THE TEETH IN GENERAL 27 



turn is a mere osseous tissue, and in all of its ele- 

 ments resembles true bone. It surrounds the 

 roots of the teeth and is in contact with the alveolo- 

 dental periosteum or peridental membrane. The 

 dentin constitutes the main body of the tooth, and 

 is but modified bone as to its histological elements. 

 It has the same organic basis as bone, — i.e., gluten. 

 In many lower forms it is the only tissue of the 

 tooth, the enamel not being yet organized. In the 

 higher forms the enamel is the main working ele- 

 ment of the tooth, for which the other tissues are 

 mere supports. It appears to have been devel- 

 oped to supply the demand for a more resisting 

 structure as the function of mastication became 

 more specialized. It is developed from the epi- 

 thelium, and consists of calcified rods, with the 

 organic basis : keratin, like horn, nails, hairs, and 

 other epithelial structures. 



Functions of the Teeth. The functions of the 

 teeth can be divided into primary and secondary. 



The primary function of the teeth is the secur- 

 ing and preparing of the food for digestion and 

 assimilation. For this purpose they were called 

 into existence and such modifications as we find 

 in animals is always one which will enable the 

 animal to eat a certain class of food. It has been 

 said that the food of the animal has been respon- 

 sible for the change in the shape of the teeth; 

 whether this is exactly true or not, we can say 



