1907.] ANATOMY OF THE PELOBATID.E. 889 



compared with Xenopliry^ monticola some difterences are seen. 

 The inner side of the thigh of the latter species is represented in 

 the accompanying figure (text-fig. 235) and there is no doubt 

 about the identification of the three adductors, the two recti 

 interni and the vastus internus. This leaves for identification 

 the two muscles which I have lettered " i" and "e./." The two 

 heads of origin are plainly seen in the case of the latter muscle, 

 while the insertion only of " ^ " is visible. The latter muscle 

 seems to be without doubt the semimembranosus, which in the 

 case of Rana does not appear upon the inside of the thigh at all 

 but is quite restricted to the dorsal aspect. It is not without 

 interest to note that in this appearance of the semimembranosus 

 upon the inner surface of tlae thigh, Xenophrys agrees with 

 Pipa* but not with the Aglossan Xeno2nis'X. There i*emains 

 now the muscle "e./." This has two heads of origin, of which the 

 posterior is much the smaller and soon joins the anterior head. 

 The supei'ficial position of the muscle and the fact that it is 

 inserted onto the knee superficially to {i. e. ventrally to) the in- 

 sertion of the recti interni, would seem to argue the identity of 

 this muscle with the sartorius of Rana, from which it would in 

 that case only difi'er by its two heads and its more posterior 

 origin, and consequently difierent position in i-elation to the 

 other muscles of the thigh. On the other hand, the two muscles 

 end in a well-marked and longish strap- shaped tendon and are 

 totally indistinguishable for some distance in front of their 

 tendinous ending, which would fit in well with the view that we 

 have here, as in Rana, a double-headed semitendinosus with a 

 slightly difierent origin and insertion from that muscle in Rana. 

 An obvious third view is to regard the two-headed muscle as 

 actually composed of two muscles which are in course of fusion or 

 of separation, and to compare them with both the sartoiius and 

 the semitendinosus of Rana. A consideration of the arrange- 

 ment of these muscles within the family Pelobatida3 ofiers no 

 clue to the determination of the homologies. For the genera 

 which I have dissected agree with Xenophrys. 



I have already described the muscles in question in Megaloplirys 

 na&utaX, where they are practically the same as in Xenophrys 

 except for the additional and slight complication caused by the 

 presence of an additional head to the posterior of the two muscles. 

 Megalophrys montana is like Xenophrys, and Lep)tobrachiuin 

 hasseltii only difiers very slightly, this difference consisting in 

 a somewhat earlier fusion between the two muscles, Avhose 

 homologies are under consideration. In Pelohates the differenti- 

 ation of the two was even slighter. If, however, we consider the 

 thigh-muscles in the Aglossa, it is possible, as I think, to arrive 

 at a reasonable conclusion concerning these muscles in the Pelo- 

 batidse. In Pipa § the same two muscles that are present in the 



* P. Z. S. 1895, p. 838, f5g. 4. f IhUL p. 844. fis;. 3. 



X p. Z. S. 1907, p. 343. 



§ P. Z. S. 1895, p. 838, woodcut, fig. 4, 3, 4. 



