204 REPTILIA. 



complete ; both have similarly-formed lower jaws ; in each 

 a single row of teeth in the mandible bites between two 

 rows of teeth fixed to a plate, which is formed by a union of 

 the maxilla with the palatine bone — a structure which is 

 quite anomalous amongst Lacertilians ; and finally, in both, 

 these teeth wear down to the bone of the jaw Ijy masticatory 

 attrition." 



From its relations with the Triassic Hyper odapedon, as well 

 as on account of its own peculiarities, the living Splunodon 

 possesses a special interest for the paleontologist. In this 

 extraordinary form — the sole remaining representative of the 

 Lacertilian family of the Bhynchoccphcdia — the vertebrae are 

 amphicoelous, and some of the ribs bear " uncinate processes " 

 similar to those of Birds. The quadrate bone is not mov- 

 aljle, and is united by suture with the skull. The teeth are 

 completely amalgamated by anchylosis with the jaws, and 

 are developed in the mandible, j)r8emaxillse, and in a longi- 

 tudinal series upon the palatine bones. The pra^maxillary 

 teeth are two in number, and are of large size and scalpri- 

 form in shape (fig. 554). The serrated edge of the mandible 

 is received in the groove between the palatine teeth and the 

 cutting edges of the maxillae, the alveolar borders of which 

 are hard and as highly polished as the teeth themselves, the 

 function of which they discharge when the latter are ground 

 down in advanced age. 



The genus Rhyncliosaurus is in a doubtful position, but 

 may also conveniently be considered here. By Huxley its 



affinities are regarded as being 

 Lacertilian, but by Owen it is 

 looked upon as belonging to the 

 Anomodontia, and as being most 

 nearly allied to Oudenodon. In 

 many points Bhynchoscmrus ap- 

 ""'" 1,. ^^tLo^;uo' Trias?"''" Peaches the existing Lizards, 



but its vertebrae are amphicce- 

 lous, and the structure of the mouth is quite unlike that of 

 any living Lacertilian. The skull (fig. 555) is pyramidal, 

 and the jaws do not exhibit any traces of teeth. If the 

 mouth be really edentulous, then lUiyncJwsaurus should prob- 



