The Rhynchocephala

This division contains only the very remarkable genus Sphenodon (otherwise Hatteria, or Rhynchocephalus). The vertebrae are biconcave. Some of the ribs have recurrent "uncinate" processes, as in Birds and Crocodiles. The sternal and vertebral ribs are connected by an articulation, and there is a very peculiar system of abdominal ribs. The infra-temporal arcade is completely osseous in this, but in no other recent, lizard. The quadrate bone is immovably fixed, not merely by anchylosis with the squamosal, quadrato-jugal, and pterygoid, but by the ossification of the strong membrane, which, in Lizards in general, extends between the quadrate, the pterygoid, and the skull, and bounds the front walls of the tympanum. The dentary pieces of the mandible are not suturally united. The premaxillae are not anchylosed together, and, as in some other Lizards (e. g., Uromastix), have a beak-like form, the large premaxillary teeth becoming completely fused with the bony substance of the premaxillae. 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 longitudinal 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 Triassic age, Rhynchosaurus and Hyperodapedon, appear to have been very closely allied to Sphenodon.