TEETH 93 



jaw-bone and are renewed by one pushing out the 

 hollowed and partially absorbed tip of the other; 

 but they have many sets, and the new teeth below 

 the gums are said to be " nested " into ea(^h other as 



Fig. 50. — Bhynchosaurs-Hyperodapedou ; Triaa (after Huxley). 



are thimbles. As a rule, modern lizards have their 

 teeth grown down to or up from the jaw-bone, though 

 they are not set in it, but are fast to it. In the 

 Tuatera there are two front peculiar teeth which are 

 a little like those of rodents (rats, rabbits), but which 

 fuse together and form almost a beak above. 



In lizards some teeth are conical, some serrate, as 

 in Igucma^ and some are flat and merely crushing or 

 grinding — according to food. Nearly all lizards re- 

 new their teeth by having the new one form directly 

 beneath the old ; but. in the Anguidoe (slow worm) 

 the new grow between the old. 



The teeth of serpents are usually recurved, sharp 

 conical points. 



The erectile poison-fangs mentioned are always 

 found with other smaller ones (to the number of three 

 or four) concealed beneath the flesh behind them, 

 which are thus ready to rise up and take the place 



