456 DE. W. G. EIDEWOOD Olf THE EYOBEANCHIAL 



note that it is not homologous with the median cartilage which 

 is lodged between the two hyoidean cornua in the larval Xenopus 

 (4. pi. 11. figs. 1 and 2, bh) ; for the latter, by coalescence with 

 surrounding parts, develops into a plate of cartilage which is 

 behind the hyoglossal foramen. The median bone of Hytneno- 

 cMrus would correspond ratlier with the anterior of the two 

 cartilages which occupy the median line in the hyobranchial 

 skeleton of the larval Alytes (see 6. figs. 1 and 2, cd). It Is 

 possible that this anterior copula of the Discoglossid larva may 

 later prove to be the true basihyal element; but, for reasons 

 already stated (5. p. 5S3), it is preferable, for the present, to 

 apply the term basihyal to the posterior copula, or to avoid the 

 use of the word altogether, until further research has satis- 

 factorily demonstrated the homologies of the constituent parts 

 of the hyoid apparatus of the Anura. 



The hyoidean skeleton is completed in front by two plates of 

 cartilage, each exhibiting a small area of calcification {pa). These 

 plates are doubtless the equivalents of the processus anteriores of 

 the common Frog (see 5. fig. 11, pa), and represent also the thin 

 lamellae of cartilage which project from the anterior edges of the 

 hyoidean cornua in Xenopus (see 4. pi. 8. fig. 1). 



The front part of the hyobranchial skeleton is quite detached 

 from the hinder part, and the relative positions of the two parts 

 to one another and to the mandible and larynx are preserved in 

 fig. 1, Plate 31. The front part undoubtedly belongs to the 

 hyoidean arch exclusively, but it is possible that in the hinder 

 part there is also some cartilage of hyoidean origin. This pro- 

 position is based upon the fact that in Xenopus and Fipa 

 the hyoglossal foramen is formed by the coalescence of the 

 right and left hyoidean cornua in front of the hyoglossal sinus (4). 

 The hyoglossal foramen of SymenocJiirus (figs. 1 and 3, h) is 

 small in size, but its identity is unmistakable, since it transmits 

 a reduced hyoglossal muscle, running from the ventral surface 

 of the larynx to the pharyngeal mucous membrane in front of 

 the glottis. The tract of cartilage which lies anteriorly to this 

 foramen {cTi') may, therefore, be considered as a hyoid derivative. 

 It corresponds with the pointed rod of cartilage which in Pipa 

 projects in front of the hyoglossal foramen (4. pi. 9. fig. 1, ch'). 



In the presence of hyoidean cornua Symenochirus diff"ers from 

 Pipa and resembles Xenopus. In fact, one may say that no. 

 portion of the front half of the hyobranchial skeleton of Hymeno- 



