296 A MANUAL OF DENTAL ANATOMY. 



deep down in the mass, from which many thin laminse are 

 sent up towards the surface, each consisting of an oblong 

 area of dentine enclosed by enamel ; and the interspaces of 

 these exaggerated cusps are solidly filled in by cementum. 



Between the Mastodon and the Indian Elephant are a 

 number of transitional forms in which we are able to trace 

 the gradual modification of the not excessively aberrant 

 tooth of the Mastodon into the very peculiar huge molar 

 of the Indian Elephant. 



The numerous transverse plates of the elephant's grinders- 

 are united by dentine at their bases, and a common pulp 

 cavity and truncate roots are formed ; but in this last 

 respect the molar teeth of the capybara depart still farther 

 from the ordinary type, for being molars of persistent 



FIG. 125 !. 



growth, their numerous transverse plates of dentine and 

 enamel do not become continuous, and there is no common 

 pulp cavity. It is as though in an elephant's grinder the 

 plates, which are for a long time distinct, never coalesced, 

 but continued to grow on separately, being united with their 

 fellows by cementum only. 



It has been suggested (J. A. Ryder, Proc. Acad. Nat, 

 Sciences, Philadelphia, 1878), that the pattern of the molar 

 teeth of herbivora is the result of the extent and direction 

 of the excursions of the mandible when it is in use, and so 

 depends upon the form of the glenoid cavity and of the 

 condyle, and that hence the greatest modification is to be 



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

 enamel united to one another !>y cementum. 



