X INTRODUCTION. 



and number of the cavities themselves. In the complex 

 grinders of the elephant, the masked boar, and the 

 copybara, the cement, which forms nearly half the 

 mass of the tooth, wears down sooner than the dentine. 

 " The enamel is the hardest constituent of a tooth, 

 and, consequently, the hardest of animal tissues*; but 

 it consists, like the other dental substances, of earthy 

 matter arranged by organic forces in an animal matrix. 

 Here, however, the earth is mainly contained in the 

 canals of the animal membrane, and, in mammals and 

 reptiles, completely fills those canals, which are com- 

 paratively wide, whilst their parietes are of extreme 

 tenuity. The hardening salts of the enamel are not 

 only present in far greater proportion than in the den- 

 tine and cement, but, in some animals, are peculiarly 

 distinguished by the presence of the fluate of lime." 



Again Prof. Owen says ("Anat. of Vert." vol. i, pp. 

 359-60) : 



" Teeth vary in number, size, form, structure, modi- 

 fications of tissue, position, and mode of attachment 

 in different animals. They are principally adapted for 

 seizing, tearing, dividing, pounding, or grinding the 

 food. In some animals they are modified to serve as 

 weapons of offense and defense ; in others, as aids in 

 locomotion, means of anchorage, instruments for up* 

 rooting or cutting down trees, or for transport and 

 working of building materials. They are characteristic 

 of age and sex, and in man they have secondary rela- 

 tions subservient to beauty and to speech. 



"Teeth are always most intimately related to the 

 food and habits of the animal, and are therefore highly 



