The anatomy of the frog
Alexander Ecker and George [Translator] Haslam
*Transcriber’s notes*:
The text of this complex e-book has mostly been preserved in its original form, including inconsistent punctuation, spacing, capitalisation, hyphenation and diacritics; however, some such flaws have been corrected silently. A list of spelling corrections is appended at the end of the book. Multiple levels of headings and subheadings, not all of which are consistently formatted, can make it difficult to follow the text coherently. The author has used [square brackets] to identify his personal additions but these are not always readily detectable and can be confused with similar brackets used for other purposes.
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In this plain text e-version, italic text is denoted by _underscores_ and bold text by *asterisks*. Superscripted text is indicated by a preceding caret mark, e.g. 2^{ab}. Footnotes have been renumbered consecutively and placed below the relevant paragraphs.
One incorrect index page reference has been changed, viz. 730 → 369 ‘pigment of the skin’
Translations
Of
Foreign Biological Memoirs
II
London
Henry Frowde
[Illustration]
Oxford University Press Warehouse
Amen Corner, E.C.
The
Anatomy Of The Frog
By
Dr. ALEXANDER ECKER
Professor Of Human And Comparative Anatomy In The University Of Freiburg
Translated, with numerous Annotations and Additions
By
George Haslam, M.D.
SCIENTIFIC ASSISTANT IN THE MEDICAL DEPARTMENT IN THE UNIVERSITY OF ZÜRICH; FORMERLY ASSISTANT LECTURER IN PHYSIOLOGY IN THE OWENS COLLEGE, VICTORIA UNIVERSITY, MANCHESTER
_Illustrated With Many Wood Engravings_
_And Two Coloured Plates Executed By Hofmann, WüRtzburg, Bavaria_
Oxford AT THE CLARENDON PRESS 1889
[_All rights reserved_]
Translator’S Preface.
I undertook the publication of a translation of Ecker’s ‘Anatomie des Frosches’ at the suggestion of Professor A. Gamgee while I was working under his superintendence in the physiological laboratory of the Owens College. The work was subsequently accepted by the Delegates of the Clarendon Press, as one of the series of ‘Foreign Biological Memoirs,’ published by them. Early in the progress of the work it became evident that a mere translation would be unsatisfactory, and that it would be desirable to recast and modify several portions of the book. It was deemed advisable to give greater completeness to the work by descriptions of the minute structure of the several organs. For these purposes the appearance of the work has been unavoidably delayed.
I have done my best to bring the book up to date by including the results of recent researches, to which I have added many facts derived from my own personal investigations. All such additions are enclosed within square brackets [ ]. More than a hundred new figures, of which one-third are original, have been added; and copious, though it is feared still incomplete, lists of references to frog-literature have been drawn up. By these additions the size of the book has been considerably increased.
In the several sections into which the book is divided the following points may be more particularly noticed:--
Sect. I. The Bones and Joints. The nomenclature of Parker and Bettany has been adopted throughout.
Sect. II. The Muscles. This section remains in its original form.
Sect. III. The Nervous System. The chapters on the central nervous system and the sympathetic system have been rewritten. The description of the arteries of the brain is entirely new, while the chapters on cranial and spinal nerves have received many smaller additions, and have been rearranged to facilitate reference.
Sect. IV. The Vascular System. The chapter on the heart is practically new, and many additions and alterations have been made in the descriptions of the blood-vessels and lymphatics.
Sect. V. The Alimentary Canal, with its appendages, the Spleen and the Peritoneum. In this section much new material has been added: the descriptions of the blood-vessels of the liver, the ducts of the liver and pancreas, etc., being the results of original investigation.
Sect. VI. The Respiratory Organs, the Thymus and Thyroid Glands. These organs have been carefully studied and numerous new details are noted. The lymphatic glands of the hyoid region have, after some hesitation, been designated tonsils.
Sect. VII. The Urino-Genital Organs. A very large number of preparations have been made to investigate the vessels and uriniferous tubes of the kidneys; and the descriptions of the remaining organs of this section have received large additions from recent publications.
Sect. VIII. The Skin and the Sense-Organs. This section has, with the exception of very small portions, been re-written and very much enlarged.
Before concluding this preface, I must thank my friend Professor A. Milnes Marshall, of the Owens College, for all the help and kindness he has extended to me before and during the time this work has been in hand; to him I am indebted not alone for the loan of books, pamphlets, etc., and for much useful information, but also for the care and patience with which he has read and corrected the whole of the proof-sheets.
To Professor G. Lunge, of Zürich, I am indebted for the use of the library of the Gesellschaft der Naturforscher of Zürich; and to my friend Mr. C. Herbert Hurst, of the Owens College, for the drawings for figures 132, 133, 134, and 136; also to Dr. Max Köppen, of Strasburg, for the proof-sheets of his valuable paper, ‘Zur Anatomie des Froschgehirns’: to these gentlemen I beg to express herewith my heartiest thanks. Lastly, I must express my sense of indebtedness to the Delegates of the Clarendon Press, who have kindly allowed me to alter the original plan of the book, and to make extensive additions far beyond the limits originally intended.
A second edition of the original German work is in course of publication. The first part, on the bones and muscles, has already appeared.
Geo. Haslam.
Zürich, 1888.
Preface To The First Part.
The idea of this manual on the anatomy of the frog, of which I now offer the first part to physiologists and to those who would become such, occurred to me during the preparation of the plates for my ‘Icones Physiologicae.’ I was then convinced of the necessity of such a book. I regret that many direct and indirect causes have hindered its earlier completion; fortunately, however, its appearance is still opportune, as the need for the book has not diminished. I am conscious that the book requires a recommendation to the indulgent judgment of my fellow-workers, since almost every one has studied the frog for one purpose or another, and each will closely criticize in that department with which he is most familiar. Although I shall not be able to satisfy all, still I hope that my work may serve as a useful basis for further investigations, and I would apply to it the words with which Sömmering prefaced his anatomy: ‘Ich wünschte ein Handbuch zu liefern und seine Einrichtung so zu treffen, dass man künftig an ihm als einer Basis nach Erforderniss leicht ändern, wegnehmen und zusetzen könnte[1].’
[Footnote 1: ‘I wished to furnish a manual so arranged that it might serve as a basis easily altered, pruned, or enlarged as the future might need.’]
Lest more be anticipated from the book than it is intended to supply, I would observe that I have throughout had in mind only a descriptive anatomy of the indigenous (German) frog; a comparative anatomy of Batrachians was as foreign to my intention as were developmental or histological questions: hence morphological details must not be expected. Any hope of formulating a systematic nomenclature of the muscles has been abandoned; as neither one based upon their mode of action, of which we know so little, nor one based upon their origins and insertions, as demonstrated by the unpronounceable names of Chaussier and Dugès, is really practicable. I have therefore preferred to avail myself, as far as possible, of the received names, which have been chosen partly according to mode of action, partly according to origin and insertion, and partly according to position and form; while in the choice of new names I have given preference to the simplest.
The figures are, with few exceptions, original, and drawn by myself. Their careful execution in woodcut has added a very necessary neatness to that correctness, which alone I claim as mine.
Alexander Ecker.
Freiburg, _February, 1864_.
Preface To The Second Part.
Sixteen years have elapsed since the first portion of this anatomy of the frog appeared; this second portion, therefore, requires a somewhat apologetic introduction.
The nervous and vascular systems have, in substance, been known for some years; still, certain points required a thorough revision: this seemed especially necessary with regard to the cranial nerves. In consequence of my anthropological investigations, and particularly through undertaking the editorship of the ‘Archiv für Anthropologie,’ my attention was drawn into another channel, and I found it impossible to work out this chapter: consequently the whole was deferred, and would have been still longer delayed had I not received assistance.
At my request Professor Wiedersheim undertook to investigate afresh the cranial nerves, the brain, the spinal cord, and the sympathetic system; and the descriptions of these parts are the result of his work alone. I regard it as most advantageous to this second part that so experienced an investigator in the anatomy of Amphibia should have given me his help.
The remaining portions appear almost unaltered as written several years ago; and the majority of the illustrations date from the same period. I had neither the time nor the zeal necessary to re-examine the whole; besides, it is doubtful whether eyes some twenty years older would improve matters.
This somewhat neglected book is therefore commended to the indulgence of my fellow-workers, with the hope that it may at least form a basis upon which further work may easily be done; to proffer more than this, as I stated, with a quotation from Sömmering, in the preface to the first part, I have never even hoped.
The final part of the work, on the viscera and sense-organs, has been undertaken by Professor Wiedersheim, and will appear in the Spring of 1882.
Alexander Ecker.
Freiburg, _August, 1881_.
Contents.
Page
Introduction 1
Section I. The Bones And Joints 11
" II. The Muscles 53
" III. The Nervous System 121
" IV. The Vascular System 203
" V. THE ALIMENTARY TRACT WITH ITS APPENDAGES, THE SPLEEN, AND THE PERITONEUM 267
" VI. THE LARYNX, LUNGS, VOCAL SACS, THYMUS AND THYROID GLANDS, AND THE LYMPHATIC GLANDS (TONSILS?) OF THE HYOID REGION 307
" VII. The Urino-Genital System, The Adrenals, And The Fat-Bodies 325
" VIII. The Skin And The Sense-Organs 351
Addenda, Etc. 425
Index 441
Illustrations.
Figure Page
1. The Green water-frog, _Rana esculenta_, L. 4
2. The Brown grass-frog, _Rana temporaria_, L. 8
3. Femur of _Rana esculenta_ 16
4. Vertebrae of do. 17
5. Vertebral column of do. 18
6, 7. Section through a vertebra of _Rana esculenta_ 20
8, 9. Urostyle of _Rana esculenta_ 21
10–14. Skull of do. 22, 23, 25, 28
15. Nasal Cartilages of frog 29
16, 17. Skull of _Rana esculenta_ 29, 30
18. Origin of suspensory cartilage from the skull 32
19, 20. Skull of _Rana esculenta_ 32, 33
21. Mandible of _Rana esculenta_ 34
22. Hyoid of _Rana esculenta_ 35
23. Omosternum of _Rana esculenta_ 36
24. Shoulder-girdle and sternum of do. 36
25. Shoulder-girdle of the frog 37
26, 27. Suprascapula of _Rana esculenta_ 38
28. Left scapula of _Rana esculenta_ 38
29. Scapula seen from behind 38
30. Left coracoid 39
31. Clavicle of the left side 39
32. Right shoulder-girdle of _Rana esculenta_ 40
33. Hinder border of the scapula and coracoid 40
34. Clavicular cartilage of _Rana esculenta_ 40
35. Humerus of _Rana esculenta_ (female) 41
36. Do. (male) 41
37. Do. (female) 41
38. Radio-ulnar of _Rana esculenta_ 43
39, 40. Bones of the forearm and hand of _Rana esculenta_ 44, 46
41, 42. Pelvis of _Rana esculenta_ 48
43. Horizontal section through the iliac bones, etc. 49
44. Femur of _Rana esculenta_ 49
45. Tibio-fibula of do. 50
46. Section of the tibio-fibula 50
47. Right foot of _Rana esculenta_ 51
48–50. Eye-muscles of do. 55, 56
51. Skull and orbital cavities of _Rana esculenta_ 57
52. M. levator bulbi of _Rana esculenta_ 57
53. Eye-muscles of _Rana esculenta_ 58
54. Facial muscles of do. 59
55. Muscles of the back and shoulder 60
56, 57. Muscles of the lower jaw of _Rana esculenta_ 61, 62
58. Muscles of the throat, chest, and abdomen of do. 63
59. Muscles of the hyoid bone and the tongue of do. 64
60. Do. (from below) 65
61. Do. (from right side) 66
62. Muscles of the throat, chest, and belly of _Rana esculenta_ 68
63. Muscles of trunk of _Rana esculenta_ (from the right side) 69
64. Second layer of abdominal muscles of _Rana esculenta_, from right side and below 70
65. M. obliquus internus 71
66. Muscles of the back and shoulder blade 72
67. Muscles of the back and pelvic girdle of _Rana esculenta_ 74
68. Muscles of the shoulder, from below 77
69. Muscles of the right shoulder and upper arm 78
70. Right shoulder, from below 79
71. Muscles of the back and shoulder 79
72. Muscles of the chest, throat, and belly of _Rana esculenta_ 81
73. Muscle of right shoulder and upper arm 83
74. Muscles of the right arm of _Rana esculenta_ 84
75. Do. (deep layer) 85
76. Muscles of forearm of _Rana esculenta_ 86
77. Muscles of hand of _Rana esculenta_, volar surface 88
78. Second layer of muscles on volar surface of hand of _Rana esculenta_ 88
79. Muscles of hand of _Rana esculenta_ 92
80. Muscles of left thigh of do. 95
81, 82. Do. (ventral surface) 98, 99
83. Deep muscles of left thigh of _Rana esculenta_ 100
84. Do. (Dorsal view) 101
85. Left half of pelvis of _Rana esculenta_ 101
86. Muscles of the right leg and foot of _Rana esculenta_ (Dorsal view) 103
87. Do. (seen from below) 105
88. Do. (Dorsal view) 106
89–91. Muscles of the plantar surface of foot of _Rana esculenta_ 107, 111, 112
92–94. Dorsal view of muscles of foot of _Rana esculenta_ 115, 117, 118
95. Pectoral region of _Rana esculenta_ 119
96. Hind portion of back and thigh of _Rana esculenta_ 120
97. The nervous system of _Rana esculenta_, from the ventral surface 136
98. Dorsal view of brain of _Rana esculenta_ 143
99. Transverse section through hinder end of Medulla oblongata 144
100. Do. at the point of origin of the abducens nerve 145
101. Do. of the auditory nerve 146
102. Ventral view of brain of _Rana esculenta_ 149
103. Lateral do. 150
104. Transverse section through the anterior portion of the optic lobes opposite the origin of the motor-oculi nerve. 151
105. Horizontal section through the brain to show the ventricles 153
106. Section through the lower division of the pituitary body 157
107. Transverse section through the hinder portion of the cerebral hemispheres 158
108. Transverse section near the middle of the cerebral hemispheres 158
109. From a transverse section through one of the cerebral hemispheres 159
110. Diagram to show the Vena spinalis posterior, etc. 164
111. Dorsal view of the orbit, etc. (deep dissection) (_coloured_) Plate I.
112. Do. (superficial do.) (_coloured_) Plate I.
113. View of roof of mouth; mucous membrane, etc. (_coloured_) Plate I.
114. Lateral dissection of head, etc. (_coloured_) Plate I.
115. Dissection of the floor of the mouth (_coloured_) Plate I.
116. Right half of skull of _Rana esculenta_ 174
117. The nervous system of _Rana esculenta_, from the ventral surface 176
118. Ventral view of the brain and spinal cord, to show the points of exit of the spinal nerves 178
119. Ventral view of the spinal ganglia 179
120. Schema of spinal ganglion 179
121. Dorsal branches of the spinal nerves 181
122. The brachial plexus 184
123, 124. Nerves of the ventral surface of the arm 185, 186
125. The N. radialis 186
126. Ventral view of the brain and spinal cord 188
127. The sciatic plexus 190
128. Distribution of the sciatic nerve 193
129. Nerves of the leg and sole of the foot 194
130. Distribution of the N. peroneus 196
131. Sympathetic cord 198
132. The heart and blood-vessels, seen from the ventral surface 213
133. The heart, seen from above 214
134. The frog’s heart, seen from the ventral surface 215
135. Dissection of a case in which the auricular septum is placed more to the left than is normal 215
136. Dissection of the heart from the left side 216
137 I. Transverse section through the junction of the hinder and middle thirds of the ventricle of _R. temporaria_ 217
137 II. Transverse section through junction of the middle and anterior thirds of the same heart 217
138. Portion of a transverse section through the middle of the ventricle of _R. temporaria_ 218
139. Course of the cardiac nerves in the auricular septum 219
140. Group of nerve-cells on the cardiac nerve, from the auricular septum 220
141_a_. Small group of nerve-cells from the auricular septum 221
141_b_. Isolated nerve-cells from frog’s heart 221
142. Arteries and veins of the Truncus arteriosus of _Bufo vulgaris_ 222
143. Schema of the arterial system of _Rana esculenta_ 223
144. Right carotid gland 224
145. Arterial system of Rana esculenta 225
146. Transverse section at level of the larynx 226
147. Dissection to show the occipito-vertebral and the cutaneous arteries 227
148. Branches of the occipito-vertebral and cutaneous arteries in the head 228
149. Dissection to show the occipito-vertebral and the cutaneous arteries 229
150. Subclavian artery of the left side 231
151. Arteries of the palmar surface of the hand 232
152. Arteries of the dorsal surface of the hand 232
153. Arterial system of _Rana esculenta_ 234
154. The urinogenital arteries 235
155. Bifurcation of the aorta and the iliac arteries 236
156. Arteries of the hinder extremity 237
157. Arteries of the dorsal surface of the foot 239
158. Arteries of the sole of the foot 240
159. Schema of the veins of _Rana esculenta_ 242
160. Distribution of the internal jugular vein and the anterior portion of the cutaneous vein 243
161. The anterior caval vein and its branches 244
162. Course of the cutaneous vein as seen from the side 245
163. Veins in the region of the kidney 246
164. Veins of the liver 248
165. Veins of the hinder extremity 250
166. Transverse section of a septum with the attached skin 252
167. The sinus abdominalis lateralis 252
168. Sinus thoracicus transversus 253
169. The lymph-sacs of _Rana esculenta_ (seen from the dorsal surface) 254
170. Do. (seen from the ventral do.) 256
171. Do. (seen from the side) 257
172. Transverse section through the trunk in the region of the iliac lymph-sac 258
173. Dissection to show the iliac lymph-sac 259
174. Plan of attachments of the inferior femoral etc. septa 259
175. Transverse section of the thigh 260
176. The anterior lymph-hearts 261
177. The posterior lymph-hearts 261
178. The roof of the mouth 276
179. The floor of the mouth 277
180. The capillaries of the submucous layer (_coloured_) Plate II.
181 I. Transverse section of the premaxillary bone, to show attachment of the teeth 279
181 II. Dentine and enamel 279
181 III. Enamel 279
182, 183. Muscles of the tongue 281, 282
184. The alimentary canal 283
185. The abdominal viscera of _Rana esculenta_ 284
186. Longitudinal folds of stomach of _Rana temporaria_ 285
187. The cells at the mouth of the gland of the fundus of the stomach. (_coloured_) Plate II.
188. The mucous membrane of the pyloric end of the stomach of _Rana esculenta_ 286
189. Mucous membrane of the pyloric end of stomach and duodenum 288
190. Isolated fold of mucous membrane of small intestine of _Rana temporaria_ 291
191. Fold of mucous membrane of _Rana temporaria_ 291
192. The large intestine of _Rana temporaria_ 292
193. Large intestine of _Rana esculenta_ 293
194. The liver 295
195. The pancreas and bile-canals 296
196 I. } } The hepatic veins (_coloured_) Plate II. 196 II. }
196 III. The hepatic arteries (_coloured_) Plate II.
197. Liver-cells 299
198. The bile-capillaries 299
199. The pancreas and bile-canals 300
201. The peritoneum of _Rana esculenta_ 305
202. The position and relations of the larynx 311
203. The cartilaginous skeleton of the larynx 312
204. The larynx and surrounding parts 313
205. The muscles of the larynx 314
206. Three sections through the larynx of _Rana esculenta_ 316
207. The Rima glottidis 317
208. The lung of _Rana temporaria_ (_coloured_) Plate II.
209. The vocal sac of the right side 320
210. The thymus gland 321
211. The thymus gland of _Rana esculenta_ 321
212. The thyroid gland of _Rana esculenta_ 323
213. The lymphatic gland of _Rana esculenta_ 324
214. The male urino-genital organs 331
215. The right kidney 332
216. The blood vessels and lymphatics of the kidney 333
217. Vertical sections through the kidney (_coloured_) Plate II.
218. The uriniferous tubes 335
219. A gold preparation of the kidney of _Rana esculenta_ (_coloured_) Plate II.
220. Transverse section of the kidney 338
221. The bladder 339
222. The male reproductive organs 341
223. Various preparations from the testis 342
224. The female reproductive organs 344
225. Preparations from ovary and oviduct 346
226. The male urino-genital organs 348
227. The fat-body of _Rana esculenta_ 349
228. The epidermis from the head of _Rana esculenta_ 367
229. Vertical section through the skin of the back 368
230. Surface view of epidermis of _Rana temporaria_ 368
231. Nerve terminations of the branched pigment-cells of the cutis 368
232. The temporary papillae in _Rana temporaria_ 371
233. The epidermis of the supplemental toe of _Rana esculenta_ 375
234 I. Fore-foot of a male frog 375
234 II. The swelling on the supplemental toe of a male frog 375
235. The blood-vessels and lymphatics of the skin 376
236. Lateral sense-organ of tadpole of frog 378
237. Various parts from the fungiform papillae 381
238, 239. Frontal sections through the nose of two tadpoles 384
240 I A. Bowman’s glands _in situ_ from _Rana temporaria_ 386
240 I B. Section of Bowman’s gland 386
240 II. Vessels of nasal mucous membrane of _Rana esculenta_ 386
241. Separations from the olfactory mucous membrane of _Rana temporaria_ 388
242. The tympanic membrane of _Rana esculenta_ 389
243. The columella 391
244. Antero-posterior section through the capsule of the right labyrinth of _Rana esculenta_ 392
245. The membranous labyrinth of _Rana esculenta_ 394
246. Part of the outer wall of the perilymphatic space 395
247, 248. The right membranous labyrinth of _Rana esculenta_ 397
249, 250. The membranous labyrinth of _Rana esculenta_ 399, 401
251. Preparations from the ear of _Rana esculenta_ 402
252. The nerve-terminations in the membranous labyrinth of _Rana esculenta_ 404
253. Endothelium from the inner surface of the sclerotic coat 406
254, 255. Preparation from cornea of _Rana esculenta_ 407, 408
256. The vessels of the choroid and iris 410
257. Fibres from the lens of the frog 414
258. Vertical section through retina of frog 415
259. Various preparations from the eye of the frog 417
260. The vessels of the vitreous body 421
261. Preparations from the nictitating membrane of _Rana esculenta_ 423
Introduction.
There is no occasion, now-a-days, to offer a lengthened apology for devoting a treatise solely to the anatomy of the frog, which enjoys the doubtful honour of being, κατ' εξοχήν, the physiological domestic animal. It is kept in every physiological laboratory, and is daily sacrificed in numbers upon the altar of science. The physiologist has recourse to it, not only to obtain answers to new questions, but for the sake of demonstrating easily and quickly the most important known facts of the science. These unlucky batrachians are to be had in any number, and are specially adapted for experimental investigation: they have consequently fallen under a harsher tyrant than the stork in the fable, and their prophetic outcry in the frog-chorus of Aristophanes, δεινὰ πεισόμεσbθα, has been literally fulfilled.
As the history of the most important physiological discoveries is closely related with the employment of the frog in physiological research, it will not be without interest to review briefly the history of its use in scientific, especially in physiological, investigations, and to record the services which it has already rendered to science. Swammerdam (1637–1685), as du Bois-Reymond justly remarks, was the first to make known the frog as an important means of research; he says concerning it:--‘An den Thieren, die das heisseste Blut haben, ist die Bewegung der Muskeln nicht so merklich oder hält vielmehr nicht so lange an, als an Thieren die mit kälterem Blute begabt sind. Dergleichen sind die Fische und viele andere Wasserthiere, wie auch solche, die so wohl im Wasser als auf dem trocknen Lande leben können. Deswegen habe ich insonderheit mit dem Frosch meine Versuche angestellt. Denn an diesem Thiere sind die Sehnen sehr sichtbar und lassen sich leicht entdecken und entblössen[2].’ Swammerdam made the earliest experiments on the contraction of muscle by means of chemical and mechanical stimulation of its nerves; thus laying the basis of our present nerve and muscle physiology, which has been built up within rather less than two hundred years; though during the first half of this period but little advance was made.
[Footnote 2: ‘In animals with warm blood the action of the muscles is neither so apparent nor so long continued as in those animals which have cold blood, such as fishes and many other aquatic animals, and those also which live both in water and on dry land. On this account I have made my investigations chiefly on frogs, for in them the nerves are very distinct, and are easily found and exposed.’ Buch der Natur, Leipzig, 1752, p. 330.]
From the famous September evening of the year 1786, on which Galvani first observed the twitchings of a frog’s leg suspended by a metallic hook to an iron balcony, the frog has, down to the present time, afforded almost the only material for the investigation of the excitability of nerve and its associated electromotive changes, and also no inconsiderable part of the remaining nerve and muscle physiology. It was not until Müller devised the method of operating on the frog that Bell’s law became capable of easy proof; and much of our knowledge of the functions of the spinal cord is derived from experiment upon it. Again, the muscles of frogs served, from the time of Swammerdam to that of Eduard Weber and his followers, for the investigation of the phenomena and the conditions of contraction; and in almost all other branches of physiology there are important doctrines which were first definitely established by experiment upon the frog. But for the web of the foot of this animal (and the gills and tail of its tadpole, in which Leeuwenhoek[3] describes the phenomena most clearly) we should not, perhaps for a long time, have arrived at a satisfactory knowledge of the existence and the conditions of the capillary circulation. As is well known, an accurate acquaintance with the constituents of the blood directly concerned in nutrition has been obtained by observation on the frog, as well as important facts in the physiology of the blood and lymph, such as the intimate knowledge of the corpuscles of both fluids, and the coagulability of the plasma; while in no less degree have experiments on these animals served to establish the laws of the heart’s action. Moreover, physiology is not the only science indebted to the frog: in histology many important results have been obtained from observations on it, and for histological instruction it is now indispensable. To it we owe much of our knowledge of the structure of nerve fibres, their origin and termination, especially in muscle, their relations within the ganglia, and even the structure of muscular fibre itself. For the study of reproduction and development the frog has, next to the chick, afforded the most important material: one need but refer to the investigations on impregnation from the time of Spallanzani to that of Newport[4], the phenomena of cleavage, and many others.
[Footnote 3: Leeuwenhoek, Arcana Naturæ III, epist. 65 ad Reg. Soc. Lond., p. 158.]
[Footnote 4: It may be well to remind the reader that this introduction was written in 1864.]
Thus with progress of time the field in which the frog has been submitted to observation and experiment, whether for the demonstration of established facts to students or for the solving of new problems, has vastly increased, and this batrachian has indeed become, as we have stated, the physiologist’s domestic animal.
That, for these manifold uses, a more exact anatomical knowledge of the frog is very necessary is self-evident. The majority of students commencing the study of physiology have little more than a superficial knowledge of the sciatic nerve and the leg-muscles; at most, of the spinal cord and its nerve-roots; and only acquire any further knowledge in a disconnected manner. For this they can scarcely be reproached, the literature of the anatomy of the frog being so widely scattered in monographs and journals that reference to it involves the expenditure of much time. This attempt, therefore, to produce a complete anatomy of the frog, based throughout upon my own observations, cannot be considered superfluous; it is rather to be feared it may be thought insufficient.
The European frogs[5] alone are treated of in the following description, _i.e._ the two species, _Rana esculenta_, L., and _R. temporaria_, L., the former being more particularly described, though such differences in structure as occur are noted. This is not the place to discuss the exact systematic characters of the two species, yet they cannot be ignored entirely. The species were, from their habitats, long ago distinguished by C. Gessner[6], and named _Rana rubeta_, _s. gibbosa_, the garden or grass-frog, and _Rana aquatica_, _s. innoxia_, the water-frog; at least, from his figure, the former can be no other than _R. temporaria_, though Gessner, probably expecting to find in it the _rubeta_ of older writers, adds that it ‘ist für giftig zu halten.’
[Footnote 5: For purposes of comparison other than European frogs were examined, especially American species of _Rana_, for which I am indebted to the kindness of my much esteemed friend Agassiz. These were _Rana Catesbyana_, Shaw (_R. mugiens_, Catesby--_R. pipiens_, Harlan); _R. sylvatica_, Leconte; _R. clamitans_, Daudin; _R. palustris_, Leconte; _R. halecina_, Leconte. To these, however, no further reference will be made in the text.]
[Footnote 6: C. Gessner, Thierbuch. Zürich. Fol., p. 157.]
Leeuwenhoek[7] also correctly distinguished between them, but it is to Rösel[8] that we are chiefly indebted for a careful discrimination and an accurate knowledge of the life-histories of the two species.
[Footnote 7: Leeuwenhoek, Arcana Naturæ, Vol. III of Ecker’s edition. Leyden, 1722. Epist. 65 ad Reg. Soc. Lond., p. 154.]
[Footnote 8: Rösel, Naturgeschichte der Frösche Deutschlands, ed. Schreber. Nürnberg, 1815, p. 36.]
[Illustration: Fig. 1.
The green water-frog, _Rana esculenta_ L.]
*Rana esculenta*, L. The green water-frog, Fig. 1, usually attains a larger size[9] and is more active than the other species, and for this reason is better adapted to the purposes of the physiologist; hence I have chosen it for description.
[Footnote 9: The extreme sizes are much more pronounced in this species. I have never found _R. temporaria_ of the size attained by large specimens of the water-frog.]
The head is flat, as broad as it is long, and triangular with an obtuse snout in front. The upper surface of the head, _i.e._ the space between the eyes, is slightly concave, grooved, and narrower than in _R. temporaria_. The tympanic membrane is circular, and relatively to the eye is larger. The upper eyelids have several transverse folds in their hinder part. The pupil is oval, with the long axis horizontal. The vomerine teeth are arranged in two clusters, which are relatively larger than in _R. temporaria_ and lie exactly between the posterior nares, without however touching them. The openings of the Eustachian tubes do not exceed in size the posterior nares to so great an extent as they do in _R. temporaria_. The male possesses a vocal sac on either side, which reaches the surface beneath the tympanic membrane through a cleft placed behind the angle of the mouth, and is, in well-developed specimens, about the size of a cherry. The hind limbs are relatively longer. The toes are long, and taper towards their tips: the webs between the toes are cut out semicircularly, and that of the longest or fourth toe is continued to the tip of the last phalanx. The supplemental toe is an oval prominence of cartilaginous hardness. The skin of the back has wart-like tubercles arranged longitudinally in raised lines; one of these lines runs on each side from the posterior canthus as far as the thigh, and is very constant: in the male a second line surrounds the posterior margin of the vocal sac; a corresponding line exists in the female.
The skin of the belly is quite smooth, the colour presenting many variations which appear to depend upon very diverse circumstances. It varies with changes in the physiological condition of the animal. Von Wittich[10] has shown that a bright green specimen changes to a dark leafy green colour on exclusion of light; also, that dark specimens become almost a lemon-yellow colour on exposure to bright sunlight; and he has pointed out that this brightening of the skin is an active condition dependent upon contraction of the stellate pigment-cells. It is therefore not surprising, as the same inquirer observes, that one should sometimes find specimens of _R. esculenta_ in which the ground colour is almost a greenish yellow (as in Rösel’s figure, Pl. XIII), whilst in others it can only be distinguished from the dorsal black patches by a faint greenish shade. There is no doubt that difference of habitat influences the colour; but this may again be modified by light[11], as has been established in the case of fish by direct observation[12]. Apparent varieties may this occur.
[Footnote 10: Von Wittich, Müller’s Archiv, 1854, p. 41.]
[Footnote 11: Lister, On the Cutaneous Pigmentary System of the Frog. Phil. Trans., 1857, p. 627.]
[Footnote 12: Agassiz et Vogt, Histoire naturelle des poissons d’eau douce (Neuchatel, 1839), Pl. IV, mention that the colour of trout is very variable and that in shaded and deep-lying brooks and rivers a variety is found which is black.]
In frog-tanks such diversities of colour may not unfrequently be observed in the same individual, as for example when the lower part of the body immersed in muddy water is dark, while the part above the water is bright. That the process of casting the skin exercises an influence on the brightness of the colouring is certain, yet there are, as von Wittich has correctly remarked, other alterations of colour which are in no way connected with this process, and are evidently more of a pathological nature; such as when the frog assumes a dirty green spotted appearance, the green fading more and more, until all the patches which are usually green appear of a dirty greyish-brown with a faint bronze shimmer. According to this author these changes are most readily brought about by starvation. The dark colour which frogs exhibit after hibernation is perhaps to be ascribed to the co-operation of several of the causes mentioned above.
The usual colouring of healthy animals is as follows: the back is bright green with three golden yellow longitudinal stripes, one median and two lateral, and a number of irregular brown or black stripes of approximately uniform width: on the head are a pair of black stripes which pass from the angles of the eyes across the nares to the tip of the nose; now and then the tympanic membrane and surrounding parts have also a black patch, as in _R. temporaria_: another black stripe is found on the anterior surface of the arm, in the region of the shoulder: and on the thighs are black, yellow, and white mottlings. The whole of the under-surface is white or yellowish. At times the yellow stripes of the back are wanting or are indistinct. It has already been mentioned that many varieties may occur; and these have in all probability given rise to the descriptions of reputed new species, such as _R. maritima_, Risso, found in South Europe; _R. alpina_, Risso, found in the high-lying Alpine lakes; _R. hispanica_ of Fitzinger and Bonaparte, and _R. calcarata_ of Michahelles, the last three of which certainly cannot be retained. It is not improbable that the water-frog, which Spallanzani[13] used in his experiments on impregnation, was the _R. maritima_ of Risso. He says, one must not confound his frog with that which Rösel calls the green water-frog; the former being much smaller, without the three dorsal golden-yellow stripes, and the spawning season (in Lombardy) occurring during April and May. Rusconi[14] also describes two varieties in Northern Italy.
[Footnote 13: Spallanzani, Versuche über Erzeugung der Thiere and Pflanzen. Leipzig, 1786, p. 5.]
[Footnote 14: Rusconi, Développ. de la Grenouille. Milan, 1826, p. 6.]
*Rana temporaria*, L., the brown or grass-frog, is so named from the large black patch in the temporal region, _i.e._ between the eye and the shoulder. While the separation of the preceding species into several varieties does not seem to be well founded, it appears that two distinct species have been included under the name of _R. temporaria_. Millet of Angers[15] first described, in his Fauna du département de Maine-et-Loire, as ‘grenouille rousse,’ a species differing from _R. temporaria_, and gave the species previously known as _R. temporaria_ the name of _R. flaviventris_, ‘grenouille à ventre jaune.’ No further notice, however, was taken of this observation, not even by Duméril and Bibron in their ‘Erpétologie.’ Quite independently Steenstrup[16], in the year 1846, pointed out that two frogs, differing in structure and habits, had been confounded under the name _R. temporaria_; these he distinguished as _R. platyrhinus_ and _R. oxyrhinus_. Von Siebold[17], and also Schiff[18] in part, have confirmed these statements. My own observations lead me to a like conclusion; I shall therefore distinguish two species, viz.:--(1) _Rana temporaria_, L., _Rana platyrhinus_, Steenstrup; (2) _Rana oxyrhinus_, Steenstrup.
[Footnote 15: Annales des Sciences naturelles. Zoologie, IV Série, Vol. IV, 1855, p. 368.]
[Footnote 16: Amtl. Bericht über die 24. Versammlung deutscher Naturforscher in Kiel, 1846, p. 141; Wiegmann’s Archiv, 1847, Vol. II, p. 341; Steenstrup, Oversigt K. Danske Selsk. Forhandlgr., 1846, p. 92.]
[Footnote 17: Wiegmann’s Archiv, 1852, Vol. I, p. 14.]
[Footnote 18: Annales des Sciences naturelles. Zoologie, IV Série, Vol. IV, 1885, p. 368.]
[Illustration: Fig. 2.
The brown grass-frog, _Rana temporaria_, L.]
*Rana temporaria*, L.; _Rana platyrhinus_, Steenstrup. The brown grass-frog, Fig. 2, does not attain the dimensions of _R. esculenta_, L., but is, however, always larger than _R. oxyrhinus_. The head is somewhat broader than long, and the upper surface of the skull is not grooved, as in _R. esculenta_, but is flat. The space between the eyes is wider (according to Duméril, equal to the width of the upper eyelid, whereas in _R. esculenta_ it is just two-thirds this width): the fronto-parietal bones are wide and flat. The tympanic membrane, in comparison with the eye, is smaller than in _R. esculenta_, and is usually less distinguishable from the surrounding parts as regards colour and transparency. The apertures of the Eustachian tubes are, relatively to the posterior nares, larger than in the water-frog. The vomerine teeth are comparatively small and lie in two groups placed obliquely to each other, their anterior ends diverging from each other and being prolonged as ridges to the anterior margins of the posterior nares. The two groups do not lie between the nasal apertures, but behind a line drawn transversely through their posterior margins. Vocal sacs are absent in both sexes. The hind legs are relatively shorter: the toes are not so evenly tapered off, indeed they are slightly swollen: the fourth toe, as compared with the third and fifth, is somewhat longer than in _R. esculenta_; the web of this toe does not extend to the tip of the toe, but terminates in both sexes at the last phalanx but one; the web on the third toe is less developed on the thumb side than on the other: on the remaining toes also the margins of the web are less developed than in _R. esculenta_, so that the free borders appear more crescentic. The supplemental toe forms only a soft and inconspicuous prominence. The back is mostly smooth; the raised glandular ridge, which extends along each side from the eye to the thigh, is present, but is much narrower and less prominent than in _R. esculenta_; another ridge passes from the angle of the mouth to the shoulder. The colouring in general, and especially the ground colour of the dorsal surface, varies from the brightest tints to the darkest brown-black; the conditions causing these variations being, no doubt, the same as those described above in _R. esculenta_. A dark-brown specimen taken from a dark frog-tank is usually yellowish red on the following day. The black patch between the angle of the mouth and the shoulder has given this species the name of _R. temporaria_, and is constant. A black stripe passes from the eye across the nostril to the tip of the snout, and a similar one is found upon the anterior surface of the upper arm. On the hind legs the bands are chiefly transverse. The ventral surface is yellowish, and sometimes spotted. The thighs have a granular appearance, and these as well as the belly and the neighbourhood of the anus have frequently a reddish coloration presenting the appearance of an irritated surface.
*Rana oxyrhinus*, Steenstrup. This species is always smaller and more elegant in shape than the preceding one. The head is conical, with the pointed snout projecting beyond the lower jaw; a feature which is especially evident on looking from below. The space between the eyes is narrower than in _R. temporaria_, and is not grooved, but convex; the fronto-parietal bones are narrow and arched. With respect to the arrangement of the vomerine teeth and the sizes of the apertures of the Eustachian tubes, this species holds an intermediate position between the other two. Next to the pointed snout, the greatest difference between this species and _R. temporaria_ is the presence of a much larger supplemental toe, which is of cartilaginous hardness, compressed from side to side, and contains a larger bone[19]. The vocal sacs are absent. In the males the web of the longest toe reaches to the last phalanx but one; in the females, on the contrary, the last three phalanges project freely beyond the web. The extremities of the toes are more pointed than in _R. temporaria_, in which respect, as also in several others, it approaches _R. esculenta_. In colouring, _R. oxyrhinus_ resembles _R. temporaria_; the throat, however, is usually pure white, at least in the males, the breast dusky white and spotted, while in _R. temporaria_ the throat and breast are more uniformly coloured and yellowish. V. Siebold has remarked that, during the pairing-season, the males are covered with a bluish bloom[20]; and, the whole ground colour being bright at this period, very beautiful tints result. V. Siebold[21] moreover states that the note which the males produce during the pairing-season is different in the two species. On the whole, _R. oxyrhinus_ appears to stand midway between _R. esculenta_ and _R. temporaria_.
[Footnote 19: According to Steenstrup, _l. c._, the size of the supplemental toe is in _R. temporaria_ one-half and in _R. oxyrhinus_ two-thirds of that of the next toe.]
[Footnote 20: I do not find, however, that this disappears when the animals are on land; in fact I have animals before me in a glass in which it is plainly seen.]
[Footnote 21: _l. c._, p. 15.]
Thomas[22], in addition, distinguishes another species, _R. agilis_, which however may be the ‘grenouille rousse’ of Millet. Schlotthauber[23] has described a frog which, in marking and colouring, might hold a middle place between _R. esculenta_ and _R. temporaria_; in my opinion this is probably a cross between the two. That attempts at copulation are made, despite the difference of the pairing-season, is well known; Pontallié[24] mentions this, and I have myself often found males of _R. temporaria_ in conjunction with females of _R. esculenta_.
[Footnote 22: Annales des Sciences naturelles. Zoologie, IV Série, Vol. IV, 1855.]
[Footnote 23: Wiegmann’s Archiv, Vol. I, 1844, p. 255.]
[Footnote 24: Annales des Sciences naturelles. Zoologie, III Série, Vol. XVIII, 1852, p. 243.]
* * * * *
I use the following terminology. I suppose the animal to be in its natural position, the belly towards the ground, the back upwards; a horizontal plane passing from the snout to the anus divides the body into a superior or dorsal half and an inferior or ventral half. The terms superior and inferior, dorsal and ventral, indicate positions with relation to this plane. I call that part anterior which looks towards the head, and that posterior which looks towards the anus. A vertical plane at right angles to the middle of the longitudinal axis of the body, divides it into an anterior or cephalic and a posterior or caudal half. All sections and planes which lie parallel to this, as well as this itself, are frontal. Lastly, by a perpendicular section along the middle line of the body the animal is divided into right and left halves; this plane is the median plane; and the position relative to this plane is expressed by the terms median or lateral. Planes parallel to the median plane are termed sagittal.
Section I.
The Bones And Joints.
The Bones And Joints.
Literature.
*van Altena*, Commentatio ad quæst. zoologicam in academia Lugduno-Batav. a. MDCCCXXVIII propositam, qua desideratur ut systematice enumerentur species indigenæ reptilium ex ordine batrachiorum addita unius saltem speciei anatomia et præsertim osteographia accurata. Lugd. Bat. 1829. 4^o. With 4 Plates.
*Ange, Martin St.*, Recherches sur les organes transitoires des batraciens. Annales des Sciences naturelles. 1^{re} Série. Vol. XXIV. 1831.
*Bell*, Article Amphibia, in Todd’s Cyclopaedia of Anatomy and Physiology. Vol. I, p. 90. 1835–1836.
*Born, Dr. Gustav*, Ue.d. Nasenholen u.d. Thränennasengang der Amphibien. Leipzig, 1877.
*Bruch, G.*, Beiträge zur Naturgeschichte und Klassification der nackten Amphibien. Würzburger Naturzeitschrift, 1862.
*Bruch, G.*, Neue Beobachtungen zur Naturgeschichte der einheimischen Batrachier. Würzburger Naturzeitschrift, 1863.
*Cuvier*, Recherches sur les ossements fossiles. Vol. V. Pt. II. Paris, 1825.
*Cuvier*, Leçons d’anatomie comparée. Paris, 1835. Vol. I.
*Cuvier*, Ueber die Rückenwirbel der Reptilien und Amphibien, Froriep’s Notizen. Vol. XIII, p. 74. 1826.
*Daudin*, Histoire naturelle des Rainettes, Grenouilles et des Crapauds. Paris, 1802.
*Ducrotay de Blainville*, Ostéographie ou description iconographique comparée du squelette et du système dentaire des cinq classes d’animaux vertébrés. Paris, 1841.
*Dugès*, Recherches sur l’ostéologie et la myologie des batraciens à leurs différents âges. Paris, 1834. 4^o. With 20 Plates.
*Duméril et Bibron*, Erpétologie générale ou Histoire complète des Reptiles. 1836.
*Gegenbaur*: 1. Ueber Bau und Entwicklung der Wirbelsäule bei Amphibien überhaupt und beim Frosche insbesondere. Abhandlungen der naturforschenden Gesellschaft zu Halle, Vol. VI. Halle, 1861.
2. Untersuchungen zur vergl. Anatomie der Wirbelsäule bei Reptilien und Amphibien. Pt. I. Leipzig, 1862. (Carpus and Tarsus.) With 4 Plates. 4^o.
*Gegenbaur*, Untersuchungen zur vergl. Anatomie der Wirbelthiere. Pt. II. Schultergürtel. 1865.
*Günther*, Ueber geschlechtliche Differenzen in Knochen von lebenden und fossilen Fröschen und Fischen. Annals of Natural History. 1859. Vol. III.
*Hallmann*, Die vergleichende Osteologie des Schläfenbeins, etc. Hannover, 1837. 4^o. With 3 Plates.
*Hoffmann, C. K.*, Beiträge zur Erkenntniss des Beckens der Amphibien und Reptilien. Leyden, 1876.
*Hoffmann, C. K.*, Bronn’s Klassen und Ordnungen des Thierreichs, Vol. VI. Amphibien. Leipzig, 1873–8.
*Huxley*, On the Theory of the Vertebrate Skull; Croonian Lecture, Proc. Royal Society, p. 381. 1858.
*Huxley*, Article Amphibia, Encyclopædia Britannica, IXth Edition. 1875.
*Huxley*, Lectures on the Elements of Comparative Anatomy.
*Huxley*, Handbuch der Anatomie der Wirbelthiere. Deutsche Ausg. von T. Ratzel. 1873.
*Kehrer, G.*, Beiträge zur Kenntniss d. Carpus und Tarsus d. Amphibien, Reptilien, und Säuger. Berichte d. naturf. Gesell. z. Freiburg. 1886.
*v. Klein*, Beiträge zur Anatomie der ungeschwänzten Batrachier. Jahres-Heft. Würtemberg, 1850.
*Köstlin*, Der Bau des knöchernen Kopfs. Stuttgart, 1844. 8^o.
*Leukart*, Zwischenkiefer. Valentins Repertoire. 1841, p. 155.
*Marshall, A. M.*, The Frog. Manchester and London. 2nd Edit., 1885, pp. 45–59.
*Mayer, A. F.*, Beiträge zu einer anatomischen Monographie der Rana pipa. Acad. Caes. Leop. Nov. Acta. 1825. Vol. XII, p. 527; and Isis v. L. Oken. 1825. col. 317.
*Meckel*, System der vergleichenden Anatomie. II. Thl. I. Abthlg. Halle, 1824. 8^o.
*Meckel*, Ueber das Zungenbein der Amphibien. Meckel’s Arch. f. Physik. 1818. Vol. IV, p. 60.
*Mertens*, Anatomiæ batrachiorum prodromus sistens observationes nonnullas in osteologiam batrachiorum nostratium. Halæ, 1820. 8^o.
*Mivart*, On the Classification of the Anurous Batrachians. Proc. Zool. Soc. 1869.
*Morren*, Observations ostéologiques sur l’appareil costal des batraciens. Bulletins de l’Acad. de Bruxelles, 1835, II.--Mémoires de l’Académie, 1837. Tome X.
*Müller*, Beitrag zur Anat. d. Amph. Zeitschrift f. wissenschaftliche Zoologie. Vol. IX. 1858, p. 178.
*Parker, W. K.*, Structure and Development of the skull of the common frog. Phil. Trans. 1871, p. 137.
*Parker, W. K.*, Skull of Batrachia. Phil. Trans. 1876, p. 601.
*Parker, W. K.*, and *Bettany, G. T.*, Morphology of the Skull. London, 1877.
*Pouchet*, Note sur les différences que le sexe imprime au squelette des grenouilles. Comptes rendus. Vol. XXV, p. 761. 1847.
*Reichert, K. B.*, Vergleichende Entwicklungsgeschichte des Kopfs der nackten Amphibien nebst den Bildungsgesetzen des Wirbelthierkopfs im Allgemeinen und seinen hauptsächlichen Variationen durch die einzelne Wirbelthier-Classe. Königsberg, 1838.
*Remak*, Untersuchungen über die Entwicklung der Wirbelthiere. Berlin, 1855.
*Rösel, von Rosenhof*, Historia naturalis ranarum nostratium. Nörnberg, 1758.
*Rudolphi and Breyer*, Observationes anatomicae circa fabricam Ranae pipae. Berolini, 1811.
*Rusconi*, Développement de la grenouille commune. Milan, 1826.
*Rusconi*, Sulle metamorfosi delle osse della testa della rana. Annali di Bologna. 1^{re} Série, Vol. II, p. 357.
*Schneider*, Historia amphibiorum. Jenae, 1799.
*Shaw*, General Zoology. London. Vol. II, Pt. I, p. 167.
*Stannius*, Zootomie der Amphibien (Handb. der Zootomie der Wirbelthiere, 2. Buch). 2nd Edit. Berlin, 1856. 8^o.
*Stricker*, Untersuchungen über die Entwicklung des Kopfes der Batrachier. Arch. f. Anat. u. Physiol. 1864, pp. 52–76.
*Stricker*, Beiträge zur Biologie der Batrachier. Verhandl. der Wiener Akademie. 1866. Vol. XVI, pp. 451–456.
*Townson, R.*, Facts and Observations in Natural History. London, 1799.
*Troya*, Mémoire sur la structure singulière du tibia et du cubitus des grenouilles et des crapauds. Mémoires de mathématique et de physique présentées à l’acad. de Paris. Vol. IX. 1780.
*Wagner*, Icones Zootomicae. Leipzig, 1841.
*Wagner*, Lehrbuch der vergleichenden Anatomie. Leipzig, 1834–1835.
*Wiedersheim, R.*, Lehrbuch d. vergleichenden Anatomie der Wirbelthiere auf Grundlage d. Entwickelungsgeschichte. Jena, 1886. 2nd Edit.
*Wiedersheim, R.*, Elements of Comparative Anatomy of Vertebrates, translated by W. Newton Parker. London, 1886.
The Bones And Joints.
The consideration of the differences in form, number, and histological structure, which the parts of the skeleton present during the various stages of development does not fall within the scope of this book: we have here but to deal with the adult frog.
The skeleton is made up of histologically different materials; these are:--(1) bone, (2) hyaline cartilage, and (3) so-called calcified cartilage. Concerning the last it is necessary to make some observations. I have chosen for it the name calcified cartilage in place of the more usual names ‘cartilaginous bone’ or ‘primordial ossification,’ as by this term its nature appears to be expressed without any ambiguity[25]: it is hyaline cartilage in which calcareous particles have been deposited to a greater or less extent: in the fresh state it has the appearance of moderately firm cartilage; when dry it becomes opaque and white, like the calcareous crusts on the cartilages of the Plagiostomata. The calcareous material is deposited in the cartilage in finer or coarser granules; after removal of the lime by means of acids, the cartilaginous structure becomes apparent although not so perfectly as in unchanged cartilage.
[Footnote 25: Compare Müller, Zeit. f. wissen. Zoolog., Vol. IX.]
This calcified cartilage is widely distributed in the frog’s skeleton: very many parts, which in higher animals consist only temporarily of this substance during the transition from cartilage to bone, are in the frog formed of it throughout life. It is especially well-marked in the epiphyses of the long bones in the hand and foot, in the bones of the shoulder-girdle, etc. To avoid repetition later on I will briefly describe it as found in the first-mentioned situation. Dugès[26] has described its external appearance, while Bruch[27] has made us acquainted with its histological peculiarities. If a long bone of the frog be dried, the femur for example, the middle part is found to differ considerably from the epiphyses in colour and in other particulars. The shaft alone has the appearance of bone, the epiphysis consisting of a white, opaque, firm substance, resembling plaster of Paris or lime, but which in the fresh moist state is exactly like cartilage. The epiphyses, which are fitted to the ends of the diaphysis like the cap of a stick-handle, have sharply defined margins (Fig. 3), as is well seen in Figs. 36, 39, 45, and 46. If a section be made through the epiphysis and part of the diaphysis, the long tube of true bone is seen to cease abruptly above _o_, Fig. 3, and over the end of it the epiphysis _E_ is fixed. This epiphysis consists almost entirely of calcified cartilage _c′_, and has merely a superficial layer of hyaline cartilage _A_. The bony cylinder of the diaphysis _o_, which contains the marrow _M_ in its interior, is shut off from the epiphysis by hyaline cartilage, the cells of which are arranged in transverse layers, _o_.
[Footnote 26: Dugès, Recherches sur l’ostéologie et la myologie des batraciens à leurs différents âges, p. 116.]
[Footnote 27: Bruch, Beiträge zur Entwicklungsgeschichte des Knochensystems. Schweiz. Denkschriften, p. 118.]
[Illustration: Fig. 3.
Longitudinal section through the upper extremity of the femur of _Rana esculenta_, magnified.
_A_ Hyaline cartilage (articular cartilage). _c_ Hyaline cartilage closing end of bony cylinder. _c′_ Calcified cartilage of epiphysis. _D_ Bony cylinder of diaphysis. _E_ Epiphysis. _M_ Marrow cavity. _o_ End of diaphysis. ]
I. The Vertebral Column.
The _vertebral column_ of the frog consists of ten bones, _viz._ nine true vertebrae, and the rod-shaped urostyle, which alone is almost as long as all the remaining vertebrae.
I. General Description Of The Nine Vertebrae.
*a.* The _bodies_ of the vertebrae are compressed from above downwards; the posterior surface of each body, with the exception of the eighth, presents an articular head covered with cartilage; the anterior surfaces, with the exception of the ninth, present corresponding articular depressions, covered with cartilage.
*b.* The _arches_, which have somewhat sharp margins both before and behind, bear the following processes:-- *1.* The *articular processes* (Figs. 4 and 5 _o o_) are similarly placed to those of the dorsal vertebrae of man: they project horizontally, the cartilaginous articular surfaces on the posterior processes being directed downwards, those on the anterior upwards.
[Illustration: Fig. 4.
Vertebrae of _Rana esculenta_, seen from below, twice the natural size.
1 to 9 First to ninth vertebræ. _c_ Urostyle. _o o_ Articular processes. _sc_ The two facets for articulation with the urostyle. ]
*2.* The *transverse processes* (Figs. 4 and 5 _t t′_) are strong, flat, and of very varying size and direction. The transverse processes of the fourth vertebra are the longest, those of the third only a little shorter; the shortest are those of the seventh and eighth. The atlas has no transverse processes. Those of the second and third vertebrae project directly outwards and slightly downwards; those of the fourth, fifth, and sixth upwards and backwards. The seventh and eighth project more directly outwards and at the same time backwards; the ninth upwards and markedly backwards. All the transverse processes have cartilaginous epiphyses; the largest are those of the second, third, fourth, and ninth vertebrae.
*3.* The *spinous processes* are generally small, but individually of varying size, appearance, and direction. The longest are those of the third, fourth, and fifth vertebrae; these are, in transverse section, of a three-sided prismatic form, as in the dorsal vertebrae of man; they are directed backwards and provided with cartilaginous epiphyses. The spinous processes of the sixth and seventh are shorter, compressed from side to side, project directly upwards, and are usually without cartilaginous epiphyses; that of the eighth is still shorter. As regards the spinous processes, those of the third, fourth, and fifth vertebrae resemble those of the dorsal vertebrae in man; those of the sixth, seventh, and eighth, lumbar vertebrae. The ninth has either no spinous process or only a rudimentary one. The first and second vertebrae may be looked upon as cervical vertebrae: the second has a short spinous process with a cartilaginous epiphysis. In the first, the cartilage which unites the two halves of the arch represents the rudiment of a spinous process.
[Illustration: Fig. 5.
Vertebral column of _Rana esculenta_, from above, twice nat. size.
1 to 9 First to ninth vertebræ. _c_ Urostyle. _o o_ Articular processes. _sc_ Facets for articulation with the urostyle. _t t′_ Transverse processes. ]
II. Description Of Particular Vertebrae.
*1.* The *atlas* or *first vertebra* has a thin body, compressed from above downwards, and an arch. The body has posteriorly a slightly raised, cartilaginous, articular head, which is broader transversely: in front it has two oval articular facets, which are separated from each other by a median projection. Each facet is concave, and directed forwards, outwards, and slightly upwards. The arch is completed above by cartilage, which projects slightly to form the rudiment of a spinous process. The hinder margin of the arch bears two articular processes. Transverse processes are wanting.
*2.* The *second vertebra* presents all the general characters of an ordinary vertebra, except that the transverse processes are directed somewhat downwards.
*3.* The transverse processes of the *third vertebra* are longer than those of the second: each is directed downwards, is broader at its extremity than at its base, and bears a hammer-shaped cartilaginous epiphysis larger than those of the remaining transverse processes.
*4.* The transverse processes of the *fourth vertebra* are the longest: each is broader at its free end than at its base, is directed upwards and backwards, and provided with a cartilaginous epiphysis.
*5*, *6*, *7*. The transverse processes of the *fifth*, *sixth*, and *seventh vertebrae* are smaller, contracted towards their free extremities, and directed upwards.
*8.* The *eighth vertebra* is distinguished from the rest by its body possessing no articular head. It presents, at each end, a concave articular depression. The transverse processes resemble those of the seventh.
*9.* The *ninth vertebra* unites the vertebral column with the hip-bones, and is hence to be regarded as a *sacrum*. The body bears on its anterior surface an articular head for articulation with the eighth vertebra: on its posterior surface are two small rounded and closely approximated processes (Figs. 4 and 5 _sc_) for articulation with the urostyle. The transverse processes are strong, broader at the free ends than at their origin, directed upwards and backwards, and provided with cartilaginous epiphyses.
III. Articulations Of The Vertebrae.
The articular heads and depressions of the vertebral bodies, together with the joint surfaces of the articular processes, are covered with hyaline cartilage. The periosteum of the bodies, as also that of the articular processes, forms true capsular joint ligaments. The articulations of the vertebrae are still further strengthened by longitudinal fibres, which extend along the anterior and posterior surfaces of the vertebrae, and correspond to the _ligamentum vertebrale commune anticum et posticum_ of man. Between the vertebral arches are membranes which represent the _ligamenta intercruralia_. Between the spinous processes are bands of connective tissue which form _ligamenta interspinalia_. (For the articulation of the atlas with the occiput, see page 24.)
IV. STRUCTURE OF THE VERTEBRAE[28] (Figs. 6 and 7).
[Footnote 28: Cf. Gegenbaur, (1) Über Bau u. Entwicklung der Wirbelsäule bei Amphibien überhaupt u. beim Frosch insbesondere. Abhand. d. Naturforsch. Gesell. zu Halle, vol. vi, 1861; (2) Untersuch. zur vergleich. Anat. d. Wirbelsäule bei Amphibien u. Rept., Leipzig, 1862. As regards the adult animal I can bear out Gegenbaur’s observations. The scope and limits of this book forbid me to go further into the developmental history.]
[Illustration: Fig. 6.
Transverse section through a vertebra of _Rana esculenta_, magnified.
_c_ Cancellous bone. _Ch_ Chorda dorsalis. _Ch′_ Sheath of chorda dorsalis. _o_ Compact bone on the upper and lower surfaces of the body. ]
Each vertebral body consists of a cylinder of compact bone, which is directly continued into the bony substance of the arch. In the interior of the cylinder is found an isolated persistent vestige of the _chorda dorsalis_ (_Ch_): this is surrounded by cancellous bone (_c_), which extends backwards towards the articular head and forwards directly into the articular cartilage, compact bone being absent in these parts. In a transverse section of a vertebral body the following parts are seen (Fig. 6):--*a.* An outer layer of compact bone (_o_) (the transverse section of the above-mentioned cylinder), which is formed of parallel lamellae of varying thickness. These, according to Gegenbaur, and as I can confirm, are arranged in well-defined groups, each of five to eight lamellae. The number of the secondary lamellae increases with the age of the animal. *b.* In the interior, in the form of a cylinder, is the remnant of the _chorda dorsalis_. It consists of a double sheath (_Ch′_) and contents (_Ch_) composed of chorda-cells. *c.* Immediately around the persistent portion of the chorda lies the central part of the vertebral body, formed by transformation of the vertebral cartilage and of the bases of the original cartilaginous arches. At each side of the _chorda_ are large marrow-spaces (_c_), filled with cells, from which proceed narrower canals, winding in various directions, and anastomosing freely with one another both before and behind. Their walls are constituted partly of true bone, partly of cartilage.
[Illustration: Fig. 7.
Longitudinal section through the posterior half of the body of a vertebra of _Rana esculenta_.
_a_ Cartilage of the head. _c_ Cancellous bone. _o_ Shell of compact bone. ]
V. THE UROSTYLE (Figs. 8 and 9).
The *urostyle* is a long, median, rod-like bone, which projects backwards, midway between the two hip-bones, and terminates over the anus. The anterior end (Fig. 8 _a_) is the thicker and broader part of the bone, and has two articular depressions (Fig. 9) for articulation with the two facets of the ninth vertebra. The hinder end is pointed and cylindrical, and terminates in a cartilage, which is fixed in the tubular end of the bone. The middle portion is almost cylindrical, and has a groove along the ventral surface which gradually becomes less marked behind. The dorsal surface bears a ridge (Figs. 8 and 9 _s_), which is high and thick in front, becomes sharper and less prominent as it proceeds backwards, and gradually disappears towards the hinder third of the bone, so that in transverse section the anterior two-thirds of the bone appear triangular, with a ventral and two lateral surfaces: while the hinder third is cylindrical. The anterior portion of the bone contains a canal, _canalis vertebralis_ (Fig. 9 _c.v._), which is a continuation of the vertebral canal, along which the hindermost spinal nerves pass. On each side of the anterior portion of the urostyle are small apertures (Fig. 8 _c.c._), which lead into canals (_canales coccygei_), which open into the vertebral canal, and through which the coccygeal nerves pass. In front of these openings and partly overhanging them are small triangular projections (Fig. 8) (_processus transversarii_): these, however, are not constant, and are more often found in _R. esculenta_ than in _R. temporaria_, in which latter species the openings are smaller.
[Illustration: Fig. 9.
Urostyle of _Rana esculenta_, seen from the side, twice nat. size.
_c_ Ventral border. _c.v._ Canal. vertebralis. _s_ Dorsal ridge (pr. spinos.). ]
[Illustration: Fig. 8.
Urostyle of _Rana esculenta_, seen from the side, twice nat. size. A bristle is passed through the _canal. vert._ and out through the _canal. coccyg._ of the right side.
_a_ Anterior extremity. _c.c._ Canal. coccyg. _s_ Dorsal ridge (pr. spinos.). ]
II. The Skull.
The flat form of the frog’s head, as in batrachians generally, depends upon the wide separation of the jaw-bones of the two sides, and on the large size of the orbital cavities and the horizontal direction of their floors. The outer circumference of the head forms a parabolic frame (Figs. 10 and 11), composed of the maxillary (_m_), premaxillary (_i_), and quadratojugal bones (_j_). In the middle of this curved framework lies the elongated prismatic cranium. Anteriorly, this is attached to the fore-part of the frame by means of the cartilaginous skeleton of the organs of smell (Fig. 11 _e′_); posteriorly, it widens out into two transverse arms (_p_), which contain the organs of hearing. From this base, on either side, a bony strut, composed of the posterior arms of the squamosal (_t′_) and of the pterygoid bones, passes backwards to the hinder end of the frame. The anterior arm of the squamosal bone (_t_) does not quite reach the framework, but is attached to it by ligament alone. Between the last-named arm posteriorly, the cranium on the inner side, and the maxillary frame-work laterally, is a large space representing the orbital and temporal fossae of human anatomy.
[Illustration: Fig. 10.
Skull of _Rana esculenta_, seen from above, twice natural size.
_e_ Sphenethmoid. _fn_ Nasal. _f.p._ Fronto-parietal. _i_ Premaxillary. _j_ Quadrato-jugal. _m_ Maxillary. _o_ Exoccipital. _op_ Opisthotic. _p_ Prootic. _pt_ Pterygoid. _pt′_ Posterior limb of pterygoid. _t_ Squamosal. _t′_ Posterior arm of the same. ]
[Illustration: Fig. 11.
Skull of _Rana esculenta_, seen from below, twice natural size.
_c_ Cartilaginous wall of skull. _e_ Sphenethmoid. _e′_ Cartilaginous skeleton of nose. _h′_ Stylo-hyoid. _i_ Premaxillary. _m_ Maxillary. _m′_ Quadrate tract. _o_ Exoccipital. _p_ Prootic. _p′_ Anterior arm of prootic (_ala magna_ autt.). _p″_ Trigeminal foramen. _pl_ Palatine. _pt_ Pterygoid. _pt′_ Posterior arm of pterygoid. _s_ Parasphenoid. _v_ Vomer. ]
A. The Cranium.
The cranium of the frog is a prismatic tube, wide behind, narrow in front, and formed in great part of cartilage (Figs. 15 and 17). Our indigenous species are characteristically distinguished from one another by peculiarities in the form of the cranium. In _R. esculenta_ it is long and narrow, in _R. temporaria_ short and wide. The superior surface in the former is markedly concave, while in the latter it is flat, and in _R. oxyrhinus_ arched. These differences are readily recognised in the living animal.
*The Bones of the Cranium.*
*1.* The *exoccipital bones*, _ossa occipitalia lateralia_, Cuvier (Figs. 10, 11, 12, 14, 16 _o_).
*Cuvier*, _l. c._, p. 387, Pl. XXIV, bb.--*Dugès*, _l. c._, n. 14.--*Parker* and *Bettany*, _l. c._, p. 166, exoccipitals.
[Illustration: Fig. 12.
Skull of _Rana esculenta_, seen from behind, twice natural size.
_a_ Stapes. _a′_ Columella auris. _a″_ Extrastapedial. _c_ Condyles of exoccipitals. _h_ Stylo-hyoid. _o_ Exoccipitals. _p_ Prootic. _p′_ Process to which the jaw is attached. _t_ Squamosal. ]
These paired bones form the hinder part of the cranium; they bound the _foramen magnum_, and articulate with the vertebral column. They are imbedded in the cartilaginous matrix of the skull, and are separated above by an unossified part of this matrix (_occipitale superius_, Dugès), which represents the tabular portion of human anatomy: below they are separated by a similar part (_occipitale basilare_, Dugès) which represents the body of the occipital bone. They therefore properly represent only the condylar portions (_partes condyloideae_) of the human occipital bone. Each possesses a cartilaginous articular head, for articulation with the first vertebra: these converge below, and surround the lower half of the circumference of the _foramen magnum_. This latter has, in _R. esculenta_, a transversely oval outline; in _R. temporaria_, a somewhat heart-shaped outline, with the apex directed upwards: in accordance with this the whole bone is wider than high in the first species; and in the latter it is higher than it is wide. From the upper and outer border of the _foramen magnum_ on each side a ridge runs obliquely outwards and downwards, in which lies the suture between this bone and the prootic bones. This bony ridge (_processus mastoideus_, autt.) is usually cartilaginous in _R. esculenta_, even in old animals; in _R. temporaria_, even in young specimens, it is bony. In the latter species the bones unite very early, while in the former they remain separated by the primitive cartilage. Between this crest and the _processus condyloideus_ there is a depression (_fossa condyloidea_), with a hole (_foramen condyloideum_) through which the vagus nerve leaves the cranium. The exoccipital take part in the formation of the labyrinth of the ear, as will be noticed later on.
_Articulation of the Exoccipital Bones with the Atlas._ From the middle of the anterior surface of the body of the atlas a ligament arises, representing to a certain extent the _lig. suspensorium dentis_, and attached to the basal portions of the exoccipital bones.
*2.* The *prootic bones*, _ossa petrosa_, Cuvier (Figs. 10, 11, and 12 _p_).
*Cuvier*, rocher, _l. c._, p. 388, Pl. XXIV, ee.--*Dugès*, n. 12, rupéo-ptéréal.--*Stannius*, ala temporalis.--*Meckel*, Schädelstück des Schläfenbeins.--*Parker* and *Bettany*, _l. c._, prootic.
These paired bones lie at the sides and in front of the exoccipital bones. As already explained, they remain in _R. esculenta_ separated from these by cartilage, while in _R. temporaria_ they early enter into bony union with them; this is due to the complete ossification of the _processus mastoideus_ in the latter species, as stated above. The prootics form the lateral expansions of the posterior part of the skull in which the organs of hearing are placed. The large cavity which contains the ear labyrinth is completed by the exoccipital: internally it opens freely into the skull, and externally on the posterior wall of the skull through the _foramen ovale_, which is formed by both these bones. The postero-lateral part of the prootic usually remains cartilaginous: at the side and in front of the _foramen ovale_ this cartilage is pierced by a small opening, through which passes the _nervus facialis_ or _ramus tympanicus n. vagi_ (Volkmann). At the side there is a process to which the suspensorium of the lower jaw is attached (Fig. 12 _p_): behind this is a hollow in which the auditory ossicles lie, and which may be designated _fossa tympanica_ (Fig. 12 _t_). The anterior border of the bone forms the hinder and inner walls of the orbit. Here also is the trigeminal foramen (Fig. 11 _p″_) through which the _N. trigeminus_ and the several nerves for the muscles of the eye pass; it represents the _foramen ovale_, _for. rotundum_, and the _fissura orbitalis superior_ (sphenoidal fissure) of the human sphenoid bone. The foramen is sometimes, especially in young animals, only a notch, which is completed by cartilage. On account of the relation of this part (Fig. 11 _p′_) of the bone to the nerves which pierce it, the whole bone has been named by Stannius the _ala magna_ or _temporalis_ of the sphenoid; it has been also looked upon as a bone which contains these elements, as by Dugès, who on this account calls it rupéo-ptéréal.
[Illustration: Fig. 13.
Skull of _Rana esculenta_, seen from below, twice natural size.
_c_ Cartilaginous wall of skull. _e_ Sphenethmoid. _e′_ Cartilaginous nasal skeleton. _h′_ Stylo-hyoid. _i_ Premaxillary. _m_ Maxillary. _m′_ Quadrate tract. _o_ Exoccipital. _p_ Prootic. _p′_ Anterior arm of prootic. _p″_ Trigeminal foramen. _pl_ Palatine. _pt_ Anterior arm of pterygoid. _pt′_ Posterior arm of pterygoid. _s_ Parasphenoid. _v_ Vomer. ]
_Appendages of the Prootic Bones._
1. The *styloid cartilage*. From the cartilaginous portion of the prootic the styloid cartilage runs downwards, backwards, and inwards, and is continued directly into the anterior cornu of the hyoid bone (Figs. 11 _h′_ and 12 _h_).
2. The *auditory ossicles*.
_a._ A thick cartilaginous disc, the _operculum_ (Fig. 12 _a_), closes the _foramen ovale_.
_b._ To the operculum is attached a bony, club-shaped piece, the _columella auris_ (Fig. 12 _a′_), which has at its inner, thicker end a cartilaginous epiphysis, the *interstapedial*; it lies transversely with the apex directed outwards, and this longer portion is the *mediostapedial*.
_c._ To the apex of the mediostapedial is attached, at an obtuse angle, the third cartilaginous piece, the *extrastapedial* (Fig. 12 _a″_). It is attached to the tympanic membrane, and by its upper portion is fastened to the cartilaginous tympanic ring by a smaller piece, the *suprastapedial*.
3. The *tympanic ring* (_annulus tympanicus_) is an annular cartilaginous frame; or more exactly, has the shape of a short, truncated cone, as it narrows towards the middle line: it is attached to the squamosal bone. (See Organ of hearing.)
*3.* The *parasphenoid*, _os sphenoideum_, Cuvier (Figs. 11 and 16 _s_).
*Cuvier*, _l. c._, p. 388, Pl. XXIV, d.--*Dugès*, n. 8.--*Meckel*, Theil des Grundbeins.--*Parker* and *Bettany*, _l. c._, parasphenoid.
A large portion of the base of the cranium is taken up by this cruciform bone. Of the two longitudinal median processes, the posterior is by far the shorter, and lies in front of and partly below the cartilaginous _os occipitale basilare_. The anterior longer longitudinal arm closes in the greater part of the cranium from below, and articulates by its outer edges with that part of the prootic bones often described as the _alae magnae_, and also with the cartilage lying in front, which forms the greater part of the lateral walls of the cranium. The anterior extremity of the bone articulates with the palatine bones. The transverse arms lie on the under surface of the exoccipitals and of the prootics.
The greater width of the cranium in _R. temporaria_ is associated with the greater relative width of the anterior arm of this bone.
4. The *fronto-parietal bones*, _ossa fronto-parietalia_, Cuvier (Figs. 10 and 14 _fp_).
*Cuvier*, _l. c._, p. 387, Pl. XXIV, c. c.--*Dugès*, n. 1.--*Parker* and *Bettany*, _l. c._, fronto-parietal.
These are a pair of somewhat long, flat bones, which form the principal part of the upper wall or roof of the cranium, and cover in superiorly the cartilaginous cranium, which is here, in great part, persistent. They are united in the middle line by the sagittal suture; posteriorly they articulate with the exoccipital and prootic bones; anteriorly with the sphenethmoid, which they overlap like tiles. The outer margin of each bone is bent somewhat downwards (Fig. 16 _fp_), and between it and the parasphenoid there is a space in the wall of the cranium which is closed in by cartilage and connective tissue only.
These bones are narrower in _R. esculenta_, and along the sagittal suture are depressed into a groove: where the superior surface bends down to become lateral the edges are much more prominent. In _R. temporaria_ the bones are broader and flat or even somewhat arched. The latter condition is still more marked in _R. oxyrhinus_.
*5.* The *sphenethmoid*, _os ethmoideum_ (Figs. 10, 11, 14, and 16 _e_).
*Cuvier*, os en ceinture, _l. c._, p. 387, Pl. XXIV, a.--*Dugès*, n. 15.--*Rathke*, anterior or sphenoidal wing (Vortr. z. vergl. Anat. d. Wirbelthiere, Leipzig, 1862, p. 42).--*Meckel*, Riechbein, _l. c._, p. 502.--*Parker* and *Bettany*, _l. c._, ethmoid.
The long tubular cranium is completed anteriorly by a single bone, which forms at once the roof, floor, and lateral walls. It is consequently more or less ring-shaped, on which account it has been named ‘os en ceinture’ by Cuvier. Only the posterior portion is annular, however: the anterior portion forms a double canal, with a median partition, for the passage of the nerves of smell, and as these canals are widened out anteriorly, this part of the bone helps to complete the nasal cavities, which, however, are bounded for the most part by cartilage, as described below. In some species of frogs (as for example _R. occellata_, Rathke) this cartilage is partly ossified.
The sphenethmoid has on each side a small bony canal, running forwards and inwards, through which the _ramus nasalis_ of the first division of the trigeminal nerve passes.
The *cartilaginous skeleton of the nose* (Figs. 14 and 16 _n_, _n″_, _n‴_, _n⁗_). The anterior borders of the funnel-shaped cavities of the sphenethmoid pass into cartilage, which forms two capsules, separated from each other by a median cartilaginous septum, and opening laterally. We can distinguish, (_a_) a cartilaginous septum, forming a continuation of the bony one; (_b_) the floor of the nasal cavity, narrower behind, wider in front; (_c_) a roof somewhat narrower than the floor. The floor and roof are united in front by an arched surface. From this cartilaginous capsule various processes project, which unite it to other portions of the facial skeleton: firstly, from the most posterior portion of the capsule there passes transversely outwards a bar of cartilage (_sn_), which, widening, becomes continuous with the cartilage (_sp″_) forming the basis of the anterior arm of the pterygoid bone. From the anterior angle a cartilaginous process passes outwards (Figs. 14, 16 _n″_), which is attached to a projection on the anterior end of the maxillary bone; from the same spot a horn-shaped cartilaginous process (_n″_, _n‴_) curves round backwards and towards the middle line. This projection bounds the nasal cavity externally, sending off a free process (_n‴_) on the way, and ends with a double point on the roof of the cartilaginous nasal cavity (_n⁗_). On the floor of the nasal capsule, on either side, is a knob-shaped cartilaginous eminence, running from behind, forwards and outwards; this may be regarded as an indication of a turbinated bone. From the anterior wall there passes into each nasal cavity an almost horizontal, partly ossified plate (_c.n._), ending posteriorly in a free pointed border. These are the _cornets_ of Dugès (_l. c._, p. 12, Pl. I, Figs. 1, 5), who correctly regarded them as turbinated bones. Cuvier described them as rudimentary nasal bones[29].
[Footnote 29: Cuvier (Ossem. fossil., V, 2. 388) says that these little bones are fixed outside the nasal cavity, so that we may suppose that he confounded them with the nasal cartilages found in this situation. Dugès correctly indicates their position to be inside of the nasal capsule. Meckel (Vergl. Anat. II, 504) also regards them as nasal bones. Bruch (Würzb. naturwiss. Zeitschrift, vol. II, 1861, p. 213) could not find them in any frog-skull, doubtless because he did not look inside the nasal capsules.]
[Illustration: Fig. 14.
Cartilaginous basis of the skull of _Rana esculenta_, from above, twice natural size. Cartilage shown by stippling.
_a.n._ Wings of nasal cartilage. _c.n._ Concha narium. _e_ Sphenethmoid. _ff′_ Foramina of cranium. _fn_ Nasal. _fp_ Fronto-parietal. _i_ Premaxillary. _j_ Quadrato-jugal. _m_ Maxillary. _n_, _sn_ Cartilaginous nasal skeleton. _n′_, _n″_, _n‴_ Processes of the cartilage. _o_ Exoccipital bones. _p_. Prootic. _pt_ Anterior arm of pterygoid. _pt′_ Posterior arm of pterygoid. _s′_ Cartilaginous cranium. _sp_ Cartilage of suspensorium. _sp′_ Cartilage under the squamosal. _sp″_ Cartilage under the pterygoid. _t_^1 Anterior } _t_^2 Middle } arm of the squamosal. _t_^3 Posterior } ]
The alar cartilages of the nose have still to be described. They are (_a.n._) shell-shaped cartilages, hollowed out on the inner sides and decreasing in width from before backwards. They are movably attached by their anterior broader ends to the tips of the projecting portions of the premaxillary bones, and are so arranged as to bound the lateral margins of the nasal apertures, which they overlap.
[Illustration: Fig. 15.
Nasal cartilages of frog, front view.
_an_ Concha narium. _i_ Premaxillary bones. _i′_ Ascending process of same. _m_ Upper jaw. _m′_ Lower jaw. _n_ Olfactory capsule. ]
*6.* The *cartilaginous basis of the skull*, _Primordial cranium_ (Figs. 14, 16).
*a.* If the fronto-parietals be removed, (Figs. 14, 16), a cartilage (_s′_) is found which partially closes the cranial cavity, and which is usually perforated on either side by a foramen (_f′_). More anteriorly in the median line is found a space (_f_) which extends to the sphenethmoid bone, and is only closed by connective tissue: posteriorly the cartilage extends between the exoccipitals as far as the _foramen magnum_, representing the _os occipitale superius_.
*b.* The base of the cranium is (Fig. 16) also partly cartilaginous. If the parasphenoid (_s_) be removed we find above it a cartilage (_s′_) which passes backwards between the exoccipitals, and extends as far back as the _foramen magnum_: it corresponds to the _os occipitale basilare_.
[Illustration: Fig. 16
Cartilaginous skull of _Rana esculenta_, from below, twice natural size. Cartilage shown by stippling.
_c_ Cartilage of prootic. _e_ Sphenethmoid. _fp_ Fronto-parietal. _i_ Premaxillary. _j_ Quadrato-jugal. _m_ Maxillary. _n_, _sn_ Cartilaginous nasal skeleton. _n′_, _n″_, _n‴_, _n⁗_ Processes of nasal cartilage. _o_ Exoccipital. _p_ Prootic. _pl_ Palatine. _pt_ Pterygoid. _pt′_ Articular surface for pterygoid. _r_ Optic foramen. _r′_ Foramen for N. abducens. _s_ Parasphenoid. _s′_ Cartilaginous cranium. _sp_ Cartilage of suspensorium. _sp′_ Cartilage under squamosal. _sp″_ Cartilage under pterygoid. _v_ Vomer. ]
*c.* The sides of the cranium are formed almost entirely of cartilage. This cartilage fills the space bounded by the nasals above, the parasphenoid below, the so-called _ala magna_ of the prootic bone behind, and the sphenethmoid in front; and has in its posterior part an aperture (_r_) through which passes the _nervus opticus_, and below this a smaller one (_r′_) for the _nervus abducens_. The extent of the cartilage in the antero-posterior direction is greater in _R. esculenta_ than in _R. temporaria_, or in other words the sphenethmoid stretches further back in the latter than in the former.
B. The Bones Of The Face.
[Illustration: Fig. 17.
Cartilaginous basis of the skull of _Rana esculenta_, from above, twice natural size. Cartilage shown by stippling.
_a.n._ Wings of nasal cartilage. _c.n._ Concha narium. _e_ Sphenethmoid. _ff′_ Foramina of cranium. _fn_ Nasal. _fp_ Fronto-parietal. _i_ Premaxillary. _j_ Quadrato-jugal. _m_ Maxillary. _n_, _sn_ Cartilaginous nasal skeleton. _n′_, _n″_, _n‴_ Processes of the cartilage. _o_ Exoccipital bones. _p._ Prootic. _pt_ Anterior arm of pterygoid. _pt′_ Posterior arm of pterygoid. _s′_ Cartilaginous cranium. _sp_ Cartilage of suspensorium. _sp′_ Cartilage under the squamosal. _sp″_ Cartilage under the pterygoid. _t^1_ Anterior } _t^2_ Middle } arm of the squamosal. _t^3_ Posterior} ]
The *Suspensorium*.
7. The *squamosal bones*, _ossa tympanica_, Cuvier (Figs. 10, 14 _t_).
*Cuvier*, _oss. foss._, V, 2. 390, Pl. XXIV, Figs. 1, 2 n.--*Dugès*, _temporo-mastoidien_, n. 10.--*Meckel*, Articular part of temporal.--*Hallmann* and others, quadrate-bone.--*Parker* and *Bettany*, _l. c._, squamosal.
The suspensorium, which forms the articulation between the cranium and the lower jaw, is T shaped; and consists of cartilage covered by bone. Of the three arms of the T the anterior has a free pointed extremity (Fig. 14 _t^1_) at the postero-lateral margin of the temporo-orbital fossa: it forms a true _processus zygomaticus_, and is bound to the upper jaw by ligaments. In _R. temporaria_ it is comparatively much shorter than in _R. esculenta_. The posterior upper arm (_t^2_) articulates with the prootic bone: the third or lower arm (_t_^3), supported by a cartilage[30], runs backwards and downwards to unite with the side of the broad hinder extremity of the quadrato-jugal bone.
[Footnote 30: This cartilage is the quadrate cartilage of Parker; others regard it as the upper end of the cartilaginous mandibular arch, of which Meckel’s cartilage is the lower distal part.]
The cartilaginous basis[30] of the suspensorium (Fig. 17 _sp_, _sp′_) is a direct continuation of the cartilaginous basis of the cranium, and proceeds from it to the outer extremity of the prootic; from this point the cartilage runs backwards and divides into two branches; of these, one (_sp′_) retains the original course backwards and outwards towards the articulation of the lower jaw, and in conjunction with the quadrato-jugal (_j_) forms this joint. The other (_sp″_) is directed forwards along the anterior arm of the pterygoid bone; it widens in front (_sn_), and becomes directly continuous with the cartilaginous strut described above as projecting from the hinder part of the cartilaginous olfactory capsule.
*8.* The *quadrato-jugal bones*, _ossa jugalia_, Cuvier (Figs. 10, 17, 19 _j_).
*Dugès*, _tympano-malléal_, n. 11.--*Cuvier*, _l. c._, p. 399, Pl. XXIV, Figs. 1 2 o.--*Hallmann*, quadrato-jugal bone, _l. c._, p. 39.--*Parker* and *Bettany*, _l. c._, quadrato-jugal.
This is a small process of bone, likened by Dugès to a comma, which rests by its posterior broader extremity on the cartilage of the mandibular arch[1], and forms with it a portion of the articular head for the lower jaw. The anterior extremity is pointed, directed forwards, and attached by ligament to the maxillary bone.
*9.* The *pterygoid bones*, _ossa pterygoidea_ (Figs. 10, 11, 17, 19 _pt_).
*Cuvier*, _l. c._, p. 389, Pl. XXIV, Figs. 1, 2 m m.--*Dugès*, n. 9.--*Parker* and *Bettany*, _l. c._, pterygoid bones.
These bones, shaped like the Greek letter λ, possess each three arms: of these the middle one is attached to the under surface of the prootic bone by a cartilaginous process (Fig. 18 _sp_); the hinder grooved arm lies upon the under surface of the cartilaginous suspensorial arch (Fig. 18 _sp′_); and the anterior arm (_pt_) runs forwards along the inner border of the anterior ramus of the suspensorium (_sp″_), in contact with the maxillary, palatine, and nasal bones.
The cartilage just mentioned, by means of which the middle arm of the pterygoid is connected with the cranium (compare Fig. 18), proceeds from the cranial origin of the cartilaginous arch (_sp_), turns downwards and then forms a sort of articular head (_cpt_), which is articulated to an oval flat elevation of the prootic cartilage by a movable joint. Externally the articular head curves somewhat abruptly into the bony substance (Fig. 18 _pt_) of the pterygoid bone.
[Illustration: Fig. 18.
Origin of the suspensory cartilage (_sp_) from the skull, with attachment of the pterygoid; front view. Cartilage shown by stippling.
_cpt_ Cartilaginous epiphyses of the pterygoid bone, from the cartilaginous suspensorium. _j_ Quadrato-jugal bone. _pt_ Pterygoid bone. _sp_ Origin of suspensorial cartilage from the skull. _sp′_ Hinder arm of same. _sp″_ Anterior arm of same. ]
[Illustration: Fig. 19.
Cartilaginous skull of _Rana esculenta_, from below, twice natural size. Cartilage shown by stippling.
_c_ Cartilage of prootic. _e_ Sphenethmoid. _fp_ Fronto-parietal. _i_ Premaxillary. _j_ Quadrato-jugal. _m_ Maxillary. _n_, _sn_ Cartilaginous nasal skeleton. _n′_, _n″_, _n‴_, _n⁗_ Processes of nasal cartilage. _o_ Exoccipital. _p_ Prootic. _pl_ Palatine. _pt_ Pterygoid. _pt′_ Articular surface for pterygoid. _r_ Optic foramen. _r′_ Foramen for N. abducens. _s_ Parasphenoid. _s′_ Cartilaginous cranium. _sp_ Cartilage of suspensorium. _sp′_ Cartilage under squamosal. _sp″_ Cartilage under pterygoid. _v_ Vomer. ]
*10.* The *maxillary bones*, _ossa maxillaria superiora_, Cuvier (Figs. 10, 11, 17, 19 _m_).
*Cuvier*, _l. c._, p. 389, Pl. XXIV, Figs. 1, 2 k k.--*Dugès*, n. 4, _maxillo-jugal_.--*Parker* and *Bettany*, _l. c._, maxillary bones.
These are elongated, curved bones, narrower behind, broader in front, and forming with the quadrato-jugals the bony support of the face. The superior surface is convex and directed outwards, the inferior surface is grooved and bears teeth along the outer edge of this groove. From the upper and inner border of the anterior half of this bone a process (_processus frontalis_) passes upwards, which articulates with the nasal bone. The anterior extremity of the bone articulates with the premaxillary bone, the posterior with the quadrato-jugal.
The maxillary bone articulates at its anterior end (Fig. 19 _n″_) with a process of the cartilaginous capsule of the nose. The broad plate of cartilage (Fig. 19 _n_), under cover of the _processus frontalis_, connects the hindermost transverse portion of the nasal cartilage with the cartilage which runs forwards from the suspensorium upon the anterior arm of the pterygoid.
*11.* The *nasal bones*, _ossa fronto-nasalia_, Dugès (Figs. 10, 17 _fn_).
*Cuvier*, _frontale anterius_, _l. c._, h.--*Dugès*, n. 2.--*Meckel*, nasal bone.--*Parker* and *Bettany*, _l. c._, nasal bones.
These flat, triangular bones, which rest upon the nasal cartilages (_n_), assist to bound the orbital cavities in front, and are connected by their external angles with the maxillary bone on either side[31].
[Footnote 31: For _os nasale_, Cuvier (_l. c._, g), _cornet_ (_concha_), Dugès, see cartilaginous nasal capsule, p. 27.]
*12.* The *premaxillary bones*, _ossa intermaxillaria_ (Figs. 10, 11, 17, 19 _i_).
*Cuvier*, _l. c._, p. 388, Pl. XXIV, Figs. 1, 2 f f.--*Dugès*, n. 3.--*Parker* and *Bettany*, _l. c._, premaxillary bones.
These two bones are united in the middle line: each consists of a tooth-supporting portion, which completes the maxillary arch, and an ascending process, to the apex of which the nasal cartilage is articulated by a movable joint (_an_). As muscles are attached to this process, it becomes a lever, by which movements are effected.
[Illustration: Fig. 20.
Skull of _Rana esculenta_, seen from below, twice natural size.
_c_ Cartilaginous wall of skull. _e_ Sphenethmoid. _e′_ Cartilaginous nasal skeleton. _h′_ Stylo-hyoid. _i_ Premaxillary. _m_ Maxillary. _m′_ Quadrate tract. _o_ Exoccipital. _p_ Prootic. _p′_ Anterior arm of prootic. _p″_ Trigeminal foramen. _pl_ Palatine. _pt_ Anterior arm of pterygoid. _pt′_ Posterior arm of pterygoid. _s_ Parasphenoid. _v_ Vomer. ]
*13.* The *palatine bones*, _ossa palatina_ (Figs. 19, 20 _pl_).
*Cuvier*, _l. c._, p. 389, Pl. XXIV, Figs. 1, 2 i i.--*Dugès*, n. 7.--*Parker* and *Bettany*, _l. c._, palatine bones.
Are two transverse bony bars, situated under the anterior portion of the sphenethmoid bone on either side: each extends outwards from the apex of the parasphenoid to the maxillary bone, where this gives off its ascending process to the nasal bone.
*14.* The *vomers*, _vomer_ (Figs. 19, 20 _v_).
*Cuvier*, _l.c._, p. 389, Pl. XXIV, Figs. 1, 2 l l.--*Dugès*, n. 6.--*Parker* and *Bettany*, _l.c._, vomer.
A pair of flat bones, placed horizontally on the under surface of the cartilaginous nasal capsule in the triangular space between the palatine bone and the anterior portion of the arch of the jaw. They limit the outer border of the floor of this capsule, which lies in a groove on the dorsal surface of the bone. The outer border of each bone has three processes, and between them two notches; the hinder of these notches bounding the posterior nares. The inner borders of the two bones touch, and the under surface of each bears a transverse row of small, pointed teeth.
*15.* The *mandible*, _maxilla inferior_ (Fig. 21).
*Cuvier*, _l.c._, p. 398, Pl. XXIV, Figs. 1, 2 _rst_.--*Dugès*, n. 16, 17, 18, 19.--*Parker* and *Bettany*, _l.c._, mandibular arch.
[Illustration: Fig. 21.
_A_ Mandible of _Rana esculenta_, from above, nat. size. _B_ External view of left side, } twice nat. size. _C_ Angulosplenial, } 1. Angulosplenial. 2. Dentary. 3. Mentomeckelian. 4, 4′ Meckel’s cartilage. _a._ Rudimentary _processus coronoideus_. _b._ Groove for Meckel’s cartilage. ]
The mandible consists of two bony arches united by ligament in the middle line, and each formed of four pieces. These are, (1) the *angulosplenial*, a strong, bony piece (Fig. 21 _C_, _B_1, _A_1), which forms the inferior and internal part of the lower jaw; below, it extends posteriorly, as far as the articulation; in front, it is attached to the dentary. In the greater part of its length it has a groove directed upwards and outwards (_C_, _b_), and above has a process which represents the _processus coronoideus_: (2) the *dentary* (_A_ 2, _B_ 2), a bony lamella which rests on the outer surface of the anterior half of the angulosplenial, and articulates in front with *Meckel’s cartilage*; it is a thin, flat lamella of bone; (3) in the groove of the angulosplenial is found a cartilage occupying its entire length (_A_ 4, _B_ 4), *Meckel’s cartilage*; it is broader behind, and here forms the articular fossa of the lower jaw; anteriorly it is covered by the dentary, and articulates with the (4) *mentomeckelian* (_A_ 3, _B_ 3) at its anterior end, which is bound to its fellow of the opposite side by ligaments, and unites the two halves of the lower jaw.
The upper part of Meckel’s cartilage, which forms the joint with the suspensorium, must be regarded as the _articulare_; to this also belongs the anterior, ossified portion of the mentomeckelian[32]; the dentary, which covers Meckel’s cartilage, must represent the _os dentale_[33]; the first and largest bone, the angulosplenial, which lies on the inner side of the cartilage, must be considered as the _os operculo-angulare_, Dugès, for it contains the elements of these bones.
[Footnote 32: Dugès, _os dentale_.]
[Footnote 33: Dugès, _surangulaire_.]
[Illustration: Fig. 22.
Hyoid of _Rana esculenta_, twice nat. size.
_H_ Body; _h h′_ processes. _H′_ Anterior horn. _H″_ Posterior horn. ]
*16.* The *hyoid bone*, _os hyoideum_ (Fig. 22).
*Parker* and *Bettany*, _l.c._, hyoid.
This consists of a broad, thin, cartilaginous plate, with processes passing from it as represented in the figure. We distinguish in it:--(*a*) the body (_H_), somewhat oblong, and wider in front than behind. From the anterior angles there projects on either side a blunt rounded process (_h_); from either posterior angle a more pointed process (_h′_). (*b*) The anterior cornua (_H′_) (_cornua styloidea_) project from the anterior border of the body, first in a forward direction, then in a curve backwards and upwards (compare Fig. 12), to unite with the cartilage of the prootic bone. Where the direction of these _cornua_ is changed each sends off a short blunt process. (*c*) The posterior cornua (_cornua thyroidea_) (_H″_) are bony rods which run from the hinder margin of the body, diverge posteriorly, and enclose the larynx.
III. THE STERNUM (Fig. 24 _es_, _hs_).
*Cuvier*, _l. c._, p. 401, Pl. XXIV, Fig. 31 _e f_.--*Dugès*, n. 27, 28.--*Parker* and *Bettany*, _l. c._, sternum.
The bones of the sternum are in very close relationship with the shoulder-girdle, and some difference of opinion exists as to the relations of the several parts.
[Illustration: Fig. 23.
Omosternum of _Rana esculenta_, twice nat. size.
_a_ Anterior, _p_ Posterior extremity. ]
The following parts must be regarded as undoubtedly belonging to the sternum:--
*1.* An anterior part, consisting of a bony and a cartilaginous portion.
_a._ The *omosternum* (Figs. 23, 24 _e.s._) is a bony rod, wider behind, narrower in front, and supports
_b._ The *episternum* (Fig. 24 _es′_), a semicircular plate of calcified cartilage, with a thin free border of unchanged hyaline cartilage.
*2.* A posterior part, which also consists of a bony and a cartilaginous portion.
[Illustration: Fig. 24.
Shoulder-girdle and sternum of _Rana esculenta_, twice nat. size. The scapula and suprascapula are turned outwards.
_c._ Connecting cartilage. _cl._ Clavicles and precoracoids. _co_ Coracoid. _es._ Omosternum. _es′_ Episternum. _h_ Hyaline cartilage. _hs._ Sternum proper. _hs′_ Xiphisternum. _o_ Bone. _o′_ Calcified cartilage. _sc._ Scapula. _sc′_ Suprascapula. ]
_a._ The *sternum proper* (Fig. 24 _h.s._), a rod of cartilage ensheathed in bone, broader in front and narrower behind. To its posterior extremity is attached
_b._ The cartilaginous *xiphisternum* (Fig. 24 _hs′_), a plate, the shape of which is best understood by referring to Fig. 24, and the structure of which is similar to that of the episternum.
*3.* The *epicoracoids*[34] lie between the episternum and the sternum proper: they are a pair of narrow cartilages, closely applied to each other and placed between the ventral ends of the precoracoids and coracoids, see p. 40.
[Footnote 34: Dugès, _l.c._, p. 61, regards the cartilaginous laminae as _os episternale_ and _proc. xiphoideus_, and the two bones _e.s._ and _h.s._ (Fig. 24) as sternum.]
IV. The Bones Of The Anterior Extremity.
A. Bones Of The Shoulder-Girdle.
The shoulder-girdle of the frog (Fig. 25) consists of four bones, two in the upper or *scapular portion*, and two in the lower or *coracoid portion*.
*1.* The *scapular portion*.
*a.* The *suprascapula*, _pars suprascapularis scapulae_, _scapula superior s. omolita_ (Figs. 25 _s′_, 26, 27). This forms the upper, thinner portion. It is trapezoid in shape, its narrowest, thickest, and lowest border articulating with the scapula. The remaining three borders are free; the posterior and superior borders are very considerably thinned out, the inferior surface is curved towards the ventral surface. Only the thin upper and hinder borders (_hh_) are of hyaline cartilage; the middle portion (_co_) consists of calcified cartilage; the lateral part (_o_) and the anterior border (_o′_) of true bone.
[Illustration: Fig. 25.
Shoulder-girdle of the frog in transverse section, diagrammatic.
_c_ Connecting cartilage. _c′_ Epicoracoids. _cl_ Clavicles. _h_ Humerus. _s_ Scapula. _s′_ Suprascapula. _ss_ Articulation of these two. _v_ Vertebra. ]
The bony part forms a thin plate striated both radially and concentrically with the margin. The anterior border (_o′_) is bent on itself so as to form a groove (Fig. 27). The dorsal surface of this bony plate is quite smooth, and covered only by periosteum; the ventral surface, on the contrary, is for the most part covered by an even layer of calcified cartilage (Fig. 27 _co′_). This passes directly into the second portion of calcified cartilage (_co_); so that if the whole be dried, the thin hard lamina of bone can easily be split away from the underlying parchment-like cartilage. The layer of calcified cartilage is, however, not so complete that the _suprascapula_ can be said to consist of calcified cartilage.
[Illustration: Fig. 26.
Suprascapula of _Rana esculenta_, from above, twice nat. size.
_co_ Calcified cartilage. _h_ Hyaline cartilage. _o_ Bony portion. _o′_ Anterior curved border. ]
[Illustration: Fig. 27.
Suprascapula of _Rana esculenta_, from below, twice nat. size.
_co_ Calcified cartilage. _co′_ Layer of calcified cartilage on the under surface of the bone. _h_ Hyaline cartilage. _o_ Bony portion. _o′_ Anterior curved border. ]
[Illustration: Fig. 28.
Left scapula of _Rana esculenta_, from below, twice nat. size.
_a_ Anterior border. _c.a._ _Cavitas articularis._ _l_ Outer border. _m_ Inner border. _p_ Posterior border. ]
[Illustration: Fig. 29.
Scapula seen from behind, twice nat. size.
_c.a._ _Cav. articularis._ _d_ Dorsal process. _v_ Ventral process. ]
*b.* The *scapula* (Figs. 25 _s_, 28, 29) is a long, flat, four-cornered plate of compact bone, contracted in the middle, and wider at either end. From above (Fig. 28 _l_) it descends to the shoulder-joint with a slight curvature, with the convexity directed outwards. The inferior or ventral border (Fig. 28 _m_), which assists in the formation of the shoulder-joint, is cleft into two processes, a ventral and a dorsal. This may be best seen by looking at the border of the bone from behind or before (as in Fig. 29). The lower ventral process (Fig. 29 _v_) may be regarded as the _acromion_, or at least as a rudiment of the acromion, _i. e._, _spina scapulae_. The upper dorsal process evidently represents a rudimentary _processus coracoideus_. The anterior border (Fig. 28 _a_) is free, somewhat sharp, and slightly concave; the posterior (Fig. 28 _p_), also concave, is free externally; while internally, where the division of the ventral border commences, it takes part in the formation of the articular cavity of the shoulder (Figs. 28 and 29 _c.a._).
_Articulation with the suprascapula._ The scapula consists of a shell of compact bony tissue and an inner portion of cancellous tissue; this latter passes, at the boundary between this bone and the suprascapula, through an intermediate layer of calcified cartilage, which is directly continuous with the cartilage of the suprascapula. The compact superficial layer ceases where the calcified cartilage begins, and the periosteum of the scapula passes directly into the perichondrium of the suprascapula.
*2.* The *ventral portion* of the shoulder-girdle consists of three parts, which lie one behind the other.
*a.* The larger and posterior bone, the *coracoid* (Figs. 24 _co_, 30), is contracted in the middle, and expanded at either end, especially at the sternal end. The inner half is flattened from above downwards; externally it becomes more cylindrical. The anterior and posterior borders are markedly concave; the outer border (Fig. 30 _l_) articulates by means of a cartilage with the _proc. coracoideus_ of the scapula; the inner border (_m_) is separated from its fellow of the opposite side by the epicoracoids. This inner border is so broad, that it almost touches the inner end of the clavicle (Fig. 24 _cl._). A *coracoid foramen* is thus formed between the two bones, similar to the _foramen ovale_ of the pelvis.
[Illustration: Fig. 30.
Left coracoid, twice nat. size.
_a_ From below. _b_ From behind. _l_ Outer extremity. _m_ Inner extremity. ]
[Illustration: Fig. 31.
Clavicle of the left side, twice nat. size.
_l_ Outer extremity. _m_ Inner extremity. ]
*b.* The small anterior bones of the ventral portion of the shoulder-girdle (Figs. 24 _cl._, 31), I, like Cuvier and others, regard as *clavicles*. Dugès (n. 33) names them ‘_acromial_.’ Each bone is narrower than the coracoid, smaller internally (_m_), broader externally (_l_), and articulates by this broader end with the cartilage uniting the dorsal and ventral portions; the inner extremity rests upon the epicoracoid. The clavicle is grooved on its superior and posterior surfaces in almost its whole length; the groove widens externally (_l_), and contains
*c.* The *precoracoid* (Fig. 34 _cl′_), a slender bar of cartilage, connecting the anterior edge of the scapula with the sternum.
[Illustration: Fig. 32.
Right shoulder-girdle of _Rana esculenta_, from above.
_ca_ Cav. articularis. _c c_ Cartilage. _cl_ Clavicle. _co_ Coracoid. _sc_ Scapula. _sc′_ Suprascapula. ]
[Illustration: Fig. 33
Hinder border of the scapula and coracoid, with the connecting cartilage and shoulder-joint, twice nat. size.
_c_ Connecting cartilage. _d_ Dorsal process. _co_ Coracoid. _sc_ Scapula. _v_ Ventral process. ]
[Illustration: Fig. 34.
Clavicular cartilage of a young specimen of _Rana esculenta_, enlarged to the adult size.
_c_ Connecting cartilage. _e_ Epicoracoids. _c′_ Ligament between the two cartilages. _cl_ Clavicle. _cl′_ Clavicle and precoracoid. _co_ Coracoid. _co′_ Cartilage of same. _es_ Omosternum. _hs_ Sternum proper. ]
*Cartilages* of the shoulder-girdle (Figs. 24, 32, 34). A cartilage (_c_), described by Dugès as the ‘paraglénal,’ connects the scapula with the coracoid, and converts the notch between the two processes (_s_ and _v_) on the inner border of the scapula into an aperture opening posteriorly into the glenoid cavity, and which is filled up by the lining cartilage. This cartilage connects the two processes with the coracoid; being thicker between this and the _proc. coracoideus_, it takes an important share in the formation of the floor of the glenoid cavity. At the outer extremity of the clavicle the cartilage projects and is then continued in the groove on this bone towards the middle line (Figs. 32, 34), where it widens out, and is united by its external margin with the sternum, thus forming the precoracoid as already described, see p. 40. These connections are best seen in young animals, as is shown in Fig. 34.
The clavicle (_cl_) is of ossifying cartilage; the cartilage (_c_), the epicoracoid, is very large, and hyaline, and at _cl_ runs directly into the epicoracoids, which are here united mesially by ligament. In the fully developed animal the whole of the epicoracoid changes to calcified cartilage, as also does the precoracoid lying in the groove of the clavicle.
B. Bones Of The Fore Limb.
*1.* The *arm* has but one bone.
[Illustration:
Fig. 35. Fig. 36. Fig. 37.
Humerus of _Rana Humerus of _Rana, Humerus of _Rana esculenta_, female, esculenta_ male, esculenta_, female, seen from below. seen from below. outer side.
Figures twice natural size.
_c_ Anterior extremity. _c_′ Posterior extremity. _cd_ Crista deltoidea. _cm_ Crista medialis. _t_ trochlea.]
The *humerus*, _os humeri_ (Figs. 35, 36, 37). The shaft of the humerus is, on the whole, cylindrical, the middle part being the narrowest; its dorsal surface is slightly concave, the ventral surface convex. In the upper half the cylindrical form is indistinct, from the presence of a well-marked crest (_crista deltoidea_) upon the under or ventral surface. The hinder half of the bone has very different shapes in the two sexes: in the female it remains cylindrical as far as the elbow-joint; in the male, on the posterior surface, where the _crista deltoidea_ ceases, a marked ridge (_crista medialis_) arises, which gradually winds inwards and terminates at the inner condyle. This sexual difference is found in all the three species described in the Introduction, and it would seem that this ridge increases in height during the pairing season. The muscle which arises from this process is the _flexor carpi radialis_ (Fig. 74 _Fc_), and it attains, in the males, a very large size at the same period; indeed, it is at its origin twice as broad as in the female. Dugès[35] has incorrectly stated that this _crista_ is a peculiarity of _Rana temporaria_, and is wanting in _Rana esculenta_. Pouchet[36] first observed that it was a sexual distinction.
[Footnote 35: _l. c._, p. 68.]
[Footnote 36: Compt. rend. vol. XXV, 1847, p. 761.]
The anterior articular extremity presents a rounded head, which is somewhat flattened externally. The inferior ventral border is sharp, and developed into the above-mentioned bony crest (_crista deltoidea_); the free border is arched and curved outwards. Above, on the outer surface of the head, is found an eminence which may be a rudimentary _tuberc. maius_. The inner half of the head is articular.
The posterior articular extremity consists of a rounded head (_c′_), attached to the posterior extremity of the shaft; internal to this is a small _trochlea_ (_t_), placed upon the inner condyle. The external condyle is but small. The head is embraced by these condyles. Upon the under surface, above the head, is the _fossa cubitalis anterior_. The structure of the two articular extremities of the humerus differs; the upper, as in long bones generally (see page 16), consists of hyaline cartilage surrounded by calcified cartilage, which again is covered by hyaline articular cartilage; the lower extremity is composed of spongy bone, with roundish marrow spaces, and for the most part covered by a layer of calcified cartilage.
The *shoulder-joint*. The socket is formed by the posterior border of the scapula, by both the processes of that bone, the outer portion of the coracoid, and besides these by cartilage, which forms the articular surface already described (Fig. 33). In the macerated bone the floor of the socket opens dorsally into a fossa between the processes of the scapula (Fig. 32). This opening, in the natural condition, is closed by synovial membrane only; the cartilage covering the rest of the space being absent (the sac may easily be inflated, either from the joint itself or through the opening). The margin of the socket consists of a _labrum_, partly fibrous and partly cartilaginous, which is easily removed entire. The capsule, which is attached beneath the _caput humeri_, arises from this. From the articular cartilage of the ventral margin of the socket, and from the adjacent part of the scapula, proceeds a strong band, which is inserted into the flattened outer surface of the head.
*2.* The *forearm*.
[Illustration: Fig. 38.
Radio-ulnar of the right side of _Rana esculenta_, twice nat. size.
_r_ Radius. _r_′ Capitulum radii. _u_ Ulna. _u_′ Olecranon. ]
The *radio-ulnar*, _os antibrachii_ (Fig. 38). The two bony elements of the forearm are fused into one, which, however, shows traces of its compound character. Of these two bones, that which forms the inferior (in man anterior) border is the radius, the other the ulna. The relative positions of the bony elements are such that they appear to be in a state of semi-pronation; by this the thumb-border of the arm is directed downwards (in man forwards). The two bones so united form a flattened, tube-like bone, the grooved surfaces of which are directed inwards and outwards respectively; the borders being dorsal and ventral. The shaft of the bone is narrower above, becoming gradually wider below. In the upper half, the groove showing the line of junction of the two bony elements is scarcely visible, and it appears as though this part consisted of ulna alone, the radius not reaching so far; below the groove is more marked. The upper articular extremity appears to consist of an _olecranon_ (Fig. 38 _u′_) and a _processus coronoideus_ (_r′_), between which is the greater sigmoid cavity (_cavitas sigmoidea major_) for the _processus cubitalis humeri_. A more careful examination shows this to be incorrect: the portion of the concave articular surface, which lies in the immediate neighbourhood of the ventral border, undoubtedly represents the articular surface of the _capitulum radii_, and the upper portion of the articular surface (at _u′_) belongs to the _ulna_ and articulates with the _trochlea_ (Figs. 35, 36 _t_) of the humerus. The inner border of the upper extremity of the bone articulates with the groove _t_ of the humerus. The inferior extremity forms one of the usual cartilaginous epiphyses, enclosing the two bones. That part of the extremity corresponding with the radius is triangular and convex, it is prolonged upon the inner or under surface of the bone by means of a process; the ulnar portion of the bone forms a _capitulum_. The structure of the inferior extremity is that of epiphyses in general, except that there are two medullary cavities in a common sheath of calcified cartilage; the anterior head consists of cancellous tissue, with a covering of calcified cartilage.
*3.* Bones of the *hand* (Fig. 39).
*Dugès*, Pl. VIII, Figs. 37, 38, 39, 40, 41, 42, 43, 52.
*a.* Bones of the *wrist*, _ossa carpi_. These are arranged in two rows, proximal and distal. The proximal or anterior row has three bones, viz.:--
1. _Os lunatum_, the middle bone (Fig. 39 _l_), Dugès, n. 38, articulates with the radial part of the articular surface of the radio-ulnar by a concave surface; with the large bone of the second row (_hc_) it articulates by means of a rounded head; and with the two other bones of this row, _os naviculare_ (_n_) and _pyramidale_ (_p_), with the former by a saddle-shaped surface, with the latter chiefly by ligament. The bone is irregularly cuboid; the dorsal and palmar surfaces are non-articular. With Dugès I regard this bone as _os lunatum_; Mertens[37] regards it as _os naviculare_.
[Footnote 37: Mertens, _l. c._]
[Illustration: Fig. 39.
Bones of the forearm and hand of _Rana esculenta_, right side, dorsum, twice nat. size.
_a_ Os antibrachii. _hc_ Os capitato-hamatum. _l_ Os lunatum. _m_ Ossa metacarpi. _n_ Os naviculare. _p_ Os pyramidale. _r_ Radial portion of the radio-ulnar. _t_ Os multangulum majus or trapezium. _t′_ Os multangulum minus or trapezoides. _u_ Ulnar portion of the radio-ulnar. _I_-_V_ First to fifth fingers, the fifth only of os metacarpi, the second and third of two, fourth and fifth of three phalanges. ]
2. _Os pyramidale_ (Fig. 39 _p_), Dugès, n. 37, articulates with the ulnar part of the posterior articular extremity of the radio-ulnar. Anteriorly the bone has a facet which receives the _capitulum ulnae_, and alongside this a small flat surface which articulates with the radius. Posteriorly, opposite to the second row, it presents a long raised articular surface, extending from the dorsum to the palmar surface; and on the palmar aspect of the bone is a ridge running from before backwards. Mertens names this bone _os lunatum_.
3. _Os naviculare_ (Fig. 39 _n_), Dugès, n. 39. The third bone of the first row does not articulate with the bones of the forearm. It is connected with the _os lunatum_ by a saddle-shaped surface, posteriorly with the _os capitatum_ by means of a concave surface. On the inner surface is a small concave articular facet for the _os multangulum minus_ or _trapezoides_ (Fig. 39 _t′_). The convex palmar surface of the bone articulates with the _os multangulum majus_ (_t_); the radial side is non-articular, and with the _os lunatum_ forms a ridge directed forwards. Mertens names this bone _os triquetrum_. It is evident, however, that if the arrangement in man obtains as a standard, the nomenclature of Dugès, which I have here used, is correct; but the _os naviculare_ is no longer in contact with the articular surface of the _os antibrachii_.
The second or distal row also consists of three bones:--
4. _Os capitato-hamatum_ (Fig. 39 _hc_), Dugès, n. 40, 41, 42, corresponds with the _os capitatum_ and _hamatum_[38], which are here fused together. It is the largest bone, and articulates with all three bones of the first row; it is crescentic, with the concavity directed posteriorly, and on the convex surface has three facets for the three outer _ossa metacarpi_.
[Footnote 38: Dugès thinks that _os trapezoides_ is also included.]
5. _Os multangulum minus_, _s. trapezoides_ (Fig. 39 _t′_), Dugès, n. 43, is a small bone lying next to the foregoing; it articulates with the _os metacarpi II_, and anteriorly with the _os naviculare_. Dugès considers it to be the _os trapezium_.
6. _Os multangulum majus_, _s. trapezium_ (Fig. 39 _t_), is a small bone, which is placed on the convex palmar auricular side of the _os naviculare_. Dugès regards this bone as _os metacarpi pollicis_ (Dugès, n. 44), Mertens as _multangulum minus_. It appears to me that the interpretation here given is justified, because it articulates with the rudiment of the thumb, and as it possesses no resemblance to a long bone it cannot be regarded as an _os metacarpi_.
*Structure of the carpal bones.* All the carpal bones consist of calcified cartilage, though variations due to age occur in the amount of the deposit.
*Wrist joint.* As stated above, the _os lunatum_ and _os pyramidale_ are articulated with the forearm. In addition to the capsules uniting the parts, there are strengthening ligaments, two of which require special mention. One of these arises from the palmar surface of the posterior extremity of the ulna, and passes to the sharp palmar ridge of the _os pyramidale_, where it is attached, and is inserted into the _os capitato-hamatum_; the second ligament passes in a similar manner on the palmar surface from the radius to the _os naviculare_. Between the two ligaments there is on the volar surface a deep excavation.
[Illustration: Fig. 40.
Bones of the forearm and hand of _Rana esculenta_, right side, dorsum, twice nat. size.
_a_ Radio-ulnar. _hc_ Os capitato-hamatum. _l_ Os lunatum. _m_ Ossa metacarpi. _n_ Os naviculare. _p_ Os pyramidale. _r_ Radial portion of the radio-ulnar. _t_ Os multangulum majus or trapezium. _t′_ Os multangulum minus or trapezoides. _u_ Ulnar portion of the radio-ulnar. _I_-_V_ First to fifth fingers, the first only of a metacarpal, the second and third of two, fourth and fifth of three phalanges. ]
*Movements* of the hand. The two bones of the forearm being firmly united, pronation and supination, as in man, are impossible. The normal position, as already remarked (see radio-ulnar), is that of semi-pronation (compare Figs. 2 and 74). If the animal be in its natural posture, with the arm bent at the elbow (Fig. 1) it can touch the ground with the ulnar border only; but when the whole surface of the hand rests upon the ground, the action is brought about as follows: the plane of the carpus is in extension parallel with that of the forearm; in flexion, almost at right-angles with that plane (Fig. 74) The _os lunatum_ glides on the prolongation of the articular surface on the inner palmar surface of the radius, while the _os pyramidale_ is held firmly by the ligament just described. The hand follows the movement of the _os lunatum_, and at the same time the three outer _ossa metacarpi_ gliding with it inwards, the fingers of the hand turn inwards.
*b.* The Bones of the *metacarpus*, _ossa metacarpi_ (Fig. 40 _m_). Of these there are five: the *second* to the *fifth* are of about equal length; the first, forming the rudiment of the thumb, hidden beneath the skin, is much shorter. This metacarpal bone of the *thumb* is regarded by Dugès and others as the first phalanx. My reason for describing it as a metacarpal has already been given. This bone also presents differences in the two sexes. Meckel’s[39] observation that it exists only in the male is incorrect; it is a large, broad and sickle-shaped mass of calcified cartilage or even true bone, while in the female it is simply a small cartilaginous rod; as this almost entirely disappears in dried specimens, Meckel’s statement is explained. The *second* finger has in the frog assumed the functions of the thumb, and, in the males, in the breeding season swells and undergoes an essential alteration of structure. The metacarpal of this finger also displays differences in the sexes, being in the male stronger, broader, and on the inner side provided with a spine-like prolongation, for the tendon of the _abductor digiti II (pollicis) longus_, which attains an unusual development during the breeding season. The remaining metacarpal bones, the *third*, *fourth*, and *fifth*, are of similar form, the last being provided with a tubercle. The anterior articular extremities are rather broad and concave, and the posterior have rounded heads.
[Footnote 39: _l. c._, II, 464.]
*c.* The *phalanges*, _phalanges digitorum_. The hand has four fingers and the rudiment of a fifth, which latter is completely hidden under the skin, and as already explained, consists of a metacarpal only. Of the four fingers, the fourth is the longest, the third the shortest, the second and fifth of intermediate and about equal length; the fourth and fifth fingers have each three phalanges, the second and third have each two. Their shape is not unlike that of the human phalanges.
V. The Bones Of The Hinder Extremity.
A. BONES OF THE PELVIC GIRDLE (Fig. 41).
The *pelvis* has a characteristic V-shape, the pubic and ischiatic bones of the two sides together forming a vertical plate (_a p_), which divides anteriorly into the two iliac bones (_il_). The pubic and ischiatic bones being united by their median surfaces, one can only speak of the pelvic cavity as the space between the two ilia.
*1.* The *ilia*, _ossa ilii_ (Fig. 42 _il_). In these a broader part or body can be distinguished, which takes part in the formation of the _acetabulum_ (_a_). The hinder and broadest part of the bone is joined to the corresponding portion of its fellow by ligament; anteriorly the two diverge, bounding a cone-shaped cavity, the pelvis. The suture, by which the body of the iliac bone is united with the ischiatic and pubic bones, runs from above downwards through the middle of the _acetabulum_ (Fig. 42, from _p_ through the _acetabulum_ to _is_). Inferiorly and in front the united _ilia_ form a prominence (_s_), which represents the _symphysis oss. pub._ of man. The expanded portions of the ilium rest directly over the articular cavity by means of a somewhat constricted part or root. The _ala_ is a sabre-like bone, with the sharper, more convex border directed upwards; the more concave, thicker border downwards. The two surfaces, of which the inner is grooved, are directed respectively inwards and outwards. The broader part of the blade springs directly from the neck or root (at _il′_), and at this end of the sharp convex border is a process, _process. sup._, from which the tendon of the _m. vastus externus_ arises. The anterior end of the blade is a hollow cylinder, containing cartilage, movably articulated to the transverse process of the last vertebra or sacrum.
[Illustration: Fig 41.
Pelvis of _Rana esculenta_, from below, nat. size.
_a_ Acetabulum. _il_ Iliac bone. _p_ Pubic bone. ]
[Illustration: Fig. 42.
Pelvis of _Rana esculenta_, left side, twice nat. size.
_a_ Acetabulum. _d_ Upper sharp border. _il_ Iliac bone. _il′_ Superior process. _is_ Ischium. _is′_ Tuber ischii. _p_ Os pubis. _s_ Inferior process of the ilium. _v_ Lower border of same. ]
*2.* The *ischia*, _ossa ischii_ (_is_), are irregular, four-cornered plates of bone, united together by the whole extent of their inner surfaces. The vertical plate formed by the union of the two bones takes only a very small share in the formation of the articular cavity. Above, it has a somewhat sharp border, continued with the ilium into a process (_is′_) corresponding with the united _tubera ischii_; the hinder border, which is united below with the pubic cartilage, is curved.
[Illustration: Fig. 43.
Horizontal section through the iliac, pubic, and ischiatic bones.
_a_ Acetabulum. _il_ Ilium. _is_ Ischium. _p_ Pubic cartilage. _s_ Ligaments which unite the bones of opposite sides. ]
*3.* The *pubes*, _os pubis_ (Figs. 41, 42, 43 _p_). Ossified pubic bones do not exist; even in old animals they are composed of calcified cartilage. Each is a triangular cartilage, wedged between the ilium and ischium, but also taking part in the formation of the _acetabulum_. The pubes of opposite sides are, as shown in section in Fig. 43, united by ligaments in the median plane.
B. Bones Of The Hind-Limb.
*1.* The *thigh*.
The *femur*, _os femoris_ (Fig. 44). The shaft is cylindrical, with a slight double or S-shaped curve. In the anterior portion the convexity is directed upwards, in the two hinder thirds downwards. Towards the hinder extremity it is flattened from above downwards. The anterior extremity is a rounded articular head placed directly on the shaft like that of the _humerus_. This head is somewhat flattened from side to side; and in structure resembles that of the humerus. The inferior extremity is rounded below, but flattened above (towards the hollow of the knee) and behind.
*Hip-joint.* The articular cavity is deepened by a fibrous ring, _labrum cartilagineum_, which fits closely upon the _caput femoris_; from this _labrum_ the joint-capsule arises, to be inserted behind the head; close to the lower border of the cavity a _ligamentum teres_ arises, which is inserted into the _caput femoris_.
*2.* The *leg*.
[Illustration: Fig. 44.
Femur of _Rana esculenta_, right side, twice nat. size.
_a_ Anterior extremity. _p_ Posterior extremity. ]
*Tibio-fibula*, _os cruris_ (Fig. 45). This consists of a single bone, the _os cruris_; it is often called the _tibia_, but presents, however, distinct indications of being formed of two bones, the _tibia_ and _fibula_. The shaft is not quite straight; it is thinner in the middle and flattened from above downwards. On the upper as also on the lower surface of the bone is a groove, passing from the middle towards each extremity; this deepens as it proceeds, and is an indication of the compound nature of the bone. In the middle of each surface of the bone is the opening of a canal, through which a bristle may be passed: the canal has bony walls. The medullary cavity is, for the most part, double, being single only in the middle. The anterior extremity is articular, and presents a median groove, which is prolonged on to the under surface. The posterior extremity forms a transverse condyle, which has at its inner part a notch for the tendon of the _m. tibialis posticus_.
[Illustration: Fig. 45.
Tibio-fibula of _Rana esculenta_, twice nat. size, seen from below.
_a a_ Grooves. _f_ Foramen nutritium. _t_ Anterior articular extremity. _t′_ Posterior articular extremity. _t″_ Groove on malleolus internus for tendon of _m. tibialis posticus_. ]
The *knee-joint* consists of a capsule strengthened by the insertions of numerous tendons. Within this the articular surfaces of the _femur_ and tibio-fibula are connected by means of fibro-elastic bands, which spring from the latter bone and cross each other, thus representing the _lig. cruciata_. The articular surfaces are moreover deepened by loose semilunar cartilages, corresponding with the inter-articular cartilages of the knee-joint of man. In addition, on either side of the joint, are found auxiliary ligaments.
[Illustration: Fig. 46.
Section of the tibio-fibula through the under extremity.
_a_ Cartilaginous epiphysis. _m_ Marrow cavities. _t″_ Connecting mass. _t t′_ The two cylinders of bone. ]
*3.* The *foot* (Fig. 47).
*a.* The *ankle*, _ossa tarsi_. The *tarsus* consists of two rows of bones.
α. The *proximal row* consists of two long tubular bones (Fig. 47 _ac_), which are parallel to each other, and undoubtedly correspond with the *astragalus* (_talus_) and *calcaneum*. The bones are separated in the middle, but approach each other at either end. The outer of these bones (_c_) I have named calcaneum, following Cuvier and Dugès; the inner, astragalus (_a_). The two bones are surrounded and enclosed at their anterior and posterior extremities in a common epiphysis of calcified cartilage, which has the usual structure found elsewhere. The _ligamentum calcanei_, which will be described below (see Muscles of Foot, Fig. 88 _lc_), may be regarded as an unattached process of the heel[40].
[Footnote 40: Meckel, _l. c._, II, p. 488, regards the cartilage in the _tendo Achillis_ as such.]
β. The *distal* row of the tarsals are all composed of calcified cartilage. They are:--
1. _Os cuboideum_ (Fig. 47 _cb_), a flat plate of cartilage, concave in front, convex behind, placed between the common epiphysis of the astragalus and calcaneum (_ac_) and the _ossa metatarsi II_ and _III_. This corresponds, as Dugès suggests, with the separated _os cuboideum_ and _cuneiforme III_ of other batrachians, _e. g._ Bufo.
2. On the inner side of the above, between the _astragalus_ and _metatarsus I_ lies a small body, concave in front, convex behind, which we may regard, with Dugès, as the analogue of the _os naviculare_ (Fig. 47 _n_).
[Illustration: Fig. 47.
Right foot of _Rana esculenta_, palmar surface, twice nat. size.
_a_ Astragalus. _ac_ Common epiphysis. _c_ Calcaneum. _cb_ Os cuboideum. _h_ First, _h′_ second cartilage of supplemental toe. _m_ Ossa metacarpi. _n_ Os naviculare. _I_ to _V_ First to fifth toe. ]
3. This latter supports a cartilage which forms a projection on the inner border, covered with skin. This consists of closely-united pieces, a small round, basal piece (_h_), and a flattened beak-like piece (_h′_). Dugès considers these pieces as the first and second _ossa cuneiformia_; I rather incline to Meckel’s opinion that they represent a rudimentary hallux, the first being the _os metatarsi_, the second a _phalanx_. Both are composed of calcified cartilage; in _R. temporaria_ the lime-deposit seems to be less than in _R. oxyrhinus_ and _R. esculenta_, and the projection consequently softer[41].
[Footnote 41: In the text these two cartilages are termed the ‘supplemental toe.’]
*b.* The *metatarsal bones*, _ossa metatarsi_ (Fig. 47, _m_ _I_-_V_). The five _ossa metatarsi_ are long, thin tubular bones, the anterior articular extremities of which are broader above and narrow below, hence are wedge-shaped, and anteriorly present flat surfaces for articulation with the _tarsus_. The shafts are long and thin; the posterior extremities have rounded heads. The comparative length of these is as follows: the fourth is the longest, then come the third, fifth, second, and first in order. In structure they resemble other tubular bones.
*c.* The *phalanges*, _phalanges digitorum_ (Fig. 47). The total lengths of the separate toes correspond with that of the _ossa metatarsi_, but the distinctive differences are increased, partly by the difference in number and partly by the varying lengths of the phalanges. The first and second toes have each only two phalanges, the third and fifth have each three, the fourth, which is the longest, has four. The terminal phalanges are somewhat hooked towards the plantar surface.
Section II.
The Muscles.
The Muscles.
Literature.
Anonymous, Ueber das Schultergerüst der Schildkröten mit den daran sitzenden Muskeln. Isis, 1827. (Contains remarks on the shoulder-muscles of the frog.)
*Carus*, *C. G.* (1) Lehrbuch der vergleichenden Zootomie. 2nd Edit. Leipzig, 1834. (2) Erläuterungstafeln zur vergleichenden Anatomie. 1 Part. 1826. (Muscles of the Leg.)
*Chappuis*, Morphologische Stellung der kleinen hintern Kopfmuskeln. Zeit. f. Anat. u. Entwickl. 1876. Vol. II, pages 287–297.
*Cuvier*, Leçons d’anatomie comparée. Paris, 1835. Vols. I, II.
*Dugès*, Recherches anatomiques et physiologiques sur la déglutition dans les Reptiles. Ext. des Annales des Sciences naturelles. Paris, 1827.
*Dugès*, Leçons d’anatomie comparée. Paris, 1835.
*Duméril and Bibron*, Erpétologie générale ou Histoire complète des Reptiles. 1836.
*Führbringer*, Zur vergleichenden Anatomie d. Schultermuskeln. Jenaische Zeitschr. 1873. Vol. VII.
*Klein*, Beiträge zur Anatomie der ungeschwänzten Batrachier (Rana temporaria, L.): in Jahrshefte des Vereins für vaterländische Naturkunde in Würtemburg. 6 Jahrgang. 1850. Page 1.
*Kuhl*, Beiträge zur Zoologie der Rana esculenta: in Beitr. z. Zool. Frankfurt, a. M. 1820. Page 115.
*de Mann*, Vergelykende myologische en neurologische studien over Amphibien en Vogels. Acad. Proefschrift. 1873.
*de Mann*, Myologie comparée de l’extrémité post. chez les amphibiens. Niederl. arch. f. Zool. 1874. Vol. II.
*Marshall*, The Frog. London and Manchester. 2nd Edit. 1885. Pages 60–71.
*Martin St. Ange*, Annales des sciences naturelles. Vol. XXIV. 1831. Page 393.
*Meckel*, System der vergleichenden Anatomie. Halle, 1828. Vols. III and IV.
*Pfeiffer*, Zur Anatomie des Schultergürtels und der Schultermuskeln bei Säugethieren, Vögeln und Amphibien. Giessen, 1854.
*Rymer Jones*, Article ‘Reptiles’ in Todd’s Cyclop. of Anatomy and Physiology. 1847–1852. Vol. IV. Page 263.
*Stannius*, Handbuch der Anatomie der Wirbelthiere. Vol. II. Zootomie der Amphibien. Berlin, 1856.
*Wagner*, Icones Zootomicae. Leipzig, 1841.
*Wagner*, Lehrbuch der vergleichenden Anatomie. Leipzig, 1834–35.
*Zenker*, Batrachomyologia. Diss. Jena, 1825.
The Muscles.
I. Muscles Of The Head.
I. Muscles Of The Eye.
*1.* _M. rectus inferior_ (Fig. 48 _ri′_).
*Dugès*, post-orbito-sous-oculaire, n. 12.--*Zenker*, _depressor oculi_.
This muscle arises by a very thin, almost thread-like tendon from the parasphenoid, near the _foramen opticum_, and becomes rapidly broader; it lies beneath the tendon of the _membrana nictitans_ and a part of the _m. retractor bulbi_: then runs forwards and outwards to be attached into the lower part of the circumference of the eyeball.
[Illustration: Fig. 48.
Eye muscles of _Rana esculenta_, from below.
On the right side (_i. e._ in the left eye) the lev. bulbi (_l_) is taken away; on the left side it is still present.
_l_ M. levator bulbi. _l.a_ M. lev. anguli scapulae _oi_ M. obliquus inferior. _os_ M. obliquus superior. _p_ M. pterygoideus. _r_ M. retractor bulbi. _re_ M. rectus externus. 1 First cervical vertebra. ]
*2.* _M. rectus externus_ (Fig. 48 _re_).
*Dugès*, post-orbito-ex-oculaire, n. 14.
Arises by a thin, thread-like tendon from the parasphenoid near the _foramen opticum_, internal to and a little behind the _m. rectus inferior_: it then passes obliquely outwards over the _m. retractor bulbi_ and the tendon of the _membrana nictitans_, to be inserted into the outer and hinder part of the circumference of the eyeball.
*3.* _M. rectus internus_ (Fig. 48 _ri_).
*Dugès*, post-orbito-in-oculaire, n. 13.
A long, thin muscle, which arises by a thread-like tendon from the parasphenoid at the inner and hinder angle of the orbit, passes along its inner wall, and is inserted into the antero-internal part of the circumference of the eyeball.
*4.* _M. rectus superior_ (Fig. 49 _rs._).
*Dugès*, post-orbito-sous-oculaire.
Arises by a slender tendon from the fronto-parietal bone, widens rapidly, and runs forwards and outwards to be inserted into the upper part of the circumference of the _bulbus_.
[Illustration: Fig. 49.
Eye-muscles of _Rana esculenta_, from above.
_n_ Membrana nictitans. _n′_ Tendon of membrana nictitans. _p_ M. pterygoideus. _rs._ M. rectus superior. _t_ M. temporalis. ]
*5.* _M. obliquus inferior_ (Fig. 48 _oi_).
*Dugès*, pré-sous-orbito-oculaire.
This muscle arises near the floor of the orbital cavity, at the inner and anterior angle, from the palatine bone by a thin and long tendon, runs under Harder’s gland outwards and backwards, and is inserted, almost at a right angle with the axis of the eye, into the anterior part of the circumference of the eyeball.
*6.* _M. obliquus superior_ (Fig. 48 _os_).
*Dugès*, pré-sus-orbito-oculaire, n. 7.
The tendon of this small muscle arises from the inner end of the palatine bone, near the origin of the _m. obliquus inferior_, runs upwards, backwards, and outwards, and passes into a flat muscle, which rapidly becomes broader, and is inserted into the upper surface of the eyeball.
[Illustration: Fig. 50.
Eye-muscles of _Rana esculenta_, from below, the m. recti and obliqui have been removed.
_n′_ Tendon of membrana nictitans. _r_ M. retractor bulbi, lower part. _r′_ Second part of same. ]
*7.* _M. retractor bulbi_ (Figs. 48 _r_, 50 _r_, _r′_).
*Dugès*, orbito-post-oculaire or choanide, n. 10.--*Zenker*, _m. opticus_.
This muscle surrounds the optic nerve, and is situated within the cone formed by the four recti muscles; it consists of three portions, which take their broad and fleshy (the _recti_ and _obliqui_ arise by thin tendons) origins from the under surface of the parasphenoid. The first portion (Fig. 50 _r_) arises from the under surface of the parasphenoid, nearly as far as the middle line, is broad and fleshy, and covers, from below, the tendon of the _rectus externus_, then runs forwards and outwards. The second portion (_r_′), which lies over this and the tendon of the _m. rectus externus_, has also a broad and fleshy origin, but runs more directly forwards, slightly crossing the preceding. The third portion arises above the two others by a strong thin tendon from the parasphenoid: it runs almost in the direction of the _m. rectus internus_, but more directly forwards. The first two portions pass more to the upper surface of the eyeball, the third more to the under surface; consequently the whole muscle forms a sheath surrounding the eyeball. The fibres to the upper surface of the eyeball are inserted somewhat in front of the equator of the eyeball, those to the under surface somewhat behind it.
*8.* _M. levator bulbi_, Dugès (Figs. 48 _l_, 51 _l_, 52 _l_).
*Dugès*, fronto-pterygoidien, n. 9.--*Klein*, _sustentator bulbi_.
[Illustration: Fig. 51.
Transverse section through the sk
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