260 NATURAL THEOLOGY. 



more satisfactory than the statement, p. 213. Two 

 objects are here attained : — first, that the cutting 

 teeth are preserved sharp ; and, in the second 

 place, these teeth differ in their condition from 

 ours, since they do not rise in consequence of 

 wanting opponents. 



The figure represents the skull of the Beaver, to show the nature 

 of their cutting teeth. 



In the class of rodentia or gnawers, the front 

 teeth must cut with a sharp edge. We know 

 how this is contrived in the tool of the carpenter ; 

 and we know also that he must from time to time 

 apply his chisel to the grindstone. The front 

 teeth of the beaver, the porcupine, and the rat, 



are sharp and yet not blunted by use ; the bone 

 of the teeth is the densest possible, consistent with 

 the material : but were the w hole tooth of the 

 same material, it would be ground dow n uniform- 

 ly, and the original form of the instrument would 

 be lost. Accordingly, a different substance, the 

 enamel, which yields more slowly to attrition than 

 the bone of the tooth, is, as it were, let in on the 



