118 ME. W. a. EIDEWOOD ON THE HTOBEANCHIAL 



" large size and attachment of the Sartorius, the single-headed: 

 Semitendinosiis, the great extent o£ the Pectoral, which com- 

 pletely covers the Sternoradialis, and the large size of the 

 Glutoeusy It would be of great interest to see whether any of 

 these nine peculiarities occur in Discoglossidse and Pelobatidse. 

 The extent of development and the almost identical form of the 

 " diaphragm," and the extension of the abdominal muscles on to 

 the thigh in both Xenopus and Pipa, Eeddard points out (2, 

 p. 849), may possibly have arisen independently, in relation with 

 the assumption of a purely aquatic habit, but he inclines to the- 

 belief that they are marks of real affinity. It is strange how 

 very many of the structural peculiarities which would appear to 

 point to a natural relationship between Xenopus and Pipa are 

 more or less explicable as physiological adaptations. 



Besides the families Xenopodidse and Pipidae, Cope (6. p. 99 

 and 7. p. 253) includes in the Aglossa a third family, the Palgeo- 

 batrachidae, represented by extinct forms only. The special 

 interest of the third family in this connexion lies in the fact 

 that "Wolterstorff (who gives, 43. pp. 3-12, a most useful list of 

 references to papers dealing with Palcjeohatrachus), regards the- 

 question of afiinity as turning largely upon the relations of the 

 thyrohyals to the other skeletal parts : — " Ob eine Zunge 

 vorhanden war, weiss man noch nicht. Dies, also die Trennung 

 von den Aglossa, miisste durch Auifindung von Zungenbein- 

 hornen bewiesen werden " (43. Theil i. p. 45). Wolterstorff,. 

 although admitting many points of affinity with the Aglossa^ 

 ap[)ears rather inclined to accept Boulenger's view (43. Th. ii. 

 p. 75 (155)), that Palccolatrachus is most nearly allied to the- 

 Pelobatidaj among living Anura, and to the genus Bafrachopsis 

 in particular. Did the genus possess an ossified laryngeal 

 sl<eleton intimately associated with the thyrohyals, the evidence 

 of afiinity with the Aglossa would be incontestable, for there is 

 nothing approaching such a condition in any other Anura. On 

 the other hand, should the hyoid apparatus prove to be free, the- 

 affinity would in no wise be disproved. A minute examination 

 of the specimens of Palaolatrachus at the Natural History 

 Museum, which by the kindness of Dr. H. "Woodward, P.E.S.^ 

 I was allowed to make, failed to disclose any trace of the thyro- 

 hyals or the laryngeal skeleton. 



In Pipa and Xenopus the third, fourth, and fifth digits of the 

 hind limb are nearly equal in length, and in Pipa the third is if 



