GENERATION OF ANIMALS, V. vin. 



working contrary to Nature " (because he says that 

 the formation of the teeth is brought about by force, 

 and " by force " means " contrary to Nature "). So 

 then it is apparent, both from these considerations 

 and others hke them, that this view is untrue. 



The teeth of which we are speaking are formed 

 earher than the flat teeth (1) because the work they 

 have to perform comes earher : breaking up (which 

 is the purpose of these teeth) comes before grinding 

 (which is the business of the flat ones) ; (2) because 

 a smaller thing naturally forms more quickly than a 

 larger one, even if they both start off together, and 

 these teeth are smaller in size than the molars, 

 because the jawbone at that point is flat, whereas it 

 is narrow by the mouth ; and, of necessity, a larger 

 amount of nourishment will flow out from the larger 

 part, and a smaller amount from the narrower.* 



Suckling, in itself, contributes nothing to the 

 formation of the teeth, though the warmth of the 

 milk makes them come through more quickly. A 

 proof of this is that* within the actual class of those 

 which suckle, those young ones which get hotter 

 milk grow their teeth quicker, because that which is 

 hot tends to promote growth. 



After having been formed, these teeth are shed 

 (o) for the sake of the better, the reason being that 

 anything sharp quickly gets blunted, and so a fresh 

 relay of teeth is needed to carry on the work. (The 

 flat ones, on the other hand, cannot get blunted ; 

 they only get worn down in the course of time by 

 friction.) They are shed also (b) as a result of necessity, 

 because, whereas the roots of the grinders are situ- 

 ated in the wide part of the jaw and upon good strong 



" But see Introd. § 14, ' i.e., orm the teeth. 



557 



