SKELETON AXD L\RTNX OF HTTMENOCmEUS BOETTOERT. 455 



The presence of a hyoglossal foramen, transmitting the reduced 

 hyoglossal muscle, and origiuatiug by a secondary union of 

 the hyoidean cornua. 



The presence of a pair of large backwardly directed carti- 

 laginous wings, developed from the branchial skeleton of 

 the larva. 



The large size and complexity of the larynx, and the incor- 

 poration of the thyrohyal bones into the laryngeal apparatus. 



The absence of vocal cords- 

 It is a singular fact that all these five characters are exhibited 

 by Symenocliirus. 



It does not follow, however, that the hyobranchial skeleton of 

 SymenoGhirus bears, on the whole, any close resemblance either 

 to that of Xenopus or that of Pipa. In certain features the 

 hyobranchial skeleton of Rymenochirus is unique. The hyoidean 

 cornua, for instance, are very large and strongly ossified. Ossi- 

 fication of the hyoidean cornua, though not uncommon in the 

 Urodela, has hitherto been unknown to occur in the Anura. That 

 Boulenger (3), describing a dried skeleton in which the larynx 

 had not been preserved, should have mistaken these bones of 

 SymenocMrus fur the thyrohyals is thus quite excusable, seeing 

 thiit in all other forms of Anura the only strongly ossified parts 

 of the hyobranchial skeleton are the thyrohyals. 



The hyoid bones (PI. 31. fig. 1, eh) are thinnest at about one- 

 third of their length from the posterior end, and are flattened in 

 the horizontal plane anteriorly. The hinder part slopes outward 

 and upward ; and the swollen extremity, which is not tipped 

 with cartilage, is bound by a short, strong ligament to the 

 inferior surface of the large otic capsule. Projecting hori- 

 zontally from the mesial surface of each bone is a thin lamella of 

 cartilage, with a convex free border, which is evidently the 

 counterpart of the similarly placed lamella of the unossified 

 hyoidean cornua of Xenopus (see 4. pi. 8. fig. 1). Anteriorly the 

 flattened hyoid bones terminate in epiphysial plates which are 

 cartilaginous in the female, but exhibit an irregular endochondral 

 ossification in the male. 



Lying antero-internally to these latter is a median element, 

 strongly ossified in both sexes, which is unique among adult 

 Anura (fig. 1, ca). It is roughly pentagonal in shape, and from 

 its relations to the surrounding parts might be regarded as the 

 equivalent of the basihyal of Pishes. It is most important to 



35* 



