IN THE LOWER ANIMALS, ETC. 



329 



alveoli are conformed to their conical shape. (Fig. 

 52.) But when the pulp of the tooth is perpe- 

 tually renewed, to repair by its gradual calcifica- 

 tion the wearing down to which the cutting or 



Tig. 52. — Human Jaws, showing completed development of roots. 



grinding surface of the tooth is exposed, the 

 alveolus is of the same diameter throughout its 

 whole length. 



This perpetual growth of the incisor teeth is 

 sometimes productive of unfortunate results to 

 the poor animal. 



If either of these teeth is lost by disease of the 

 socket, or is displaced by accident, so that its 

 edge is no longer opposed to that in the corre- 

 sponding jaw, the latter tooth becomes prodigiously 



