THE TEETH OF REPTILES. 241 



outside them. The Labyrinthodon was possessed also of 

 palatine teeth. 



The teeth were anchylosed to slight depressions or sockets, 

 and the successional teeth were probably developed, as in 

 the frog, at the inner side of the bases of the teeth already in 

 position, as there are no indications of crypts within the bone. 



In many reptiles teeth are developed for the merely tem- 

 porary end of effecting an exit from the egg-shell. This 

 purpose is sufficiently answered by the hard snout of the 

 crocodiles, and by a sort of snout developed in Ckelonia, but 

 snakes and lizards have sharp teeth, which afterwards are 

 lost, developed on the preinaxillary bones (Owen). 



The CHELONIA, comprising the Tortoises and Turtles, have 

 no teeth, but the margins of the jaws are sheathed in horny 

 cases, which are variously shaped in accordance with the 

 habit of the animal, being sharp and thin edged in carnivor- 

 ous, and blunt and rugged in herbivorous species. 



SAURIAN reptiles (lizards, &c.), have, as a rule, rather 

 simple teeth, which are confined to the margin of the jaws, 

 the occurrence of palatal teeth being less usual. The 

 teeth are of various forms, being blunt and rounded in many 

 genera, whilst in others they are long and pointed. They 

 are generally made up of a central body of hard dentine, 

 more or less completely invested by a cap of enamel ; and 

 they are attached to the bone by anchylosis. 



When the tooth is anchylosed by its outer side to an 

 external parapet of bone, the creature is said to be " pleu- 

 rodont," when by the end of its base it is attached to the 

 summit of a parapet it is " acrodont." 



The succession of teeth in the Lizards is constant, new 

 teeth being developed at the inner side of the bases of the 

 old teeth, which become undermined by absorption and fall 

 off when the successional tooth has attained to a certain 

 stage in its development. 



The accompanying figure of the lower jaw of a Monitor 



B 



