THE TEETH OF REPTILES 97 



mostly upon land. They have four limbs, except 

 one large order, — the Ophidia, or Snakes, which 

 are without limbs. 



The teeth in the class Reptilia are not so numer- 

 ous nor so widely distributed as in the class 

 Fishes. They are confined to the borders of the 

 jaws, except in some of the Batrachians which 

 resemble the Fishes in having the dentary bone 

 and vomer carrying teeth also. Reptiles usually 

 have an endless succession of teeth, which are 

 replaced or shed as in the Fishes, and which are 

 composed of hard dentin with a thin layer of 

 enamel in some species. One entire order, Che- 

 Ionia (Turtles), are without teeth, but have horny 

 sheaths for the jaws instead, like the beaks of 

 birds. The beaks of turtles differ according to 

 the food habits of the species. The teeth of Rep- 

 tiles, like those of Fishes, are employed for pre- 

 hension and for holding struggling prey, for mas- 

 tication is not performed to any extent in this 

 class. 



In the Batrachians, the teeth, when present, are 

 disposed in rows upon the borders of the jaws 

 and the two vomers above, between which the 

 mandibular row closes. Some types, as the Siren, 

 have the jaws ensheathed with horny beaks. In 

 the larval stage the Frog (the "tadpole") also 

 has the jaws covered by horny sheaths, which are 

 lost at the time of the metamorphosis when the 



