ANIMAL DENTISTRY. 



69 



gain in length and volume by expansion of the fang, but 

 lose slightly by wear. The growth, however, exceeds the 

 wear during the first year. During the second year the wear 

 and growth are about equal. The greatest length of the 

 teeth is therefore attained during the second twelve months 

 of their existence within the mouth. During the succeed- 



FlG. 46. 

 The Destruction of a Temporary Tooth by the Permanent. 



A. Temporary shell. 



B. Permanent tooth. 



ing years the teeth do not grow, but instead undergo a 

 gradual and regular process of destruction under two in- 

 fluences : 



(i) Wear from mastication, which slowly shortens the 

 length of the tooth. 



(2) Receding of the alveolar margin, which gradually 

 shortens the depth of the alveolar cavity. 



In the herbivorous animals both of these influences are 



