368 A MANUAL OF DENTAL ANATOMY. 



the crown, which comes to be an area of dentine, surrounded 

 by a ring of enamel. 



But in those whose food is of a more refractory nature, 

 the molars, like the incisors, grow from persistent pulps (as 

 is exemplified in the Capybara here figured), and their 

 working surfaces are kept constantly rough by the enamel 

 dipping in deeply from the side of the tooth, as may also be 

 seen in the common water-rat. The inflection of enamel 

 may be so deep as to divide the areas of dentine completely 

 up, the result being a tooth like that of the Capybara, which 



FIG. 158 ! ). 



4& 



NdbS&c 



is composed of a series of plates of dentine, or f denticles,' 

 surrounded by layers of enamel, and all fused together by 

 the cementum. The result of this disposition of the struc- 

 tures is that the working surface is made up of enamel, 

 dentine, and cementum, three tissues of different hardness, 

 which will consequently wear down at different rates, and 

 so maintain its roughness. Various intermediate forms of 

 the molar teeth are met with ; thus there are some in 

 which complexity of the surface is maintained by folds of 

 enamel dipping in for a little distance, but which never- 

 theless after a time form roots and cease to grow. When 

 the molar teeth grow from persistent pulps, they are always 

 curved, like the incisors, with the effect of relieving the 

 pulps from direct pressure during mastication ; and the last 



( x ) Molar of Capybara, showing the transverse plates of dentine and 

 enamel united to one another by cementum. 



