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, 

 which is a combination of initial letters and figures in 



Fig. 35.— Teeth of the right lower jaw of adult male Chimpanzee {Troglodytes niger), 

 natural size. The molar series does not form a curve, as in Man. 



fractional form, to show the number and kind of teeth 

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



. ^ . 2 — 2. 1 — 1. 2 — 2. 3-3 QO 



is : tj 2^ ; e > jzri 5 Pi 2^2 5 m i 3^3 ~~ 



The teeth of Mammals are always restricted to the 

 margins of the jaws, and form a single row in each. But 

 they rarely form an unbroken series. 28 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 tooth behind the premaxillary, if sharp 

 and projecting, is a canine. 



Each tooth has its particular bony socket. 29 The molars 



