol. II, 1843, p. 345). In the adult, the articular cartilages are non-vascular, although the vessels of the synovial membraue, at their border, often advance to some distance over them. What Liston (' Med. Chir. Transact.,' 1840, pp. 93-4) describes as " vessels in the articular cartilage of several diseased joints, and as running straight in parallel lines from the injected membrane of the bone into the cartilage, and as joining at their further extremities in that tissue, thus forming long loops," were certainly nothing more than the normal vessels of cartilage, which {vide infra) may be very beautifully displayed even in individuals 18 years old. There cannot, therefore, be any question of inflammation of the cartilages in the adult, though they doubtless suffenin morbid conditions of the bones upon which they rest, or in inflam- mation of the synovial membrane. They frequently assume a fibrous structure, a change which is often attended with a simultaneous increase in thickness, Cruveilhier, (' Diet, de Med. et Chir. prat.' Ill, 514) having noticed fibres of this kind as much as 6'" in length, thus far exceeding the normal thickness of articular cartilage. They sometimes wear away rapidly, or even disappear altogether (in suppuration in the bone or in the articulation), so that the surface of the bone is left exposed; they also undergo partial losses of substance ; when they exhibit ulcerous excavations, which may penetrate to the bone, or commence on the osteal surface of the cartilage.] § 96. The articular capsules {capsules s. membranes synoviales) are not closed capsules, but short, wide tubular sacs, which are attached by two open ends to the borders of the articular surfaces of the bones, and thus connect them together. They are essentially more or less delicate, transparent membranes, but are in many situations so closely and completely invested externally by THE OSSEOUS SYSTEM. 325 fibrous layers — the fibrous capsules as they are termed^ — as on cursory inspection to present the aspect of tolerably tough capsules. These fibrous coats are met with especially in situations where the articulation is either wholly unprotected, or but thinly covered by soft parts, or where a very firm connection is required (as in the hip-joint) ; they are absent for the most part, or are undeveloped, where muscles, tendons, and ligaments rest upon the articulation, or where, for special purposes, the synovial membrane is exposed to more considerable movements (as in the knee and elbow). The relation of the articular capsules to the bones and articular cartilages, more precisely described, is as follows (fig. 126) : — The articular capsule is attached, either simply to the border of the cartilaginous surface, j.- ^ge in the first place, besides the border of | | the cartilage, also invest a larger or rJl \\ smaller extent of surface of the bone / sft||i|]||i||lji^^ | itself, and then pass to the second bone, | i? ^""""X""'''^ jj with which it is connected in the one W^====li==^^^%/" way or the other. In either of these \i||i' '^ h'''// cases the synovial membrane does not w |,|,| adhere immediately to the hard tissues if/''' subjacent to it, but is more or less closely '•' connected with the periosteum and perichondrium, ultimately ceasing without any distinct margin, not far from the border of the articular cartilage, with the perichondrium of which it is inseparably united. With respect to the intimate structure of these tissues, the synovial membranes, distinct from the fibrous capsules, as they are termed, which possess in all respects the structure of fibrous ligaments, consist : — 1. of a layer of connective tissue, with not very numerous vessels and nerves; and 2. of an epithelium. The latter is composed of from one to four layers of large tesselated cells, measuring 0-005 — 0-008'", with Fig. 126. Diagram of a transverse section of a phalangeal articulation, partly after Arnold; a, bones; b, articular cartilage; e, pmos/cum continuous viith the perichon- drium of the articular cartilage ; d, synovial membrane at the edge of the cartilage, connected at first with the perichondrium ; e, its epithelium. 336 SPECIAL HISTOLOGY. roTindish nuclei of 0-003 — 0-003'". The former, in its inner- most part, is constituted of a layer of parallel fasciculi, with iudistinct fibrils and elongated nuclei or fine elastic filaments ; more externally of decussating bundles, with a fine elastic network, occasionally also of a network of bundles of connective tissue of very various thickness, with winding elastic fibres, exactly as in the arachnoid. Not unfrequently, common fat- cells occur, dispersed here and there in the meshes of the connective tissue, although upon the whole very rarelyj and also a few scattered cartilage-cells, with tolerably thick, opaque walls, and a distinct nucleus. The synovial membranes possess neither glands nor papillae, whilst they present large adipose masses {plica adiposes) and vascular processes {plicce vasculosa, plica synomales, ligamenta mucosa, Autor.). The fdrmer, at one time erroneously termed "Haversian glands," are foimd principally in the hip- and knee-joints, in the form of yellow or yellowish -red, soft processes or folds, and consist simply of large collections of fat-cells in vascular portions of the synovial membrane. The latter are met with in almost every joint, con- stituting, provided that the blood-vessels are filled, red, flattened projections of the synovial membrane, with an indented and plicated margin, and furnished with minute processes. These folds are usually placed close to the junction of the synovial membrane with the cartilage, upon which they lie flat, thus forming, in many cases, a sort of coronal around it; in others they are more isolated, and placed in other parts of the articulation. In their structure, they differ from the rest of the synovial membrane, principally in their great vascularity, con- sisting as they do of little else than minute arteries and veins, and delicate capillaries forming wavy loops at the edge of the processes, and consequently they are very similar to the choroid plexuses in the ventricles of the brain. Besides the vessels, they present a matrix of, frequently, distinctly fibrous, connective tissue, the usual epithelium of the synovial membrane, occa- sionally solitary or numerous fat-cells, and, more rarely, isolated cartilage-cells. At the edge, they are almost invariably fur- nished with minute, foliated, conical, membranous processes of the most extraordinary forms (often resembling the stems of a cactus), which also frequently contain vessels, but are for the most part constituted merely of an axis of indistinctly fibrous THE OSSEOUS SYSTEM. 327 connective tissue, with occasional cartilage-cells, and an epithe- lium, very thick in places. The smaller ones frequently consist even of nothing but epi- ' fig. 127. thelium.) or of little else than connective tissue. In many joints there are firm, whitish-yellow fibrous plates, the so- termed interarticular car- tilages or ligaments which, either projecting in pairs from the synovial cap- sule, are interposed be- tween the bones consti- tuting the articulation (knee), or form a single diaphragm transversely across the joint (articu- lations of the jaw, clavi- cle, sternum, and wrist). These processes consist of a firm, fibrous tissue, the fibres of which, usually cross each other in various directions, and are in all respects closely allied to connective tissue, but presenting less distinct fibrils; and besides this, of cartilage-cells and fine elastic fibres. The cartilage-cells, in the most superficial layers, are more solitary, in the deeper, disposed more in rows and smaller, ultimately being replaced by fine elastic fibres, a certain number of which, at all events, appear to originate from cells resembling the cartilage-cells. The interarticular ligaments, which, from what has been said respecting them, must be enumerated among the fibro-cartilages, are not covered by synovial membrane, though they probably have an epithelial investment at the attached border, but only for a small Fig. 127. From the synavial membrane of a phalangeal articulation : A, two non- vascular appendages of the synovial processes, X 250 diam,; a, connective tissue in its axis ; b, epithelium (in the peduncle of the larger process not distinctly cellular) continuous with that on the free borders of the process ; c, d, cartilage cells : B, four cells from the epithelium ot the synovial membrane of the knee, one with two nuclei, X 350 diam. 328 SPECIAL HISTOLOGY. extent, — ^never over the entire surface. The articular ligaments, with the exception of the softer ligamentum teres, are composed of the same firm connective tissue (in the costal ligaments containing cartilage- ceUs), as that of which the tendons and the fibrous ligaments, elsewhere, are constituted. The internal ligaments {lig. cruciata), however, present softer connective tissue, containing vessels, and covered with epithelium. Within the synovial capsules, is con- tained, in small quantity, a clear yel- lowish fluid, which may be drawn out into threads, — the synovia, — and which, in its chemical composition, appears very closely to resemble mucus, and particularly in its containing mucin in solution. Examined under the microscope, in its normal condi- tion, this secretion exhibits nothing worthy of much remark, consisting simply of fluid which is rendered turbid by acetic acid, and very frequently contains epithelial cells, which have often undergone a fatty metamorphosis, nuclei of such cells, and fat globules ; under conditions, not quite normal, it may also contain, blood- and lymph-corpuscles, detached portions of the synovial processes of the articular cartilage, and a structure- less gelatinous substance. [The normal, healthy synovia, which in the Ox, according to Frerichs (Wagn. 'Handb.' Ill, 1), contains 94-8 water, 0'5 mucus and epithelium, 007 fat, 3*5 albumen and extractive matter, and 0'9 salts, is a secretion, not having essentially any formed elements in it, which simply exudes from the vessels of the synovial membrane with the intermediation of the epithelium; and, in fact, from all its vascular processes, which are destined as it were for this special function, and always exist at the border of a cartilage requiring a lubricating covering. The non- vascular appendages of these processes give Fig. 128. From the falciform ligament of the knee: a, a filament of connective tissue with oval cells disposed in a series, and resembling cartilage cells j b, a. similar filament with more elongated cells and nuclei. THE OSSEOUS SYSTEM. 329 origin to the "loose cartilages/' as they are termed; they do this by their increasing in size and solidity, and becoming detached from the vascular folds. These bodies are also met with, in mucous bursse and the sheaths of tendons, which are also furnished with vascular folds {vid. sup. § 83); they consist of connective tissue with elongated nuclei, coated with epithe- lium, and, though not always, contain a variable number of scattered fat- and true cartilage-cells ; and they are not deve- loped externally to the synovial membrane, but from an out- growth of that membrane itself. Similar solid bodies, more- over, may probably be produced in other ways; Bidder ('Zeitsch. f. rat. Medicin.,' vol. iii, p. 99, et seq.) at all events, and Virchow ('Med. Zeitung,' 1846, Nos. 2 and 3) have observed similar bodies presenting no trace of organization . I am inclined, with Virchow, who has actually demonstrated the presence of fibrin in them, to regard them, in many cases, as fibrinous exudations, and in others as solidified deposits from the synovia, which latter supposition is supported by the frequent occurrence of curdy, more or less consistent, struc- tureless masses, evidently inspissated synovia, in the tendinous sheaths of the hand. Portions of bone, also, detached from outgrowths at the circumference of the articular ends of the bones, may find their way into the interior of the articulation. The plic(B adiposis have perhaps less to do with the formation of the synovia, than with the mechanism of the joint, serving the purpose of filling up hollows.] § 97. Physical and chemical properties of the Bones, and their accessory Organs. — The bones are composed, besides a small quantity of water (3 — 7g, according to Stark in the compact substance), and fat (2 — 32 Bibra), principally of a substance afi'ording gelatine, and of inorganic elements. The latter, in the adult, constitute two thirds (68-82 Bibra) of dry bone, and are nearly all left when the bone is calcined; in which case, if due care be taken, the bone completely retains its external aspect, although it may be readily reduced to a white, opaque, friable, heavy powder, the so-termed "bone earth." This consists chiefly of 57 — 595 basic phosphate of lime (according to Heintz, 3 atoms base, 1 atom acid), of carbonate of lime (7 — 82) and 330 SPECIAL HISTOLOGY. traces of fluate of lime, phosphate of magnesia, silex (traces), and alkaline salts. A small part of the salts of bone is also contained in the walls of the vessels and in the lacunae, and this part is dissolved in water. The collagenous substance is the so-termed bone, formative, or ossifying cartilage. It is obtained when bone is treated at a low temperature with dilute hydrochloric, or nitric acid, in the form of a soft, flexible, elastic, light-yellowish, cartilaginous, transparent sub- stance, retaining accurately the shape of the bone. This bone-cartilage constitutes about g of the dry bone, putrefies when moist, and when dried, may be burnt away, leaving a small quantity of ash. It is dissolved by boiling, and from its combination with water is produced the gelatine, usually to the amount of 3 or 4 times its volume, and which may also be obtained directly by long boiling of the bone in a Papin's digester. With regard to the mode in which the principal constituent elements of the osseous tissue are combined, it is certain that the bone earth does not exist as a distinct deposit in any of the constituent parts of healthy, fully formed bone, but rather, although in a solid form, only in a very intimate union with the tissue. Since both the cartilage and the calcined bone retain the figure of the bone, in all its particulars, inde- pendently of each other, there can be no doubt, but that the most intimate union of the two substances exists throughout the entire bone, which, however, cannot be regarded as a chemical combination, principally for the reason, that the pro- portional relations between the collagenous substance and the phosphate of lime are very variable; and that, by simple boiling under an increased pressure, the gelatine is separated from the calcareous salts. iLhe physical properties of the bones correspond with their composition. Their hardness, density, and rigidity are due to the earthy, whilst their elasticity and flexibility depend upon the organic constituents. In the normal bone of the adult, the two principal constituents are united in such proportions, that the bones, together with considerable hardness and rigidity, have a certain degree of elasticity, though slight, so that they possess a considerable resisting power, and are broken, though not very readily, by the application of greater mechanical THE OSSEOUS SYSTEM. 331 force. At an earlier age, when the cartilage is in greater relative proportion, the hardness of the bones is much less, their sus- taining power consequently less considerable, and they are more liable to be bent; whilst on the other hand, owing to their greater elasticity, they are much less liable to be broken. This is the case in a much higher degree in rachitis, in which morbid condition, the organic constituents amount to from 70 to 80 per cent. A condition the reverse of this is observed in old age, when the bones, though certainly harder, are more brittle, and therefore more readily fractured, to which liability, however, the rarefaction of the tissue which takes place in consequence of age, partly contributes. The inflammability of bone depends upon its organic basis, and its capability of resisting putrefaction to the inorganic con- stituents. The latter being so intimately combined with the animal tissues, serve as a protection to them, so that bones from ancient burial places, and those of fossil animals still retain the full proportion of cartilage. The true cartilages, even in the foetus, contain, in their organic basis, from 50 to 75 per cent, of water, 3 to 4 per cent, of salts (chiefly of soda and carbonate of lime, and also some phosphate of lime and magnesia). The organic basis, has been hitherto supposed to consist entirely of chondrin, a substance allied to gelatin, soluble in boiling water and gelatinising as it cools; but it was noticed by Bruns (p. 216), that the matrix and the cells of cartilage were not equally soluble in water, and Mulder and DoiTders have rendered it probable that the chondrin, which had hitherto been investigated, is not a simple substance, and that the cartilages consist of several bodies of diff'erent natures, the matrix, and the membranes of the parent cells, their contents, and the secondary cells, of which the first is more soluble in water, potass, and sulphuric acid, than the others. The fibro-cartilages (cartilages containing connective tissue) have been, as yet, but little investigated. J. Miiller, in the interarticular cartilages of the knee of the Sheep, found no chondrin; whilst Bonders, on the other hand, met with it in the intervertebral ligaments ('Holl. Beitr.,' p. 264); he did not determine whether they also contained gelatin. According to Virchow, the gelatinous, nuclear portion of these ligaments, 333 SPECIAL HISTOLOGY. ia the new-born child, consists of a substance very nearly allied to that of "colloid" (Wurzb. 'Verhandl./ IT, 383). The ligaments have the same chemical composition as the tendons. § 98. Vessels of the Bones and their accessory Organs. — A. Blood- vessels. The periosteum, besides the numerous vessels passing to the bone by which it is traversed, presents in its outer layer, composed of connective tissue, a tolerably close network of minute capillaries (0005"'). The blood-vessels of the bone itself are very numerous, as may be seen in injected specimens, and also in recent bone full of blood. In the long bones, the marrow and the spongy substance of the articular ends are supplied by particular vessels, as is also the compact substance of the shaft. The former, or vasa nutritia, enter the bone through large special canals, one or two of which are found in the diaphyses, and many in the apophyses. These vessels, with the exception of a few twigs given off to the innermost Haversian canals of the compact substance, and which possess all the tunics proper to the vessels elsewhere (even to the muscular), ramify in the marrow, where they form a true capillary plexus — the vessels in which vary in size from 0'004"' to 0'0053"'. The vessels of the compact substance arise, in great part, from those of the periosteum, very soon lose the muscular coat, and form, in the Haversian canals, which they either occupy by themselves, or together with some medullary substance, a network of wide canals, which from their structure, can only in the most trifling extent be referred to the capillary system, most of them possessing a layer of connective tissue and an epithelium, and as it is only in the larger canals that fine capillaries co-exist with the main vessel. The venous blood is returned from all the long bones, in three ways : — 1. by a large vein accompanying the nutritious artery, the ramifi- cations of which it follows; 3. by numerous large and small veins at the articular extremities; and, 3. lastly, by many small veins, which arise independently of each other from the compact substance of the diaphyses, in which their roots, as is correctly stated by Todd and Bowman, occupy the wider spaces and sinuses, or pouch-like excavations, which are very evident even in sections of bone. THE OSSEOUS SYSTEM. 333 All the vessels of bonCj — the meduUary vessels oi the apophyses and of the diaphyses, as well as the vessels of the compact substance, — communicate in a multiplicity of ways, so that the vascular system throughout the entire bone constitutes a con- tinuous whole, in which it is possible for the blood from any one part to reach every other part; for it was observed by Bichat (' Anat. General.,' 1813, III, p. 37), in an injected tibia, the nutritious artery of which was obliterated, that the bifurcation of the vessel in the medullary canal was well injected, and that the nutrition of the marrow was evidently unaffected. In the short bones, the blood-vessels present pretty nearly the same conditions as they do in the apophyses of the long bones ; the arteries and veins of larger and smaller size enter- ing and quitting the bone at numerous points on the surface, and sometimes, as in the posterior aspect of the bodies of the vertebra, in very large trunks, — the verns basi-vertebrales of Breschet, furnishing a capillary plexus to the medulla, and also penetrating into the few Haversian canals of these bones. In the flat bones, such as the scapula and os innominatum, there are distinct nutritious foramina for the larger arteries and veins ; the compact substance receiving finer vessels from the periosteum, and the spongy substance being supplied by numerous and even large vessels, as in the neighbourhood of the articular cavities. In the flat cranial bones, the arteries, for the most part, enter both the cortical and spongy substance from without, on both surfaces, presenting the usual conditions, whilst the ven^M\m /•! « canals, — from the cartilage-cells, by the thickening of their wall, with the simultaneous formation of canalicular vacuities in it, and its ossification. In the ossifying shaft of a rickety bone (fig. 132) the morphology of this process may be most beauti- fully observed. If the rows of cartilage-cells of the ossifying Kg. 132. From the ossifying border of the condyle of the femur of a rachitic child, two years old, x 300 diam.: a, cartilage cells, simple and parent cells in series; b, more homogeneous; c, striated matrix between them; d, cartilage-cells at the commencement of their transformation into bone-cells ; e, the same further advanced, with very much thickened walls, indication of canaliculi, commencing deposition of calcareous matter in the walls, whence their darker colour, though still with distinct nuclei ; /, bone-cells still more developed and more ossified, in an equally ossified matrix. I. 23 354 SPECIAL HISTOLOGY. border, which in this case are of larger size, be traced from without to within, it will soon be found, that at the point where the deposition of calcareous salts (which takes place for the most part without the formation of the calcareous granules) commences, they exhibit, instead of a membrane indicated by a single, tolerably strong line, a thicker coat, which on the inner side presents delicate indentations. Even when the thickness of this membrane does not exceed O'OOl'" (fig. 133, d), it is obvious that the cartilage-cells are about to be transformed into bone-cells; and this becomes still more evident, when, further on in the bone, the thickness of the membranes in question, together with the simultaneous diminution of the cavity of the cell, is seen to be constantly increasing, the indentations of the interior contour line to become more and more marked, and, accompanying the progress of these changes,, the walls to become more and more dark from the addition of calcareous matter (fig. 132, e). The slow ossification of the matrix between the cells is very favorable to the obser- vation of these changes, allowing not only of the accurate investigation of the first alterations in the cartilage-cells, but also of their subsequent conditions, at a time when they must be termed bone-cells and lacunce, being traced step by step. To this circumstance alone is also due the establish- ment of the interesting fact, that cartilage-cells, enclosing secondary cells within them, are converted, as a whole, into a single, compound bone-cell. Cells of this kind are very fre- quently met with, having two cavities, which cells, according to their degree of development, are sometimes wide and furnished with short prolongations, and sometimes, from their contracted cavity and long canaliculi, resemble in all respects perfect bone- lacunse. Compound cells, with 3, 4, and 5 cavities, each with the remains of the original contents and nucleus, occur more rarely, though even such are occasionally, to be found in almost every preparation. The cartilage-cells lying free, and in close apposition, though in a non-ossified matrix, having thus evidently become transformed into bone-cells with nuclei and other contents, the ultimate changes now take place from which the rickety bone-substance acquires pretty nearly the nature of the sound tissue. These changes, in as far as they affect the bone-cells, chiefly depend, in the first place, upon the com- THE OSSEOUS SYSTEM. 355 mencement of ossification in the matrix, but vnthout any- primary formation of calcareous particles; and secondly, upon the continually increasing deposition of earthy matter in it, and in the thickened cell-walls, owing to which, the new bone^ substance, to the naked eye becomes more and more white, and under the microscope appears more and more dark and transparent; it now, also, becomes more homogeneous, and the abrupt limits of the bone-cells gradually less and less defined, till at last they appear, not as cellular organisms lodged in the matrix, but to be confused with it, being recognisable only from their peculiar stellate cavities, — the so-termed bone-cor- puscles, or lacunce and canaliculi. -^ With the knowledge thus obtained of the formation of the lacunae in rachitic bone, the endeavour to arrive at an insight into the same process in normal bone, is no longer attended with as much difficulty as before, when the inquirer was involved in a maze of hypotheses of the most various kinds, and all without any certain foundation. The investigation of the con- ditions attending the development of bone, both in man and other animals, must nevertheless still be regarded as trouble- some, and frequently little worth the pains bestowed upon it. It is, perhaps, certainly manifest {^pid. 'Mik. Anat.,' tab. iii, fig. 6), that the bone-cells, a little beyond the limit of ossi- fication, become thickened, and, still presenting the remains of their cavity and the nucleus, beset with calcareous particles; and although such encrusted cells may even be isolated, yet the mode in which the changes are effected further on, is not, beyond a short distance, I must affirm, to be seen with anything like the distinctness that it is in rachitic bone, because, more internally, the newly-formed medulla with its vessels, and the calcareous particles, render almost everything indistinct; and it is not till we get to the homogeneous and more transparent osseous tissue beyond, that distinct, but almost perfectly- formed lapunse come into view. Nevertheless, from all that we see, there cannot be the least doubt, but that the processes are essentially the same as in rachitis, only, that in the healthy bone the ossification of the thickened walls of the cartilage- cells, presents two stages, instead of only one, as in the former case, inasmuch as they first appear granular from the deposition of .the calcareous particles, and afterwards homogeneous. More- 356 SPECIAL HISTOLOGY. over, even in perfectly normal bone, in the adult, I have met with places (some of which, independently of me, have also been lately described by H. Meyer (1. c.) ), such as the symphysis pubis, the synchondroses of the vertebreB, and those of the ilium, sacrum, and the points of insertion into the bones of certain tendons containing cartilage-cells. In all of these situations, at the line of junction between the cartilage or tendon and the bone, cartUage-cells of the most characteristic aspect may be seen, lying free in the cartilaginous matrix, and presenting the most various degrees of transformation into bone^cells ; some, in particular, having thickened walls, and a more or less copious deposit of calcareous particles ; while others are almost perfectly-formed bone-cells, with pores and a more homogeneous wall (fig. 123); so that I am able to afford a certain support to the statement given above with respect to the mode of origin of the bone-cells, by the conditions pre- sented in normal tissues also. In the last-named situations I have, likewise, very distinctly and very frequently noticed, half or wholly ossified parent-cells, containing from 2 to 13 secondary cells. There is another point in the development of the bone-cells still obscure, or at least that has not been directly observed, viz.: how their pores or canaliculi became branched cavities, communicate with those of other cells, and acquire open orifices in certain situations. All that is apparent in rachitic bone and elsewhere, is merely the circumstance, that the thickening of the ossifying cartilage-cells does not proceed with a straight but with an indented border, which is the case in fact from the beginning up to their completion, and that the bone-cells have, at first, more simple prolongations than afterwards. Observation teaches nothing beyond this. Now, as there can be no doubt that the canaliculi anastomose very freely, and also, that they frequently open on the outer surface of the bone, or into the cavities in its interior, I do not for a moment hesitate to express the opinion, that the canaliculi, arising as simple branches from the lacuna, are continued or further developed by absorption of the already formed bone- substance. How such an absorption takes place, cannot, it must be confessed, be explained; but that affords no ground of objection to the opinion, because we see a similar process. THE OSSEOUS SYSTEM, 357 though on a widely different scale, take place in the formation of the medullary cavities and cancelli {vid. infra). It would appear to me, that currents of the nutritive fluid in the bone were chiefly concerned in this further development of the canaliculi; and the more so, because the first rudiments of the canaliculi, like the pore-canals of lignifying plant-cells, mani- festly indicate nothing more than the points at which the ossifying cartilage- cells continue to admit and emit fluid; on which account, also, their direction is principally towards the internal and external surfaces of the bone, from which the nutritive plasma is derived. It appears to me highly probable, that after the complete ossification of the cartilaginous tissue, the nutritive fluid derived from the blood-vessels of the periosteum and of the medullary cavities (1.) finds new ways for itself towards the lacuna and their prolongations, which, as it may be said, alone are still open to it, and in this way effects their opening on the internal and external surfaces of the bone, and (3.), also burrows passages from the cavities lying nearest to it, and thus 'ultimately produces a ramification of them, and brings about numerous communications between the different cavities. In accordance with which, a secondary formation of canaliculi must take place, not only in the region of the thickened walls of the original cells, but also in the osseous matrix, and this to a considerable extent, as is at once evident, when the distances between the anastomosing cavities are compared with the diameter of the original cartilage-cells. The development of the medullary spaces {cancelli) and of the medulla, is to a certain extent the last act in the trans- formation of cartilage into bone. The medullary spaces do not arise in a coalescence of the cartilage-cells, but from a solution of the more or less perfectly formed bone-substance, exactly like the large medullary cavities of the cylindrical bones. This is most distinctly and satisfactorily shown by the examination of the diaphyses of a sound .or rachitic bone, but especially in the latter. At the limit of the ossification itself, the osseous tissue for a distance of about \ to i'" is quite compact, without a trace of larger cavities, and is composed in part of the ossified matrix, and in part of cartilage- cellsj more or less advanced in their transformation into bone-cells ('Mik. Anat.,' tab. iii) ; beyond this part, however, cavities, at 358 SPECIAL HISTOLOGY. first small, and more internally, larger, come into view, the whole relations of which show most convincingly that they do not originate in any development of the existing elements. They have an extremely irregular contour, are oval, or roundish and angular, and for the most part broader than the cartilage- cells, appearing to be eaten out, as it were, in the substance of the bone, and involving severally the compact tissue, matrix, and bone-cells. When the borders and limitary surfaces of these spaces are closely regarded, it is, in many instances, easy to notice bone-cells more or less removed, half projecting from, or buried in the wall, and between them projections of the ossified matrix, so that no doubt can any longer be entertained with respect to the origin of the cavities. It must be confessed that there is as little to be stated, in this case, as in that of the origin of the analogous cartilage-canals, and the further development of the canaliculi of the bone-cells, with respect to the mode in which this absorption takes place ; and the process is even still more inexplicable, because, allowing that it really does take place, there would then exist in the -ossifying bone, at the same time and almost in immediate contiguity, a formation of bone and a resolution of the tissue, but very little less energetic. The above-described mode of formation of the cancelli, nevertheless, is a morphological fact, and con- sequently, the explanation of such a curious phenomenon becomes a problem to be solved by chemistry and physiology. As in the diaphyses, so in. the ossification of all the other cartilages, medullary spaces are formed by the resorption of the inner portions of that part which is half ossified. But it must be stated, that these spaces do not present the same form, direction, and size in every bone; though with respect to this, it is unnecessary to off'er any special remarks, since the relations of this primitive spongy substance are, in the main, the same as they are afterwards. Still, it may be remarked, that in many bones, solitary spaces are apparently developed immediately from cartilage-canals, seeing that some at least of the latter, at the limit of ossification, communicate directly with the spaces in the bone; and, moreover, that not unfrequently, cartilaginous elements not yet wholly converted into bone-cells, are drawn into the process of resolution. The medullary cavities, however they arise, are filled with a THE OSSEOUS SYSTEM. 359 softj reddish substance — -f(Btal medulla. This substance at first consists of nothing but a small quantity of fluid and many rounded cells, with one or two nuclei and faintly granular contents, of which I am unable to say how they originate, but only this much, that they are altogether new formations. In process of time these cells, which are in all respects identical with those which occur, in the adult, in certain bones {vid. supra), are developed in the usual way into connective tissue, blood- vessels, fat-cells, and nerves. The formation of blood-vessels proceeds with great rapidity, so that the bones, very shortly after the development of the medullary spaces, exhibit blood- vessels in them; that of the fat and nerves takes place more slowly, although the latter, at the period of birth, of course with fewer filaments than subsequently, may be very readily perceived in the large cylindrical bones, even more readily than in the adult, because at this time the medulla may be more easily washed away from them and the great vessels. The fat- cells at this period are but few in number; the medulla, in man at least, being coloured entirely red by the blood and the light reddish medulla-cells. After birth they gradually multiply, till at last, the marrow, in consequence of their great increase and the disappearance of the medulla- cells, which are ultimately all transformed into the elementary tissues of the permanent medulla, acquires its subsequent colour and consistence. In many of the primarily cartilaginous bones of Birds and Amphibia, the ossification of the cartilage commences, according to Rathke and Reichert (1. c), on the outer aspect of the cartilage, so that at first a cylinder of bone is formed with cartilage internally and at the extremities. The remainder of the internal cartilage then affords space to the medulla, whilst the epiphyses are formed out of that of the ex- tremities. [If the contents of the cartilage-cells, the "cartilage-cor- puscles" of authors, be really surrounded by a membrane, as Virchow supposes, it may be assumed that a similar tunic, analogous to the primordial utricle of the plant-cell (vid. sup. § 8), exists also around the contents of the bone-cells, and that it takes an essential part, by its throwing out stellate processes, in the first formation of the canaliculi, their further elonga,- 360 SPECIAL HISTOLOGY. tion and ultimate anastomoses. In this case, also, the stellate and readily isolated cartilage-cells from an enchondroma described by Virchow ("Wiirz. 'Verb./ Bd. 1), around the internal portions of which the contours of rounded cells were visible would be intelligible, and even the possibility of the isolation of stellate organisms from normal bone {vid. sup.) be explicable. My exposition of the formation of the lacuna in rachitic bone, is confirmed by Rokitansky and Virchow (Wiirz. 'Verb.,' TI) ; whilst Robin declares that it is incorrect, giving a description of their formation which is, to me, unintelligible. I recommend to his notice rachitic bone, the cementum of the horse's tooth, and the symphyses (§ 95), with which he is manifestly unacquainted, and hope that he may then be induced no longer to regard Schwann's and my views as antiquated.^] ' [As we have already said, we must deny the existence of endogenous cell- development in ossifying, or any other cartilage. In fact, the process of multiplication of the corpuscles (nuclei (?) of Kblliker, granular cartilage-cells of Tomes and De Morgan) is so clear, that we are at a loss to comprehend how it can he mistaken. What is meant in the text by " contents," as distinct from the corpuscles, we do not know. Messrs. Tomes and De Morgan describe the real changes which precede ossification, very exactly in a few words, thus : " Cartilage previous to its conversion into hone undergoes a rapid growth, which takes place principally in the direction of the long axis of the future bone. Each granular cell becomes divided into two, by segmentation transverse to the line of ossific advance. These are again divided, and the process repeated from time to time, until in the place of a single granular cell we have a long line of cells extending from the unchanged cartilage to the point where ossification has taken place" (1. c, p. 16). " If attention be directed to the end of the line furthest from the bone, the cells will be found small in size, granular, and with a perceptible nucleus, but without an outer wall, distinguishable from the hyaline substance, which is abundant between the contiguous lines, but small in quantity between the cells composing the lines. But if the other end of the line be examined, very different conditions will be observed. The granular cells will be seen to have become rounded in form, to have increased to three times their original bulk, and to possess well-marked, circular nuclei " p. 17. (See fig. 129 A, 8.) So far, our own observations are in perfect accordance with those of Tomes and De Morgan. They go oUj however, to observe, "in addition to which, each granular cell will have acquired a thick, pellucid, outer wall ;" and with this last statement we can by no means agree. Neither in Man, the Calf, the Rabbit, the Skate, nor in enchondroma, have we been able to see anything of the regular develop- ment of such an envelope : in fact, in the great majority of instances, we have con- vinced ourselves of the absence of anything of the kind — there being nothing but a clear space between the corpuscle and the ossified wall of the cavity in which it lies. Bodies corresponding with the lacunal cells — cartilage-corpuscles that is,— invested THE OSSEOUS SYSTEM. 361 105. Elementary processes in the Layers formed from the Periosteum. — The periosteum of the primarily cartilaginous bones, is propor- tionally very thick and vascular, consisting, as early as at the fifth month, of common connective tissue and fine elastic filaments, the latter of which in process of time become stronger and stronger, occasionally assuming the nature of elastic fibres. On the inner aspect of this fully formed periosteum, there is now deposited an ossific blastema firmly adherent to the bone by a thick coat of more or less granular, calcareous matter, may indeed often be ob- tained free ; but they arise, like the corresponding bodies in rickety bone, simply from the deposition of calcareous matter in the cartilage-cavity before it has taken place in the matrix, or from a want of union between the two deposits ; and are therefore quite accidental. The lacMnce are developed; according to these authors, by the shooting out of the granular cells into processes, and their direct conversion into the laaime, the nucleus of the granule-cell remaining as the nucleus of the lacuna. On this point also, we must differ from them, and agree with Virchow (1. c, note, § 101) and Kblliker (supra, § 104), that the development of the canaliculi is, by a process of resolution, quite independent of the corpuscles, which simply diminish in size, and either remain as the so-called " nuclei" of the lacunae or totally disappear. We can especially recommend the Skate (fig. 136 A, 2) as a subject in which to trace the process of formation of lacunae, as the bone is homogeneous and transparent, and in consequence of being inclosed in a large mass of firm cartilage, may be cut with ease into very thin sections. We have observed it with great clearness also in enchondroma. There is one argument which seems to us conclusive on this point. Wherever the canaliculi can he seen at all, however young the tissue, they are perfectly clear and transparent. If, however, they were formed by processes of the granular cells, they ought to he granular, and more or less opaque. Taking the same view of the structure of cartilage as Messrs. Tomes and De Morgan, then, our view of the nature of the lacunse, resulting from its ossifica- tion, agrees with that of Professor Kblliker. Cartilage becomes bone by the deposit of calcareous salts in the matrix, and occasionally in its cavities. The lacunae are spaces left round the corpuscles, from which, by resorption, processes — the canaliculi, — are subsequently developed. If it be asked how it is that the lacunae may fre- quently be demonstrated both optically and chemically as distinct bodies, we must call to mind the fact already referred to, that in cartilage, the walls of the cavities have frequently undergone less change than, or a different change from, the surround- ing matrix ; and therefore appear both optically and chemically distinct, though they are by no means so, morphologically : and, therefore, that there is no difficulty in supposing the same thing to occur in bone. The chemical differentiation of the wall of the lacuna is, in fact, exactly comparable tp that of the wall of the cavity which contains the " nucleus" in connective tissue, and in fibro-cartilage ; and which gives rise to the formation of the elastic element in those tissues. — Eds.] 362 SPECIAL HISTOLOGY. Fig. 133. (fig.l33,B) ; so that when the periosteum is removed, it generally remains upon it as ^a moderately thick, soft, whitish yellow lamella, in which, microscopic ex- amination shows the existence of — •* a fibrous tissue, with a not particu- -9b larly distinct fibrillar formation, something like immature connec- tive tissue, and granular, oval, or round nucleated cells, measuring 0-006— 0-01'". When this lamella is raised from the bone, it is found to be very intimately connected with the most superficial layers, and on its internal surface a few little detached fragments of bone, and scattered masses of reddish, soft medulla, from the most su- perficial cancellar spaces, wiU be observed. The bone thus laid bare, when the removal of the periosteal layer has been carefully conducted, presents a rough, and as it were porous surface, with numerous medullary spaces, and remains, superficially, in spots of greater or less extent, quite soft, pale-yellow, and transparent, whilst more internally it becomes firmer and whiter, ultimately acquiring the usual appearance of perfect osseous tissue. When it is inquired, how the formation of bone, which indubitably takes place in this situation, is effected, we refer to the blastema just described, the cells of which, scattered in the fibrillated connec- tive tissue, have not the least resemblance to those of carti- lage, but appear exactly like the foetal medulla-cells, or forma- tive cells of the embryo. In fact, it is now, not difiicult to show, that the outermost, still soft bone-lamellae pass into the blastema in question, with their separate spiculae and projections, and that (1.) the matrix of the bone arises from its fibrous tissue, by the simple uniform deposition of calcareous salts, although usually, as it seems, without the previous appearance of cal- careous granules ; and (2.) that the bone-cells are formed out of Kg. 133. Transverse section from the surface of the shaft of the metatarsus of the Calf, X 45 diam. : A, periosteum ; B, ossifying blastema ; C, young layer of bone, with wide cavities, a, in which are lodged remains of the ossifying blastema, and reticular spiculae, t, which towards the blastema present a tolerably abrupt border ; D, more developed layer of bone, with Haversian canals, c, which are surrounded by their lamellae. THE OSSEOUS SYSTEM. 36S the formative cells of the blastema. With respect to the latter, however, the transformation cannot be followed step by step, as in rachitic bones. This much, however, is always apparent, that the bone-cells at first present larger cavities, less developed rays, and more distinct nuclei (the latter, as we know, remain- ing), and, as their occasionally visible outlines prove, correspond entirely in size with the cells just mentioned, so that I do not for a moment doubt, that they are formed in this situation exactly as they are elsewhere. With respect to the development of the ossifying blastema itself, it is at least clear, that it is derived from the numerous vessels of the foetal and young periosteum ; the origination of its fibres from fusiform cells, I have very frequently observed in man and in animals, but with respect to the cells, can only state that they occur of various sizes, and occasionally intermixed with free nuclei. The formation of bone in this blastema occurs wherever it is in connexion with the bone ; it does not, however, take place in connected but in interrupted, reticular lamella. The roundish or elongated spaces (fig. 133, a), which, from the first, remain between the layers of osseous tissue, and in the difi^erent layers communicate with each other, are nothing else than the rudi- ments of the Haversian or vascular canals of the compact sub- stance, and contain a soft, reddish medulla, which at first is obviously nothing more than the unossified portion of the ossific blastema, although it sometimes contains more formative cells than connective tissue. The cells of these spaces are very soon transformed into the usual, light-reddish medulla-cells, and partly into vessels which communicate with those of the interior of the bone, and in part also with those of the periosteum, with which, having once formed a junction, they remain continuous during the entire growth of the bone in thickness, so that the formation of the spaces in the bone is, at least afterwards, pre- indicated by those, which, in accordance with what has been said, proceed from the periosteum through the ossific blastema to the bone. Besides medulla-cells and vessels as well as some con- nective tissue, the bone-cavities of the periosteal layers also con- tain round, elongated, or dentate, flattened, faintly granular cellular corpuscles of 0'01-^0"02"' or more in size, with from 3 to 12 or more vesicular nuclei and nucleoli, which are probably referable to the multiplication of the medulla-ceUs [vid, § 11). 364 SPECIAL HISTOLOGY. The periosteal layers, whichj agreeably to what has been stated, are from the first deposited in the form of cribriform lamellae around the ossific-nuclei formed from cartilage, continue to be produced so long as the general growth of the bone goes on, essentially in the same way, constituting the material by which it increases in thickness ; but at the same time, more or less important changes are set up in them ; the most considerable of which take place in the large cylindrical bones. In these, we find, more distinctly indeed after birth, that a large cavity is gradually formed in the interior, which at first contains foetal medulla-cells, and afterwards perfectly formed medulla. This medullary cavity is formed, in exact analogy with the medullary spaces described in the preceding paragraphs, by the solution of the osseous tissue of the shaft ; at first, only of that which is formed from.the primitive cartilaginous rudiment, but soon, also of that deposited from the periosteum upon the former, its de- velopment proceeding in a remarkable manner, as long as the general growth of the bone continues. Whence it comes to pass, that, as, at the ends of the diaphyses, so also on its surfaces, whilst new bone is continually deposited exteriorly, that which is already formed is us continually absorbed in the interior; and in fact these two processes are so combined, that the bone, during its development is, in a certain measure, several times regenerated; and, for instance in the humerus of the adult, does not contain an atom of the osseous tissue which existed at the time of birth, nor does the bone at that period contain any of the tissue of which it was constituted in the embryo at three months. These conditions will be rendered most distinctly intelligible, and especially with respect to the periosteal and cartilage layers, by means of a diagram (fig. 134) which I have for a long time employed in my lectures. If, in this figure, we compare the primordial bone E E with the almost complete .bone E* E*, it is apparent, that in the longitudinal growth of the diaphysrs of the latter on both sides, at the expense of the continually growing epiphysal cartilage, an elongated cone of osseous substance, 1, 2, 1^ 3\ and 3, 4, 3^, 4^, is produced, to which, ultimately, the epiphysal nuclei E* E*, also originating in the cartilage, are joined, whilst, to increase its thick- ness, the tubular layers P, P\ P^ P^ which are constantly increasing in length and, in the middle, in thickness, are applied THE OSSEOUS SYSTEM. 365 to it. In a cylindrical bone of this kind consequently, the entire portion formed from cartilage, presents the figure of a double cone with rounded bases ; and that formed from the periosteal layers, 1, 2, 3, 4, P^ and 1^ 2\ 3\ 4\ P^, the form of an elongated tube thickest in the middle, and re- sembling an elongated vertebra of a Fish,with conically hollowed, termi- nal surfaces. The articular cartilage C, is the unossified portion of the epiphysal cartilage, and the medul- lary cavity which is not shown in the figure (it may be supposed to be indicated pretty nearly by the outlines of the fourth bone E* E^), is formed by the resorption of the entire osseous substance derived from the cartilage and periosteum of the younger bones j— .in this case the first three, E E, E^ E^, and E^ El In the cylindrical bones, with- out a medullary cavity, and in all other bones containing nothing but spongy substance in the in- terior, the absorption does not pro- ceed to nearly the same extent as it does in the above-described cases, that is to say, only to the production of a looser spongy substance in the interior, and> consequently, we find, for instance in the vertebrae, more or Fig. 134. Diagram of the growth of a cylindrical bone. B, primary rudiment the diaphysis ossified and the epiphyses cartilaginous : A, the same hone in four stages of further advance, E'PPE', E=P'P'E', E»P=P=E', E^'P^P^E' ; PP'P'Ps, peri, osteal layers of these four bones ; the space contained within 1, 2, 3, 4, and 1', 2', 3', 4', indicates the portion which in the largest bones is formed from cartilage ; E'E', cartilaginous epiphyses of the second bone; E'E', epiphyses of the third bone, in one of which is an osseous nucleus ; E'E', E^E', epiphyses of the fourth and fifth bones, all with larger epiphysal nuclei : G, articular cartilage ; /, K, interstitial car. tilage between the ossified epiphysis and diaphysis. j:x. 366 SPECIAL HISTOLOGY. less considerable remains even of the earlier bone-substance. In this situation also, the absorption always affects not merely the osseous nucleus, formed from the cartilage, but likewise the periosteal layers, the latest of which only remain more in their original form, as the substantia compacta. The Haversian canals do not originate, as is sufficiently apparent from what has been said, like the cancelli of the primary bone-substance, from a solution of a pre-existing tissue, but are nothing more than open cavities, left from the commence- ment, in the periosteal layers. They are, relatively, of a conside- rable size at an early period, (vid. also 'Valentin. Entw.' p. 263), measuring in the foetal humerus at five months 0'016 — 0'024"', in the femur at birth, according to Harting (p. 78), 0*10 — 0*024"', just as in the most recently formed layers also of a later period. Their contents have been already described. The most impor- tant circumstance connected with them remaining to be noticed, is the mode in which their lamellar systems originate. These lamellae also are formed without the intervention of cartilage, and are nothing more than deposits from the contents of the canals, which substance, as has already been said, iu respect of its fibres and cells, entirely corresponds with the ossific blastema beneath the periosteum, and, in a certain degree, is merely an originally unossified remainder of it. These con- ditions are easily observed in young bones, in which, the periosteal layers, before they have undergone any resolution, are rendered more and more compact by these new, secondary lamellae; but even at a later period a more or less ossified blastema (always without calcareous granules) may very fre- quently be perceived on the walls of the canals in question. Whilst the vascular canals are thus, on the one side undergoing contraction by the deposition of these secondary layers, which, just as in the periosteum itself, appear laminated, — either be- cause the ossific blastema itself is so constructed, or because the deposition of bone takes place with periodical pauses, — they afterwards widen, or at least some of them, by absorption, as for instance, the canales nutritii, the great vascular openings in the apophyses, &c, ; and the compact substance, as has been already remarked, is also, in many places partially, and in some even entirely, absorbed. In what way the bone increases in thickness in the situa- THE OSSEOUS SYSTEM. 367 tibns where tendons and ligaments, without the intervention of periosteum, are directly implanted into it — has not yet been made out. From the circumstance, that in the adult, in many of these situations, true cartilage-cells occur among the tendinou* fibres, and also, that their passage into bone-cells may very clearly be observed, it might perhaps be concluded that a similar process may take place at an earlier period also. In fact, I have seen, even in young individuals, at the points of insertion of many tendons and ligaments {tendo Achillis, lig. calcaneo-cuboideum, aponeurosis plantaris, S^c.) into the bone, cartilage-cells, and their metamorphosis into bone-cells.. Very frequently, also, tendons and ligaments are attached to portions of the bone which remain long in the cartilaginous conditionj epiphyses, tuberositas calcanei, &^c., and the growth of these parts of course, is simply to be referred to the cartilage. [The formation of bone on the inner aspect of the periosteum is a fact long well known, although it has, hitherto, generally been thought, that in this situation also, it was preceded by a thin cartilaginous layer, until the contrary was shown by Sharpey and myself. Since the discovery by Duhamel ('Memoires de PAcademie de Paris,' 1742, p. 384, and 1743, p. 138), that the bones of animals fed upon madder are coloured red, a great number of experiments have been made with that substance, especially by Flourens, in growing animals ; it being at first believed, that it only coloured those parts of the bones which were formed after its administration. This method, however, has lost a good deal of its value since it has been shown by Eutherford (in ' Roberti Blake, Hiberni, Dissert, inaugural, med. de dentium formatione et structure, in homine et in variis animalibus,' Edinb. 1780), Gibson (' Memoirs of the Literary and Philosophical Society of Manchester,' 2d series^ vol. I, p. 146), Bibra (1. c), BruUe and Hugueny (1. c), that when animals are fed upon madder, the whole of the growing bones, as well as the bones of adult animals, become coloured, and especially so wherever they are in more immediate con- nexion with the blood-vessels j for even the medulla is coloured (Bibra). For which reason also, the innermost layers of the Haversian canals, the periosteal surfaces, and the vascular, young bone-substance, acquire a deeper colour. There are, however. 368 SPECIAL HISTOLOGY. still some points worth investigating in this way, particularly with relation to the more recent statements of Brulle and Hugueny, who, relying upon the circumstance, that, as they assert, the decoloration of growing, coloured bones, is effected merely by the absorption of the coloured portions, bdieve they have found that the cylindrical bones also deposit osseous sub- stance from within, particularly in the apophyses ; whilst on the outer surface, absorption to the same extent takes place; statements upon which I will not, at present, give any decided opinion, although at the same time I hold it as quite certain, that in many places an absorption does take place, on the exterior of the bone to a greater or less extent. It is only by such an absorption that the enlargement of the foramen magnum from the sixth year upwards, at which time the portions of bone surrounding it are united, can be ex- plained. And the same may be said with respect to the arches of the vertebra, and numerous vascular and nerve- openings {foramen ovale and rotundum of the sphenoid bone, foramina inter transversaria, canalis caroticus, ifc. ^c). Con- sequently, the law propounded by Serres (Meek. 'Archiv,' 1822, p. 455), that the openings in bone enlarge by the growth of the individual pieces by which they are bounded, is wholly incorrect, as applied to the openings and canals in the middle of bones ; as had been already, to some extent, declared by E. H. Weber and Henle ; and even in other cases it holds good only for the earliest periods. The periosteal layers present a certain contrast to the osseous tissue developed from cartilage. The former constitute prin- cipally thfe firm cortex of the primarily cartilaginous bone, and are characterised by the occurrence of Haversian canals and their lamellar systems, whilst the latter produces the spongy substance, and contains no vascular canals. It must not, how- ever, be forgotten that even the periosteal layers all have, at first, in a certain degree, a spongy structure, and in all these bones, without exception, contribute, and frequently very essen- tially, to the formation of the spongy substance; moreover, that in the cellular substance, which originates from the cartilage, in the apophyses for instance, secondary layers, similar to those of the Haversian canals, and of the spongy substance which is formed out of the periosteal layers, only not THE OSSEOUS SYSTEM. 369 so much developed, appear to be formed. The morphological and chemical relations of the matrix of these two forms of osseous tissue have not as yet been determined. On the other hand the bone-lacunse of both kinds of tissue do not present the least difference.] § 106. Bones not primarily cartilaginous occur, in Man, only in the cranium. They originate outside the primordial cranium, be- tween it and the muscular system, and thus within the struc- tures constituting the vertebral system. They by no means exist as membranous and cartilaginous capsules on the first appearance of the cranium, their formation not commencing till after that of the primordial . cranium, from a secondary blastema, whence, in contradistinction to the other primary bones, the formative material of which exists prior to the com- mencement of ossification, they are termed secondary bones — or, also, because in most places they are in contact with portions of the primordial cranium — covering or overlaying bones (belegknochen). To this class belong, the npper half of the expanded portion of the occipital bone, the parietal, and frontal bones, the squamous portion and tympanic ring of the temporal bone, the nasal, lachrymal, malar and palate bones, the upper and lower jaw, the vomer, and apparently, the internal lamella of the pterygoid process of the sphenoid, and the cornua sphenoidalia. The blastema of these bones, which differs from that of the primary bones, in its being successively developed in a membranous matrix, simultaneously with the process of ossification, not existing previously in any considerable quantity, presents essentially, exactly the same conditions as that of the periosteal layers, and is also ossified in precisely the same way. [The notion that certain cranial bones, in man and the Mammalia, are not developed from cartilage, is by no means new, although the morphology of the question was first established by Rathke, Reichert, Jacobson, and myself; and its histology by Sharpey and myself. But with respect to the latter subject, a controversy still exists as to the true nature of the ossific blastema (as also, of that of the I. 24 370 SPECIAL HISTOLOGY. periosteal layers), — ^whether it be a kind of connective tissue, as I believe, or a sort of cartilage, as Reichert and A. Bidder assert, with respect to which more will be found in my ' Mikroskop. Anat.,' pp. 374, 375.] § 107. The secondary cranial bones, all, in the first instance, com- mence in the form of a minute, elongated, or rounded, osseous nucleus, consisting of a portion of fundamental substance or matrix, with a few lacunae, and which is surrounded by a small quantity of soft blastema. How this nucleus origi- nates, has not yet been observed, although from the way in which its growth proceeds, it might be assumed with certainty, that shortly previous to its first appearance, a minute lamella of the soft blastema is formed in the situation of the future nucleus, which lamella spreading from a single point, becomes ossified by the addition of earthy salts and the metamorphosis of its cells. The primary point of ossification having thus appeared. Fig. 135. for instance in the parietal bone, its growth advances simultaneously with the hori- zontal extension of the mem- r V L'^'^Aw'IWCJ ^Z braniform blastema, in such '' -^ i^'^t^^^X^^^^^'^^ S- * ^^^ *^^* ^ delicate lamina "v.^ -"•f'«R^i.f»T /C Jt!» - composed of reticulated os- seous spicules is shortly pro- duced, from which, slender rays stretch out into the still X ./Vi'mJ JhS^ v!^''^^ uuossified blastema (fig. 135). *" If this formation be ex- amined more closely, it will be observed, that the indi- vidual bone-spicules originate in the membranous blastema, by the ossification of its elements, and, that to a cer- tain extent, the latter is absorbed in the spaces occupied by the spicules, remains of it being left in the interstices; and moreover, that the formation of the osseous elements pro- Fig. 135. Parietal bone of a fourteen-weeks old foetus, x 18 diam. THE OSSEOUS SYSTEM. 371 Kg. 136. A. ceeds exactly in the same way, that it does in the periosteal layers ; the rays of bone as they extend further into the soft blastema becoming softer and paler, and containing less earthy matter, whilst their cells become more and more like the soft formative cells, till, at last, the spicules lose all distinct limitary outline, and are lost in the blastema. At first, the growth of these bones proceeds in a superficial plane only, the rays, as they extend and become connected by transverse branches continuing to add to the size of the original, reticulated lamella, which, however, shortly begins to in- crease in thickness by the deposition of layers upon both sides of it ; the difierent portions, also, in proportion to their age becoming more and more compact. The formation of the thickening layers is to be referred to the periosteum, which is found on the surfaces of the secondary bones, very soon after their formation has begun, being developed either from their original blastema, or from the p '^fi^'^^S; ^ contiguous tissues (perichondrium of the primordial cranium, muscular and tendinous coverings), and proceeds exactly in the same way as in the periosteal layers of the primary bones ; that is to say, on the inner side of the periosteum, a soft blastema is de- posited, which gradually ossifies, from the bone outwards, without its ever being cartilaginous (fig. 136). In this way are now formed, chiefly on the outer, but also on the inner sur- face of the primary osseous lamella, and proceeding outwardly from it, ^ successive, new laminae, in consequence of which, the rudi- mentary bone continually increases in thickness. All these Kg. 136. From the inner surface of the parietal bone of a new-born child, x 300 diam.: a, bone with lacunae, still pale-coloured and soft; i, border of the same i e, ossifying blastema with its fibres and cells. B, three of these cells, x 350 diam. WMSb 373 SPECIAL HISTOLOGY. new lamellaej like the primary one, are at first perforated by reticular openings, and the various sized, roundish or elongated interstices communicate with those of the pre- viously and subsequently formed layers, so that the secondary osseous nuclei, like the periosteal layers, are, from the first, penetrated by a network of canals, which, as in those layers, in part at least, soon present the appearance of Haver- sian canals. At first, filled only with a soft blastema, the remains of the plastic material of the various lamellae, these spaces, in consequence of. the advance of ossification in their interior, — which sometimes takes the form of bridges stretch- ing across them, sometimes of a deposit on their walls, — become more and more contracted. Ultimately, some are entirely closed, whilst others are converted into true vascular canals, the vessels being developed from their contents, which are composed during this time of medulla-cells, and com- municating with those of the periosteum. "V^hen the bone has arrived at this stage, its subsequent changes are readily followed. It continues to increase in breadth and thickness by the constant addition of new blastema on its edges and surfaces, until it has attained its typical form and size, and at the same time, .by the solution of its compact substance, additional spongy tissue (or even large cavities), is formed in its interior, so that eventually, like bone developed from cartilage and periosteal layers, it presents, externally, compact substance with Haversian canals j and internally, medullary spaces (cancelli), although with distinct secondary deposits. [The secondary cranial bones ossify, in part, earlier than the primary, and mostly with only a single nucleus. The soft blastema out of which they are formed, and which, so long as the bones continue to grow, is to be found on their surfaces and edges, does not, like cartilage, grow independently with them, but is developed by degrees, from a plasma successively secreted from the vessels of the periosteum, the two lamellae of which are conjoined at the margin of the ossifying plate. The cells of this plasma, the metamorphosis of which, as in the periosteal layers, cannot be followed in every particular, are elongated, measuring in man, for the most part, 0006 — 0-0 1'", and presenting granular contents THE OSSEOUS SYSTEM. 373 with oval nuclei of 0-0028— 00048'". Such of these cells as are destined for the growth of the bone in thickness, with the exception of those of the glenoid cavity of the temporal bone, never present the slightest resemblance to cartilage-cells, and, together with their matrix, invariably ossify without the appearance of any calcareous particles ; those on the borders or extremities, on the contrary, may, as it appears, subsequently, take on the nature of true cartilage. The most striking example of this kind occurs in the condyle of the inferior maxiUa, where, even during foetal life, a thick cartilaginous layer is deposited, which so long as the growth of the bone continues, precedes its longitudinal growth, exactly like an epiphysal cartilage. I have noticed the same thing in the articular fossa of the temporal bone, where, however, the cartilage is less developed ; at the angle of the inferior maxilla (in the Calf), and at the anterior extremities of each half of the same bone, which are connected by a semi-fibrous, semi- cartilaginous substance, corresponding very nearly with the symphysis. This fact loses much of the singularity which at first sight attaches to it, when we consider that all cartilage is at first soft, and consists of common formative cells. It is, consequently, only necessary, that the formative cells of the soft blastema of the secondary bones, should, at a certain period, pass through the same changes as those undergone by the formative cells of embryonic cartilage, in order to effect the production of cartilage in the bones now in question. Further investigation is required to show, whether cartilage of this kind also occurs as a supplementary addition to other secondary bones, and to what extent, in animals. Still, it may be noticed, that in asserting as I have done, that all ossifications from a soft blastema take place without the deposition of calcareous granules, this statement is only in part correct, because it is quite true, in many cases, that this sort of deposition does occur in them, though never at an early period, and, generally speaking, but rarely. The ossifying margin, moreover, in these cases is never abrupt, as it is in ossifying cartilage. The ultimate changes of the secondary bones have not yet been closely investigated. Their mode of connection with each other, and also with primary bones by suture and coalescence, is tolerably well known. In the vault of the 374 SPECIAL HISTOLOGY. cranium, for instance, as the primary ossific points first appear in the situation of the tuberosities of the parietal and frontal hones, the hones are at first placed widely asunder, and are connected merely hy a fihrous membrane, the continuation of the periosteal lamella of each, and which is united on the internal aspect with the remains of the membranous cranium of the embryo, and with the dura mater. The bones then continue to grow towards each other, and at last, constantly advancing in the above-described continuation of the 'peri- osteum, come very nearly into contact at the frontal and sagittal sutures ; there remains, however, for a long time, one large vacuity, in particular, between them, — the anterior fon- tanelle, — ^but which closes in the second year after birth ; whilst at the same time, the bones, which, up to this period, adjoined each other with a straight line of juncture, send out inter- digitating tooth-like processes, tiU ultimately, when their blastema is wholly consumed, they continue united only by the remains of the periosteum (the sutural cartilage, as it is termed, or better, the sutural ligament), but which also is capable of becoming ossified sooner or later, and, indeed, in- variably first on the inner aspect of the suture, where the tooth-like processes are very little developed. The changes of form in the entire bones during their development are very remarkable, and have hardly been attended to. If a parietal bone, for instance, of a foetus or new-born child, be compared with that of an adult, it will be found that the former is much more curved, and in no way at all represents a piece cut out of the middle of the latter. The adult parietal bone con- sequently must have undergone a very important alteration in the curvature of its surfaces, and this, as mechanical conditions are out of the question, can only have been effected by an unequal deposition of bone internally and externally, in the middle and at the borders ; or by deposition on the one side and absorption on the other. That unequal deposition does actually occur, is seen, for example, in the juga cerebralia and impressiones digitat and which has been particularly shown by Reichert to occur between the primary and secondary bones of the skull (' Zur Streitfrage iiber die Gebilde der Bindesub- stanz, iiber die Spiralfaser und iiber den Primordial-Schadel,' Miiller's 'Archiv,' 1853). Now it seems to us that a tissue which is identical with the embryonic form of 378 SPECIAL HISTOLOGY. ble or active morphological changes. It is true that, during this period, some of the processes above considered go on — such cartilage, which passes into adult cartilage, and differs from cartilage only in the absence of chondrin (in which respect ossified cartilage agrees with it), — is in a mor- phological point of view homologous with cartilage. 3. With respect to the third question, — Sharpey and Kblliker are of opinion that the deposit of calcareous matter and the formation of lacunee take place in the same manner as in cartilage, t. e. that the calcareous salts are deposited evenly through the matrix, leaving spaces round the corpuscles or " nuclei," from which the canaliculi are subsequently developed by resorption. Messrs. Tomes and De Morgan, on the other hand (see passage cited above), maint^n that secondary bone differs from primary, in so far as certain of the corpuscles — " osteal cells," — " arrange them- selves side by side, and together with the transparent blastema in which they lie, become impregnated with ossific matter, and permanently fused with the bone-tissue with which they lie in contact. By the linear arrangement of these osteal cells, lamination is produced. In the case of new laminated bone, the cells are simply ossified without arrangement. Lying amongst the osteal cells will be seen gome which have accumulated around them a quantity/ of tissue which forms a thick invest- ment to them I they then, become granular, and take on in every respect the charac- ters of a lacunal cell. These are found deposited at intervals along the line of ossifi- cation, and becoming blended with the general mass, the granular cell remaining as a lacuna, and sending out processes in all directions" (' Abstract in Proceedings of Royal Society'). We must confess that all we have seen leads us to believe that the former of these accounts is correct. We have never been able to find evidence of any of the cor- puscles becoming converted into "osteal cells," and we believe, for the following reasons, that this process does not take place. In examining the growing Haversian canals in Man, and particularly in the Calf (fig. 136 A, 1), we have very frequently found the innermost layer transparent, glassy, and structureless — exhibiting nothing but the corpuscles {d) lying in lacunae without canaliculi. This layer would be as much as jj^th of an inch thick ; in the layer (c) immediately external to it, however, the " osteal cells" were exceedingly well marked. The inner layer looked like smooth ice, and the outer like ice which had cracked into innumerable tolerably even por- tions — but these cracks were by no means produced by the canaUculi, which, as yet, were hardly at all developed. Now it seems clear that if the " osteal cells" were pro- duced by the calcification of certain of the corpuscles, they ought to be more obvious in the young, inner layer, than in the outer j whereas just the reverse occurs. The fact stated by Messrs. Tomes and De Morgan, that lamination is less obvious in young than in old bone, tends to exactly the same conclusion. Again, if the granular substance between the lacnnse were composed of calcified corpuscles — " osteal cells," — the action of acids ought to bring them out as strongly as it does those of the lacunse ; whereas neither in young bone nor in old can anything of the kind be seen. With respect to the lacunae, again, we have the same remarks to make as when speaking of cartilage. We have never been able to find any trace of the development of the corpuscles (granular cells) into lacunae. As to the tissue which accumulates round them and forms an investment, we have frequently observed the appearance THE OSSEOUS SYSTEM. 379 as the enlargement of the sinuses in the cranial bones, of the points of insertion of muscles and hgaments, and of the vascular described; but this investment vras nothing but the clear, often homogeneous, calcareous matter, gradually encroaching on the matrix and inclosing the cor- puscles. We consider, then, that the process of ossification in primary and secondary bone is identical; the deposition \ \ f ' i ,jr '^^ 4iJ of the calcareous matter in pig_ 135 _^. granules or as a homogeneous infiltration, being of no con- stancy or importance. In r each case the deposit takes place in the matrix, and leaves spaces (lacunae) round the corpuscles (nuclei, granular cells). Subsequently, the canaliculi are developed in the matrix by a process of resorption ; while their walls and those of the lacunae may or may not become chemically dififerentiated from it. At the same time, the matrix may or may not break u into laminae and " osteal cells or granules. Its variabilit in this respect is neithe more nor less remarkabl than the greater or less fibril lation of the correspondin element of connective tissui or than the inconstancy ( the disposition of the cleavag lines of the same element in striped muscle. As little is any line of demarcation to be drawn between primary and secondary bone as regards the tissues from which they proceed. Indifferent tissue, in which calcareous matter is deposited at once, is the basis of secondary bone; an identical tissue — in which to serve a temporary purpose chondrin is deposited, being subsequently withdrawn and replaced by calcareous salts — is the basis of Fig. 136 A. 1, wall of Haversian canal from the metatarsal bone of a Calf; a, structureless matrix ; b, homogeneous calcareous deposit replacing it and forming the inner lamina of the canal; c, more external lamina broken up into "osteal cells;" d, corpuscles; e, lacunae : 2, ossifying cartilage of the Skate, for comparison ; letters as above. Both x 600. 380 SPECIAL HISTOLOGY. channels; but a more extensive new formation of bone, whether periosteal or in the Haversian systems, together with a simultaneous and more considerable absorption, never occurs in them. It was formerly believed that the coloration of the bones of adult animals by madder, proved that deposition of bone substance continued to take place even in them, it being assumed that newly forming osseous tissue only became coloured; but since it has been shown, that bones already formed were likewise coloured by the same agent, and that coloured bones in the adult did not lose their colour (Brulle and Hugueny), this view becomes untenable. Whether in the perfect bone a change, if not of the elementary parts, but still of the atoms, takes place, the same external figure remaining, is another question, for the solution of which microscopy affords no facts. This much is certain, that the organisation of bone is such, that notwith- standing the rigidity of their structure, they are in the most general and most intimate relation with the nutritive plasma of the blood. In every situation where the osseous tissue is in connection with vessels, as on the external surface, in the walls of the medullary cavities and cancelli, and those of the Haversian canals, millions of closely crowded minute openings exist. These convey the blood-plasma, by means of the canalieuli, into the lacunae lying nearest to the surfaces men- tioned, from which it is then conducted by wider canalieuli to the more distant lacunse, as far as the outermost layers of the Haversian lamellae, and those laminae of the great lamellar system which are most remote from the vessels. When the enormous number of the canalieuli and their multifarious anastomoses are considered, it must be allowed that no tissue in the human body is better provided for in respect of the distribution of the blood-plasma, whilst in scarcely any other is the direct conveyance of the fluid to the most minute particles more immediately necessary than in it. There can be no doubt that the fluids, which this "plasmatic vascular system" (Lessing) of the bones, obtains from the blood-vessels, probably somewhat modified by the influence of the nucleus primary bone. And this paragraph may serve as an answer to the fourth ques- tion. If it be correct, we cannot imagine that any distinction of the bones into primary and secondary, upon the ground of their development or non-development from cartilage, can be other than arbitrary. THE OSSEOUS SYSTEM. 381 which, as I have before endeavoured to show, is still retained in every lacuna, are most indispensably requisite for the main- tenance of the. bone; for we see, that when the supply of blood to a bone is impeded by the destruction of the periosteum or of the medulla, by ligature of the vessels of the limb, or by oblitera- tion of the periosteal vessels by pressure from without (aneurism, tumours), necrosis of the parts involved certainly ensues, and can scarcely in any case be altogether obviated by the collateral circulation which actually exists also in the bones {vid. supra). On the other hand we are scarcely, at present, in a condition to say, how the circulation of the plasma in the bones is carried on, though its movement to and from vessels (perhaps from the arterial, through several lamellar systems to the venous) must probably be assumed; or what special changes in the course of the nutrition of bone take place; with the latter in particular we are unacquainted, because the chemical investigation of these changes, and especially of the organic products of decom- position, is stiU altogether imperfect. That the osseous tissue is in a state of constant, and indeed very energetic molecular change, is evidenced not only in its various morbid conditions; but also by the alterations it undergoes in old age. These alterations consist more especially in the disappearance of entire portions of the bones, either externally or internally; of the former, an instance is afforded, in the entire removal of the alveolar processes of the jaws, and the latter is seen in the greater porosity and fragility of every kind of bone, such as the cylindrical bones and those of the cranium, in the enlargement of the vascular openings {vertebra, apophyses), and in the greater roughness of the surfaces of the bones. This senile atrophy of the bones may also be attended consecutively with an internal addition of bone-substance, a sclerosis as it is termed, as in the flat bones of the cranium, in consequence of which, in direct contrast to the phenomena elsewhere presented by senile bone, the diploe disappears, its cancelli becoming filled up by new osseous tissue, whilst the venous spaces and foramina emissaria are obliterated and the entire bone rendered heavier. With, this abundant vascular supply, and certainly not sluggish molecular change, it cannot be surprising that the bones should be so richly furnished with nerves, the principal 383 SPECIAL HISTOLOGY. function of which appears to me to consist in the regulation of the conditions of the vascular system, by their conveying to the central organ (spinal chord) through the sensitive fibres intelli- gence of the state of the vessels, of the quantity of nutritive fluid in the bone, and probably also of the modus of the molecular change going on in themselves, and by means of the motor elements their bringing a reflex influence from it, to the arteries and veins which are manifestly furnished with contractile fibres. These unconscious and involuntary alternations of influence of sensible and motor filaments, are, as it appears to me, the most important phenomena of the innervation in bones, as well as in all other organs, the nerves of which are not constantly in relation with the external world, and make it intelligible, why it is, that no organ, containing nerves and vessels at all, possesses nerves of only one kind. It is not, however, by this, intended to imply that the nerves of bones do not convey conscious perceptions ; it is possible that, through them, we obtain a certain degree of knowledge of the processes going on in the bones, of the degree of fulness of the vascular system, the mechanical influences to which they are exposed from without in the movements caused by the action of the muscles, the weight of the body or of external objects, in lifting weights, mastication, &c.; but in any case this knowledge would be very indeterminate, and the sensation excited not definitely localised, being confused in the general feelings of fatigue, effort, or relaxation. On the other hand it is quite certain that the bones, in man, in many diseases, and in consequence of mechanical injury, afford pain, which latter fact has also been frequently noticed in animals, at all events, upon irritation of the larger nervous trunks of the diaphyses. In man the apophyses in particular, and the vertebral and cranial bones, seem readily to become painful, which is explained by the considerable number of nerves immediately in the spongy substance. The compact substance on the other hand might probably be regarded as scarcely obnoxious to pain; as, for instance, in resections, but not so perhaps the periosteum, which less from its own nerves than as the vehicle of those of the bones before they enter their destination, must naturally be affected in the same way that they are. Whether the nerves of the bones through which, perhaps, the conscious THE OSSEOUS SYSTEM. 383 perceptions, but in any case the painful impressions are conveyed, be identical with those through which the reflex actions, above referred to, are carried on, is not determined; but, looking at the origin of most of the bone-nerves from the cerebro-spinal nerves, such an opinion might perhaps be main- tained, it being premised that the connections of the nerves with the brain are to be regarded as less intimate than in the case, for instance, of the cutaneous nerves. I would, in addition, call attention to the remarkable occurrence of nerves in the cartilage of the septum narium in the Calf, although I am unable to say anything more with respect to their nature than with regard to that of the nerves of bone. [On the subject of the numerous pathological changes which occur in the bones, only some brief remarks can here be made. Fractures readily unite, under but moderately favorable circum- stances, by true bone-substance, which, in the cylindrical bones of animals is preceded by the formation of a true cartilage, a fact of which I and others are satisfied ; whilst, according to Paget, this rarely appears to be the case in man. In the spongy bones, in fractures within the articular capsules, and under unfavorable circumstances, the fractured ends frequently unite merely by a fibrous callus, a sort of articulation being formed between them. After loss of substance the osseous tissue is readily regenerated; and it is the periosteum especially, which, in this case, as in the growth of a bone in thickness, plays the principal part in the restoration; of course by means of the exudation poured out from its vessels. In animals, entire bones of the extremities, and ribs are rege- nerated, pretty nearly in their original figure, not only when the periosteum has been saved, of which many examples are exhibited in Heine's collection in Wiirzburg, but even after entire excision with the periosteum, a rudiment of the bone is reproduced (Heine). In man also, a good many instances have been aflbrded of the reproduction of entire bones, such as the lower jaw, the ribs, the scapula (Chopart); and the cases of isolated, — ^in some instances large, portions of bone being so regenerated are very numerous. It is especially the diaphyses, which are readily replaced, when they have been lost in one way or another, less frequently the spongy bones and spongy 384 SPECIAL HISTOLOGY. parts of bones, and those of the cranium ; in the lattei", how- ever, openings made by the trephine are in many cases filled up, instead of fibrous membrane, with isolated patches of bone, or even with an entire piece of bone; in fact, trephined portions of bone have united exactly in the same way as has been observed to take place with portions of bone half cut off (Pauli). Hypertrophy of bone assumes the most various forms, all of which may be reduced under two principal types: 1. deposits on the surface, or external hyperostoses, which are formed chiefly from the periosteum; and 3. internal or scleroses, which consist in the filling up of the medullary cavities and Haversian canals with new bone, and these two forms may occur either separately or combined. The former takes place in inflammations of the periosteum, either idiopathic or in con- nection with cancer, arthritis, syphilis, &c., the latter not only consecutively in old age, but also in rachitis, osteomalacia and syphilis. With respect to the microscopic conditions of these growths, Virchow deserves the credit of having distinctly indicated ('Archiv, f. pathol. Anat. I,' p. 135), that the bony growths or osteophytes on the cranium are formed by a direct ossiflcation of connective tissue without any preliminary deve- lopment of cartilage, which is also undoubtedly the case in the filling up of the losses of substance in the cranium, in rege- neration proceeding from the periosteum, and in most cases of sclerosis. The newly formed osseous substance is sometimes like the normal (many exostoses), sometimes more dense, with small vascular spaces and large irregular lacunae. Atrophy of the bones is shown in their disappearance in totality in consequence of chronic diseases, paralysis, anchylosis; or in rarefaction of the osseous tissue analogous to senile atrophy, in syphilis, lepra, mercurial cachexy, paralysis, &c. Death of bone {necrosis) is observed in cases where the periosteum has been destroyed ; in inflammations of that membrane and of the bone, &c., for the most part attended with an excessive growth of the remaining sound parts. Peculiar morbid conditions exist in osteomalacia and rachitis, but in neither of these diseases have microscopical researches afforded anything worth mention here, except what has been made known by H. Meyer and myself (11. cc.) with respect to ossification in rachitis. In this case I have found: 1. that in the disproportionately large THE OSSEOUS SYSTEM. 385 epiphysal cartilages, the layer of the ossifying cartilage-cells (those disposed in rows), measured, instead of I'", 2 — 5'" j 2. that the ossifying border is toothed, owing to the circum- stance that the cartilage and bone interlace in various ways; 3. and lastly, that in decidedly rachitic bones, the deposition of calcareous granular particles is wanting, and the cartilage-cells almost invariably, shortly before the matrix, and also without any appearance of calcareous granules, are metamorphosed into bone- cells, on which account the formation of the latter can, in no case, be so well studied as in these bones (vid. supra). Accidental cartilage- and bone-formations are very frequent. The former tissue is met with, notwithstanding that it is incapable of regeneration, and that wounds of it heal only with a fibrous tissue, more rarely with bone (ribs), in very many organs (bones, mammary glands, parotid, testicles, lungs, and skin) forming what is termed enchondroma ; moreover, as a new covering on the osseous growths, at the border of the worn articular ends of bones (Eckei'). The latter is seen in ossi- fications of the permanent cartilages (ribs, larynx, epiglottis, very rarely) of tendons {exerdr-knochen, for example), in the dura mater and arachnoid (Miescher, Eokitansky), in the eye (Valentin), in the ovary, in fibrous membranes {membrana obturatoria), in enchondroma, in fibrous and carcinomatous growths, and in the lungs (Mohr's cysts containing hair). Even in these cases the osseous tissue does not essentially difier from the normal, and it is formed, sometimes from a cartilaginous, sometimes, and in fact mostly, from a soft blastema (Virchow, 1. c. p. 137). In investigations relating to the structure of bone, good sections are, above all things, requisite. With a fine saw, thin slices are made, which are ground with water upon a smooth stone with the finger, or with a second smaller stone, for some minutes (5 — 10), until they are rendered uniformly trans- parent. The sections are then cleaned, and (the fat, if they contain any, being removed by ether) may be employed, being wetted with water, for the study of the Haversian canals and disposition of the lacunae ; and with iurpentine, for that of the various lamellar systems. The lacunae and their prolongations, which, in sections, are dark and very distinct, owing to their being filled with air, are completely filled by thin turpentine, 25 386 SPECIAL HISTOLOGY. so that the latter in great part, and also the former, are very frequently rendered invisible; the same thing happens in water and thicker turpentine, though less rapidly, whence, before these agents have produced their effect throughout, many of the lacunae and canaliculi are beautifully shown. If it be desired to preserve the lacunse and canaliculi permanently visible, it is best to polish a thin section, by rubbing it between two glass plates. It may then be examined without the addition of fluid, and presents as perfect figures as those repre- sented in figs, 115 — 117. The grinding of the bone with oil is not to be recommended, because the lacunse then become filled with the oil, and even after thorough treatment with ether can seldom be rendered distinct. Next to sections of bone, the investigation of the bone-cartilage is the most worth while. This tissue is prepared by the treating of bone in the cold, with diluted hydrochloric acid (1 part acid, 10 — ^30 water), until the fluid, which is to be frequently changed, no longer affords any precipitate with ammonia ; for which purpose, in small fragmenjis of bone, some hours, in entire bones several days, are required. From the cartilage thus obtained, sections are now to be made with a sharp knife in all directions, suitable chiefly for the study of the Haversian canals and lamellae, which may even be raised from the surface. The lacunae, also, are still visible ; their prolongations or canaliculi appear as fine streaks, and their nuclei are seen without fur- ther trouble, especially also after treatment with potass, or in cartilage which has been half dissolved by boiling in water. After longer maceration in hydrochloric acid, the lacunae even become isolated, as stellate bodies with delicate walls, or, in the cementum of the horse's tooth, as structures corresponding to the former cartilage-cells. After long softening of bone- cartilage in water, the lamellar systems of the Haversian canals become more or less completely separated, presenting the appearance of short, coarse fibres among the larger lamellae (Gagliardi's claviculi). If bone be exposed in a platinum capsule to a strong white heat, the organic parts burn away, the bone becoming at first black, and ultimately perfectly white; and if due care be taken, the earthy constituents are left, completely retaining the original figure of the bone. Pre- parations of this kind are proper for the study of the laminated THE OSSEOUS SYSTEM. 387 structure of the compact substance and of the lamellar systems of the Haversian canals, which, in this case also, sometimes appear isolated, as in macerated bone. For the microscopic examination of the inorganic constituents of bone, sections are subjected to heat on platinum foil, but they must be very thin, as they afterwards become more opaque, and, on account of their fragility, except in minute fragments, do not admit of being ground thinner (Bruns) j or sections may be boiled in caustic potass. In either case, the lacunae are seen distinct, and empty, with the beginnings of the canaliculi, in a finely granular matrix. The natural condition of the lacunae is readily seen in perfectly recent bone, in thin sections or lamellse ; as, for instance, in many parts of the bones of the face. In recent bone, also, the vessels may be studied, naturally injected, and with the microscope, being thus, far fitter for the purpose than when injections, which often fail, have been practised, and for the closer examination of which, more- over, the bones must afterwards be macerated in hydrochloric acid, and preserved in oil of turpentine. The nerves of the bones may be seen by the naked eye, on the Nutritious arteries of the larger cylindrical bones, and readily, by the microscope, on the smaller vessels ; those of the periosteum must be studied after the membrane has been rendered transparent by caustic soda or acetic acid. The costal and articular cartilages are the most suitable for the study of cartilage, tlie membranes of the cartilage-cells being evident, sometimes without any addition, sometimes after that of acetic acid or soda, which render the matrix transparent. The development of bone may be investigated in a cylindrical bone, and in the parietal bone ; the formation of the lacunae, in specie, in rachitic bones, and in the osseous surfaces of the symphyses and synchondroses. "^ Literature. — Besides the works cited in §§ 22 and 25, are to be noticed, F. Bidder, 'Zur Histogenese der Knochen,' ('On the Histogenesis of Bone'), in Miiller's 'Arch.,' 1849, p. 292; E. V. Bibra, 'Chemische Untersuchungen iib. die Knochen und Zahne des Menschen und der Wirbelthiere,' (' Chemical Researches on the Bones and Teeth of Man and the Vertebrata') ; Schweinfurt, 1844; Votsch, 'DieHeilung der Knochenbriiche per primam intentionem,' ('Union of Fractures, fee.'); Heidelberg, 1847; KoUiker, 'Ueber 388 SPECIAL HISTOLOGY. Verknocherung bei Rachitis, u. iib. den Bau der Synovialhaute/ ('On Ossification in Rachitis, and on the Structure of the synovial Membranes') ; ' Mitth. der Ziirich. nat. Gesellsch./ 1847, p. 93 ; Rokitansky, ' Beitrage zur Kenntniss des Verknocherungsprocesses,' (' Contributions to a knowledge of the process of Ossification'), in the 'Zeitschrift der Wiener Aerzte,' 1848, p. 1 ; A. Krukenberg, ' Zur Lehre vom Rohrensysteme der Zahne und Knochen,' (' On the Tubular System of the Teeth and Bones'), in Miiller's ' Archiv.,' 1849, p. 403; H, Meyer, 'Der Knorpel u. seine Verknocherung ('Cartilage and its Ossification'), in Miill. 'Archiv.,' 1849, p. 293 ; Virchow, in ' Verhandl. der Wiirzb. phys. med. Ges.,' vol. i. No. 13 ; Robin, 'Observations sur le developpement de la substance et du tissu des os,' in ' Mem. de la Societe de Biologic,' 1850, p. 179; BruUe and Hugueny, 'Experiences sur la developpement des os dans les mammiferes et les oiseaux, Ann. d. Sc. Nat.,' 1845, Nov. p. 283 ; Flourens, in 'Ann. d. Sc. Nat.,' 3 serie XIII, 103, ibid. XV, p. 302, ibid. 1845 ; Aout, p. 105, and Dec. p. 358 ; 'Compt. rend.,^ T. XIX, p. 631 ; all his observations collected in 'Theorie experimentale de .la formation des os,' Paris, 1847-8, avec 7 pi. ; Beck, ' Abh. iib. ein. in Knochen verlaufende Nerven,' Freiburg, 1846; KoUiker, 'Ueber die Nerven der Knocken,' (' On the Nerves of Bone'), in Wurzb. ' Verhandl.,' I ; Luschka, 'Die Nerven in der harten Hirnhaut,' ('The Nerves in the Dura mater'), Tiibingen, 1850 : and ' Die Nerven des Wirbel- canales und der Wirbel,' ('Nerves of the vertebral Canal and of the Vertebrae'), Tiib. 1850. OF THE NERVOUS SYSTEM. ^ 109. The nervous system, regarded in the more general anatomical sense, constitutes a connected whole, consisting of two princi- pal masses — the spinal cord and brain, and of numerous cords — nerves — extending from them to almost all the organs of the body. The two former — or the central nervous system, the THE NERVOUS SYSTEM. 389 central organs, are to be regarded not merely from an anato- mical point of view, as affording origin to the nerves, but, also, in a physiological sense, as excitors of the movements, and seat of the sensations, as well as of the mental or psychical actions, and consequently as belonging to a higher or governing order of parts, whilst to the latter must be ascribed more of a ministerial office — the communication of the contractions and sensations. This mode of regarding the two divisions of the nervous system, however, is only partially correct, because, in the first place, in the central organs, as in the nerves, very many subordinate parts exist; and, secondly, because in the peripheral nervous system, the so-termed ganglia, physiologi- cally and anatomically, represent central organs. The older division also of the nervous system into animal and vegetative, after the observations of recent times, can no longer be main- tained; and the latter, — ^the sympathetic or ganglionic nervous system, can only be regarded as a portion of the peripheral system, though undoubtedly peculiarly constituted. ELEMENTS OE THE NERVOUS SYSTEM. § 110. The nerve-tubes or fibres (figs. 137 — 139), also termed primitive tubes, or primitive fibres of the nerves, are soft, fine, cylindrical filaments, having a diameter of 0-0005^^"01"' ; they constitute the principal part of the nerves and of the white substance of the central organs, although they are not wanting in the greater part of the grey substance of the latter and in the ganglia. When examined in the recent state and by trans- mitted light (fig. 137) they appear as clear as water, transparent, and with simple dark contours ; by reflected light — glistening, opaline, like fat, in larger quantities together, white, and for the most part their appearance does not indicate that they are composed of different constituent parts. But it is readily seen upon the application of various methods, that they consist of three, entirely distinct, component structures, viz. : of a delicate coat, and a viscid fluid, in the centre of which is a soft but elastic fibre. The coat, or sheath of the nerve fibres (limitary membrane. 390 SPECIAL HISTOLOGY. Valentin) (fig. 139, 1, 3, 3, 4, a) is an excessively delicate, flexible but elastic, perfectly structureless and transparent membrane, which, in quite unaltered nerve fibres, except in certain situa- tions, is altogether invisible. But on the application of suitable reagents, at least in the thicker fibres of the nerves and of the central or- gans, it comes readily in- to view, corresponding, in its chemical characters, in all essential particulars with the sarcolemma of the muscular fibres. In the finest fibres of the peripheral, as well as of the central nervous sys- tem, the existence of this membrane has not yet been demonstrated, and it must consequently, for the present, be left un- decided whether these fibres possess sheaths or not. Within the structure- less sheath, lies the nerve-medulla, or pulp, ("medullary sheath," Rosenthal and Purkinje, "white substance," Schwann), (fig. 137, 3, b, fig. 139, 3, 4, b) in the form of a cylindrical tube, closely and exactly surrounding the central fibre. In the recent nerve-fibre this substance is perfectly homogeneous, fluid, but viscid like a thick oil, and, according to the light by which it may be viewed, transparent and clear. Fig. 137. Nervre-iibres, x 350 diam. 1, from the Dog and Kabbit, in their natural condition; a, fine; b, of medium thickness; c, coarse fibre from the peripheral nerves : 2, from the Frog, with the addition of serum ; a, drop of the contents ex- pressed ; b, axis-cylinder within the drop, continued into the tube : 3, from the spinal cord of Man, recent, with serum added; a, sheath; *, medullary sheath with double contour; c, axis-cylinder: 4, double-contoured fibre from the fourth ventricle in Man ; the axis-cylinder, a, projecting and visible within the fibre : 5, two isolated axis-cylinders from the cord, one undulated, the other of unequal thickness, with some medullary substance attached to it. \ V V THE NERVOUS SYSTEM. 391 Fig. 138. or whitisli and pearly, and it is obviously to it that the peculiar glistening appearance of the nerves is due. The nerve- pulp, is rapidly and invariably altered by the application of cold water, of most acids, and of many other reagents, the change consisting principally in a coagulation of it, which takes place gradually from without to within, sometimes involving the entire thickness, sometimes only its outermost layer. In the latter case, are produced the well-known nerve-fibres with double contour lines (fig. 137, 2, 3, 4), or in which the medullary sheath is, externally, coagulated to a greater or less extent, remaining fluid internally ; in the former case, with the con- tents apparently wholly grumous and opaque (fig. 138). The coagulated nerve-medulla, in fact, seldom appears homoge- neous, but most generally grumous, granular, and as if composed of separate, irre- gular, larger and smaller masses, and, upon the ap- plication of acetic acid, as if formed of minute, separate, or reticularly united rods. The nerve-pulp is also al- tered very readily by pres- sure. It sometimes escapes from the ends of the tubes, or from hernial protrusions 'SJ» V i) /// II 1 1 vM // or ruptures of the sheath, forming larger or smaller drops of every imaginable shape, regularly spherical, clavate, fusiform, cylindrical, filamentary, or of the most bizarre figures, which likewise coagulate either on the surface merely, or throughout, and thence, like the nerves, appear with a double contour, or half or wholly grumous. But, within the fibres also, its structural conditions alter, for, in- stead of being continued through them as before, — as a cylinder of uniform size, — it accumulates in places into larger masses. In this way are produced the frequently described, varicose nerve- Fig. 138. Nerve-tubes of Man, x 300 diara.: four fine, two of which are varicose; one of medium size with simple contours ; and four thiclt, two of which have double contours, and two, grumous contents. 392 SPECIAL HISTOLOGY. H- fibres (fig. 138), in which the medullary sheath presents some- times, minute moniliform enlargements, sometimes, various sized, irregularly distributed nodosities, or even, in places, complete interruptions. All these forms, in which the sheath frequently participates, but in which the central fibre takes no part, arise artificially, and are developed most readily in the finer fibres with more delicate sheaths, such as are found in the central organs. The central or axis-fibre of the nerve-tubes ("primitive band," Kemak, cylinder axis, Purkinje, fig. 137, 2, 3, 4, 5. 139, 1), is a cylindrical or slightly flattened filament, which, in entire and unaltered nerve-fibres, is as little recognizable as the sheath, being surrounded by the pulp, and possessing the same refractive power, whilst it comes readily into view when the fibre is torn or treated with various reagents; and it may thus be recognised as a constant structure, sometimes in the interior of the fibre, and sometimes isolated. Un- der natural circumstances it is pale, most generally homogeneous, more rarely, finely granular or striated, bordered by straight or occasionally by irregular, pale contour lines, and it is, generally, everywhere of uniform thickness : it is distinguished from the medullary sheath, especially by the circumstance, that although soft and flexible, it is still, not fluid and viscous, but elastic and solid, something like coagulated albumen, with which it also appears to agree in most of its chemical characters. This axis-cylinder- exists in all nerve-fibres without exception, even in the finest, and invariably presents the same characters, except only, that it Fig. 139. Nerve-fibres, x 350 diam. 1, from the Frog, boiled with alcohol and acetic acid; a, sheath; i, axis-cylindei;; c, crystals (fat ?) : 2, isolated sheath of a Frog's nerve, boiled with soda : 3, from the floor of the fourth ventricle in Man, after treatment with soda ; a, sheath ; 6, medulla flowing out in drops, the axis-cylinder is wanting (having been drawn out in the preparation), and the pale streak is medulla: 4, from the root of the n. abducent of Man, treated with soda; a, sheath; b, medulla, axis-cylinder not visible. w THE NERVOUS SYSTEM. 393 is sometimes thicker, sometimes more slender, according to the size of the fibre itself. The nerve-fibres in which the three structures above described can be distinguished, and which we would designate as the medullated or dark bordered, constitute, it is true, the greater proportion of those existing in the body, but besides these there are still some forms requiring more particular description. These are the nerve-fibres in which there exists no trace of a medullary sheath ; whilst they have an outer sheath and con- tents, sometimes identical with the axis-fibre of the other kind of nerves, sometimes similar but more clear. These non-medul- lated nerve-tubes occur, in the first place, as continuations to the other sort, where the latter are in connexion with nerve- cells; and also as more elongated, independent fibres, represent- ing the so-termed processes of the nerve-cells of authors; and lastly, at the terminations of the dark bordered nerves. They may again be arranged in several sub-divisions, distinguished respectively by their having, or not having nuclei, and more or less transparent, more or less consistent contents. It must also be added, that the dark bordered fibres difier extremely — partly in respect of the delicacy or firmness of their structure, and partly in their diameter, which varies from 00005 — to 001"' or more, so that they may be distinguished into fine and coarse, delicate or firm fibres; from which it is evident that the nerve-fibres, notwithstanding their general tubular character, still differ pretty widely from each other in various respects. [The tunic or sheath of the nerve-fibres, discovered by Schwann, in most nerves is brought into view with some difficulty. It is only rarely, as in the roots of certain cerebral nerves (those of the muscles of the eye for instance), and of the spinal nerves that it appears distinct from the contents; its presence how- ever is, with certainty, and readily demonstrated by the aid of chemical reagents. When the nerves are boiled in absolute alcohol, soon after the removal of a considerable part of the fatty matter of the pulp, the sheaths become tolerably distinct, as dark boundary lines; and they are rendered remarkably and beautifully so by a short boiling in acetic acid, during which, the remaining contents of the nerve-sheaths, with the excep- 394 SPECIAL HISTOLOGY. tion of tKe central fibre, escape from them, whilst at the same time numerous (fat) crystals (fig. 139, I) are formed. When boiled in alcohol and treated in the cold with caustic soda, the nerve-fibres also exhibit the sheaths very beautifully, as pale, frequently undulating contours of the colourless, remaining con- tents ; and when such fibres are boiled for a moment in caustic soda, numerous, elongated fragments of perfectly empty, some- what swollen nerve-sheaths, are detached, which, from their delicacy, present a striking resemblance to the empty tubules of the Twrnhrana 'propria of the tubuli uriniferi (fig. 139, 2). The sheaths, however, are rendered most distinct by means of fuming nitric acid and the subsequent addition of caustic potass. In this case the fatty matter of the medullary sheath escapes from the tubes in the form of colourless drops, the axis cyhnder is dissolved, and the yellow sheaths are left empty, dilated and with swollen walls of 0-0004— 0-0008"' in thickness. In nerves treated with corrosive sublimate, according to Czerm^k (' Zeitsh f. wissenjsch, Zoologie.' 1 850) the sheaths are, also, often very prettily shown. It has not yet been determined whether the finest nervei-fibres in the central organs, and in the peripheral nerves (under 0"001"') possess a structureless sheath. Analogy with the coarser fibres is in favour of the existence of such sheaths, but on the other hand there are some facts which would seem to indicate that there are also, sheathless primitive nerve fibres, both of the medullated and of the non-meduUated kinds. I have already (in my 'MicroscopicalAnatomy,' 11,1,396) remarked, that according to my observations in the Tadpole, several dark-bordered fibres are developed in one and the same structureless, sheath formed by the coalescence of cell membranes ; and that a similar thing (at least from R. Wag- ner's figures) occurs in the electric organ of the Torpedo .- in which cases special tunics can scarcely be supposed to exist around each separate fibre. And, quite recently, Stannius ('Giott. Nachr.,' 1850) has found, in Petromyzon, that the nerve fibres of the central organs possess neither membranous sheath nor pulp,. and are, as it may be expressed, nothing more than free axis-fibres. When to this, it is also added, that the impossibility of demonstrating membranes, by no means certainly proves their non-existence, still, the facts stated are worthy of all consideration, and we must, in this ques- THE NERVOUS SYSTEM. 395 tion^ for the present, abstain from all conclusions drawn from analogy. In order to see the medullary sheath or nerve-pulp in its normal condition, a nerve of an animal just killed, without any addition, must be quickly brought under the microscope ; in which case some isolated fibres will always be seen quite unchanged, although, as the nerve dries, they are very rapidly altered. Besides this method, I would also recommend the examination of the nerves in the transpareint parts of animals, either alive or just killed (nictitating membrane, mucous mem- brane of the Frog, tail of Tadpole, &c.), the observing of them on warmed pieces of glass (Stark.), and after treatment with chromic acid, which frequently preserves, particularly the cere- bral fibres, quite uninjured. The nerve-pulp or medulla is obviously a viscid, fluid, extensible, glutinous substance, to be compared in point of consistence with thick oil of turpentine, and which under pressure assumes all possible figures, appear- ing in the form of globules, filaments^ and membranous masses, of very difierent aspects, with pale or dark borders, and opaque or clear. In chemical composition it consists principally of fatty matter. The central filament of the nerve-fibres, which was perhaps seen as early as by Fontana, and with which we have become better acquainted under the name of " primitive band " given to it by Remak, or " cylinder-axis/' as it has been termed by Rosenthal and Purkinje, is indisputably the most difiicult of investigation, and the least known portion of the nerves. There is no microscopist who has not frequently seen this axis- fibre, but it may, vrithout fear of contradiction, also be asserted, that there is none, not even excepting Remak himself, its dis- coverer, who can boast that he has studied and learned its relations in every particular. For this reason, but few, as Hannover and J. Miiller, are unconditionally agreed, with Remak and Purkinje in regarding the axis-cylinder as a con- stant element in recent nerve, whilst most observers have adopted the views of Valentin ('Repert.' 1838, p. 76, 1839, p. 79), and Henle (' Allg. Anat.^), who regard it as not always present, but rather as a secondary formation, which does not exist during life, and as the uncoagulated central portion of the contents of the nerve-fibre, which, during life, are homo- 396 SPECIAL HISTOLOGY. geneous. I have endeavoured to the utmost of my power to investigate the relations of this structure, and have arrived at the following results : 1. The axis-cylinder, is constantly present in every nerve- fibre, both central and peripheral, in fine and in coarse fibres, and after death is apparent be/ore the nerves are treated with any reagent whatsoever. In the human nerves, in the brain and spinal cord, as they are commonly obtained for examination, the axis-cylinder, when duly sought for, is everywhere and with certainty to be recognised ; and in fact by far the most easily in the central organs, where the absence of neurilemma and the delicacy of the nerve-sheaths oppose but little hindrance to the tearing asunder of the fibres. In these situations it may he seen in nearly the finest fibres. It always presents the aspect of a pale filament, which, together with a tolerable degree of con- sistence, is still very flexible and at the same time highly elastic, as may be readily observed on compression of small portions of the spinal cord (in which case very many axis-cylinders are stretched and torn, retracting considerably and forming undu- lating curves). On the average it is about one third as wide as its nerve-fibre, and consequently varies a good deal in diameter, is obviously quite solid, most generally homogeneous, but not unfrequently also, faintly striated or very finely granular. It most usually follows a straight course, bordered by two parallel, pale contour lines, occasionally, however, it is, in parts, thicker or more slender, though it never presents varicosities like the nerve-fibres ; and it may, moreover, be curved or even slightly undulating, and also perhaps with an irregular, even jagged border. 2. When recent nerve-fibres of an animal just killed are treated with proper reagents, the axis-fibre instantaneously appears. If a thin cutaneous nerve of the Frog, whilst under examination with a power magnifying 100 times — ^be touched with a drop oi glacial or concentrated acetic add, the nerve retracts and there appear instantaneously, at each of the cut ends, large particles of the grumous nerve-pulp, and pale, clear fibres ; and the same thing happens if the nerve have been previously teased out, and the fibres brought separately into view. The clear fibres are evidently the axis-fibres, as they may readily be traced into the projecting medullary sheaths and entire nerve-tubes. THE NERVOUS SYSTEM. 397 and in other respects, also, present all the characters of those fihres, only that they are much paler and broader (as much as 0'004"' in the peripheral thick fibres) and evidently swollen ; they frequently, also, appear convoluted, or even spirally rolled, which is owing, simply to the shortening of the whole nerve caused by the acetic acid. The nerve-pulp itself is rendered grumous by the same reagent ; the grumous particles are some- times granules, sometimes very short rods, like fat-crystals, which latter may be very often seen on the nerve- fibres, form- ing stellate, acicular groups (margaric acid) ; alcohol and ether, also render the axis-cylinder very distinct, both, when recent nerves are treated with those reagents in the cold, in which case their action must be rather more prolonged, and when they are boiled in them. I can particularly recommend the boiling in absolute alcohol, by which means excellent preparations of the axis-fibres may be made, and in the shortest time. Under this treatment the nerves become firmer, but stUl admit of being readily torn into fibres, and always exhibit very numerous, isolated central fibres of considerable length, which, contrasted with those brought into view by means of acetic acid, are, as it were, contracted (at most 0"002"' wide), yellowish, firmer, and often convoluted or twisted. Ether acts in the same manner. By both reagents the medullary sheaths are rendered paler and grumous, the grumous particles frequently appearing, as it were, to be united into a delicate network. When nerve-fibres are boiled, first in ether and afterwards in alcohol, they become quite pale, but the sheath and axis-cylinder perfectly dis- tinct, the latter presenting precisely the same appearance as after treatment with alcohol alone. Consequently, it would seem, that the axis-fibres contain no trace of fatty matter; at all events, except that they shrink a little, they are not altered by the action of ether and alcohol, and afterwards, also, again enlarge, under acetic acid, into broad pale bands. Besides the reagents above mentioned, the axis-fibres are particularly well displayed by chromic acid (Hannover), corrosive sublimate (Purkinje, Czermkk), and gallic acid, but less readily in recent nerves, in which, it is true that they become instantaneously manifest, although it is never, except by accident, and rarely, that they can be isolated, than, especially after a more prolonged immersion in those fluids. The nerve-fibres under these 398 SPECIAL HISTOLOGY. circumstances appear contracted, the medullary sheath grumous, the axis-cylinder more opaque and somewhat diminished, in chromic acid yellowish, hut in other respects exactly as above described. In the acoustic nerve of the Sturgeon, Czerm^k, by means of corrosive sublimate, has demonstrated, in dividing nerve-fibres, the existence, also, of bifurcating axis-cylinders. Iodine also or iodine combined with aqueous hydriodic acid (Lehmann) act very powerfully. In quite recent nerves it instantaneously renders the medullary sheath wholly grumous, and, not only isolates numerous, somewhat shrunken axis-fibres, for a considerable length, but renders them in many nerve- fibres very distinct in situ, and usually appearing convoluted or serpentine. Hydrochloric-, sulphuric-, and fuming nitric acids, in certain cases, also render the axis-cylinders apparent (Lehmann). 3. The axis-cylinder consists of a solid protein compound differing from common fibrin, and from the fibrin of the muscles. The chemical nature of the axis-cylinder is difficult of investi- gation, because it cannot be obtained in an isolated form in large quantity ; something, neverthelessj may be learned from microchemical reaction as has been shown by Lehmann and myself. In concentrated acetic acid it swells up considerably, but is dissolved with difficulty, and even after it has been boiled continuously for several minutes, although pale, it always remains unchanged. When boiled for a longer time in acetic acid it dissolves, exactly like coagulated albumen, whilst the sheaths and some of the contents remain undissolved. Alkalies (p6tass, soda, ammonia), in the cold, attack the axis-cylinder but slowly, though in soda it instantaneously becomes very pale and swells up to 0-004 — O'OOS or even 0'006"'. Longer immersion in soda dissolves it, and the same thing takes place upon its being boiled, soon after the commencement of ebullition in the fluid. In fuming nitric acid, it disappears in a short time — less than half a minute, — exactly as is the case with coagulated albumen. Treated with nitric acid and potass the axis-cylinder is rendered yellow (xanthoproteinic acid) and maybe seen spirallycontracted, within the nerve-fibres, which are also shortened, but not to the same extent. On the other hand it is not coloured by sugar and concentrated sulphuric acid, which redden coagulated albumen, at most acquiring a yellowish or pale-reddish hue. In water the THE NERVOUS SYSTEM. 399 axis-cylinder is unchanged, even when boiled, in which case it is readily isolated and appears somewhat contracted ; by ether and alcohol it is undissolved even by boiling, but shrinks to some extent. The latter effect is produced also by corrosive sublimate, chromic acid, iodine, and carbonate of potass. Viewing all these reactions together, it might perhaps be stated with certainty, that the axis cylinder is a coagulated protein compound which, however, differs from fibrin, inasmuch as it is insoluble in carbonate of potass and solution of nitre, and offers much greater resistance to acetic acid and caustic alkalies. On the other hand, it agrees with the substance of which the muscular fibres are composed, in its elasticity and insolubility in carbonate of potass, differing from it in its insolubility in dilute hydrochloric acid, and difficult solubility in acetic acid. These are the most important facts connected with the axis- cylinder. The conclusion which may be drawn from them, appears to me, to be simply this, that the axis-cylinder is not an artificial product, but that it must be regarded as an essential constituent of the living nerves. The only objection which can be urged against this opinion consists in the circumstance, that the axis-fibre cannot be seen in living fresh nerves, and that it cannot generally be distinguished, as a special structure, in the interior of the nerve-tubes without the aid of reagents. But it must be remarked that it can also be brought into view in nerves that are still warm. Thus I find well-marked projecting axis-fibres at the roots of the cerebral nerves in Frogs just killed, which I have examined as quickly as possible, after the application of a solution of sugar, particularly in those of the optic, trigeminal, and vagus, also in the spinal nerves, for instance in the second. I see them under the same conditions in the peripheral nerves of the Frog that have been teased out, and, in these nerves, have on several occasions, even distinctly noticed the axis-fibres in the form of convoluted filaments, in larger drops of the nerve- pulp expressed from the tubes (fig. 137, 2). The only fact, therefore, that can be adduced in opposition, is this, that it is quite true that the axis-fibre cannot, with certainty, be perceived in the interior of the recent nerve-tubes themselves, except upon the application of some reagent ; but this circumstance obviously proves nothing at all, because neither can it be seen in the interior 400 SPECIAL HISTOLOGY. of tubes of less recent nerve substance, all of which, as innumera- ble examples of isolated axis-fibres occurring in them, show, invariably contain such fibres. The axis-cylinder, possessing the same refractive power as the still fluid part of the medullary sheath, is necessarily indistinguishable from it, but from this circumstance we cannot conclude that it is absent, nor, equally, can such a conclusion be drawn from its invisibility in the recent nerve-fibril. Taking all these circumstances together, I am firmly convinced that a special, central structure exists even in recent nerves, which is distinguished from the more ex- ternal portion, — ^that is, from the medullary sheath, — not only by its chemical composition, as appears to me to have been placed beyond all doubt, but also by its consistence and elasticity, as well as by its possessing a determinate form. The condition in which we obtain the axis-fibre in the human nerves and central organs, by the addition of the serum of the blood, albumen, or vitreous humour, appears to me to represent its natural state ; on the other hand alcohol, ether, iodine, corrosive sublimate, gallic-, and chromic acid render it more consis- tent than it is normally; whilst acetic acid, dilute nitric, acid, and alkalies exhibit it paler and more swollen. The nerve-pulp forms a semi-fluid cortex around the axis-fibre, and, though intimately connected, is not continuous with it. By pressure, therefore, the pulp may very frequently be expressed, by itself, from the ends of the tubes or from lateral rents of the sheath. The drops of pulp thus formed, usually coagulate on the surface, remaining clear and transparent in the interior, like the central portion of the nerve-tubes. Many authors have described these bodies as portions of the whole contents of the nerve-tube, and have regarded their formation as a proof against the pre-existence of the axis-fibre, but incorrectly. They belong to the medullary sheath only, which, in the interior of all nerve-fibres with only a double contour, is still for some space perfectly clear and bright. An axis- fibre and a clear space, in fibres having a double contour, are therefore by no means identical, and it is not at all surprising, nor opposed to the existence of an axis-cylinder, that a multitude of drops with a double contour and clear contents should be obtained from such fibres. The medullary sheath may also coagulate entirely, and then the axis-fibre remains evident. THE NERVOUS SYSTEM. 401 sometimes as a transparent streak of uniform breadth throughout; sometimes, when the grumous particles are more numerous, it may be concealed by them, so that the entire contents of the nerve appear to be coagulated; They are so, however, only in appearance, the clear fibre always lying in the interior ; and I have never yet seen it coagulated or grumous; Non-medullated nerve-fibres occur in many situations. I enumerate among them : ] . the pale fibres in the Pacinian bodies ; 2. the nucleated pale fibres in the terminations of the olfactory nerves ; 3. the perfectly transparent, non-nucleated nerve-fibres in the cornea ; 4. the pale, branched, and partially anastomosing terminations of the nerves in the electrical organ of the Torpedo and Ray (E. Wagner, Ecker) ; 5. the similarly constituted terminations of the nerves in the skin of the Mouse {vid. 'Mikroskop. Anatomic,' § 11); 6. the pale processes of the nerve-cells in the central organs and ganglia, even though they may not all pass into dark-bordered fibres. Of these fibres, those which occur at the extremities of nerves were, even by the earliest observers of them, unconditionally regarded as nerve- fibres; and as respects the processes of the nerve-cells, I described this to be their nature as early as the year 1846; but these views could not be considered as fully established, until the relation of the fibres with the elements presenting the dark borders was completely elucidated. But since it has been ascertained by Schwann, Ecker, and myself, that the nerve-fibres of the embryo are in precisely the same condition as the pale fibres now in question, and since I, Wagner, Robin, and Bidder and Reichert, have shown that the pale processes of the nerve-cells pass into dark -bordered fibres, it has become more possible to arrive at positive conclusions on the subject. R. Wagner was the first to broach the supposition, that the pale fibres in the Pacinian bodies, and in the electric organs, were nerve-sheaths, with axis- cylinders, and that the processes which pass into nerve-fibres^ were themselves bare axis-cylinders, and, moreover, that the entire granular contents of a nerve-cell are nothing but an axis-cylinder enlarged into a globular form ; and after I had demonstrated the constant existence of the axis-cylinder in the living nerve, and that it was a structure distinct from the medullary sheath, I considered myself fully justified in asserting that the dark-bordered nerve-fibres were in direct connection on I. 26 402 SPECIAL HISTOLOGY. the one side through the axis-cylinder, with the pale processes of the nerve-cells and the contents of those cells, and on the other, that they passed into the pale terminal nerves in the situations above mentioned. But this, by itself, as I believe, affords no ground for the identification of the pale fibres in question, or the contents of the nerve-cells, with the axis-cylinders. This could only be established, if we knew with certainty that the medullary sheath of the dark-bordered nerve-fibres is super- added from without to the contents of the pale embryonic fibres during the development of the nerves, and is an entirely new formation between those coiitents and the membranous sheath. This is not the case, however, it being on the contrary more pro- bable that the medullary sheath, which is also albuminous, is developed merely from a metamorphosis of the outermost part of the embryonic nerve-contents, that is to say from the development of fat in it, and that the axis-cylinder is the unaltered innermost part of those contents. In this case all the structures, the nature of which we are now discussing, would represent, not bare axis-cylinders, but an entire embryonic nerve-tube, the contents of which were still homogeneous, or had not undergone differentiation, and would also be in continuous connection with all the parts of the dark-bordered fibres, — a mode of explaining them to which, at all events at present, I am disposed to give the preference. In addition I would remark, that the pale nerve-fibres are also met with in different stages of development. The nucleated fibres in the olfactory membrane remain altogether in the stage of embryonic fibres, as also, to all appearance, do the pale ramifications in the electric organ, and the contents of both these kinds of nerve-tubes would appear to have little agreement, in their consistence, with an axis-fibre J in the Pacinian bodies the contents of the pale fibres, in all respects, represent an axis-fibre, for it is probable that a sheath also exists in this situation ; in the cornea, the contents of the transparent terminal nerve-tubules are appa- rently more fluid ; and, lastly, with respect to the processes of the nerve-cells, they consist, whether they have a delicate sheath or not, of a substance often exactly resembling an axis-cylinder, but which is also frequently of softer consistence, corresponding with the contents of the nerve-cell. The contents of the pale non-medullated nerve-tubes, therefore, although genetically THE NERVOUS SYSTEM. 403 comprehending more than an axis-fibre, still in all probability are capable pretty nearly of assuming its nature.] § 111. The nerve-cells, (accessory corpuscles (Belegungskorper), • nerve-corpuscles, Valentin), (fig. 140), are nucleated cells, occurring in great numbers in the grey or coloured substance of the central organs, in the ganglia, and occasionally also in the trunks, and peripheral expansions of the nerves {retina, cochlea, vestibule). The nerve-cells are covered externally by a delicate, structureless membrane, which in the cells of the ganglia (ganglion-cells, -globules, -corpuscles), may be demonstrated easily, but with great difficulty in those of the Fig. 140. central organs; the application of re-agents, however, will suffice to show, pretty distinctly, that the membrane exists around the larger cells, even in these situations, whilst in the smallest, just as in the finest nerve-fibres, no membrane has rig. 140. Nerve-cells, x 350 diam., from the acoustic nerve: 1, nerve-cells with the origin of a fibre, from the anastomosis between the facial and auditory nerves, in the meatus audit, int. of the Ox ; a, membrane of the cell ; b, contents ; c, pigment ; d, nucleus ; e, continuation of the sheath upon the nerve-fibre ; /, nerve-fibre : 2, two nerve-cells with fibres, from the n. ampii^l. infer, of the Ox ; a, sheath with nuclei ; b, membrane of the cell ; c, nucleus ; d, the origin of a fibre with nucleated sheath : 3, isolated contents of a nerve-cell, with nucleus and two nucleoli. For these draw- ings I am indebted to Dr. Corti. 404 SPECIAL HISTOLOGY. yet been observed, although one probably exists. The contents of the nerve-cells are a soft, but tenacious, elastic substance, which besides the nucleus consists of two elements ; firstly, of a clear, homogeneous, light-yellowish, or colourless matrix, upon which the physical properties of the contents depend, and which is a protein-compound; and, secondly, of minute granules of different kinds. In the colourless nerve-cells these present the form of uniform, roundish, for the most part, minute and pale, more rarely, darker and larger corpuscles dispersed throughout the entire contents of the cell, and imbedded in the tenacious matrix; whilst in the coloured cells, instead of these granules, more or less yellowish, brown or blackish corpuscles occur. The latter are most usually of a larger size, and are placed, closely aggregated, in a mass near the nucleus ; in other instances, they nearly fill the entire cell, giving it the aspect, in all respects, of a brown or blackish pigment-ceU. In the midst of these contents lies the nucleus, for the most part as a very clear, spherical vesicle with distinct walls, perfectly transparent contents, and one, or more rarely several, large opaque nucleoli, which occasionally exhibit a cavity. The size of the nerve-cells varies very much ; like the fibres, they occur as large, small, and middle-sized. The extreme dimensions of the cells are 0003 — 0-003'" and 005 — 0-06'". The nuclei, which for the most part are in proportion to the cells, measure from 0-0015 — 0-008'"; the nucleoli 0-0005 — 0-003"'. The nerve-ceUs, moreover, are distinguished accord- ing as they are : 1. thin or thick-walled, of which the former are found almost wholly in the spinal-cord and brain ; and 2. as they are independent cells, or are furnished with pale processes, of which they may have one, two, or several (uni-, bi-, multi- polar cells), and which are frequently ramified, and the former, in many situations, continuous with dark-bordered nerve-fibres, and even having the nature of non-meduUated nerve-fibres. Besides the nerve-cells, there also exist in the grey substance of the higher central organs, as constant constituents, a finely granular pale substance, which has the greatest resemblance to the contents of the cells, and besides this, in places, large accumulations of free cell-nuclei. Similar elements are con- tained in the retina, and according to Wagner and Robin in the ganglia of the Plagiostomata. THE NERVOUS SYSTEM. 405 [The nerve-cells are simple cells, as which they were under- stood even by Schwann ; this is clearly and manifestly shown by their form, their chemical composition, and their develop- ment. When Bidder, more lately (1. c), relying upon the fact that the nerve-cells in many situations are in connection at each end with dark-bordered nerve-fibres, propounds the opinion that they are membraneless masses, imbedded in dilatations of the nerve-tubes, he has overlooked those cells from which no fibres are given off, which possess exactly the same membrane as those with processes ; and has not considered that there also exist nerve-cells with a single, and others with numerous processes, as applied to which, his view would be altogether unnatural; and lastly, that the development of these bodies indicates that the nerve-cell is formed, in toto, whether it possess processes or not, from a simple cell. It has not yet been determined whether the nerve-cells of the large central organs have membranes or not; Stannius was unable to detect them in the Lamprey, and E. Wagner says the same of the nerve-corpuscles of the electric lobes of the Ray. I think I have seen a membrane in the large, many- rayed corpuscles in the spinal-cord and cerebellum of man, and occasionally, also, in others, but I freely acknowledge that no membrane can be detected in all the smaller cells, nor in the processes of the central cells in general. This does not, however, appear sufficient to justify the denial of the existence of membranes in these instances, and I believe, that in this case, as in that of the finest nerve-tubes, we must for the pre- sent abstain from any definitive opinion. The processes of the nerve-cells, in the brain and spinal-cord, which were first noticed by Purkinje, will be more minutely described when we come to speak of the central organs, and the question will there be discussed as to their relation to the central fibres. In the ganglia, there are no cells with branched processes, instead of which we find only those with one, two, rarely three or four, pale appendages, which are continuous with dark- bordered tubes. The nerve-cells consist, for the most part, of a coagulated, although soft protein-compound, which appears to correspond very closely with that of the axis-fibres. It has not been ascertained whether the membranes and nuclei differ essentially from it. The fatty matter, which has also been 7-5 9-9 10 13-9 3-7 0-9 1-4 10 1-2 1-3 406 SPECIAL HISTOLOGY. found iu small quantity in the grey substance, constitutes in every case the opaque granules in the cells, and appears to exist in other conditions also, in their contents. When isolated nerve-cells are compressed, they become much flattened, re- suming their pristine form when the pressure is removed. Their processes also are very elastic, and like the axis-fibres may be considerably extended, and afterwards again retract themselves. As our knowledge of the chemical composition of the grey and white substance still leaves much to be desired, I content myself with the following statements. Lassaigne, in the brain of a lunatic, found — Grey mhstance. White substance. Water 85.2 73-0 Albuminous matter Colourless fat Red fat Osmazome, lactates Phosphates According to Premy (Comptes rendus, torn, ix, p. 703, 'Ann. d. Chem, und Pharm. 1841,' vol. xl, p. 69), the brain (both substances together) contains — Water 80 Albumen 7 Fatty matter 5 Osmazome and salts 8 100 Which almost exactly agrees with Vauquelin's analysis, who moreover estimates the osmazome at 1-12, and the salts at 6-65; whilst it differs from that of Denis, who found much more fatty matter (12-40 in man 20 years old, 13-3 in one aged 78), and less water (78 and 76g). CENTEAIi NEEVOUS SYSTEM. § 113. Spinal Cord, — The nervous elements are so disposed in the spinal cord, that its external, white substance is constituted almost exclusively of nerve-fibres, whilst the grey nuclear por^ THE NERVOUS SYSTEM. 407 tion with its prolongationSj the cornua, or horns, is formed, in almost equal proportions, of nerve-fibres and cells. The white substance of the spinal cord may, for the purpose of description, be most conveniently, and in accordance with usage, divided into two halves, and each of these into three columns. The anterior columns {funiculi anteriores), are, towards the interior, almost completely separated from each other by the anterior fissure (fissura anterior), which extends the whole length of the cord, and into which a vascular pro- cess of the pia mater penetrates. At the bottom of the fissure, however, the columns are united by. the anterior^ or white com- missure {com. alba) ; externally, they extend as far as the points of exit of the anterior roots of the nerves, or to the sulcus lateralis anterior, but are here inseparably connected with the lateral columns {funiculi laterales), which again, at the points of exit of the posterior roots, where the sulcus lateralis posterior is situate, are continuous, without any line of demar- cation, with the posterior columns. The latter {funiculi pos- teriores) appear indeed as if they were in contact in the posterior mesial line, because the posterior longitudinal fissure described by many anatomists, does not exist in man, except in the lumbar enlargement of the cord, and in the superior cervical region ; but they are nevertheless separated, to such a degree, throughout the whole length of the cord by very numerous vessels, which in the posterior mesial line penetrate as far as the grey nuclear portion, that the columns in most places are not even in contact, and even where they are, they are merely in juxtaposition, and never by any means continuous into each other. Thus the white substance of the cord represents two halves, united only by the anterior white commissure, and each of which is divided more artificially into three columns, which occupy the depressions left between the projecting processes of the grey substance. The grey substance presents a central portion, more of a riband-like form, and four laminse projecting laterally from it, so that its transverse section forms a cross. The central por- tion or the grey commissure, in the adult, does not, normally, contain any canal, such as exists in the foetus, and consists of a central, cylindrical, or flattened tract, constituted principally of nerve-cells, of a yellowish colour, — the g7-ey nucleus 408 SPECIAL HISTOLOGY. {subst. ffrisea centralis), and of nerve-fibres running trans- versely, continued beyond the nucleus, before and behind it — the grey, or posterior commissures. Of the laminae, in a transverse sec- tion also termed horns, the anterior are thicker, and shorter, of a uni- form grey colour, composed of larger and smaller nerve-cells, and of deli- cate nerve-fibres of medium fineness; the posterior, longer and thinner, are constituted at their roots like the former, only most usually of _ smaller cells ; but at the free edge are invested with a more transparent layer, containing a preponderance of smaller nerve-cells — ^the substantia gelatinosa of Rolando. Of the roots of the spinal- nerves, the anterior penetrate between the anterior and lateral columns, directly to the anterior horns, and the posterior are lost between the lateral and posterior columns, passing through the substantia gelatinosa into the posterior laminae or horns. With respect to the intimate structure of the spinal-cord, we have to distinguish, in the white substance: — 1. horizontal; and 2. longitudinal fibres. The latter, in all situations, ex- cept in the anterior commissure, are in great part altogether unmixed with horizontal fibres, and everywhere, both super- ficially and deeply, run parallel with each other, but they are never interlaced, nor do they ever constitute smaller fasciculi. The number diminishes from above downwards, because, as Fig. 141. Transverse section through the spinal cord in the superior lumbar region, magnified about 30 diam., half diagrammatic : a, anterior column ; h, lateral columns, motor portion ; c, lateral columns, sensitive portion ; d, posterior columns ; e, anterior longitudinal fissure ; /, posterior longitudinal fissure ; g, motor roots ; h, their internal fasciculus ; i, their external fasciculus ; k, decussation of the anterior columns in the anterior commissure ; /, grey fibres of the lateral columns passing into the anterior. grey commissure; m, grey central nucleus, here internally with two groups of somevphat darljcr cells ; n, posterior grey commissure, with a vessel cut across ; o, fibres of the posterior column passing into the grey commissure ; p, fibres of the sensitive roots going ofi" to the lateral columns ; q, similar fibres entering the posterior column ; r, longitudinal fasciculi of fibres passing into the sensitive roots ; », substantia gelatinosa, with traversing bundles of the sensitive roots, le; t, sensitive radical fibres running horizontally forwards to the grey commissure ; «, large cells of the anterior cornua (the puncta), inner group ; », the same, outer group. THE NERVOUS SYSTEM. 409 will be afterwards shown, they successively pass inwards towards the grey substance, presenting the general characters of the central nerve-fibres; that i^ to say, the delicacy of sheath, disposition to the formation of varicosities, and to the breaking up into separate fragments, which" are constituted either of all the elementary parts of the nerve-tubes, or consist of nothing more than an axis-fibre, or of the medullary- sheath. Their diameter accounts to 0"0012 — 0'0048"', on the average 0*002 — O'OOS'", and, in one and the same fibre is, evidently, always nearly the same, since, in the white substance, neither divisions nor any other kind of alteration in diameter of the fibres are found to exist. The transverse fibres occur: — 1. in those portions of the lateral and posterior columns which adjoin the horns of the grey substance, and the description of which will be given afterwards with that of the grey substance; 2. in the white commissure; and, 3. at the points of entrance of the roots of the nerves. The white, or anterior commissure (fig. 141, k) is not a commissure in the common sense of the word. It is formed by those nerve-fibres of the anterior columns, which are, in succession, the most deeply placed, and which bending obliquely inwards, cross in front of the grey commissure; the fibres coming from the right anterior column, passing, in a radiating manner and hori- zontally, to the left anterior horn of the grey substance, and those from the left anterior column passing in like manner to the right anterior horn. The anterior commissure, therefore, represents a decussation, or crossing of the anterior columns, and would be better designated as such. It varies both in thickness and breadth; it is thickest id the region of the two enlargements, and is least so in the middle of the dorsal portion of the cord. Its breadth is regulated pretty nearly by that of the cord, and of the bottom of the anterior fissure ; being greatest in the cervical enlargement, and from this point decreasing pretty uniformly in both directions. The decussating fibres measure 0-0012 — O'OOS'", and, as they diverge in the anterior horns, evidently in some degree decrease in diameter. The roots of the spinal-nerves (fig. 141, g, w), without any communication with the longitudinal fibres, are continued, in, larger fasciculi, from the sulcus lateralis anterior and posterior, either horizontally or slightly ascending between those fibres. 410 SPECIAL HISTOLOGY. in order, all of them, to eater the anterior and posterior, grey laminae, where we shall again meet them. Their nerve-fibres (in the posterior roots, about | measuring 0'004i — O'OOS'", and i 00012 — 0-003'", in the anterior about | measuring from 0-006 — 0-011'", and i 0-0035— 0003"') present, as soon as they have entered the cord, all the characters of the central fibres, the largest, at their commencement, measuring about 0-004 — 0-006"' in the sensitive, u^ to 0-008'" in the motor roots. They continue, however, distinctly and constantly de- creasing in size, until ultimately, the former, when they enter the grey substance, have a diameter of scarcely more than 0-0013 — 0-0038'", and thp latter in like manner one of not more than 0-004'" (or in some of 0006'"). In the grey substance, the nerve-cells and fibres deserve spe- cial consideration. The former present very various forms, all, however, corresponding in one respect, that they are invariably furnished with processes or prolongations, and, for the most part. Fig. 142. with many such, which repeatedly branching, ultimately terminate in extremely fine, pale fibrils, like the finest axis-fibres, I distin- guish : — 1. The cells of the central grey substance. These (fig. 143) are 0-004 — 0-008'" in size, always pale and finely granular, with mul- tiple nuclei and branching pale processes, constituting as it would seem the principal bulk of the central grey substance; but in which, dark, true nerve-fibres also occur, although of nearly the finest kind, which can scarcely be recog- nised as such, and are indeed very few in number, and quite isolated; besides these, there are a good many extremely fine, pale fibrils, like the processes of the cells, only more extended, and running in a transverse and lon- gitudinal direction, of which nothing more can be said, as Fig. 142. Cells from the gvey central nucleus of the cord iu Man, x 350 diam. THE NERVOUS SYSTEM. 411 to whether they are nerve-tubes, or are to be referred to the pro- cesses of the cells. The grey central substance, taken altogether, is thickest in the lumbar enlargement, and on a transverse section is of a pyriform, scutate, or cordate figure; next to this stands the cervical enlargement; and lastly, the superior cervical and dorsal portions, in which latter parts its trans- verse section presents an ellipse, in the cervical region, with the longer diameter much developed. It occasionally exhibits, especially in the lumbar region, indications of its being con- stituted of two halves, inasmuch as the middle appears some- what clearer, and the lateral portions, owing to the accumula- tion of fatty granules in the cells, more opaque. 2. With the above-described cells, those of the substantia gelatinosa pretty nearly agree, only that they are of a faint yellowish colour, and have 1 — 3 processes and simple nuclei. Besides these cells, the substantia gelatinosa also contains the fasciculi of fibres of the posterior roots which pass through it, and nume- rous other true nerve-fibres {vid. infra). 3. Much developed, well marked nerve-cells, are seated, especially at the apex of the anterior horn, forming an internal and an external group (fig. 113, u, v), but occurring also in the other portions of the anterior, as well as, though in less number, in the posterior horns, whilst they are never met with -in the suhst. gelatinosa, nor in the grey commissure. All these cells (fig. 143) are 0-03 — 0-06'", in size, with nuclei measuring 0-005 — 0-008'", are fusiform or polygonal, frequently containing brown, pig- mentary matter, and furnished with from 3 to 9, or even more branched processes, which at their origin are often 0-004 — 0-005'" thick. These processes may be traced to a length of 0-1 — 0-24'", and ultimately terminate in fine fibrils, all of which, scarcely more than 0-0004'" thick, are contained within the grey substance. Besides these large and, for the most part, many-rayed cells, there are also found in the grey sub- stance, though more widely scattered among its nerve-fibres, very numerous, smaller cells, which constitute a complete series between the large cells and those of the substantia gelatinosa, and consequently require no further description. The nerve-fibres of the grey substance are excessively nume- rous, so much so as to constitute in any case the half of its bulk, if not more, and exhibit the same conditions as those of 413 SPECIAL HISTOLOGY. the medullary substance, except that, on the average, they are not more than half as thick, or even less (not more than Fig. 143. 0"0008"') J fibres, however, also occur of the same size as those in the white substance and in the entering roots of the nerves, especially in the anterior horns, though more widely scattered, and principally towards the anterior roots. The investigation of the course of these nerve-fibres in the grey substance is one of the most difficult tasks in microscopy. If we observe, above all, the roots of the peripheral nerves (figs. 141, 144), it is apparent : — 1. that the motor filaments in them, after they have entered the sulcus lateralis anterior, and the contiguous portions of the anterior and lateral columns, and penetrated horizontally between the longitudinal fibres of the white substance, are continued further in the grey substance of the anterior horns, principally in two directions. The fibres of one bundle, and indeed of that which enters the most internally (fig. 141, h), proceed directly backwards and Fig. 143. Large nerve-cells with processes from the anterior cornua of the spinal cord in Man, x 350 diam. THE NERVOUS SYSTEM. 413 a little inwards, without forming any plexus, or sub-dividing to any considerable extent into subordinate fasciculi, to the innermost portions of the anterior horns, skirting the ante- rior columns. In this course they pass through the innet group of the many rayed, large nerve-cells, in perfectly com- pact bundles, however, and having no connection whatever ■with the processes of the cells, as may be readily perceived under a strong magnifying power, when the individual nerve- fibres may be traced quite beyond these cells. Now, if these bundles derived from the anterior roots are traced further, it wiU be perceived, in favorable sections, that they extend to the lateral parts of the anterior commissure, continuing to run in the anterior horns, and, that ultimately, forming more or less well-marked curves, they are continuous with its fibres^ and in fact are disposed in such a way, that the root-fibres of the right side pass into the left anterior column, and those of the left side into the right. Consequently there is established in the white commissure a connection of the longitudinal fibres of the anterior columns and of a part of the motor roots, together with a total decussation. A large number of the fibres of the motor roots take no part in the above-described decussation, and are wholly unconnected with the anterior fasciculi, — these are the root-fibres which enter the anterior horns the most externally. Forming, for the most part, smaller fasciculi, or even as separate fibres, and therefore less easily observable, they run in part directly backwards, and in part arch outwards, but ultimately bend towards the anterior half of the lateral column, where they pass between the outer groups of the large, many-rayed cells of the anterior horns, and then enter the lateral column in a horizontal direction. These transverse fibres now penetrate to various depths (nearly half, or even more) into the lateral column, then curve upwards, and after running thus a short distance, appear as longitudinal fibres. Consequently, to express the same thing in other words, a second portion of the motor roots arises from the anterior half of the lateral column of the same side, and quits the spinal cord without previously undergoing any decussation. It is, moreover, worthy of remark, that most of the fibres, perhaps all, which join the motor roots from the anterior and 414 SPECIAL HISTOLOGY. Kg. 144. H f S .-, lateral columns^ undergo considerable changes in their diameter. Those of the anterior columns measure, as has been observed before, at their commencement, on the average, 0-002 — 0-004'", in the anterior commissure scai-cely more than 0003'", and in the grey substance hardly more than 0-002"'; and the same is the case also with those of the lateral columns ; which, however, even while still in the interior of the column, where their direction is horizontal, measure scarcely more than 0-002'". This diminution in size, however, is again succeeded by an increase in thick- ness, which takes place, in part, within the grey substance, in part at the point where the radical bundles quit it, the amount of which increase has been already stated in numbers; so that, proceeding from the peripheral nerves, we find them gradually diminishing in size from their entrance into the cord until they reach the grey substance, and again enlarging from the point where they join the longitudinal elements of the white substance, but not to such an extent as ever to attain, nearly their pristine diameter. Of divisions in the fibres of the anterior roots in the anterior horns, I have seen as little in- dication, as elsewhere in the spinal cord. The posterior roots of the nerves, as has been already noticed, penetrate, like the an- terior, also horizontally, or in a slightly ascending direction, from the sulcus lateralis posterior, through the longitudinal fibres of the white substance as far as the posterior horns. Fig. 144. Vertical section through the cord, midway between the grey cornua and the point of entrance of the roots of the nerves, x about 25 diam. : a, posterior column with the sensitive roots, A, traversing it ; b, substantia gelaimosa ; c, pro- longations of the posterior roots, which bend round in front of the substantia gelaiinosa and run longitudinally, in order there to join more particularly the posterior column ; d, basis of the posterior cornua, with the ends of the horizontid portion of the sensitive roots apparent (owing to their being cut across) ; e, anterior cornu with the large nerve-cells (the spots), and the also horizontal and divided continuatious of the motor roots ; /, anterior column traversed by the motor roots, «. /i i ■■,!■-.-*; y A THE NERVOUS SYSTEM. 415 Here they divide into separate, slenderer, or thicker fas- ciculi (from 0-01 — 0-Oa'") (figs. 141, s, 144, b), and con- tinue, each bundle by itself, in a straight course, and with- out any direct connection with nerve-cells, quite through the substantia gelatinosa into the substantia grisea. In this course they follow two directions. One portion of them bends upwards, in a uniform curve, or nearly at a right angle, proceeds in the most posterior part of the substantia grisea, close in front of the substantia gelatinosa in a longitudinal direction, and gradually joins chiefly the posterior column, but in part also the posterior portions of the lateral column, being continued further, as its longitudinal fibres (figs. 141, r, 144, g), A second portion of the sensitive roots (figs. 141, t, 144), penetrates, always in a fascicular form, between the above- mentioned longitudinal bundles further forwards, losing itself in the posterior and in the lateral columns, and also entering the grey commissures. In horizontal sections, the former fibres are frequently very distinct, particularly those going off to the posterior columns (fig. 141, p, q). I have seen them most distinctly in the inferior extremity of the spinal cord, below the lumbar enlargement, where they ran towards the conus medullaris, close up to the grey central nucleus, and did not bend backwards until they reached the posterior columns ; they were also well displayed in the lumbar enlargement, between the substantia gelatinosa and the pos- terior commissure. The horizontal radical fibres, also, which proceed to the lateral columns, are often exceedingly numerous, although much less so, apparently, than those which enter the posterior columns. The connection of the grey commissures with a portion of the sensitive radical fibres, is, as regards the posterior fibres,not difficult to be seen, these fibres, in part, at least, running backwards along the posterior columns, and being continued directly into the fasciculi of the substantia gelatinosa. In the anterior grey commissure, I have also noticed, though not a direct connection with the sensitive roots, still, fibres which, running horizontally in a direction towards the summits of the posterior horns, entered those processes. The com- missural fibres are, besides, connected not only with the sensitive roots, but also, and indeed quite evidently, with the posterior columns, and less distinctly with the lateral ; from the 416 SPECIAL HISTOLOGY. anterior portions of which, adjoining the base of the posterior horns, arched fasciculi pass into the commissures and become intermixed with the other commissural fibres (fig. 141, o and I). These fibres probably pass over to the opposite side, into the commissures connected with the posterior roots; in which case, Hke the anterior halves of the cord, a decussation of fibres also takes place in the posterior commissure. In accordance with what has been remarked, the sensitive roots derive their fibres principally from the posterior and lateral columns (the posterior halves) on their own side, and probably also through the grey commissures from the same columns on the other side. The fibres of the sensitive roots also decrease in size as they traverse the grey substance of the posterior horns. In the roots themselves they still measure about 0"008"'j in the substantia gelatinosa, never more than 0004'"; in the sub- stantia grisea^ 0*001 — 0"003"'; in the grey commissures, not more than 0-0008 — 0"0012"'; in the posterior and lateral columns, again, 00013 — 0"004"'; in connection with which, however, it should be remarked, that, in this situation, the increase of size in the fibres which enter these columns hori- zontally, is not perceptible at their commencement, as is shown more particularly in vertical sections, made in the direc- tion from within to without, through the posterior comua. The variation in diameter may even be directly observed, in many fibres in this situation; as, for instance, at the entrance of the roots into the gelatinous substance. Besides these fibres, belonging to the motory and sensitive roots, there exist, in the grey substance, a considerable number of nerve-fibres not referable to the roots, and which until more is known about them may be termed special spinal- medullary fibres. The filum terminale contains, so far as it is hollow, as a continuation of the grey substance of the cord, a grey, soft substance, consisting chiefly of round, nucleated, pale cells, like nerve-cells, and measuring 0*005 — 0'006"'. Besides these there occur, in its upper part among the cells, true dark- bordered nerve-fibres, of various, and for the most part small diameter, and also numerous, fine, pale fibres, the nature of which is not clear to me; that is to say, whether they are THE NERVOUS SYSTEM. 417 processes of cells or belong to the finest nerve-fibres. Remak ('Observ./ p. 18) supposes, that in the Mammalia the true nerve-fibres of the filum all go ofi' in lateral branches of it, the existence of which were detected by him. [In the investigation of the course of the fibres in the spinal cord, chromic acid, or instead of it, chromate of potass, affords the principal aid. It is not easy to hit upon the proper pro- portion of acid, and so to harden the cord, previously stripped of its dura mater, and cut across with a sharp knife at the points selected, that very thin transverse sections may be taken from it. If the solution be too much diluted, the substance of the cord remains soft in the interior and spoils, if too concentrated it becomes fragile and friable, and larger sections of it cannot be obtained. I have unfortunately neglected to estimate precisely the proper per centage of acid or salt in the solution; and can only say this much, that one of a wine-yellow colour acted the best. Objects thus properly hardened may be cut at pleasure with a razor, or other very sharp instrument, if due care be taken, particularly in the avoiding of any sawing motion ; and sections suitable even for the highest magnifying powers may be procured and examined, either with or without pressure or reagents, under various degrees of enlargement. The grey substance is scarcely altered by the chromic acid, except that its elements are more easily separated, and I have in hardly any other way seen its nerve-cells, together with their processes, and the nerve-fibres, more beautifully displayed. If it be desired to examine the former, the grey substance is broken up in water, which now no longer produces any change; or, what is best, in the solution of chromic acid itself; but if the examination of the latter be wished, it is by far the best to employ diluted caustic soda or potass, which renders all the nerve-cells pale. To those who may consider the application of these reagents as too powerful for such delicate organs as the spinal cord, I would remark : I. that, as stated by Hannover, chromic acid alters the nerve-fibres, especially of the grey substance, so little, that most of them do not even become varicose; and 2. ihat soda, added to a preparation made with chromic acid, does not act upon the fibres for a long time, and only so far as I, 37 418 SPECIAL HISTOLOGY. to render them more transparent and their medullary contents fluid. I have never, under any circumstances, seen more beautiful nerve-tubes of the grey substance, than in prepa- rations made with chromic acid, and I think that of all known means this is the best for their study. In employing pressure, however, great care is requisite. I make use of a compressorium by Nachet, which allows extremely thin covering-glass to be employed, and consequently the highest magnifying powers ; if I wish to apply more considerable pressure for the study of the coarser conditions, the common apparatus sufi&ces, with which, however, with a shorter focal distance of the microscope, only lower powers can be employed. I have, had entire transverse sections of the spinal cord before me, in which it might be said, that no part was disturbed from its relative position, and yet, which admitted of the application of a magnifying power of 350 diam. I would, moreover, remark, that the most favorable place in the cord for the first investigation, is the lumbar enlargement. In this situation the cord is not so thick, but that entire sections of it may be obtained, besides which the white substance, which is only an impediment, is thin, and the roots and commissures large and more readily traced. Whether the nerve-fibres in the cord divide, has not yet been fully ascertained, yet I think that I saw such an appear- ance, on one occasion, in a dark-bordered fibre, and on another in an isolated axis-cylinder. In any case such divisions cannot be frequent, otherwise I must have noticed them more often, having examined innumerable nerve-fibres and axis-cylinders, expressly with reference to this point. Anastomoses between the processes of branched nerve-fibres, which Schroder van der Kolk thinks he has seen, I must, from my experience so far, doubt, but I am not able to deny their possible occurrence.] § 113. Probable course of the Fibres in the Cord. — We have found that the motor and sensitive roots do not terminate at the point where they are implanted into the grey substance of the cord, as at first sight appears to be the case, but that the greater proportion of them are curved upwards, accompany- ing the longitudinal fibres of the white substance. The THE NERVOUS SYSTEM. 419 important question now arises, viz. : to ascertain what becomes of theses fibres, whether, after running a shorter or longer distance, they, terminate in the cord, or whether they all ascend to the b/ain. It is well known, that until recently, most observers lave been of the latter opinion, which was founded less upon direct observation than on the ground of probability, until Volkmann, in his deservedly celebrated article, 'Physiology of the Nerves,' shook it to its foundations, carrying the greater number of physiologists with him. I also was among these, until I had myself investigated the conditions, for there could be no doubt that Volkmann's theory connected, in the most harmonious way, the anatomical facts and the results of physiology as at that time exhibited. When I now, notwith- standing this, abandon Volkmann's theory of the termination of the spinal nerves in the cord, I am induced to do so by weighty reasons, and much regretting that I am unable to maintain a view, which appeared to throw so much light upon many difficult parts of the physiology of the nerves, and to be in accordance with so many other anatomical conditions (ganglia, invertebrate animals). [Volkmann, in his hypothesis of the origination of the fibres in the cord, relies upon the circumstance (1. c, p. 483, et seq.), that the spinal cord is not of a pyramidal form with the base above, as must have been the case had all the fibres of the roots of the nerves ascended towards the cerebrum, but that it rather presents a local increase of the nervous substance at the points of origin of large nerves, which enlargement is not confined to the grey substance, but equally involves the white. That this is the case Volkmann shows from four transverse sections of the spinal cord of the Horse, and from a comparison of the diameter of the cervical cord of Crotalus horridus, with that of all the nerve-roots of the same animal, which was found to be eleven times greater than the former. He also supports his view by the consideration : 1. that the enlarge- ments of the cord are always regulated by the size of the nerves of the extremities, being sometimes wanting and some- times enormously developed ; 2. that the cord, at the points of exit of the largest nerves, instead of becoming suddenly thinner, is in most cases enlarged ; and 3. that the origin of 420 SPECIAL HISTOLOGY. Fig. 145. A the spinal accessory nerve in this case loses all that is remark- able in it. Now, if the spinal cord in man be examined with reference to the above points, it will present, in almost all of them, exactly the contrary of what Volkmann noticed in animals. In the first place, the white substance constantly incr.eases in thickness from below upwards, and the enlargements of the cord depend upon an increase of the grey substance more than anything else. That this is the case, is evident at a glance, when sections, such as are represented, after nature, in fig. 145, are compared with each other, and it also admits of being estimated in numbers {vid. 'Mikroskop. Anatomic,' II, 1, ■ a m This fact being established, it remains to deter- ^—^ mine the proportion borne by the white substance in the superior cervical region to the peripheral nerves. For this purpose I instituted Volk- mann's measurements in man, and in a male and female body estimated all the roots of the spinal nerves on the left side ; I determined, from the ascertained diameters, the transverse sectional surfaces of all the nerves in square lines, and compared with them the transverse sectional area taken with the utmost possible nicety, of the white substance of the spinal cord, at the level of the second cervical vertebra. It is quite true that there was now evident a very con- siderable difference against the spinal cord; but when the very great attenuation of the nerve-fibres of the roots, at their entrance and in their further course in the cord, was brought into account, which was not done by Volkmann, the matter was entirely altered, and it became clear that the cord in the male subject contained more than suflScient fibres to furnish Tig. 145. Five transverse sections through a human spinal cord, hardened by chromic acid, to show the relative proportions of the grey and white substances, — of the natural siize : A, from the comts medullaris, the diameter of the cord being 3f"' ; B, from the lumbar enlargement, transverse diameter 4f"', antero-posterior 4J"' ; C, from the dorsal part of the cord, 4J"' and 33'" ; D, from the cervical enlargement, 6§"'and4J"'; E, from the superior cervical portion, level vfith the second nerve, 6i"' and 4f"'. THE NERVOUS SYSTEM. 431 the peripheral ones, and in the female nearly sufiBcient, particu- larly when it is considered, moreover, that in the entire enume- ration, the numbers were stated rather in favour of the roots of the nerves {vid. the calculation in 'Mikroskop. Anatom.,^ II, 1, § 116). It appears, therefore, scarcely to admit of doubt, that the notion of a termination of the peripheral nerves in the cord, has no support in measurements such as those which, following Volkmann, I have adduced; and that the latter, even when all due allowance is made for the uncertainty always incidental to such an inquiry, on the contrary indicate, at all events the probability, that the spinal nerves ascend to the cerebrum. They give no further information, however, and it depends upon other facts, whether such a central origin should be admitted or not, because it is even conceivable, that the peripheral nerves may end in the cord, and that the longi- tudinal fibres in the cord have a wholly different source. Since it is scarcely probable that the tracing of the nerve- fibres through the entire cord will be effected either at present or perhaps at any time, it is necessary to look round for other facts, which may possibly afford conclusive evidence on the subject,- and such facts do exist. In the first place, let us consider the course of the roots of the nerves in the cord, such as it has been described above. We found, that after they had all come, more or less, into contact with the grey substance, the greater number of them could be directly traced into connection with the longitudinal fibres of the anterior, lateral, and pos- terior columns. From this fact, together with my measure- ments, the passage of the greater part of the peripheral nerve- fibres into the cerebrum, will appear to many to be proved; but, not to overlook anything, it may further be remarked, that the radical fibres, running longitudinally in the substance of the cord, may terminate in it, or after running in it may again enter the grey substance higher up. The former sup- position is now, it must be confessed, but little probable, because in the first place, no one has yet seen the terminations of nerve-fibres in the white substance ; and in the second, because anything of the sort, for other reasons, would be very surprising, nerve-fibres being nowhere known to commence ia the white substance; and with respect to the latter, any rq. 423 SPECIAL HISTOLOGY. entry of the roots of the nerves into the grey substance could not escape notice. Since the junction of the radical fibres with the anteriorj posterior, and lateral columns, can be so well and so directly observed, the relation in question would necessarily be evident also; and yet in the course of my perfectly unpre- judiced observations, I have never seen anything of the kind. Nothing, therefore, remains but to assume, that the great majority of the peripheral nerves really have a cerebral origin. Whether they all originate in the brain (where, we shall afterwards see) or in part, though, from my observations, but to a small extent, from the cord, cannot be determined, any more than the question can be decided, whether the white substance of the cord, besides the fibres derived from the peripheral nerves, also contains others passing from the brain to the cord.] § 114. The medulla oblongata and pons Varolii belong to the most complex parts of the central nervous system, containing white and grey substance, intermixed in very various modes. The white substance is, in part, a continuation of that of the cord, in part distinct from it, and is disposed in the following manner: the anterior columns of the spinal cord diverge from each other at the commencement of the medulla oblongata, allowing the decussating fibres of the corpora pyramidalia to appear. As they proceed, a smaller division joins the pyramids, forming their outer part, whilst the principal portion surrounding the olivary bodies, internally and externally, whence they are also termed the olivary columns, passes laterally, and then, divided into two bundles, proceeds above the second transverse layer of fibres, through the pons. One of these divisions constitutes the fillet, [laqueus,) which continued above the crura cerebelli ad cerebrum, enters the posterior corpora quadrigemina, joining, within them, the corresponding division of the opposite side. The second division, or bundle, lies externally and inferiorly to the crura cerebelli, and enters the tegmentum of the cerebral peduncle. Besides this, the olivary columns, corresponding to the anterior columns of the cord, also, as it seems, give off fibres to the pedunculus cerebelli. The lateral columns of the spinal cord divide, on reaching the medulla oblongata, into three THE NERVOUS SYSTEM. 423 bundlesj one of which, ascending in a tolerably straight direc- tion, is continuous with the fasciculus lateralis of the restiform body, and with it enters for the most part into the peduncle of the cerebellum, and in small part into the tegmentum; a second division penetrates forwards between the divergent anterior • columns, decussates in two or three fasciculi with that of the other side {decussatio pyramidum), constituting the principal bulk of the pyramids; a third division, lastly, appears between the posterior columns at the bottom of the rhomboid fossa, or fourth ventricle, as the eminentia teres. These latter are con- tinued, on the floor of the fourth ventricle and applied to each other, into the tegmentum of the cerebral peduncles, whilst the pyramids, passing between the first and second transverse layers of fibres of the pons, are continued into the base of the cere- bral peduncles. The posterior columns of the cord, lastly, chiefly constitute the fasciculi graciles and cuneati, the latter of which, in great part, enter the peduncuU cerebelli, whilst the remainder, and the fasciculi graciles, situated externally to the eminentia teretes, may be traced into the tegmentum of the crura cerebri. All these fasciculi consist, besides the grey substance, of parallel nerve-fibres of the same dimensions as those of the cord, that is to say, from 0-001 — 0004'", seldom more. Besides this white substance, the pons Varolii and medulla oblongata, omitting the roots of the nerves, present a system of mostly horizontal fibres. This system consists : 1. of the well-known transverse, arcuate fibres, external to the corpora pyramidalia and olivaria; 2. of straight fibres, which extend from before backwards, iu the middle, through the medulla oblongata, contributing to the formation of the so-termed raphe (Stilling); 3. and lastly, of very numerous fibres pro ceeding from this raphe into the lateral halves of the medulla, following a more or less curved direction. These latter, the internal transverse fibres, commence behind the pyramids, and the anterior of them as a large mass, very minutely broken up by fine flattened fasciculi of the pyramidal and olivary columns, penetrate from within into the corpus dentatum olivts^ the white substance of which is constituted by them; they then expand in a brush-like form, and are continued through the grey substance of the corpus dentatum, ultimately turning 434 SPECIAL HISTOLOGY. backwards towards the fasciculus cuneatus and lateralis. In this course, the fibres describe larger or smaller curves. m The latter is the case with those which come out from the posterior part of the olivary nucleus [corpus dentatuni], and which go almost directly backwards and outwards through the accessory olivary nucleus (Stilling), and the grey substance, containing large cells, situated on its exterior; the former con- Fig. 146. Transvsrse section through the medulla oblongata in Man, x 15 diam,: P, pyramids; O, olivary bodies ; J.Z, fasciculus lateralis ; F.c,fasciculi cuneaii; F.ff, fasc. graciles; H, root of hypoglossal nerve; V, root of n. vagus i F.a, flsaura an- terior ; F.p, fisaura posterior in the floor of the fourth ventricle, or rhomboid fossa ; S, raphe: a, longitudinal fibres of the rap Ae; J, central grey layer with transverse fibres; c, expansion of these fibres in the olivary column and body; d, accessory olivary nucleus ; e, hypoglossal nucleus ; /, decussation of the hypoglossal nerve ; g, nucleus of the vagus; hhh, larger nerve-cells in the restiform bodies; i, medullary mass in the interior of the olivary body, belonging to the internal transverse fibres ; *, arcuate fibres external to the olivary body ; I, transverse fibres external to the pyramids ; m, ■», o, grey nuclei in the pyramids and olivary columns. THE NERVOUS SYSTEM. 425 dition obtains in the anterior fibres, which spread out in a radiating manner, passing at first forwards between the pyra- mids and olivary nucleus, and afterwards backwards in a sharp curve, superficially round the latter, into the lateral fasciculi. A second division of the internal transverse fibres goes behind the olivary nucleus with which it has no connection, directly from the raphe, through the posterior part of the olivary columns and the eminentia teretes, outwards and backwards, also into the restiform body. All these fibres, and most of them obviously so, are associated together, and appear to me to be continued from the restiform bodies and the peduncles of the cerebellum, into the anterior divisions of the medulla oblongata. With respect, however, to their more intimate relations, concerning which Stilling's work and my ' Micro- scopical Anatomy' may be consulted, little is as yet known. The grey substance, in the medulla oblongata, is collected into larger masses, chiefly in three situations, viz. in the olivary and restiform bodies, and on the floor of the rhomboid fossa (fourth ventricle): 1. the grey substance of the olivary bodies forms, as is well known, a folded lamella, constituting a capsule closed on all sides except the inner, which, although it occupies the situation of the anterior horns of the spinal cord, which are continued nearly to its inferior border, still has no direct connection with them; appearing, also, to be otherwise isolated from all other grey substance. Within it, besides the very numerous nerve- fibres of the transverse fibre- system, which traverse it for the most part in straight lines, there occur in great numbers smaller nerve-cells, measuring 0'008 — 0013"' in diameter, and of a rounded form, with 3 — 5 branching processes, and containing in the interior yellowish granules, to which the colour of the olivary bodies is due. The closest observation has failed to afford me any indication of a connection between these cells and the fibres which run among them. On a level with the two upper thirds of the olivary body, is placed, behind the nucleus and wholly isolated from it, the body termed by Stilling the accessory olivary nucleus, in the form of a flattened, yellowish band, of exactly the same structure as the grey substance of the olivary body, and also traversed by horizontal nerve-fibres, and in fact by fibres which have for the most part already passed through 426 SPECIAL HISTOLOGY. the olivary body; 2. in the restiform bodies, the grey substance {corpus s, nucleus cinereus) assumes the form of an ill-defined, elongated mass intermixed with very numerous nerve-fibres, and which occupies mainly the fasciculus lateralis, but also extends into the fasciculi cuneatus and gracilis. This struc- ture may be described as a continuation of the posterior horns of the spinal-cord, even presenting, as Stilling correctly states, an indication of the substantia gelatinosa of those processes, of which it may moreover be observed, that it is very remarkably developed in the uppermost portions of the cord, as far as the commencement of the decussation of the pyramids, and has a position entirely lateral. The elements of the grey substance of the restiform bodies are, besides, numerous finer fibres, which appear to pass chiefly into the horizontal, internal fibre- system, and many, rather pale, but in part brownish nerve- cells with processes, pretty regularly disposed, and most of them of the same size as those of the olivary bodies; 3. the grey substance on the floor of the fourth ventricle, is the con- tinuation of the grey nucleus of the spinal-cord, and forms a tolerably thick layer, extending from the calamus scriptorius as far as the aqueductus Sylvii. It contains throughout, nume- rous nerve-fibres, in part of very considerable diameter, up to 0-006"', or even 0008'", in part of the finer and finest kinds, and besides these, nothing but caudate nerve-cells of all dimensions from 0-006'", up to 003'", and more. The largest of these are contained in the ala cinerea at the posterior extremity of the fourth ventricle, and in the subst. ferruginea s, locus cinereus (fig. 147), in which latter situation, the cells also • present well marked pigmentary matter, and very numerous, delicately branched processes. The small multi- nuclear cells, which in the grey nucleus of the cord occur in the form of a compact structure, are here entirely wanting, not being found beyond the decussatio pyramidum. Besides these three masses of grey substance, which can in part be referred to that of the spinal cord, there are found, in the medulla oblongata, some small collections of it, as in the pyra- mids near the olivary bodies, and in the olivary columns, external to the accessory nucleus, in all of which, as has been already stated by Stilling, are also to be seen in part larger cells, all caudate (in the latter situation measuring as much THE NERVOUS SYSTEM. 427 as 0-025'"), and finer nerve-tubes. One part of the grey sub- stance just described, that namely of the anterior half of the Kg. 147. fourth ventricle, belongs properly to the pons Varolii. It also contains, in its interior, besides the just described elements, above the transverse fibre-layer, both in the middle as well as more laterally, many accumulations of grey substance, with larger and smaller (as much as 0'02"' and more) nerve-cells, all caudate, which are so irregularly imbedded among the longi- tudinal and transverse fibres, as to require no detailed descrip- tion, and are connected on the one side with the grey nuclei of the medulla oblongata, and on the other with the substantia nigra of the crura cerebri. The relations of the tea. pairs of nerves which arise from the medulla oblongata, the pons, and the crura, constitute a very difiBcult question. But few inquirers have endeavoured to solve it by other means than those usually employed, that is to say, by the tracing of the fibres, with the aid of the scalpel, Fig. 147. Nerve-cells of the substantia ferruginea in tie floor of the fourth ven- tricle or rhomboid fossa, of Man, x 350 diam. 438 SPECIAL HISTOLOGY. which here goes no way at all. Among the exceptions are E. Weber (Art. ' Muscular Motion/ in Wagner's ' Handw. d. Phys.' Ill, 3, pp. 30 — 33), who made his examination in pre- parations, hardened by carbonate of potass; and Stilling, who pursued his by the microscopical examination of sections, simi- larly hardened by means of alcohol. My own results, obtained from preparations in chromic acid, which had been for the most part made transparent by soda, agree in almost every point with those of Stilling, which at all events, among all observations on the subject, have gone most deeply into the matter. The nerves in question arise, without exception, not from the columns or fibrous substance, out of which they proceed, but all penetrate more or less deeply into the central parts, and all probably become connected, some not till they have decussated like the trochleares, with definite parts of the grey substance, which Stilling not inappropriately terms nerve- nuclei {accessory nucleus, for instance). It is the floor of the fourth ventricle, and of the aqueduct of Sylvius, which are more particularly concerned in this respect, since all the nerves above named, at least in part, extend to them. The more minute consideration of these relations may be seen in Stil- ling's Work, and in ' Mikroskop. Anatomic,' II, 1, pp. 458—463. [Although a favorable judgment cannot be given upon Stil- ling and Wallach's work on the spinal cord, I am still very far from disposed to look down upon Stilling's anatomical writings in general, as would seem to have been the fashion for some time past. I am much rather of opinion, in which R. Wagner also coincides, that we have great reason to thank this author for his works on the medulla oblongata and pons Varolii; for although there are some things in them which cannot be maintained, and sufficient attention is not paid to the elementary constituents, stiU it cannot be denied that they contain a mass of important facts. I have tested, if not all, still the most important of Stilling's statements, and have found them almost all fully confirmed, and am therefore glad to take this opportunity of naming him, as the observer to whom we are indebted for the first accurate investigation of the course of the fibres in the central organs. I would also here, THE NERVOUS SYSTEM. 429 add: 1. that in further investigations of this kind, chromic acid, or chromate of potass, is to be preferred to alcohol, particularly also when caustic soda is cautiously employed for the tracing of the course of the nerve-fibres in the grey substance thus rendered transparent; and, 2. that in con- junction with lower magnifying powers, the most powerful should be employed, and the relations of the elementary con- stituents should also be otherwise accurately investigated. The question as to the origin of the nerves in the me- dulla oblongata, presents itself as one of the most difficult nature. Most anatomists have hitherto been content to trace the roots of the nerves as far as one or the other column; but this is not sufficient. All the nerves enter at least once, or even several times, into grey substance, in which and no where else are their origins to be sought for. Now, it must be con- fessed, that through Stilling's great pains, the fruits of which I can, as it may be said, fuUy confirm, — all the ten pairs of nerves at present under consideration have been traced in their roots as far as perfectly definite points of the grey sub- stance; but now comes for the first time the further question: do they commence in these situations, or do they proceed beyond them ? As true origins in the brain have never yet been seen with certainty by any one, there remains nothing but physiological analogies and reasons. As regards the former, we see in all the spinal nerves, that they first penetrate trans- versely as far as the grey substance, and then, only passing through this, join the white columns, and we may thence suppose that the cerebral nerves, which, in general, so closely resemble them, are in the same condition, and the more so, because these also at first penetrate transversely into the interior of the medulla, and the grey substance, with which they come in contact, corresponds with that of the cord. To this may be added also, that if we make the ten last cerebral nerves ter- minate in the grey substance, into which they may so readily be traced, the decussated influence of the parts above, upon them, which appears to be established by pathological pheno- mena, cannot be explained in the case of any one of them except the trochlearis, which decussates before it reaches its grey substance. Now, in the accessorius and hypoglossus it is actually possible to see that the fibres come out from the grey 430 SPECIAL HISTOLOGY. substance, reached by them in the first instance, and after- wards decussate; and the same thing is also at least probable in the oculo-motorius ; so that I think it may be, that all the nerves now in question undergo decussation, and do not terminate in the so termed nuclei of Stilling. Further investigation will have to show whether this [decussation] takes place in the floor of the fourth ventricle, as would appear to be the case; whether all the fibres of these nerves take part in it; and where the fibres proceed to after decussation. With respect to the latter, it may be supposed from analogy with the spinal nerves, that the true origin of the cerebral nerves is probably not in the medulla oblongata, but in the corpora striata and optic thalami. Of that portion of the ^or^io major n. trigemini, which is continued into the restiform body, this may especially be remarked, that it certainly does not originate in that part, but winds round it to somewhere above, as is the case also with the n. accessorius. However, in stating, in accordance with what has been said, that I do not consider it directly probable, that the sensitive and motor cerebral nerves originate in the medulla oblongata and pons, it is by no means intended to imply that these parts may not, as central organs, exert some influence upon them and the more deeply placed nerves. If the medulla oblongata preside over the respiratory movements, if it and the pons be the agents of multiplied reflex motions, this may be the case, without its following that all the nerves called into action should terminate in them, and simply for the reason that the grey substance, so abundantly contained in them influences the nerves which traverse it, exactly as must be supposed to be the case in the spinal-cord.] §115. The cerebellum, with respect to the distribution of the elementary tissues, exhibits tolerably simple conditions, grey substance occurring only on the surface of the convolutions, in the nucleus dentatus, and in the roof of the fourth ventricle; all the remainder consists of white substance. The latter is wholly constituted of parallel, probably unbranched, dark-bor- dered nerve-fibres, possessing all the characters of central fibres (softness, proneness to become varicose, easy isolation of the THE NERVOUS SYSTEJI. 431 axis-cylinder, &c.), are essentially alike in all situations, as far as their condition can be observed, and present a diameter of 0-0012 — 0-004'" in the extremes, and of 0-002'" in the mean. The grey substance occurs, in the first place, very scantily in the roof of the fourth ventricle above the velum medullare inferius, in the form of brown nerve-cells, measuring 0*02 — 0-03'", scattered in the white substance, and recognisable by a sharp eye without further aid, (the substantia ferruginea superior) ; and, secondly, in the nucleus dentatus, the greyish red lamella of which contains a considerable number of yel- lowish pigment nerve-cells of a medium size (0-008 — 0-01 6'"), with four or five processes, and which have no direct connection with numerous nerve- fibres proceeding from the nucleus dentatus into the medullary substance of the hemispheres, which pass through among them. The relations of the grey substance on the surface of the convolutions of the cerebellum are more complex, {vide 'Mikrosk. Anatomic,' PI. IV, fig. 4), It consists everywhere, as is well known, of a layer, internally of a rusty colour, externally grey, which, except in the fissures, where the internal layer is most usually thicker, present pretty nearly the same, but not everywhere an equal thickness. The internal ferrugineous layer contains nerve-fibres and large masses of free nuclei. The former arise, without exception, from the white substance, and run, in general, parallel to each other, although on a transverse section of any convolution slightly diverging in a penicillar manner, directly into the ferrugineous layer. Within this layer they also run from within to without as far as the grey layer, but are broken up into numerous, for the most part, fine fasciculi, which are much interlaced, so that the whole ferrugineous layer is pene- trated by a close but delicate network of nerve-fibres, which recalls in appearance the terminal plexuses in peripheral parts, as, for instance, in the n. acusiicus, in the follicles of the vibrissa, &c. In the meshes formed by these nerve-fibres lie a vast number of opaque, round corpuscles, measuring 0-002 — 0-004'", in the mean 0-003'", which are nothing else than free nuclei, and which frequently also exhibit a distinct nucleolus, and not unfrequently other granules. In their passage through the ferrugineous layer, the nerve- 432 SPECIAL HISTOLOGY. fibres of the white substance become gradually attenuated, most of them to a diameter of 0-001 3'", and in this state enter the external grey layer. This layer, although to outward appearance everywhere perfectly homogeneous, consists of two, not well defined laminae, the inner of which contains nerve- fibres and very well marked, large nerve-cells, whilst the outer presents nothing but a finely granular, pale, light yellowish substance, which is distributed generally throughout this grey layer, and contains no nerve-cells. The granular sub- stance agrees chemically, morphologically, and physically in all respects with the already described contents of the nerve- cell; it is tenacious, elastic, rendered more opaque by acetic acid, and more transparent in caustic soda, in which it is, for the most part, dissolved, and exists in the purest form in the outer half of the grey layer, that is to say next to the pia mater. The small nerve-cells, speaking generally, are very few in number and indistinct. They occur scattered throughout the grey layer, having a diameter of 0-004 — 0-008'", more frequent towards the ferrugineous layer than more externally, and when successfully prepared, particularly by means of chromic acid, most of them exhibit delicate processes, which, however, can never be traced to any distance, and are frequently torn off close to the cells. Besides these cells, there also occur here and there, but on the whole rarely, nuclei of 0-002 — 0-0048'", which, to all appearance, are free, as they are met with even in the most carefully made preparations. Entirely different from these smaller elements, and very peculiar, are the large cells of the grey layer (fig. 148) discovered by Purkinje. These cells, measuring 0016 — 0-03'", and of a round, pyriform, or oval figure, with finely granular, colourless contents, occur only in the innermost portions of the grey, close to the ferrugineous layer, and they are, not unfrequently, at least some of them, partly imbedded in its nuclei, in single or multiple layers, and presenting 2 — 3, rarely 1 — 4, long and much branched processes, directed particularly towards the outer surface of the convolutions, which are, almost without exception, at all events the strongest of them, given off from the sides of the cells which look from the ferrugineous layer. At their origin these processes are even 0*007, or as much as 0-008'", thick, and extremely finely granular or very delicately THE NERVOUS SYSTEM. 433 striped. As they proceed they become more homogeneous, and at the same time divide into very numerous and extremely Fig. 148. slender branches, so that at last, from each process a large bundle of very fine filaments, having a diameter, in the finest, of scarcely 0'0002"', is produced. A portion of these fibrils penetrate more horizontally into the grey layer, although most of them stretch directly outwards, and appear to extend nearly to the outer surface of the grey layer. That they extend very far is certain, for in preparations made with chromic acid, I have isolated some measuring 015 — 0'3"', which were still not the finest j and in successful perpendicular sections through the cortical layers of the convolutions, their principal branches appear as parallel, slightly undulating fibres in close contiguity, extending through more than two thirds, or even three fourths, of the grey layer, to which they give a peculiar striated aspect. Whilst the principal prolongations of the processes are, in this way, continued through the grey layer, they give off their branches at acute or right angles, whence not unfrequently a second striation is produced, crossing the one just described at a greater or less angle. In the innermost portion of the grey layer, among the large Fig. 148. Large cells of the grey layer of the cortical substance of the human cerebellum, x 350 diam. I. 28 434 SPECIAL HISTOLOGY. cells, there moreover exist some nerve-fibres; but which, owing to their delicacy and the ease with which they are destroyed, it is very difficult to trace. Quitting the ferrugineous layer, and forming a continuous plexus, they are distributed in the inner third of the grey lamina among the large cells and their processes; their mode of termination has escaped my ob- servation, the result of which amounts only to this : 1. that they become finer and paler, decreasing from their original thickness of 00012'", ultimately to one of 00006"' and 0'0004"', their dark outlines also being replaced by a paler contour ; 2. that they certainly do not form terminal loops, such as Valentin and Hyrtl, who have probably mistaken a fine plexus for such, think they have noticed; but becoming isolated, and running in a more straight direction, and almost as pale as the processes of the nerve-ceUs at the border of the inner third of the grey lamina, are lost towai'ds the middle of it. The crura cerebelli are composed of nothing but parallel nerve-fibres, without any admixture of grey substance, cor- responding with those of the medullary substance of the cerebellum itself, as a continuation of which they are to be regarded. § 116. Ganglia of the Cerebrum. — The three pairs of cerebral ganglia, the corpora quadrigemina, optic thalami, and corpora striata, all consist of bulky collections of grey substance, and of nerve- fibres ; the former of which are in part quite isolated {corpus striatum), in part mutually connected, and with more deeply lying portions of grey substance {thalami optici, coip, quadrige- mina); the latter connect the ganglia, on the one hand, with the cerebellum and medulla oblongata, and on the other with the hemispheres of the cerebrum. The corpus striatum contains two large grey nuclei, the nuclexis caudatus anteriorly and superiorly, and the n. lenticularis posteriorly and inferiorly, which are, however, connected in front, constituting a single mass; and besides these, the slender n. tcsnicefmrmis, with the amygdalce external to the lenticular nucleus, and is in connection principally with the basis of the cerebral peduncle or continuation of the pyramid. THE NERVOUS SYSTEM. 435 which expands in it, forming numerous white fasciculi. The grey substance presents, as almost universally, nerve-cells and fine nerve-fibres. The former, which measure from 0*006 — O'OIS"', are, in part, colourless, and in part, contain pigment, as, especially, in the caudate nucleus and third segment of the lenticular nucleus; they are furnished with from two to five processes, and occur in greater numbers according to the depth of colour of the grey substance. The nerve-fibres may be referred for the most part to those of the basis of the crura cerebri. They present the form of dark-bordered tubes from O'OOIS — O'OOS'", most of them from 0'002 — 0*004"' in size, which, running parallel and close together in a straight direction, enter the first division of the lenticular nucleus, and the most anterior, thickest portion of the caudate nucleus. When traced further in the lenticular nucleus, it will be seen that they form larger and smaller fasciculi, decreasing somewhat in size (most of them measuring from 0*0012 — 0-003'"; and that, passing straight through the more scanty grey substance of the first divisions of the lenticular nucleus, they are all ultimately lost, spreading out in a penicillar form in its outermost and largest division. That is to say, white fasciculi measuring from 0-04 — 014"', with fibres of 00012— 0-002'", enter this division of the nucleus from the second; and these fasciculi in close con- tiguity, slightly diverging and subdividing into smaller bundles, are continued further in a direction towards the outer border of the lenticular nucleus, before reaching which they disappear to the naked eye. If traced microscopically in preparations made with chromic acid, it is apparent, that the fasciculi proceed nearly to the outermost part of the lenticular nucleus, though gradually broken up into smaller bundles and separate fibres, and most intricately interlaced with each other. That these fibres terminate here, 'and do not proceed any further into the medullary substance of the hemispheres, may be considered as made out, not the faintest indication of any further continuation being afforded, which, if it existed, could not escape being seen; on the other hand it is doubtful how they terminate here. All I have to state on the point is this : that the fibres of the nerve-fasciculi, entering the third division of the lenticular nucleus, as may be directly observed in a very great 436 SPECIAL HISTOLOGY. many instances, gradually become so much attenuatedj as ultimately to measure not more than O'OOOS'", 0"0006"', or even hardly 0'0004"', and present an almost entirely pale aspect, so that they can scarcely any longer be distinguished from the finer processes of the nerve-cells ; with which in fact, unless everything is deceptive, they most probably are actually con- nected. All the fibres, also, which enter the caudate nucleus, present exactly the same conditions; some of these enter the nucleus directly from the basis of the cerebral peduncle, others, which appear in its thinner portion, are manifestly derived from the lenticular nucleus, the first two divisions of which they tra- verse in the first instance ; in this case, also, there is no transition of the fibres into the medullary substance of the hemispheres, but a separation of the fasciculi into a plexus of the finest, almost non-medullated fibres takes place, and probably a con- nection between them and the cells. Besides the above described, in any case very numerous, nerve-fibres derived from the cerebral peduncles and terminating in the corpora striata, the nuclei of those bodies contain a considerable number of other fibres, whose origin it is, in part, difficult, and, in part, impossible to assign. I think I can trace one set of these fibres to their source. In the most external part of the large nucleus of the corpus striatum, we find, on making various sections, a considerable number of moderately strong fasciculi, though not visible to the naked eye, which in their relative thickness and the diameter of their tubes (0-0012 — 0003'") difl"er from the fibres derived from, the crus cerebri, which in this situation are reduced to the most extreme attenuation and dispersed in a plexiform manner. It is easily seen, that all these fasciculi proceed from the medullary sub- stance of the hemispheres ; and, as it appears, after they have run a certain distance parallel with the surface on the border of the nucleus of the corpus striatum, that they enter it. Many of these fibres are continued directly from the medullary substance into the ganglia, and, in this way, decussate, at right angles, with the former fibres. Assembled in fasciculi, these fibres penetrate more or less deeply into the grey substance of the corpus striatum, and of the third division of the lenticular nucleus; and these terminate, as I think I have observed, without any considerable expansion, the formation of a plexus. THE NERVOUS SYSTEM. 437 or undergoing any farther decrease in size, their fibres formiag loops with closely approximated sides. Although, speaking relatively, it is not difficult to make out the structure of the corpus striatum, at all events, in its prin- cipal features, it is quite otherwise with the optic thalami and corpora quadrigemina, chiefly because the nerve-fibres in these situations are not so much assembled into fasciculi, but are more isolated and most intimately intermixed with the grey substance, on which account they cannot be traced to any great distance. The examination of the grey substance itself, however, is perfectly easy even in these bodies, and its elements — the nerve-cells — present nothing peculiar, except that, in the optic thalami, they are for the most part more deeply coloured, whilst those in the corpora quadrigemina are paler. With respect to the nerve-fibres, it is quite certain that the superior portion of the crura cerebri, that is to say, the crura cerebelli ad corpora quadrigemina, the continuations of the ohvary columns, portions of the corpora restiformia, and the eminenti which Remak ('Obs.,' p. 26) supposed them to be, accord- ing to Harless (Miill. 'Arch.,' 1845, p. 354), do not exist. Lastly, also, may be mentioned the Pacchionian granula- tions of the pia mater, and ossifications of the membranes. The former, which are situated principally on both sides of the falx major, on the flocculi, in the choroid plexuses, &c. consist chiefly of a tough fibrous substance, not unlike imma- ture connective tissue, containing also undeveloped elastic tissue, and corpuscula amylacea. The latter, which are true osseous plates, occur sometimes on the inner surface of the cerebral dura mater, sometimes on the arachnoid, particularly of the Cauda equina.'} PEBIPHEEAL NERVOUS SYSTEM. ^ 119. Spinal nerves. — The thirty-one pairs of nerves springing from the spinal cord, arise, with few exceptions, by anterior and posterior roots. Receiving a delicate tunic from the pia mater, they converge, and are continued across the subarach- noid space, to perforate, independently of each other, the 460 SPECIAL HISTOLOGY. araclinoid and dura mater, from the latter of which they obtain a firmer coat. Proceeding further, the posterior root forms its ganglion, by the deposition around and among its nerve- fibres, of ganghon- cells, which, to all appearance, give origin to special nerve-tubes, the ganglionic fibres of the spinal-nerves, each for the most part arising from a cell, and which have no further connection with the fibres of the posterior root passing through the ganglion, than that, in their invariably peripheral course, they are in apposition, and intermingled with the latter. The motor root never acquires ganglion-cells, merely passing by the ganglion, in more or less close apposition with it. Beyond the ganglion, the two roots are united in such a manner that their elements are very intimately commingled, and a common nervous trunk formed, containing in all its divisions sensitive and motor elements. It is usually con- nected with the neighbouring nerves above and below it, in the formation of the well-known plexuses, afterwards giving off its terminal branches to the muscles, integument, vessels of the trunk and extremities, articular capsules, tendons, and bones. As in the roots, so also in the branches of the com- mon trunk, it is seen that the motor twigs contain principally thick fibres, and those destined for the integument and other organs above named, finer ones; ultimately, however, in the terminal ramifications, all the fibres are of uniform size. The fibres of all the spinal nerves appear to run quite distinct from each other, and to present no divisions in the trunks and branches, whilst, in the terminal ramifications of them, divisions frequently occur, and, at all events in certain animals (Mouse, batrachian larva), also reticular anastomoses. They terminate either in loops, or in free prolongations, the latter being the case, particularly, in the Pacinian bodies, which are structures composed of numerous concentric capsules separated by fluid, of an oval form, and measuring \ — 2'", found prin- cipally in the hand and foot, and which usually contain the termination of a nerve-fibre. [In the first and last pairs of spinal nerves occasionally only a single root can be perceived, in the former case the motor, and in the latter the sensitive. I have communicated the diameters of all the anterior and posterior roots on the left THE NERVOUS SYSTEM. 461 side in a male and female body, in the ' Verb. d. Wiirzb. phys. med./ Gesellscb. 1850, Heft II, and the transverse sectional areas deduced from these observations are given in my 'Micro- scopical Anatomy,' § 116. The roots are furnished with a delicate neurilemma, derived from the pia mater, and present- ing a similar structure, which forms both an external sheath 0003'" in diameter, as well as internal septa to the individual fasciculi. The contiguous roots frequently anastomose, and this is much more usually the case with the sensitive roots; in the cervical nerves in Man in particular, it is found to take place constantly in one or other of the nerves.] § 120. The structure of the spinal ganglia, in the Mammalia, is a difiB.cult subject of investigation, but I think the following may be stated with cer- tainty respecting them. The sensitive roots, so far as I have hitherto been able to make out, enter into no connection with the nerve-cells in the " ganglion, but forming one, or, in the larger ganglia, several, or even numerous fasciculi^ which Fig. 154. A lumbar ganglion of a young Dog, treated trith soda, and magnified 45 diam. : S, sensitive roots ; M, motor roots ; R.a, anterior branch of the spinal nerve ; R.p, posterior branch ; in both their composition from both roots is manifest; G, ganglion, vrith the cells and ganglion-fibres, which assist in the strengthening of the sensitive roots traversing the ganglion. 463 SPECIAL HISTOLOGY. in the latter case anastomose, simply traverse it, to be re- united below the ganglion into a single trunk, which is then immediately blended with the motor root. Most of the nerve- cells themselves appear to be in connection with nerve-fibres, giving off either one or two, or, more rarely, several. These fibres, which I term ganglion-fibres, proceed in a prepon- derating majority, perhaps all of them peripherally, joining and strengthening the perforating root-fibres; so that each ganglion is to be regarded as a source of new nerve-fibres. [The structure of the spinal ganglia (fig. 154) is a difficult subject for investigation, in Man. No complete results can be obtained from the larger of them, but more may be made out in the smaller or smallest, as in those of the fifth sacral nerve and n. coccygeus, which are to be sought within the sac of the dura mater, also perhaps in the fourth sacral and first cervical nerves. If a comparative examination be instituted, of the spinal ganglia of the smaller Mammalia (Rabbit, Puppy, Mole, Mouse, Rat), and if not only the scalpel and needle be em- ployed, but if the entire gangha be examined after the applica- tion of acetic acid, and above all, of a dilute solution of soda, with the aid of the compressorium, a satisfactory insight into their structure may be obtained. The fibres of the roots of the nerves while passing through the ganglia present nothing at all peculiar, that is to say, no change in size; nor have I ever observed any divisions of them, and I think it may be positively asserted, that such an occurrence, if it take place at all> must be extremely rare, as, notwithstanding that I have specially sought for it, and have been able, in the lower Mammalia, to trace numerous nerve-fibres through the entire ganglion, I have never noticed anything of the sort. The principal constituents of the ganglia — the ganglion- globules or -cells [nerve-cells] (figs. 155 and 157), have a dis- tinct outer coat, are for the most part roundish, elongated, or pyriform, usually a little flattened, and measure from 0'012 to 0-036'", or even 0-04'"; on the average 0-02— 0-03"'. The contents are throughout finely granular, and not unfrequently exhibit, in the vicinity of the nucleus, an accumulation of yellow, or yellowish-brown, larger pigment granules, which increases in age, and to which the ganglia are chiefly indebted for their THE NERVOUS SYSTEM. 463 yellow colour. The nuclei measure 0004 — 0-008'", tte nucleoli 00008 — 0-003'". These uerve-cells are situated, in the first place, in larger numbers on the sur- face of the ganglion, between the neurilemma and the perforating radical fibres j and secondly, at all events in Man, in the interior, where they occupy the interstices of the plexus formed by the nerve-fibres. The individual cells are retained in their situations by a special tissue, which also separates them from the contiguous cells and from the nerve-fibres. This tissue appears on iso- lated cells, as if it formed a special coat to them, and is consequently termed their external sheath, but in fact it re- presents a system of small septa, connected in a complex man- ner, and pervading the entire ganglion, receiving the separate cells in its meshes, and only more rarely appearing as a definitely bounded coat on individual cells. This structure is evidently to be referred to connective tissue; it presents, however, several forms, which have been, in part, already, properly distinguished by Valentin (Miill. 'Arch.,' 1839, p. 143), viz. 1. in the form of a sometimes homogeneous, sometimes more fibrous substance, with scattered, flattened, roundish nuclei of 0002 — 0"003"'; and, 3. in that of isolated elongated, triangular or fusiform cells, measuring 0*003 — 0005'", with nuclei as above, and which sometimes may be supposed to resemble epi- thelial cells, although, as is evident from a comparison of their difi'erent forms, they rather correspond with the developmental cells of connective, or of elastic tissue (fig. 156). Besides these two forms, the former Fig. 155. Ganglion-globules (nerve-cells) from the Gasserian ganglion of the Cat, X 350 diam.: 1, cell with a short, pale process, showing the origin of a fibre ; a, sheath of the cell and nerve-tube, contaiiiing nuclei ; h, cell-membrane of the nerve- cell : 2, cell with the origin of a fibre, without sheath ; b, cell-membrane of the nerve-cell ; 3, nerve-cell, deprived, in the preparation of it, of its membrane and ex- ternal sheath. Fig. 156. Cells from the sheath of the nerve-cells of the spinal ganglia in Man, X 350 diam. Fig. 156. 454 SPECIAL HISTOLOGY. Fig. 157. of which occurs everywhere, and the latter principally in the larger ganglia, certain intermediate types are met with in Man, which consist, as it were, of nucleated ' fibres of Remak,' as they are termed (vid. infra), or, at all events, in the pre- paration, break up into such. From by far the greatest number of the nerve-cells, in Man and the Mammalia, are given off pale processes, 0"0015 — 00025'", in all respects corresponding to those of the central cells, but furnished w?th a special sheath, and which, as I dis- covered in the year 1844 (' Selbst. u. Abh. des Symp. Nerv.,' Ziirich, 1844, p. 23), are each of them continued into a dark- bordered nerve-tube (figs, 155, 157), The cells observed by me had but one pro- cess, the so-termed unipolar-cells, and I at first thought that such only existed in the spinal ganglia. It now appears, how- ever, from more re- cent researches, es- pecially from those of Stannius, that they also contain cells with two processes, one of which may again divide; fresh and more extended investigations therefore are required to show how the matter really stands. At present I think the following should be remarked : 1. in Man and the Mammalia I have certainly established the fact of the existence of unipolar-cells, and think it may also be asserted that they are very numerous ; 2. quite lately I have myself, although rarely, noticed cells with two, pale processes, and I am willing to admit the pos- sibility that such cells frequently occur, as it is certain that many processes must be torn off in the comparatively rude methods necessarily employed to isolate the cells; 3, when Stannius very recently noticed in a human foetus, and in a foetal Calf, together with unipolar and apolar cells, in the latter numerous bipolar cells, it should be inquired whether Fig. 157. Twigs of the coccygeal nerve within the dura mater, with an adherent, pedunculated nerve-cell in its nucleated sheath, ftom which the derivation of a fibre is very distinctly seen, x 350 diam. From Man. THE NERVOUS SYSTEM. 465 the latter were not cells which afterwards divide? — because divisions of the nerve-cells undoubtedly take place (vid. infra), — and in this way become unipolar ; 4. whether the cells give off one or two fibreSj one of the latter does not go towards the centre and the other towards the periphery, but both proceed in the latter direction; at all events, in the examination of all small ganglia, only such ganglion-fibres are visible. Stannius, in bipolar-cells of this kind from the Calf, also found the two processes closely approximated; 5. it is difB.cult to determine whether cells without processes also occur in the spinal ganglia, seeing that the processes are very readily detached, and that cells thus truncated may very easily be regarded as apolar cells. In small ganglia in theMammaUa a fibre may be traced to each cell, whilst in the smallest spinal ganglia in Man, and in the inconstant gangha of the posterior roots (vid. seq.), cells are not unfrequently met with, to which no fibre is attached, and, consequently, I would, at present, merely state that, in any case, fibres arise from the majority of the cells. In order to examine these conditions, either the larger ganglia in Man are selected, which are torn into fibres as carefully as possible under a simple microscope, until the fibres are traced to their origin, which may be done with a little trouble in almost every ganglion, or the small ganglia of the fifth sacral and coccygeal nerves are taken for the purpose. In these ganglia, in almost every individual, sohtary and completely isolated, pedunculated, ganglion-globules are met with, close to or in the neighbourhood of the ganglia, each in its special sheath, which in this case appears to be homogeneous (fig. 157), and in many cases, the simple, dark nerve-fibre lying in the peduncle of the globule, and frequently also its connection with the cell, by means of a pale process, may be distinctly perceived. In the ganglia aberrantia also of Hyrtl, that is to say the inconstant, larger or smaller collections of nerve-cells, which are found in every subject upon the posterior roots of the larger nerves, the simple origins of fibres may occasionally be distinctly noticed. The dark-coloured fibres, arising from the nerve-cells, simply con- stitute the continuation of the pale processes of the cells, so that the membranes and contents of each part pass con- tinuously into each other, and thus also the membrane and the contents of the cells are connected with the sheath of the I. 30 466 SPECIAL HISTOLOGY. Fig. 158. nerve-tubes, tie medullary sheath, and the axis-cyliiider. In older nerve-cells, or by the operation of re-agents (arsenious acid, chromic acid, iodine), the contents of the cell become detached from the membrane, and the axis-cylinder appears as a direct continuation of the former (fig. 158), as was first shown by Harting [vid. also Stannius in 'Gott. Anzeig.,' 1850, and Leydig, 1. c. Tab. 1, fig. 9), which is the best proof that the contents of the nerve- cells cannot be understood as con- tained in a dilated nerve-tube. The nerve-tubes or ganglion-fibres thus originating, which frequently arch round or embrace the cells with several circular turns, are at first fine, measur- ing 0-0015 — 0-0025'", but (not con- tinuing so as I formerly supposed, when I was acquainted only with their origin), they all very soon increase in size, as may be very readily observed in many fibres, whilst still within the ganglion, up to 0-003'" and 0004'", many even to as much as 0*005 and 0'006"' ; becoming, consequently, '■" medium-sized, and thick nerve-Jvbres. The processes of the cells and the nerve-fibres springing from them are also furnished with nucleated sheaths like the cells themselves, the vaginal processes, as they are termed, which they lose, however, at the point where they join the emergent trunk, obtaining instead of it, as a coat, the common neuri- lemma of the nerves. The description I have above given of the conditions ob- servable in the spinal-ganglia in Man and the Mammalia, difi'ers very considerably from what was found by Bidder, Reichert, R. Wagner, and Robin, to be the case in Fishes. Fig. 158. Nerve-cell of the Pike (bipolar, as they are termed), vfhich is continued at each end into dark-bordered nerve-tubes, treated with arsenious acid, x 350 diam.: a, sheath of the nerve-cell ; i, sheath of nerve ; c, nerve-medulla ; d, axis-cylinder continuous with the contents of the nerve-cell ; e, which have shrunk away from the sheath. THE NERVOUS SYSTEM. 467 The chief difference consists in this, that whilst in the Mam- malia, from all we know, the roots of the nerves have no direct connection with the nerve-cells, and merely pass through the ganglion, in Fishes, all the radical fibres are connected with the cells, so that each fibre is interrupted by a bipolar cell, and independent ganglion-fibres are wholly wanting. R.Wagner has thought, that what obtains in the Fish might be applied, unconditionally, to all theVertebrata, and asserts, that the occur- rence of bipolar cells in the course of the posterior radical fibres is in accordance with BeU's doctrine, and a necessary contingent in the mechanism of the sensitive fibres; and moreover, that in this case the highly important and long-sought distinction between sensitive and motor primitive fibres, has been dis- covered. In opposition to this I have expressed the opinion, that it is not a necessary postulate, that what is found in the Fish should be applied to Man, and that the interruption of a sensitive fibre by a nerve-cell does not distinguish it from a motor fibre. Although Wagner has very recently characterised this opinion of mine as unphysiological, he will not, at the same time, convince any one that the spinal ganglia of the Mammalia are constructed as he thinks, and I shall therefore wait to see whether further observations will confirm my observations or not. In order to complete them, I will moreover mention, that direct measurement of the sensitive roots above and below the ganglia, shows a not inconsiderable difference in favour of the latter situation (vid. 'Mikroskop. Anat.,' II, p. 509), which as differences in the thickness of the entering and emergent nerve-fibres, and divisions of them within the ganglion do not exist, can only be referred to the fibres which originate in the ganglion and proceed towards the periphery, a view which is also confirmed by direct observation (fig. 154). With respect to the interesting observations on the structure of the spinal ganglia of the lower animals, and particularly of Fishes, I would refer especially to the works of R. Wagner, Bidder, Robin, and Stannius, cited below.] § 131. Further course and termination of the Spinal Nerves. — Below the spinal ganglion, the sensitive and motor roots unite to form a common trunk, their fibres being intermixed in diverse ways, 468 SPECIAL HISTOLOGY. as may be very distinctly perceived in small animals. All the subsequent branches, both of the anterior and posterior main divisions, as well as their further continuations, are consequently of a mixed nature, formed of portions derived from both roots ; a condition which they retain up to their ultimate distribution. Here, however, an alteration takes place, the motor fibres going oiF in by far the larger proportion into the muscular branches, and the sensitive chiefly to the cutaneous. Where the ganglion- fibres which arise in the spinal ganglia are distributed, cannot be ascertained anatomically. When their physiological relations, however, are considered, it would appear as by far the most probable supposition, that they do not, as at first sight one would be inclined to suppose, join the sympathetic in the rami communicantes, but, that accompanying the spinal nerves, they are continued chiefly into the vascular branches, and consequently are distributed in the integuments, muscles, bones, joints, ten- dons, and membranes (periosteum, pia mater, &c.), but also, perhaps, to the glands and involuntary muscles of the skin. The nerve-fibres in the main trunks of the spinal nerves present the same diameter as in the roots, that is to say, there are finer and thicker tubes, and a certain number of intermediate forms; but, as they proceed, the fibres separate, the thicker going more to the muscular branches, and the thinner into the cutaneous nerves. According to the statements of Bidder and Volkman, the proportion of the fine to the thick fibres is, in Man, as 1. 1 : 1, in the muscular nerves as 0. 1 — 0'33 : 1; statements which I can but confirm, adding to them, that the nerves of the bones contain, in the trunks, one third of thick and two thirds of fine, whilst those of the articulations, tendons, and membranes, exhibit a great preponderance of fine fibres. In my opinion, most of the fine fibres contained in the branches of the spinal nerves must be regarded as derived from the spinal cord, and as being, in their function, qmte of equal importance with the thick fibres, and, at present, the only thing that remains unascertained, is whether they all ascend to the brain, or perhaps in part arise in the spinal cord ; upon which point reference may be made to § 112. The spinal nerves are composed in general of parallel tubes, for the most part undulating, upon which circumstance their transversely banded aspect depends; they exhibit, THE NERVOUS SYSTEM. 469 however, in their course, very frequent anastomoses, in which way the various larger and smaller plexuses with decussating fibres are formed. The formation of these plexuses is due to an interchange of entire fasciculi or fibres, never to a connec- tion between the individual primitive fibres, and in a micro- scopical point of view afibrds no point worthy of remark. Divisions of the nerverfibres do not occur, according to our present experience, in the trunks and larger branches of the spinal nerves of the Mammalia [in Fishes, Stannius noticed numerous divisions in the trunks of the motor and mixed nerves ('Archiv fiir phys.,^ Heilk. 1850, p. 77)'], nor do they* exhibit any considerable chaiige in their diameter; but in the ultimate ramifications, on the other hand, it is certain that such divisions do take place, even in Man, accompanied by a very considerable diminution in the size of the fibres ; with respect to which conditions, and the terminations in the skin, muscles, bones, and membranes in general, reference may be made to the detailed descriptions given in the proper places. One kind, only, of termination of the spinal nerves, is still to be noticed here, — that in the Pacinian bodies. The " small bodies, so named by Henle and myself (' Ueber die Pacin. Korperchen des Menschen und der Thiere,' Ziirich, 1844), were first accurately described by the Italian, Pacini ('Nuovi organi scoperti nel corpo umano,' Pistoja, 1840), especially in the nerves of the palm of the hand and sole of the foot, and, in fact, as Langer of Vienna afterwards showed, had been previously noticed by A. Vater (J. Gr. Lehmann, 'De consensu partium corp. hum.,' Vitembergse, 1741), although their nature had not been recognised. These organs are of an elliptical or pyriform shape, of a whitish transparent colour, with whiter streaks internally, and measure i — 2'" in size ; in Man, they are constantly found on the cutaneous nerves of the palm of the hand and sole of the foot, in the subcutaneous connective tissue itself, and most numerously in the fingers and toes, particularly on the third phalanx, — according to Herbst ('Die Pacin. Korperchen und ihre Bedeutung,' Gott., 1847) there are about 600 in the hand and not quite so many in the foot j besides which, it must here also be stated, that they are invariably found on the great sympa- thetic plexus, in front of, and close to the abdominal aorta. 470 SPECIAL HISTOLOGY. Fig. 159. behind the peritoneum, particularly near the pancreas, fre- quently also in the mesentery, close to the intestine ; and also occasionally on other nerves, such as the n. pudendus communia, on the fflans penis (Fick) and bulb of the urethra, on the inter- costal nerves, sacral plexus, cuta- neous nerves of the upper- and fore-arm, on the dorsum of the hand and foot, and the cutaneous nerves of the neck. The structure of the Pacinian bodies is, upon the whole, simple (fig. 159). Each of them consists ..-d of very numerous (20 — 60) con- centric layers of connective tissue, of which layers the external are separated by wider, and the internal ' by narrower interspaces, in which is contained a clear serous moisture, which is collected in larger quan- tity in an elongated central cavity, bounded by the innermost lamella. Each body presents a rounded pe- duncle, formed from the continua- tions of its lamellae, and connected with a nervous twig, and in which a dark nerve-fibre, 0-006 — 0068'" (in the Cat, 0'0044— 0-0077'") thick, runs to the Pacinian body. This fibre enters the central cavity from the peduncle, where it becomes 0-006'" wide and 0-004'" thick, pale, non-meduUated, almost like an axis-cylinder, and ter- minates in the upper part of the cavity, in a free, slightly granular tubercle, the extremity being frequently bifid or trifid. Further observations, and comparative anatomical details with regard to these bodies, which are also foimd in great number in many Mammalia, as well as in Birds, in the Fig. 159. A Pacinian body in Man, x 350 diam.: u, its pedunde; *, nerve-fibre in it ; c, external ; d, internal layer of the sheath ; e, pale nerve-fibre in the central cavity ; f, divisions and terminations of the same. THE NERVOUS SYSTEM. 471 skin, beak, and tongue (Herbst, Will), and with respect to which physiology is still wholly in the dark, will be found in the works above quoted, and also in Reichert (' Bindegewebe,' p. 65), Herbst ('Gott. gel. Anz.,' 1848, Nos. 162, 163, 1850; 'Nachr. v. d. Univ./ p. 204, 1851, p. 161), Will (' Sitzungsber. d. Wiener Acad.,' Feb., 1850), Osann (' Bericht iiber d. zoot. Anst. in Wiirzb.,' 1849), Strahl (Miiller's 'Arch.,' 1848, p. 163), and Pappenheim ('Comptes rendus,' xxiii, p. 68). [Todd and Bowman, ' Physiol. Anatomy,' Part II, p. 395, figs. 74, 75, 76 ; and Bowman, art. 'Pacinian Bodies,' ' Cyc. of Anat. and Phys.'] The spinal nerves, from their point of exit through the dura mater, are enclosed by a firm sheath of connective tissue — the nerve-sheath, or neurilemma — which also sends finer prolonga- tions into the interior of the nerves, and, as in the muscles^ forms boundaries to larger or smaller fasciculi, as well as ex- tremely delicate septa between the individual tubules (fig. 160). In the ultimate ramifications, where isolated primitive fibres, or some few of them, still often retain pjg. leo. an external coat, the neurilemma pre- sents the aspect of a homogeneous membrane, with elongated nuclei of O'OOS'"; and it presents this cha- racter also in the smaller twigs of the cutaneous and muscular nerves, only that gradually the substance begins to split, in a longi- tudinal direction, into fibres, the nuclei become longer (0005 — O'OOS"'), frequently almost like those in smooth muscles, and elastic fibres also make their appearance, which are not ■[infrequently entwined around whole fasciculi. The larger nerves, lastly, present common connective tissue, with distinct longitudinal fibrils, as in fibrous membranes, intermixed with numerous reticulated elastic filaments; they still, however, exhibit, especially in the interior, immature forms of con- nective tissue. All the larger nerves contain vessels, although not in great number ; they run principally in a longitudinal direction, and form a loose plexus of minute capillaries of 0"003 — 0004'", Fig. 160. Transverse section of the ischiatic nerve, x 15 diam.: a, general sheath of the nerve ; *, neurilemma of the tertiary fasciculi ; c, secondary nervous fasciculi, in part vfith special sheaths. From the Calf. 47S SPECIAL HISTOLOGY. with elongated interstices, which invests the fasciculus, and, in fact, penetrates between its elements ; never, however, sur- rounding individual primitive fibres, but only entire divisions of them. The ganglia contain a delicate capillary plexus, in the form of a network, so that each nerve-cell is surrounded by special vessels. The Pacinian bodies also contain vessels, which even penetrate as far as the central cavity (Todd and Bowman, II, p. 397, fig. 75, and p. 399, fig. 76; Herbst, Tab. IV, figs. 1 and 2). [On the subject of the condition of the cutaneous nerves of animals, I would here add a few remarks. In the skin of the tail of batrachian larvae {Rana, Bufo, Triton, Bombinator, Alytes), I have described the very delicate ramifications and plexuses of the embryonic pale nerve-fibres ; and moreover, quite evident loops of the fully formed dark nerve-tubes, and isolated divisions of the latter ('Ann. des S. Nat.,' 1846, p. 102, pi. 6, 7). In the full-grown Frog, according to Czermak (Miill. 'Archiv,' 1849, p. 252), the nerves destined to the skin, form, on its inner aspect, a wide network, already described by Burdach, from which again numerous fasciculi are given oflF, penetrate the derma perpendicularly, and, having reached the superficial glandular layer of the skin, form a superficial nervous- plexus between the glands. With respect to the true ter- mination of the nerve-fibres, Czermdk arrived at no definite results, but made the interesting discovery that thick and thin nerve-fibres of the deeper plexus divide dichotomously very fre- quently and repeatedly, and thus spread themselves over larger surfaces ; of which divisions I have most fully satisfied myself from preparations furnished by Czermak. Similar conditions were found by Leydig (' Zeitsch. f. wissen. Zool.,' Ill) in the skin of Fishes j where also exist superficial and deeper plexuses, with numerous divisions of finer and thicker tubes, all of which on the surface ultimately become quite fine, pale, and finally invisible. In the Invertebrata, as appears from Leydig's re- searches in Argulus, and especially in Carinaria, conditions are met with perfectly analogous to those described by me in the nerves of the Tadpole ; and I cannot agree with Leydig, when he describes the nucleated enlargements as nerve-cells. On the other hand, the conditions observed in Artemia and Corethra THE NERVOUS SYSTEM. 473 are, perhaps, peculiar, because in these instances larger branches of the cutaneous nerves are, at their extremities, in connection with numerous roundish vesicles, which might have the function of nerve-cells (' Zeitsch. f. wiss. Zool.,' vol, T, iii). In the integuments of the Mammalia and of Man, except in the Pacinian bodies, until a short time since, no one had seen anything of divisions in the nerve-tubes ; all observers rather agreeing that terminal loops existed there, especially in the papillse. But it now appears, from the researches of my- self, J. N. Czermdk, and C. Gegenbaur, that probably loops and divisions, and occasionally even free terminations, all exist in that situation. That in Man, terminal loops occur in the papillse, and divisions in the terminal plexuses, I have already mentioned ; the latter are especially well shown in the conjunc- tiva scleroticce, where free terminations also appear to exist, and where peculiar convolutions of nerves (nerven-knauel), similar to those formerly described by Gerber^ {vide ' Mikrosk. Anat.,' II, i, p. 31, fig. 13 A, 3), present themselves. Czermdk, moreover, observed divisions of the cutaneous nerves in the Mouse, and I myself a transition of the dark-bordered nerves into pale anastomosing filaments, of O'OOl — 00005'", exactly resembling the embryonic fibres in the Tadpole ('Mikrosk. Anat.,' IT, i, p. 24) ; lastly, Gegenbaur has noticed numerous divisions in the expansion of the nerves of the tactile hairs in the Mammalia. Further experience will have to show in what relative proportions the. loops, divisions, and free terminations, stand with respect to each other, and whether in the dififerent Mammalia, notwithstanding any apparent difference, some correspondence obtains or not.] ^ 123. Cerebral Nei'ves. — The sensitive and motor-nerves arising in the brain, correspond in most particulars so closejy with the spinal-nerves, that a short description of them wUl suffice ; and with respect to the higher nerves of sense, they will be after- wards described, more fully, in connection with the organs to which they belong. The motor cerebral-nerves, the third, fourth, sixth, seventh, and twelfth pairs, with respect both to their roots and to their ' ['General Anatomy,' translated by G. Gulliver, p. 263, pi. 19, figs. 99, 100.— Eds.] 474 SPECIAL HISTOLOGY. course and distribution, present exactly the same conditions as the motor-roots and muscular branches of the spinal nerves, with the sole exception, that by all these nerves, from their anastomosing with sensitive nerves, some sensitive fibres are conveyed to the muscles. It deserves remark : 1. that accord- ing to Rosenthal and Purkinje, nerve-cells exist in the trunk of the oculo-motorius in the Ox, which, however. Bidder (p. 33) was unable to find; 2. that the facial-nerve, in its gangliform enlargement, presents a number of larger nerve- cells, through which, however, according to Bemak, only part of the fibres pass (Miill. 'Archiv,' 1841) ; 3. that according to Volkmann (in Bidder's 'Ganglien-korper,' p. 68), the small root of the hypoglossal nerve in the Calf, which is furnished with a ganglion, produces motor effects. What is the signifi- cance of this occurrence of nerve-cells in motor-nerves has not been ascertained. Probably simple fibres having a peripheral destination arise from them, exactly as in the spinal ganglia. In any case it shows that ganglia are not necessarily placed only on sensitive nerves. The fifth, ninth, and tenth pairs, resemble the spinal-nerves, inasmuch as that they all contain motor and sensitive elements. In the trigeminus the small root exhibits a preponderance of thick fibres ; the larger, numerous fine fibres. "The Gasserian ganglion, as well as the smaller ganglionic body seated upon it, contains many larger and smaller nerve-cells of 0008 — O'OSO'", with nucleated sheaths, and presents the same conditions, according to my observa- tions, in small Mammalia and in Man, as a spinal ganglion, that is to say, it is simply traversed by the fibres of the greater root, and, from unipolar cells, gives origin to numerous nerves- fibres of medium size, which go to join the emergent branches. Bipolar cells also occur, but, as it appears, in less quantity, and anything that can be said about apolar cells is as applicable here as in the case of the spinal ganglia. The ultimate dis- tribution of the n. trigeminus is for the most part similar to that of the cutaneous nerves, and, in particular, the existence of divisions of the nerve-tubes may be distinctly demonstrated in the mucous membranes, as in the conjunctiva at the edge of the cornea, in the ciliary ligament, in the tooth-pulp, and in the papillae of the tongue. Terminal loops and free ter- minations appear to exist in the papillae of the mucous mem- THE NERVOUS SYSTEM. 475 brane of the mouth and tongue, and in the conjunctiva, whilst in the cornea, the extremities of the nerves are quite trans- parent and pale, and constitute a wide meshed plexus without any divisions. With respect to the ganglia, which are placed on the n. trigemmus (ganglion ciliare, oticum, sphenopalatinum, linguale, supramaxillare), I find their structure more to resem- ble that of the sympathetic ganglia, only that they contain a considerable number of larger nerve-cells. The glossopharyn- geus, although endowed with motor properties, still, according to Volkmann (Miill. 'Arch.,' 1840, p. 488), has no fibres which do not pass through one or other of its ganglia. In its roots, which contain numerous fine fibres, there are, according to Bidder (1. c. p. 30), in the Mammalia, not unfrequently, isolated nerve-cells, often placed free upon it, in which, as in similar cells, on the roots of the n. vagus, the giving off of two middle-sized fibres, it is said, may occasionally be readily perceived. The ganglia of the glossopharyngeus present the same conditions as the spinal ganglia, that is to say, the radical fibres simply traverse them, and, within the ganglion, fibres arise from cells, which are for the most part unipolar; its ultimate ramification in the tym- panic cavity and in the tongue, contains small ganglia, and otherwise corresponds with that of the n. trigeminus (p. major). In Man, all the roots of the n, vagus enter the jugular ganglion, whilst in some of the Mammalia — Dog, Cat, Rabbit, according to Uemak (in Frorieps 'Not.,' 1837, No. 54), in the Dog and Sheep, according to Volkmann (Miiller's 'Arch.,' 1840, p. 491), but not in the Calf, in which nerve-cells occur in the apparently motor-root, it has also a primary fasciculus, which has no connection with the ganglion. In the ganglion jugulare and in the intumescentia ganglioformis of the facial nerve, I have not been able to find anything different from the spinal ganglia, only, that the nerve-cells measure occasionally no more than 0"009"', although it is true that there are also a great many as large as 0'03"'. The ultimate distribution of the nerve exhibits, as Bidder and Volkmann correctly state, a constant kind of separation of thicker and more slender fibres, so that the branches to the oesophagus, heart, and stomach, are composed almost entirely of fine fibres, whilst in those going to the lungs, and in the laryngeus superior, the fine are to the thick fibres as 2 to 1; and in the laryngeus inferior and the 476 SPECIAL HISTOLOGY. rami pharyngei, as 1 to 6 — 10. All these fine fibres are very far from being derived from the sympathetic, as they occur in preponderating quantity even in the roots of the vagus, and are also numerous in the laryngeus superior. Many of them, moreover, may be nothing more than attenuated or originally finer ganglion-fibres, as they are termed, arising in the ganglia of the vagus itself, and which likewise I should not refer to the sympathetic. With respect to the terminations of the vagus, reference must be made below to the proper places. The n. accessorius Willisii, although perhaps also in part sensitive, has no nerve-cells, and in its distribution and termi- nation, so far as is known, presents nothing peculiar. [Terminal loops within the trunks of nerves had been already noticed by Gerber, and have lately been described by Valentin in the vagus (pectoral portion) of the Mouse and Shrew-mouse, but without their expressing any opinion with respect to their signification. Still more mysterious are the nervous filaments seen by Remak and Bochdalek, coming out from, and again re-entering the brain.] § 123. Ganglionic Nerves. — Under this name, perhaps, is most suitably designated the n. sympathicus, as it is termed, — the sympathetic or vegetative nervous system, — as it presupposes no physiological hypothesis, but simply expresses the fact, which, anatomically, is most apparent to the eye. The ganglionic nerves are neither a wholly independent part of the nervous system (Reil, Bichat), nor a mere section of the cerebro-spinal nerves; but on the one hand, from the very numerous fine nerve-fibres originating in their ganglia — ganglion-fibres of the sympathetic, — form an independent system; whilst ou the other, they are also connected with the spinal cord and brain, owing to their receiving a smaller number of fibres of the other nerves. Upon comparing the ganglionic nerves with the cerebro-spinal, we find, that the former, as they are con- stituted from a double source, in a certain respect undoubtedly resemble the latter, which are also formed from ganglionic fibres of the spinal ganglia, and from others proceeding from the cord; but they diflfer, particularly in this respect, that they THE NERVOUS SYSTEM. 477 possess a much greater number of independent elements, of ganglia and ganglionic fibres, and enter into much more nume- rous anastomoses with each other. Consequently, although we appear to be justified from an anatomical point of view, in con- sidering the ganglionic nerves by themselves, still they must not be regarded as something altogether peculiar, seeing that, essen- tially, every nerve exhibits the same principal elements, and some cerebral-nerves, vagus, glossopharyngeus, possess even numerous peripheral ganglia; and moreover, because comparative Ana- tomy shows that they are produced from the spinal nerves, and Physiology the absence of peculiar functions in them. § 134. Fig. 161. The principal trunk of the gang- lionic nerves, [nervus sympathicus). The n. sympathicus in man appears as a whitish, or white nerve, the dark-bordered fibres of which usually run parallel with each other, witliout divisions or anastomoses, some measur- ing 00025 — 0-006'" or even more, and others not more than O'OOIS — 0-0025'". These finer and coarser fibres are partially intermixed, partly disposed more in a fascicular manner, the latter being the case near the ganglia of the main trunk and in that part itself. The structure of the ganglia is, in the main, similar to that of the spinal ganglia. Each of them consists : 1. of perforating nerve-fibres, proceed- ing from one part of the trunk to the other ; 2. of a certain number of finer tubules originating in the ganglion ; and 3, of numerous nerve- Fig. 161. Sixth thoracic ganglion, on the left side, of the sympathetic nerve of the Rabbit, viewed from behind, treated with soda, and magnified 40 diam.: T.2, trunk of the sympathetic ; R.c, R.c, rami communicantes, each dividing into two branches; Spl., n. ^lanchnicus ; S, twigs of the ganglion with two stronger fibres and finer filaments, probably going to vessels ; G, nerve-cells, and ganglion-fibres joining the main trunk. 478 SPECIAL HISTOLOGY. cells j besides these the rami communicantes also enter the ganglia, and a certain number of peripheral branches are given oif from it. The nerve-cells in the sympathetic (fig. 16.2 B), ^. ,„„ present, in all essential Fig. 162. ^ . ' • , .1 ^ ^ particulars, precisely the same conditions as those in the spinal ganglia, only that they are, on an average, smaller, mea- suring 0-006 — 0-01 8'", 0-008 — O-Ol'" in the mean, with less and paler pigment, or even colour- less and usually pretty uniformly rounded. As respects the origin of the nerve-fibres of the main trunk, it is, in the first place, evident, that they are in great part derived from the rami communicantes which arise immediately below the spinal ganglia from the trunks of the spinal nerves ; that they are in general formed like the sensitive roots of those nerves (that is, contain a pre- ponderance of finer fibres), and, whether simple or compound, that they are manifestly connected with both roots.. From all that has hitherto been made out, the fibres of these connecting branches are derived chiefly from the spinal cord and from the spinal ganglia, and are consequently roots of the sympathetic ; in a smaller proportion, however, they might be derived from the sympathetic, and joining themselves to the spinal nerves are further distributed peripherally together with them. Having entered the main trunk of the sympathetic, the rami com- municantes, so far as they are derived from the spinal nerves, almost invariably run, dividing into two or several branches upwards and downwards in it, towards its cephalic and pelvic extremities, being in apposition with the longitudinal fibres of the trunk. In the Rabbit, the fibres of a given ramus com- municans may very frequently be traced as far as the nearest ganglion and beyond it, in separate peripheral branches, but, in general, the course of the individual fasciculi very soon escapes the eye. It may nevertheless be asserted with great certainty. Fig. 162. From the sympathetic in Man, x 350 diam. A, a portion of a grey nerve, treated with acetic acid ; a, fine nerve-tnbes j b, nuclei of the fibres of Remak. B, Three nerve-cells, one with a pale process. THE NERVOUS SYSTEM. 479 that they all gradually go off in the peripheral branches of the main trunkj for in the first place all these branches frequently contain^ in considerable quantity, the same dark-bordered thicker fibres, as those which are contained in the rami communicantes, and secondly their termination or origin is never observed in the main trunk itself; which circum- stance is also the principal reason why the rami communicantes can be regarded not as branches of the sympathetic, but only as its roots. Besides the fine and coarser fibres of the rami communi- cantes, the main trunk of the sympathetic contains other fibres in very great numbers, which are dark-bordered, but pale, finest nerve-tubes measuring O'OOIS — 0"002"', with respect to which I unhesitatingly assert, that they originate in it, and are in no way continuations of the rami communicantes, as has been quite recently supposed, since the discovery of the bipolar ganglion- cells in Fishes. In the Mammalia it is, in fact, extremely easy to prove, by the examination of entire sympa- thetic ganglia under the careful application of dilute soda and compression, that the great majority of the fibres of the rami communicantes have not the slightest connection with the ganglion-cells, but much rather that they simply pass through the ganglia, and ultimately go off in the peripheral branches. Now, as, besides these fibres in the main trunk, numerous other fibres of the finest kind exist, which can in no way be assigned- to the rami communicantes, it is clear, that they must be structures of entirely new formation. This con- clusion appears to be the more legitimate, when it is added, that it is not, as I first and many since have shown, by any means so difficult to demonstrate simple origins of fibres in the sympathetic ganglia of the Mammalia and Amphibia, and that, in the ganglia a considerable portion of fine fibres assume the aspect of so-called convoluted fibres, that is to say, of fibres winding about in various directions through the mass of cells. From what I have seen in the Mammalia and man, the sympa- thetic ganglia correspond so far with those of the spinal nerves, that they contain a preponderance of unipolar, rarely of bipolar cells, differing, however, in this respect, that apolar cells certainly exist in them in more considerable quantity, and the ganglion fibres arising in them are invariably of the finest kind. 480 SPECIAL HISTOLOGY. occurring in the peripheral nerves, and probably in most cases, quit the ganglia in various directions. As for a topographical tracing of the various fibres in the main trunk of the sympa- theticj with reference to their origin from particular 7-ami com- municantes and ganglia, and their continuation into particular peripheral branches, — if more be required than what has already been stated — it is not by any means at present to be thought of, but must be reserved for future investigation. [It has been asserted, that the smaller cells in the ganglia of the sympathetic are different from the larger cells in the spinal ganglia, for instance; and also that they are connected only with fine nerve»tubes (Robin), but this is not correct, as is apparent in part from the observations of Wagner and Stannius; for we find: 1. in the ganglia of the cerebral and spinal nerves of the Mammalia and of man, all intermediate sizes between larger and smaller nerve-cells, and also, occasion- ally, though rarely, larger cells, measuring as much as 0"03"' in the sympathetic ganglia ; and we may also be convinced, 2. that the diameter of the nerve-fibres originating in the first-named ganglia, is not at all regulated by that of the cells, all their ganglion-fibres being pretty nearly of the same size, and which is confirmed also by the bipolar cells of Fishes, where the one fibre arising from the cell is often considerably thicker than the other ; in Petromyzon, according to Stannius, even six times. Should it be at all supposed that the small cells are peculiar to the sympathetic nerve alone, I must, as above, with respect to the nerve-fibres, remark, that not to mention the ganglia of the roots of the cerebral and spinal nerves, small nerve- cells also occur in situations where there can be no question about the sympathetic, as in the spinal cord and brain, and, — if instances of the same kind in the peripheral nerves be desired — in the retina and cochlea. At all events, this much is certain, that the ganglia of the ganglionic system of nerves constantly present smaller nerve-cells, and that the fibres arising from them are of the fine kind only. Bidder and Volkmann have shown, in the Frog, that the greater part of the fibres of the rami communicantes are dis- tributed peripherally, with the spinal nerves, and that only a small portion of them, which moreover are derived from the THE NERVOUS SYSTEM.' 481 spinal ganglia, should be regarded as roots of the sympathetic. But I think I have noticed in the Rabbit and in Man, that the rami communicantes have chiefly a central destination. Still, in man, fibres also occur very frequently — according to Luschka always, — which must be regarded as branches of the sympa- thetic going to the peripheral distribution of the spinal nerves, from which again twigs are given off to nerves of the vertebrae ; with respect to which conditions the more detailed observations given in my ' Mikroskop. Anatom.,' II, p. 525, and particularly those of Luschka ('Nerven des Wirbelcanals,' p. 10 et seq.) may be consulted. With regard to the question, whence the fibres are derived which join the main trunk of the sympathetic from the spinal nerves, it is certain that that portion of the rami communicantes, which arises, from the motor root, and which, according to Luschka, is always a white filament, takes its origin from the cord (or brain) itself, but as regards the other, proceeding from the sensitive root, it may be formed, in part or wholly, from fibres originating in the ganglion. The latter, however, appears to be improbable, for two reasons : 1. because in that case, the existence of conscious sensations from parts supplied by the sympathetic would scarcely be conceivable j and 2. because the fibres originating in the spinal ganglia are of medium size, whilst, in the rami communicantes, upon the whole, only a few of that kind occur, and these, moreover, must be referred to the motor root. We may here offer a few remarks upon the fine fibres 6f the ganglionic nerves. It has been long known, that the sympa- thetic contains a larger proportion of finer nerve-fibres than the cerebro-spinal nerves, but it was not till 1842 that Bidder and Volkmann laboured to show, that these fibres are not only smaller, but also, in other respects, anatomically different ; on which account, in contra-distinction to the thick fibres of the cerebro-spinal nerves, they termed them sympathetic nerve-fibres. In opposition to this, Valentin ('Rep.,' 1843, p. 103) and I ('Sympath.,'p.lO et seq.) have endeavoured to prove, that the fine fibres in the sympathetic do not constitute a special class, and in this I think we were tolerably successful. The principal reasons are as follows : 1. Fine and thick nerve-fibres do not differ in- trinsically in any essential respect except in size, and present the most numerous intermediate dimensions. 2. Fine nerve-fibres I. 31 483 SPECIAL HISTOLOGY. having exactly the same characters as those of the so-termed sympathetic exist in many other situations, as for instance, — ^in Man and the Mammalia, — in the posterior roots of the spinal nerves and of the sensitive cerebral nerves, in which situations, as I have already shown, there can he no question whatever as to a derivation of the fibres from the sympathetic, and where we have, presented to us, nothing but fine cerebro-spinal fibres ; similar fibres are contained by thousands in the spinal cord and brain, as well as in the two higher nerves of sense. 3. All thick nerve-fibres decrease in size in their ultimate ramifications, owing to divisions, or direct diminution, so that ultimately they acquire the diameter and nature of the fine, and finest kinds of fibres. 4. All thick nerve-fibres in the course of their develop- ment are, at one time, exactly in the condition of the so-termed sympathetic fibres. From these facts it would appear certainly evident, that it is impossible to regard the fine fibres of the sympathetic as altogether of a special nature, and peculiar to it alone, and that it wiU not do, in the anatomical point of view, to classify the fibres according to their size, very many in fact, in their course, assuming all possible degrees of thickness. Allowing that the great number of very fine pale fibres in the sympathetic is a prominent anatomical fact, as is also indeed the case in the higher nerves of sense and in the grey substance, still, speaking physiologically, I am by no means of opinion that the fineness of the fibres in the sympathetic indicates any- thing of a special nature in them, and which does not exist elsewhere, but perhaps, that where this condition does exist both in them and in other situations, it is connected with a distinct kind of function.] §125. Peripheral distribution of the ganglionic Nerves. — Prom the main trunk of the sympathetic arise the branches proceeding to the periphery, which, without exception, receive finer and thick fibres from it, b1)?t besides these, in part at least, contain other special elements, to which is due their varied aspect. Some of them, for instance, are white, as is the main trunk in most situations, such are the n, splanchnici ; others greyish white, as the nervi intestinales, the nerves of the unimpregnated uterus (Kemak, 'Darmnerven System,' p. 30); others again THE NERVOUS SYSTEM. 483 grey, and at the same time less firm to the feel, as the n. caroticus internus, the nn. carotid externi s. molles, the nn. cardiaci, the vascular branches in general, the branches con- necting the large ganglia and plexuses in the abdomen, those which enter the glands, and the pelvic plexuses. The peculiar condition of the latter nerves depends, in part, upon the paler colour of the fine fibres of the sympathetic itself, but in great measure upon the presence of the fibres, named after their discoverer, the fibres of Remak ("gelatinous fibres" of Henle), which were at first regarded as a kind of nerve-tubes, and of which, even now, some cannot be convinced that they are only a sort of connective tissue. They are sometimes more readily isolated, sometimes more united into a compact sub- stance resembling homogeneous connective tissue. In the former case they present the aspect of flat, pale fibres, O'OOIS — 00025'" broad and 0-0006'" thick, of an indistinctly striated, granular, or more homogeneous substance ; and which, under the action of dilute organic acids, exhibit precisely the same conditions as connective tissue, and from point to point are furnished with, mostly elongated, or fusiform nuclei, 0-003 — 0007'" long, 0002 — 0-003'" broad. These fibres, again, are found in almost all the grey portions of the ganglionic nerves — I cannot find them in many parts of the pelvic plexuses in Man, where they are replaced by a non-nucleated abundant connective tissue, though they are said by Remak to abound in the nerves of the impregnated uterus, (' Darmnervensyst.,' p. 30) in very great quantity, so that they amount to from three to ten times the number of the dark-bordered true nerve-fibres. They constitute the main piart of the proper basis of these trunks, and the dark-bordered tubes extend through them, sometimes more isolated, sometimes assembled in larger or smaller fasciculi; more rarely, and only in the neighbourhood of the ganglia themselves, do they appear to form sheaths to individual tubes of the finest kind. Besides these ' fibres of Remak,' the peripheral ramifications of the sympathetic are, above all, distinguished by a great number of ganglia. These bodies, of a larger or less size, some even microscopic, are placed on the branches or terminations, and, indeed, the microscopic ganglia, so far as is hitherto known, on the nervi carotid, in the pharyngeal plexus, in the 484 SPECIAL HISTOLOGY. heart, at the root of the lungs and in the lungs, on the supra- renal capsules, in the lymphatic glands, in the kidneys of Man occasionally, on the posterior wall of the bladder, in the mus- cular substance of the neck of the uterus in the Sow, in the plexus cavernosi, and with respect to their distribution, will be further adverted to when we come to speak of the viscera. I will here remark, in general, concerning them, that with respect to the size and figure of the nerve-cells, and the origination of fine fibres, they present precisely the same con- ditions as the ganglia of the main trunk. As regards the last pointj it may be especially noticed, that in one situa- tion the origin of nerve-fibres from unipolar cells, and the rarity of the double origin of fibres, is particularly well dis- played, viz. in the septum of the heart in the Frog (fig. 163), pj 163. where R. Wagner has also described their occurrence. These ganglia, therefore, are also sources of nerve-fibres, and the emer- gent branches always contain more than the roots, on the supposition that the fibres come out only in one direction, which perhaps in most places may be the case. In the same situation also, it is most readily and satisfac- torily seen that many of the cells are apolar and without any processes (fig. 163); as is also most plainly shown in the cardiac ganglia and small ganglia on the wall of the urinary bladder in Bombinator, in which ganglia, as well as in the similar ganglia in the Frog, the conditions described are as manifest as possible. How the fibres arising from these various localities, from the rami communicantes, the ganglia of the main trunk, and the peripheral ganglia, are disposed in their ultimate distribu- tion, is as yet very doubtful. Many peripheral branches anastomose with other nerves, and thus escape all further re- search, as the nn. carotid externi and intemus, the latter of which, containing scarcely anything but fine fibres and nume- rous 'fibres of Bemak,' I do not look upon in the common sense as a root, but as a branch, arising from the superior cervical ganglion, and probably the other cervical ganglia; as well as Fig. 163. Nerve-cells from the cardiac ganglia of the Frog, x 350 diam.; one with the origin of a nerve-tuhe. THE NERVOUS SYSTEM. 485 the rami communicantes, seeing that individual fibres of them, actually join peripherally the spinal nerves ; and the rami car- diaci, pulmonales, &c. Other branches in the parenchyma of the organs become so fine, that it is impossible to trace them. What has been as yet established respecting their ultimate course, is as follows : 1. Divisions occur in the branches and terminal ramifications of the sympathetic, as in the nerves of the spleen, the Pacinian bodies in the mesentery, in the nerves accompanying the mesenteric vessels in the Frog, in those which exist temporarily in the uterus of the Rodentia, of the lungs and stomach of the Frog and Rabbit, of the dura mater on the meningeal arteries, in branches of the sympathetic of the Sturgeon, in the cardiac nerves of the Amphibia, and in those of the urinary bladder in the Rabbit and Mouse. 2. There are free terminations of the nerves, as in the Pacinian bodies and on the mesenteric vessels in the Frog. 3. The thicker fibres of the sympathetic ultimately so decrease in size, as to become of the fine kind; as may be readily seen in the rami intestinales, lienales, and hepaiici, which, indeed, even in the interior of the organs in question, contain some coarser nerve-fibres, but ulti- mately lose them. The actual terminations, however, in the organs themselves, in the heart, lungs, stomach, intestine, kidneys, spleen, liver, uterus, &c., are as yet quite unknown ; although from the impossibility of finding any dark-bordered fibres in the ultimate ramifications of these nerves, it may be supposed that they terminate, almost everywhere, in non- medullated, embryonic fibres. In fact, I have, at all events hitherto, in vain endeavoured to find a trace of them. Schaflfner says, that in the heart of Bombinator he has seen the passage of the dark-bordered fibres into pale, anastomosing fibrils of the finest kind, whilst Pappenheim (1. c.) describes loops in the nerves of the kidney. [As regards the nature of the " fibres of Remak," most, re- cent observers incline to the opinion first advanced by Valentin (' Repert.,' 1838, p. 72 ; Miiller's 'Archiv,' 1839, p. 107), that they are not nerve-fibres at all, but to be referred to the con- nective tissue of the nerves ; whilst Remak still thinks himself obliged to adhere to his previous opinion, that they are, or may be, in part at least, nerve-fibres (' Darmnervensyst.,' p. 30). As 486 SPECIAL HISTOLOGY. for myself, I freely acknowledge the force of the reasons adduced by the latter observer, which are based chiefly upon the similarity of the fibres in question to the pale embryonic nerve-fibres, inasmuch as that even in the adult, nucleated nerve-fibres are met with in the olfactory nerve ; but I am com- pelled, nevertheless, as before, fully to concur with Valentin, as do also Bidder and Volkmann, and many others. My reasons are the following: 1. The "fibres of Remak," as may be easily shown, arise from the sheath of the nerve-cells of the sympathetic ganglia, and are continued in the nervous trunks, surrounding the nerve-fibres arising from the ganglia. Now as it is certain that these sheaths are a sort of connective tissue, as is apparent also from the spinal ganglia, where they occur in precisely a similar way, only more scautily and without their being continued into the nerves, it follows that the "fibres of Remak" can scarcely be anything else. 2. The finest twigs of the spinal nerves also exhibit nucleated fibres, in all respects like those of Remak, as for instance, those going to the skin, &c.; with respect to which, as they are wanting in the trunks of the nerves, there can be no question at aU of their not being nerve-fibres. 3. The quantity of the " fibres of Remak" always diminishes towards the finest ramifications, which could not be the case were they nerves. It is not, in- deed, altogether correct, as stated by Valentin, that they are not to be found in the finer intestinal nerves, for there can be no doubt that they do exist there, though much more rarely than in the trunks of the nerves, and are only to be brought into view by compression. According to Remak (MiiD. 'Arch.,' 1844, p. 464), they also exist in the cai-diac nerves of the Mammalia ; although as far as I can perceive, only in the im- mediate neighbourhood of the ganglia. Relying upon these reasons, I continue in the firm persuasion that the nucleated fibres in the sympathetic nerve of adult Mammalia are a form of the neurilemma ; but I will not omit to remark, that I consider it quite impossible to determine, in undeveloped nerves, what is neurilemma and what young nerve-fibres. Thus in the Rabbit, 2 — 6 months old, in the n. caroticus internum, not a single developed nerve-fibre is to be met with, and apparently nothing but "fibres of Remak," although it is quite certain that together with them, there must also exist the rudiments THE NERVOUS SYSTEM. 487 of numerous dark-bordered fibres. In the nerves of the spleen, in the Calf, in like manner, numerous nucleated fibres are met with, though in the terminations (vide ' Cyclopaedia of Anatomy,' III, p. 795, figs, 539 and 540), which, probably, afterwards become nerve-fibres. In young animals, conse- quently, we must not look far a decision of the question; whilst in older ones, it is quite otherwise. In them, a nucleated fibre can only be regarded as nerve when it can be traced into a dark- bordered fibre, or to a true process of a nerve-cell ; and this, as we have seen, is not the case in those of the sympathetic system. It may, however, be remarked, that "fibres of Remak^' also occur in the ganglia of the main sympathetic trunk, but that they do not, for the most part, extend to any distance beyond them, so that usually but few are contained in the trunk of the nerve itself.] § 136. Development of the elements of the Nervous System. — The nerve-cells, wherever they may occur, are nothing else than transformations of the so-called embryonic-cells; some of which simply enlarge, whilst others throw out a varying number of processes, and are, ^'S' ^^*" at all events in part, connected with nerve-fibres. Many nerve-cells also appear, at a subsequent period, to increase by division j at all events, I do not know how other- wise to explain the frequent occurrence of two nuclei in the nerve-cells of young animals, especially in the ganglia; and the cells connected by communicating filaments, which have been noticed by various observers. The peripheral nerve-fibres all originate on the spot, but their subsequent development proceeds in such a way that the central extremities always precede the peripheral. With the Fig. 164. Nerve-cell from a spinal ganglion of a sixteen-weeks' human embryo : a, nucleus in the pale process of the cell ; 2, self-developing nerve-tubes from the brain of a two-months' human embryo ; 3, cells from the grey cerebral substance of the same embryo. 488 SPECIAL HISTOLOGY. exception of the extremities of the nerves, they are developed from fusiform nucleated cells, which are nothing else than modifications of the primordial formative cells of the embryo, and are conjoined into pale, flattened, elongated, nucleated tubules or fibres 0-001 — 0-003'" broad. Now, at first the nerves consist only of fibres of this kind, and of the rudiment of the neurilemma, being grey or dull white, like the sympa- thetic filaments J subsequently, in the human embryo at the fourth or fifth month, they always assume a whiter colour, and the proper white or medullary substance continues to be more and more developed in them. Of the three possible modes of development of this substance propounded by Schwann, one only, in the present state of things, can come into question, that namely, as to whether the medullary sheath is a structure deposited between the membrane and the contents of the embryonic nucleated fibresj in which case the contents of the latter would become the axis-fibre. But besides this, the medullary sheath may originate in what did not occur to Schwann, viz., a chemical metamorphosis of the external por- tion of the contents of the embryonic-fibres; and the axis-fibre may be onlythe remainder of those contents which has not under- gone a fatty metamorphosis. It is difficult to determine which of these two views is correct. ' Direct observation shows only this much, that the contents of the pale embryonic fibres invariably, by degrees, obtain dark contours, and ultimately present the aspect of a true dark-bordered fibre, whilst it Fig. 165. 1, two nerve-fibres from the ischiatic nerve of a sixteen-weeks' embryo . 2, nerve-tubes from a newly-littered Rabbit ; a, their sheath ; b, nucleus ; c, medul- lary sheath : 3, nerve-fibre from the tail of the Tadpole; a, t, c, as before; at d, the fibre retains its embryonic character ; the dark-bordered fibre shows a division. THE NERVOUS SYSTEM. 489 teaches nothing with respect to the proper origin of the white substance. Since, however, it can be proved, that the fibres, whilst they undergo this change, do not alter in size, the supposition I have expressed would still appear the more correct. The development of the terminations of the nerves, which appears in some respects to present conditions different from those exhibited in the trunks, may, as I have shown ('Annal. d. sc. nat.,' 1846, p. 103, tab. 6, 7), be readily traced in the tails of the larvae of the naked Amphibia (fig. 165, 3 ; fig. 166). We there find, as is mentioned by Schwann (p, 177), the primary rudiments of the nerves to be pale branched fibres, measuring 0-001— 0-003'", which here and there anastomose, all finally terminating in free fibrils of thefinest kind, mea- suring 0-0002 — 0-0004'". There is no difficulty in showing that these fibres arise from the coalescence of fusiform or stellate cells, for, in the first place, such cells may be seen, in part still in close apposition with, but independent of them; in part more or less connected by means of their processes ; and, secondly, cell-nuclei occur at the divisions of the fibriss, which are there somewhat dilated; and, at all events in young larvae, Fig. 166. Nerves from the tail of a Tadpole, x 350 diam.: 1, embryonic nerve- fibres, in which more than one dark-bordered tube has become developed ; 2, similar fibres containing but one tube, which in one fibre ceases at 6 ; 3, embryonic pale fibres; 4, fusiform cells connected together, and with a complete nerve-fibre. 490 SPECIAL HISTOLOGY. with them are associated the well-known angular viteLine corpuscles, with which, at first, aU the cells of the embryo are filled. At first the number of pale embryonic nerves is very small, and limited to a few short trunks closely applied to the muscular structures in the tail; but they are gradually de- veloped, in the direction from the centre towards the periphery, further into the transparent portion of the tail, new cells being continually added in connection with the existing trunks, whilst the latter themselves, almost in the same manner as the capillaries of these larvae, unite directly by delicate off-sets. When these fine ramifications — with respect to the nervous nature of which no doubt can be entertained, as it is evident that the larvae in which they exist already possess very acute sensibility — are once formed, the following further changes then take place. Whilst the fibres gradually enlarge to twice or four times their original diameter, there are by degrees developed in them, and in fact from the trunk towards the branches, dark-bordered, fine primitive fibres, which in no case owe their origin to newly added medullary sheaths, but are certainly formed solely from a metamorphosis of a part of the contents of the pale fibres. In connection with this, however, the following conditions, which have not yet been observed in the higher animals, are to be remarked : 1. where a pale embryonic fibre bifurcates, there occasionally, though not always, also takes place a division of the dark-bordered tube developed within it; 2. the dark-bordered tubes scarcely ever completely fill the pale fibres in which they are formed, but a space, frequently of the same diameter as that of the tubes, is most usually left between them and the membranes of the embryonic fibres, in which space occasionally the nuclei of the primordial formative cells m&y be perceived; 3, in the trunks and main branches of the embryonic fibres, several (2 — 4) dark- bordered tubules are undoubtedly developed within one and the same embryonic fibre; a very remarkable condition, which shows that there are even dark-bordered fibres which do not possess a structureless sheath {vid. note to § 110), and resembling what exists in the muscular fasciculus, in which, in hke manner, within a single tubule, numerous finer elements are produced. As the tail of the Tadpole is afterwards thrown off, it is to be regretted that its interesting nerves cannot be traced to the THE NERVOUS SYSTEM. 491 same state of completion, as can be done in those of other situations. It is obvious, however, in the oldest Tadpoles, that the nerves are somewhat thicker than they are originally, and that they extend towards the periphery, sometimes in loops, sometimes with free ends, but in such a way that the primary pale fibres continue to exist, and, proceeding from the dark- bordered fibres, constitute a very fine terminal nervous-plexus, with anastomoses and free ends. I should not have delayed so long on the subject of the nerves in the Tadpole, did not similar conditions most probably also obtain in many other terminations of nerves. This is certain as regards those of the electric organ of the Ray, which, even when developed, agree in many respects with those of the more advanced Tadpole, and as Ecker has lately shown ('Zeitsch. fiir wissensch. Zoologie,' 1849, p. 38), are developed in precisely the same manner. The nerves, also, in the skin of the Mouse {vid. note to § 121), evidently belong to the same category; and consequently it may hereafter be shown, that wherever peripheral divisions of nerves occur, their de- velopment proceeds essentially as it is here described. With respect to the development of the nerve-fibres in the central organs, we possess but few researches. Of the fibres in the ganglia, I can only observe, that they are developed subsequently to those of the nerves, and probably from smaller fusiform cells, which may be noticed in association with the nerve-cells. On one occasion, in a spinal ganglion of a four months' human embryo, I noticed a cell of this kind in con- nection with the process of a nerve-cell (fig. 164). The formation of the fibres in the cord and brain is extremely difficult of investigation, and is best studied with the aid of chromic acid. In the human embryo, I find, as early as the end of the second month, the commencement of the formation of the tubules in question, the white substance being distinctly finely striated, and manifestly containing, in places, very deli- cate fusiform cells, which are sometimes independent or isolated, sometimes connected, two or three, or several together (fig. 164). All these cells are at first pale, invest- ing the nucleus, which measures 0003 — 0003'" quite closely, and having processes almost as fine as the fibrils of connective tissue. In the fourth month, when the two kinds of substance 493 SPECIAL HISTOLOGY. are quite distinct, nuclei are still occasionally to be seen in the now wider fibres, but in some they have disappeared, although the fibres are without dark contours; which are not developed before the middle period of foetal life (in the foetal Calf, when more than 12" long, according to Valentin), and, indeed, first in the spinal cord. As regards the subsequent changes in the nerve -fibres, it has already been remarked, that they occasionally increase very considerably in thickness. According to Harting (1. c, p. 75), the fibres of the median-nerve which have not yet acquired dark contours, measure in a four months' human embryo, on the average 3-4"'-™-, in a new-bom chUd 10-4°""-, in the adult 16-6""-"-. The increased thickness of the nerves themselves appears, according to Harting, from the foiu-th month onwards, to depend solely upon the enlargement of the already existing elements, the foetus and new-born child already possessing the same number of primitive fibres as the adult. [It remains to be observed, that extremely few pathological changes of the nervous elements are known. In the nerve- cells of the brain, the deposition of pigmentary matter becomes excessive, particularly in old age; and fatty deposition also takes place (Virchow, 'Archiv,' I, 1). Valentin thinks that he has observed a regeneration of nerve-cells in the superior cervical ganglion of the Rabbit. Nerve-fibres are readily destroyed, as in consequence of extravasation of blood, tumours, softening, fibroid growths, &c., in which cases the meduUary substance breaks up into larger or smaller, coagulated or fiuid masses, of very various configuration, whilst the axis-fibres seem to disappear. In atrophied nerves, the fibres are ob- served to be thinner, easily broken up, and, instead of the medxdlary matter, are frequently, in parts, entirely occupied by minute fatty molecules, as was seen on one occasion by Virchow, in a human optic nerve, and by myself in the nerves of a ¥rog. Nerves that have been cut across, readily unite ; portions of peripheral nerves from 8 — 12'" in length, even, are restored by true nervous tissue (Bidder, 1. c, p. 65j Valentin 'defunct, new./ p. 159, § 323; and 'Phys.,' 2 Aufl. I, 2, 716). Should the union of a divided nerve not take place, the peri- pheral end undergoes a gradual change in a particular way, THE NERVOUS SYSTEM. 493 with a simultaneous extinction of the nervous activity. The nerve-fibres generally become yellowish, soft, lacerable, and lose their transversely banded and glistening aspect. They no longer present any trace of a double contour, their me- dullary substance is wholly coagulated, and their breadth frequently very various (Stannius in Miill. 'Arch;,' 1847, p. 453). Whether the axis-fibres undergo change, we are, unfortunately, not informed. According to Brown- Sequard, incised wounds, even of the spinal-cord, in the Rabbit, united. Hypertrophies of the nerve-substance itself are unknown, although probably such a condition occurs in the neurilemma. Virchow noticed a new formation of fine nerves in pleuritic and peritoneal adhesions, and, according to the same observer, it would appear that grey nerve-substance may be formed on the walls of the cerebral ventricles.] § 127. With respect to the functions of the nervous system, the following remarks which are immediately pertinent to the anatomical facts — ^may suffice. As regards the two elemehtary portions of the nervous system, anatomical investigation shows, that all its divisions, which preside over the higher functions, contain grey substance in greater or less quantity, as in the sympathetic, the ganglia of the spinal and cerebral nerves, and in the spinal cord and brain ; whilst the nerves, which act only as a conducting apparatus, contain nothing but nerve-fibres. This being admitted to be the attribute of the grey substance, it may further be inquired whether it presents differences in its structure, as it does in its functions. With respect to this I would remark as follows : the largest nerve-cells are met with in situations from which motory eflfects proceed, as in the anterior horns of the spinal cord, amongst the fibres of the anterior roots, in the medulla oblongata, at the points of origin of the motor cerebral nerves, in the cortical substance of the cerebellum, the pons Varolii, and crura cerebri; whilst the smallest cells are found in the sensitive regions, as in the pos- terior horns of the spinal cord, the corpwa restiformia, and quadrigemina. There does not however, appear to be any con- stant relation between the size of the cells and the existence of sensitive or motor functions, for, in the ganglia of the cerebro- 494 SPECIAL HISTOLOGY. spinal nerves aud of the sympathetic^ and in the optic thalami, both sorts of fibres arise, in one place, from small, and in another from large cells. It seems, therefore, as in the case of the nerve-fibres, that there are large and small motor cells, as well as sensitive cells of various dimensions, a fact which is confirmed by comparative anatomy, as the large bipolar cells in Pishes are manifestly sensitive. No essential difference can be pointed out between sensitive and motor cells, whether the latter be of uniform or of different size, and in particular the variations ex- isting between such cells are not greater than those between the motor cells in different localities. Even the cells in the cortical substance of the brain, to which Physiologists assign the mental manifestations, with our present means of research, exhibit no perceptible peculiarities. The nerve-cells, however, may be divided into those which are in direct connection with nerve-fibres, and those which are not thus connected, but in- dependent. The former, of course, are to be especially regarded as sensitive and motor, with respect to the latter, anatomy to some extent affords no information, inasmuch as, that they present no processes, as in the sympathetic ganglia, and in some situations in the brain; as regards those furnished with pro- cesses, particularly the many- rayed cells, which in many situa- tions undoubtedly are not prolonged into nerve-fibres, it might be considered certain that they, — both larger and smaller, by means of their processes which fulfil the functions of nerves, and whether the latter anastomose or not, — bring different regions of the central organs into mutual connection, and par- ticipate in the reflex phenomena, the sympathies, and other modes of association of the functions. Cells of this kind exist in the spinal cord and brain everywhere in very large quantity, but not in the ganglia, although it is not, from this, intended to imply that no reflex actions are performed in those bodies. Respecting the nerve-fibres, anatomy is not in a condition to point out any difference in them, between the sensitive and motor nerves ; a circumstance, however, which, physiologically, can afford no reason to ascribe identical functions to them. As regards the various sizes of the nerve-fibres, the numerous changes in diameter, undergone in their course by all the cerebro-spinal nerves, very obviously indicate that these pro- portions have no relation to the functions of the fibres in THE NERVOUS SYSTEM. 495 general. Nevertheless, 1 do not look upon these relations of size as altogether of little consequence, and in particular does the attenuation of the fibres, where they extend through grey substance {vid. sup., § 112), appear to me to be important, as also their diminution at their origins and terminations. It is, however, difficult to perceive the physiological import of these facts. Were it the case, that in the nerve-fibres the axis- cylinder alone was the conducting, and the medullary-sheath, an insulating substance, and could it be proved that the medullary sheaths were wanting in the attenuated portions, the peculiar activity of the nerve-fibres in these situations (the transverse conduction in the spinEil cord, the acuteness of sensibility at the terminations, &c.) would be satisfactorily explained. It is well known that such a notion has already been entertained by various writers, and its conception has usually proceeded upon the idea that a close alliance or identity exists between elec- tricity and the nervous force, and the medullary sheath abound- ing in fatty matter, has from this point of view been regarded as an insulator. But (1.) it is anything but demonstrated, that the nerves possess no other active force but electricity; and (3.) there is nothing to indicate an absence of the medullary sheath, and a free condition of the axis-fibres in many peripheral extre- mities of the nerves (skin, muscles), and in those portions of the central organs (spinal cord) in which a transverse conduc- tion is evident. The question always remains, whether the medullary sheath, although not altogether, yet at all events partially, may not insulate more or less, according to its thick- ness. Since, however, this membrane is wanting not only in many terminations of nerves, where an insxdated conducting faculty might not be required, but also in other situations, as in the Invertebrata and the nerves ofPetrom^zon generally, as well as in the processes of the nerve-cells which certainly act as nerves, in the central organs of the higher animals, and in the finest nerve-fibres in those situations (brain), the notion that such is its efi'ect in the dark-bordered nerves loses all ground of support. It would seem to me, that the medullary sheath represents nothing more than a protective soft envelope for the tender central fibre. This mode of explanation also, renders it intelligible, why it is, that in dark-bordered nerves, where the medullary sheath is thin or wanting, and the central fibre is in 496 SPECIAL HISTOLOGY. a more free condition, the nerve-fibres are more readily excited and able to communicate their conditions ; and as regards the pale nerve-fibres, in this case they would essentially have the same functions as the others, and the absence of the medullary sheath in them could either be explained on the supposition, that they are less readily excitable, as in the invertebrate animals, and the Cyclostomata, or because they occur in situa- tions where a protective tunic to the nerve-fibres is no longer required, as in the retina, in the nasal mucous membrane, in the grey substance, and in the electric organs, or even where its refractive power upon light would be prejudicial to a certain object, as in the cornea. A similar mechanical function appears to me to be performed by the fine granular substance, which in the higher central organs is found in so many situa- tions supporting the most delicate nerve-fibres, cells, and processes. [With respect to the methods to be employed in investiga- tions of the nervous system, the principal have been noticed in the preceding sections. I will, here, once more advert to the importance of preparations made with chromic acid in the in- vestigation of the course of the fibres, and in the examination of the central nerve-cells j and direct attention to the dilute solution of caustic soda for the detecting of nerve-fibres in non-trans- parent tissues, — without which two means very many points would remain in the dark. In this way also the extreme pr one- ness to become changed, of the grey and white substances, and particularly the ready disruption of the processes of the nerve- cells, and the varicosity, coagulation, and destruction of the nerve-fibres, are at once removed or avoided. The brain and spinal cord, as well 'as the elements of the ganglia, are best studied in the human subject, but the course of the fibres in them, and, above all, the terminations of the nerves, are best investigated in the smaller Mammalia, and only in the second place in Man. In the searching for the minute ganglia in the heart, Ludwig recommends the treatment with phosphoric acid and the solution of iodine in hydriodic acid, the latter so diluted that it has only a tinge of brown. For the development of the nerves, the human and mammalian embryo are quite suitable ; but the batrachian larvse, and if opportunity offer, the electric THE NEEVOUS SYSTEM. 497 organs of the embryo Eay, in which the conditions are by far the most clearly displayed, should not be overlooked.! Literature of the Nervous System. — C. G. Ehrenberg, ' Beo- bachtung einer bisher unbekaunten Structur des Seelenorgans des Menschen' (Observation of a hitherto unknown structure in the Human Brain), Berlin, 1836; Gr. Valentin, in Miill. 'Archiv,' 1839, p. 139, 1840, p. 318, in Valentin's 'Reper- torium,' 1838, p. 77, 1840, p. 79, 1841, p. 96, 1843, p. 96, and : ' Hii-n- und Nervenlehre' (Treatise on the Brain and Nerves), Leipzic, 1841 ; J. E. Purkinje, in the ' Bericht iiber die Versammlung deutscher Naturforscher,' in Prague, for the year 1837, Prague, 1838, p. 177, and in Miill. 'Archiv,' 1845, p. 281 ; R. Remak, in Miill. 'Archiv,' 1841, p. 506, 1844, p. 461, 'Ueb. ein selbstandiges Darmnervensystem' (On an independent system of intestinal nerves), Berlin, 1847 ; J. F. Rosenthal, 'De formatione granulosa in nervis aliisque partibus organismi animalis' Vratisl., 1839 ; A, W. Volkmann, in Miill. 'Archiv,' 1838, p. 274, and 1840, p. 510; Artie. 'Nerven- physiologie,' in Wagner's 'Handw, der Phys.,' II; F. H. Bid- der and A. W. Volkmann, ' Die Selbstandigkeit des sympath- ischen Nervensystems durch anatomische Untersuchungen nachgewiesen' (The independence of the sympathetic Nervous System, proved by anatomical Researches), Leipzic, 1842; Stilling and Wallach, ' Untersuchungen iiber die Textur des Riickenmarks' (Researches on the Texture of the Spinal Cord), Leipzig, 1842; StUling, 'Ueber die Medulla oblongata,' Erlangen, 1843 ; ' Researches on the Structure and Functions of the Brain. I. On the Structure oi the pons Varolii,' Jena, 1846 ; A. Kolliker, ' Die Selbstandigkeit u. Abhangigkeit des sympathischen Nervensystems, durch anatomische Unter- suchungen bewiesen' (The independence and dependence of the Sympathetic Nervous System, shown by anatomical re- searches), Zurich, 1844; P. Savi, 'Etudes anatomiques sur le systeme nerveux de la Torpille.' Paris, 1843. As an appendix to Matteucci, ' Traite des phenomenes electro-physiques des animaux,' Paris, 1844 ; R. Wagner, ' Ueber d. innern Bau der* electrischen Organe im Zitterrochen' (On the intimate Struc- ture of the Electric Organ in the Ray), Gottingen, 1847. With a plate ; ' Sympathetic Nerve,' ' Structure of Ganglia,' and 'Terminations of Nerves,' in Wagner's ' Handw. d. Physiol.,' T. 32 498 SPECIAL HISTOLOGY. part III, p. 360 ; ' Sympathetic Ganglia of the Heart/ ibid., p. 452 ; ' Neurological Researches/ in Getting. ' Nachricht v. d. Universit., &c./ Feb, 1851, No. 14; H. Stannius, 'Das peripherische Nervensystem der Fische' (Peripheral Nervous System of Fish), Rostock, 1849. Moreover, in the 'Archiv fiir phys., Heilk. 1850, and in Gott. ' Nachricht, &c.,' 1850, Nos. 6 — 16, 1851, No. 17; J. N. Czerm^k, ' Ueber die Haut- nerven der Frosche' ( On the Cutaneous Nerves of the Frog), / Miill. 'Archiv/ 1849, p. 253 ; ' Verastelung der Primitivfasem des N. acusticus' (Ramifications of the primitive Fibres of the Acoustic Nerve), in 'Zeitsch. f. wissen. Zoologie,' II, 1850, p. 105. Besides these, should be consulted the general works of Schwann, Henle, Valentin, Todd and Bowman, Bruns, and myself, which also give figures; the Reports of Henle and Reichert ; and the memoirs cited under the description of the nerves of the different organs, and in the various sections. END OF VOL. I. C. and J. Acllardj Printers, Bartliolomciv Close-