SKELETON A1S"D LARTlSrX OF XENOPUS AND PIP A. 53 



On the Structure and Development of the Hyobrancliial Skeleton 

 and Larynx in Xenopus and Pipa ; with Remarks on the 

 Affinities of the Aglossa. By W Gr. Sidewood, B.Sc, 

 r.L.S., Lecturer on Biology at St. JVj. ry's H^.c^'iLal Medical 

 School, London. 



[Read 19th November, 1896.] 

 (Plates 8-11.) 



Contents. Page 



Introduction 63 



Hyobranchial Skeleton oi Xenopus Icevis, female 56 



Laryngeal Skeleton of Xenofus Imvis. 



Female 60 



Male 64 



Hyobrancliial Skeleton of Tipa americana, female 67 



Laryngeal Skeleton of Vipa americana. 



Female 69 



Male 71 



Laryngeal Muscles of Xenopus lavis. 



Female 77 



Male 83 



Laryngeal Muscles of Pipa americana. 



Female 85 



Male 89 



. Development of the Hyobranchial and Laryngeal Skeleton. 91 



Xenopus Imois 93 



Pipa americana 102 



General Conclusions, and Discussion of the AfBnities of 



the Aglossa Ill 



List of Authorities referred to 122 



Explanation of the Plates 126 



Inteoduction. 

 CoNSiDEEABLE interest has for many years centred around 

 the little suborder of the Anura Aglossa and the question of the 

 affinities of the two sole genera, infer se, and with other Anura. 

 JPipa and Xenopus, so remote from one another geographically 

 and so essentially different in general configuration, size, denti- 

 tion, spawning-habits, and many peculiarities of internal struc- 

 ture, yet exhibit numerous anatomical resemblances which appear 

 to point conclusively to a common ancestry. Standing out pro- 

 minently from among the latter characteristics is the remarkable 

 complexity of the larynx and the extraordinary sexual dimorphism 

 which it exhibits. It is with this organ that the present paper 

 essentially deals. It both I'lpa and Xenopus the relation of the 

 larynx to the hyobranchial skeleton is so intimate, that a minute 



