TEETH 93 



jaw-bone and are renewed by one pushing out the 

 hollowed and partially absorbed tip of the other ; 

 but thev have many sets, and the new teeth below 

 the ij:ums are said to be "nested" into each other as 



Fig. 50. — Eliynchosaurs-Hyperodapedon ; Trias (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 Iguana^ and some are flat and merely crushing or 

 grinding — according to food. J^early all lizards re- 

 new their teeth bv havino: the new one form directly 

 beneath the old; but in the AnguidcB (slow worm) 

 the new s^row between tlie old. 



The teeth of serpents are usually recurved, sharp 

 conical points. 



The erectile poison- fangs mentioned are always 

 found witli other smaller ones (to the num])er of three 

 or four) concealed beneath the flesh behind them, 

 which are thus ready to rise up and take the place 



