SKELETON ATS"D LABTKX OP XEISTOPUS AND PIPA. 117 



'primitive condition. Similar expansions of the anterior cornua 

 are to be seen in JBomhinator and Discoglossus. The absence of 

 the anterior cornua ia Pi'pa indicates a high degree of specializa- 

 tion, which finds its nearest parallel in Pelohates * and Felodytes. 

 In the adults of these genera we have a retention of the condition 

 seen in Stage Y. in tbe development oiPipa. The greater part of 

 the cornua are missing, but the more posterior parts have not 

 shared in the absorption. These remnants are flat and broad in 

 front, but are rod-like behind, where they rise up behind the 

 auditory capsule and become attached to the skull. 



The laryngeal muscular anatomy, more especially the excep- 

 tional relations of the hyoglossus and petrohyoideus of Pipa and 

 Xenopus, would seem to indicate a close afiinity between the two 

 genera ; but, on the other hand, it must not be lost sight of that 

 these relations are correlated with skeletal resemblances, and 

 care must be exercised not to weigh the same evidence twice 

 over. The absence in Pipa of the geniohyoideus internus, the 

 posterior position of the origin of the byoglossus, and the 

 insertion of the laryngeal division of the obliquus internus into 

 the roof of the larynx instead of the extremity of the thyrohyal, 

 are differences of no slight importance, and differences, more- 

 over, which are not connected with skeletal dissimilarity. The 

 relations of the hyoglossus to the floor of the mouth prove, I 

 think, most conclusively that both Pipa and Xenopus are de- 

 scended from tongued forms. Both Mivart (29. p. 283) and 

 Cope (7. p. 247) have regarded the absence of tongue as 

 secondary, and the union of the eustachian tubes in the middle 

 line as evidence of a higher development. The breadth of the 

 pterygoid bones is evidently related to this second feature. 



"With regard to the general muscular anatomy, Beddard (2. 

 pp. 84S and 849) has shown that Xenopus differs from Bana and 

 sresembles Pipa in the " enormous extension backwards of the 

 Latissimus dorsi, the absence of the Pectoro-cutaneus, the attach- 

 ment of the muscles covering the abdomen to the fascia covering 

 the thigh, the presence of a sheet of muscle below the Mylo- 

 Jiyoid which joins the Deltoid, and the existence of a special 

 muscle running from the ilium to the lung and oesophagus." On 

 ^he other hand, Xenopus differs from both Rana and Pipa in the 



* Parker (34- PL 25. fig. 9) shows the hyoid cornua of Felobates as 

 4X)mplete, but this is a mistake. 



