64 COMPAKATIVE DENTAL ANATOMY 



flat tooth-shaped plates of horn which answer the 

 purpose of grinding teeth. In some of the ant- 

 eaters, the tongue and roof of the mouth are 

 armed with horny plates for crushing. In the In- 

 sectivora the molars are highly developed, with 

 many long, pointed cusps for crushing the hard 

 coverings of insects. In man, the molars are of 

 simple tuberculate form of a lower grade of or- 

 ganization. His molar teeth are indeed of the 

 type of the early Eocene mammals. In the 

 Carnivora the molars are reduced in size and 

 number, and the premolars are highly developed. 

 In the more omnivorous species the number of 

 molars is increased, and they have rounded tuber- 

 cles for grinding a mixed diet. In the Herbivora 

 the molars are highly developed for the mastica- 

 tion of an extreme diet, with pleatings and fold- 

 ings of the dental tissue which insure a constantly 

 rough face for the difficult reduction of resisting 

 vegetable fiber. In the Quadrumana the molars 

 are similar to these teeth in man, being simply 

 tuberculate for a mixed diet. 



The molar teeth of the Mammalia are classified 

 as follows, according to shape : 



Haplodont. The crown undivided or simple 

 (as in the single teeth of the Getacea, Carnivora, 

 Rodentia, etc.). 



Ptychodont. The crown folded on the sides (as 

 in the Rodentia molars). 



