24 



AGE OF THE DOMESTIC ANIMALS. 



exceedingly rare to find excess of depth due to increased deptli 

 of the enamel, which condition will, however, be considered in 

 the study of the abnormalities of the teeth. 



The cement is a protecting layer which offers only a mod- 

 erate resistance to the friction of food and other substances, and 

 disappears at an early date from tlie periphery of the tooth, while 



t'ementation of thi' roots 



Fig. 13. 



• f thrt incisors. A, dental tables 

 alveolar cavities. 



B, roots in theii 



it persists in the cup of the tooth so long as the latter remains 

 on the table, where it forms a whitish spot, surrounded by a 

 band of enamel. (Fig. 10, A^ B, and C.) The cement is shown 

 by microscopical examination to be a bony formation, secreted 

 by the alveolar periosteum (germ sack), and is not a transformed 

 ivory or dentine as given by Simonds. 



It is found in greatest quantity at the crown or free 



