70 COMPARATIVE ZOOLOGY. 



of enamel. In the Cats and Dogs, they are narrow and 

 sharp, passing by each other like the blades of scissors, 

 and therefore cutting, rather than grinding, the food. 

 The more purely carnivorous the species, and the more 

 it feeds upon living prey, the fewer the molars. In ani- 

 mals living on mixed diet, as the Hog and Man, the 

 crowns have blunt tubercles. Premolars, or bicuspids, 

 are those which were preceded by milk-teeth; the true, 

 or back, molars had no predecessors. 



The dentition of Mammals is expressed by a formula, 

 wliich is a combination of initial letters and figures in 



Fio. 35 — Teeth of the right lower jaw of nflnlt male Chimpanzee (Troglodyte» niger), 

 iiatnval size. The molar series doetf not form a curve, as iu Mau. 



fractional form, to show tlie number and kind of teeth 

 on each side of both jaws. Thus, the formula for Man 



, 2 — 2 1 — 1 3 — 2 3 — 3 



is: *, ^n^; c,^^;^, jTr^; m, 3^1 = 32. 



The teeth of Mammals are always restricted to the 

 margins of tlie jaws, and form a single row in eacli. But 

 they rarely form an unbroken series." The teeth im- 

 planted in the premaxillary bone, and in the correspond- 

 ing part of the lower jaw, whatever their number, are in- 

 cisors. The first tootli behind the premaxillary, if siiarp 

 and projecting, is a canine. 



Each tooth has its particular bony socket." The molars 



