SKELETON. 



35 



The membrane bones, all paired with the excep- 

 tion of the parasphenoid (and in Pelobates the fronto- 

 parietal), are the following : — Prsemaxillary, maxillary, 

 squamosal, pterygoid, palatine, vomer, parasphenoid, 

 nasal (often called prae frontal), and fronto-parietal. 

 A small ossification behind the narial opening is the 

 turbinal, regarded by some as the true nasal. The 

 cranial ossification may be feeble, and a considerable 

 portion of the cartilaginous primordial cranium remain 

 exposed, — as, for instance, in Bombinator, which, 

 together with Pelodytes, is remarkable for the lack of 

 palatine bones ; or it may be extraordinarily developed, 

 with superaddition of dermo-ossification, as in Pelo- 

 bates, one species of which (P. cultripes) is distin- 

 guished by the expansion of the fronto-parietal and 



Fig. 13. 



Upper view of skull of Pelobates cultripes. 



squamosal, which join to form a complete roof over 

 the prootic (Fig. 13). The genus Pelobates is further 

 remarkable in having the fronto-parietal single, 

 whilst in all other European genera it is paired, 

 and in many species so separated along a portion 

 of the median line as to leave the endocranial or 

 fronto-parietal fontanelle exposed between the two. 

 The nasals may join in the middle line, or be more or 

 less widely separated from each other. The upper 

 lamina of the ethmoid is usually exposed between the 

 fronto-parietals and the nasals, and in Pelobates fuscus 

 it is so prolonged forwards as to reappear between 

 the nasals and the praBmaxillaries. 



