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

141a. Small group of nerve-cells from the auricular septum 221

141b. 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.’ 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.

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 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, the phenomena of cleavage, and many others.

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 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, 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.’

Leeuwenhoek also correctly distinguished between them, but it is to Rösel that we are chiefly indebted for a careful discrimination and an accurate knowledge of the life-histories of the two species.

The green water-frog, Rana esculenta L.]

*Rana esculenta*, L. The green water-frog, Fig. 1, usually attains a larger size 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.

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 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, as has been established in the case of fish by direct observation. Apparent varieties may this occur.

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 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 also describes two varieties in Northern Italy.

*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 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, 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, and also Schiff 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.

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. 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; and, the whole ground colour being bright at this period, very beautiful tints result. V. Siebold 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.

Thomas, in addition, distinguishes another species, R. agilis, which however may be the ‘grenouille rousse’ of Millet. Schlotthauber 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 mentions this, and I have myself often found males of R. temporaria in conjunction with females of R. esculenta.

* * * * *

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.