70 COMPARATIVE ZOOLOGY. 
cept Man." The teeth implanted in the premaxillary bone, 
and in the corresponding part of the lower jaw, whatever 
their number, are incisors. The first tooth behind the pre- 
maxillary, if sharp and projecting, is a canine. 
Each tooth has its particular bony socket.*° The molars 
are still further strengthened by having two or more di- 
verging fangs, or roots, a feature peculiar to this class. 
The incisors and canines have but one fang; and those 
that are perpetually growing, as the incisors of Rodents 
and Elephants, have none at all. The teeth of flesh-eat- 
ing Mammals usually consist of hard dentine, surrounded 
with cement and capped with enamel. In the herbivo- 
rous tribes, they are very complex, the enamel and cement 
being inflected into the dentine, forming folds, as in the 
molar of the Ox, or plates, as in the compound tooth of the 
Elephant. This arrangement of the three tissues, which 
Fria. 34.—Upper Molar Tooth of Indian Elephant (Elephas Indicus), showing trans- 
verse arrangement of dentine, d, with festooned border of enamel plates, e; ¢, 
cement; one-third natural size. 
differ in hardness, secures a surface with prominent ridges, 
well adapted for grinding. The cutting teeth of the Ro- 
dents consist of dentine, with a plate of enamel on the 
anterior surface, and the unequal wear preserves a chisel- 
like edge. Enamel is sometimes wanting, as in the molars 
of the Sloth and the tusks of the Elephant. 
In Fishes and Reptiles, there is an almost unlimited 
succession of teeth; but Mammalian teeth are cast and 
renewed but once in life. 
