36 INTRODUCTION. 



The squamosal is a hammer-shaped bone, the anterior 

 branch of which may be much reduced, as in Bafo, 

 long and free, as in Bana, or join the maxillary, as in 

 Discoglossus and Pelobates. 



The vomers vary much in size according to the 

 genera ; they are largest in Discoglossus, where their 

 posterior toothed border covers over the palatines. 

 The latter bones, if present, are narrow and transverse, 

 and extend across the whole palate ; in Bufo their 

 lower surface forms a cutting, sometimes serrated edge, 

 which makes up for the absence of vomerine teeth. 

 The pterygoids are trifurcate, and the anterior branch 

 may or may not reach the palatines, or may be much 

 produced forwards when the latter bones are absent, 

 as in Bombinator. The parasphenoid is a large bone 

 shaped like a T, or like a dagger with very short 

 handle. 



Most genera have a cartilaginous tympanic ring 

 applied to the outer surface of the hammer-shaped 

 squamosal, in the upper portion of which ends the 

 slender, ossified, stapedial rod (columella auris). 

 The tympanum is absent in Pelobates, and both the 

 tympanum and the stapedial rod in Bombinator, 

 which in this respect again resembles the tailed 

 Batrachians. 



In Discoglossus three bones invest the Meckelian 

 cartilage which forms the ramus of the mandible : the 

 dentary in front, the angular or angulo-splenial behind, 

 and extending more to the front on the inner side, 

 and a small bone which articulates with the quadrate, 

 the articular. In Bana the articular remains cartila- 

 ginous, but the symphysial cartilages ossify, forming 

 the so-called mento-Meckelian or symphysial bones, 

 which in adult specimens fuse on the upper side 

 with the dentary (Fig. 14). These symphysial bones 

 are less distinct in Hyla and Bufo, less still or even 

 almost indistinguishable in the Pelobatidse and Disco- 

 glossidse. 



The hyoid varies very considerably in the different 



