22b THE ANATOMY OF VEETEBEATED ANIMALS. 



goid, and the skull, and bounds the front walls of the 

 tympanum. The dentary pieces of the mandible are not 

 suturally united. The premaxillse are not ankylosed to- 

 gether, and, as in some other Lizards (e. g. Uromastix), have 

 a beak-like form, the large premaxiUary teeth becoming 

 completely fused with the bony substance of the pre- 

 maxillse. There is a longitudinal series of teeth upon the 

 palatine bone running parallel with those on the maxilla, 

 and the mandibular teeth are received into the deep longi- 

 tudinal groove which lies between the maxillary and the 

 palatine teeth. By mutual attrition, the three series of 

 teeth wear one another down to the bone in such a way, 

 that the mandibular teeth are ground to an edge, while the 

 maxillary and palatine teeth are worn upon their inner and 

 outer faces respectively. 



The extinct Lizards of the Ti-iassic age, Bhynchosaurus 

 and Hijperodapedon, appear to have been very closely allied 

 to Sphenodon. 



3. The Homososauria. — The remains of Lizards of small size, 

 and agreeing in the most important points of their osteology 

 with the ordinary LacerUlia, but having amphiccelous ver- 

 tebrae, have been found in the older Mesozoic rocks, from 

 the Solenhofen slates to the Trias inclusively. They cannot 

 be identified with either the BhyncJwcephala, or the Ascala- 

 bota, and may be provisionally grouped as Homoeosaiiria. 

 The genera Homoeosaurus, Saphoeosaurus, and Telerpeton 

 belong to this group. 



4. The Protorosauria. — These are the oldest known Sau- 

 ropsida, their remains occun-ing in the Kupferschiefer of 

 Thuringia, which is a part of the Permian formation, and 

 in rocks of corresponding age in this country ; but no more 

 modern representatives of this group are known. 



The Thuringian Lizard [Protorosaurus] does not appear to 

 have attained a length of more than six or seven feet. 

 The neck is remarkably long, the cervical region being 

 equal to the dorsal in length, and it bears a skull of mode- 



