SKELETON AND LABTNX OF HTMENOCHIRUS BOETTGERI. 459 



wLieh has been regarded above as tlie united anterior epiphyses 

 of the thyrohyals. The actual roof, i. e. the part of the cricoid 

 behind the arytenoids, is saddle-shaped, and differs from that 

 of the female in beinj^ longer, than broad, and in the greater 

 thickness of its cartilage. The arytenoids are completely ossified, 

 no cartilage reiiiaining ; and the glottis appears in the prepared 

 skeleton as a rectangular hole. The sides of the glottis are 

 formed by thick folds of mucous membrance occupying the 

 right and left halves of this rectangle. The arytenoids are 

 not confluent with one another as they are in the male Xenopus, 

 nor are they backwardly produced into the interior of the larynx 

 as in the male Pipa. 



The larynx of both sexes is thus of simpler construction tha.n 

 those of the two sexes of Pipa and JLenopus ; but in its hyo- 

 branchial skeleton Hymenochirus exhibits a most conflicting set 

 of features. It is quite impossible to conclude, from evidence 

 derived from this source, whether Hymenochirus is more 

 primitive than the two previously known aglossal toads, or with 

 which of these forms it is the more closely allied. Inconclusive, 

 however, as the results are for this purpose, they constitute a 

 strong argument in support of the view that the Aglossa are a 

 natural group, and that the three genera now composing it have 

 had a common ancestry. The discovery of Hymenochirus binds 

 Pipa and Xenopus more closely together than before. 



Papers quoted. 



1. BouLENGER, Gr. A. — " A new Genus of Aglossal Batrachians." 



Ann. & Mag. Nat. Hist. [6] xviii. 1896, p. 420. 



2. BoFLENQBR, G". A. — " Ou Hymenochirus, a new Type of 



Aglossal Batrachians." Ann. & Mag. Nat. Hist. [7j iv. 

 1899, pp. 122-125, 



3. HE]srLE,D. J. — Beschreibung des Kehlkopfs. Leipzig, 18.39. 



4. EiDEwooD, W. G. — " On the Structure and Development of 



the Hyobranchial Skeleton and Larynx in Xenopus and 

 PipaJ" Linn. Soc. Journ., Zool. xxvi. 1897, pp. 53-128. 



5. EiDEWooD, W. G. — '' Ou the Structure and Development of 



the Hyobranchial Skeleton of the Parsley-Frog {Pelodytes 

 punctatus):' Proc. Zool. Soc. 1897, pp. 577-595. 



6. EiDEWOOD, W. G. — " On the Development of the Hyo- 



branchial Skeleton of the Midwife-Toad {Alytes obstetri- 

 cans)" Proc. Zool. Soc. 1898, pp. 4-12. 



7. ToRNiER, G. — Kriechthiere Deutsch-Ost-Afrikas. Berlin, 



1897 (1896). 



