THE SKELETON OF REPTILES 



27 



to the surface of the bone (acrodont). And they are usually 

 reproduced indefinitely by new teeth growing at the side of the 

 base or below them. More usually they _ _ . 



are pointed and curved; sometimes they 

 are flattened, with sharp cutting edges 

 in front and behind in the more strictly 

 carnivorous reptiles; in those of her- 

 bivorous habits they are more dilated 

 and roughened on the crown, not 

 pointed; in not a few they are low, 

 broad, and flat and are used only for 

 crushing the hard shells of invertebrates. 

 With the very few exceptions among 

 certain dinosaurs, they never have more 

 than one root for attachment. The 

 evolutional tendency for reptiles, as for 

 the mammals, is to loose teeth, especially 

 those of the palate. Among living rep- 

 tiles it is only the most primitive types, 

 such as the lizards, snakes, and the 

 tuatera, which have teeth on the palatal 

 bones, and in none are there teeth on 

 the vomers, as was the rule in the ancient 

 reptiles. The lizards may have them on 

 pterygoids and palatines, and the tuatera 

 has them on the palatines only. There 

 may be as many as eighty on each 

 jaw, above and below, and hundreds of 

 smaller ones on the palate, or they may 

 be reduced in number to five or six, or 

 even to a single one; some reptiles, like 

 the turtles and later pterodactyls, have 

 none. The teeth of reptiles are com- 

 posed of the same kinds of tissues as 

 are the teeth of mammals, that is, of 



dentine and enamel, but the enamel is always thin, perhaps because 

 the teeth are so easily replaced that a thicker protective covering 



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