THE TEETH OF REPTILES 103 



jaws, and also large canine-like tusks projecting 

 downward from the upper jaw which grow from 

 persistent pulps, — a very rare thing in the Eep- 

 tiles. 



The extinct lizards were remarkable animals. 

 The Plesiosaurus was a form of lizard with long 

 neck and small head, and the limbs modified into 

 paddles for swimming. They varied much in 

 size, some being very small. The teeth were 

 sharp-pointed, recurved, and the external surface 

 of the crown striated. Each tooth was lodged in 

 a distinct socket. Some were of triangular shape 

 on section, with two cusps, and sometimes rounded 

 off. The Ichthyosaurus is an extinct lizard of 

 gigantic size, with paddle-like limbs, and was re- 

 markable for the extraordinary enlargement of 

 the eyeballs, which had ossified sclerotics. It had 

 long, narrow, flattened teeth, formed of folded 

 plates of enamel. The Iguanodon had remark- 

 able teeth. Some were flat and spread out like 

 a fan with serrated edges, — the base constricted 

 and composed of folded laminae of dentin and ce- 

 mentum, similar to the teeth of the Labyrintho- 

 dont. The Pteryodactyls were flying lizards with 

 wings like a bat, which in large species reached 

 the width of twenty-five feet. Most species were 

 quite small, however. The jaws were armed with 

 long, slender teeth for their whole length. The 

 Mososaurs were marine lizards of great size, with 



