114 



INTRODUCTION. 



the Guinea Pig, are shed before birth. In the Hare tribe, it is a few 

 days after birth that the shedding of these teeth takes place ; at which 

 period, the little rudimentary incisors, which lie behind the large pair, 

 make their appearance. 



The teeth of Mammalia have been divided into three kinds : First, 

 incisors, or cutting teeth, arising from the anterior part of the superior 

 maxillary (intermaxillary in the lower orders) bones, above and from the 

 corresponding part of the lower jaw ; secondly, canines, succeeding the 

 incisors, one on each side; those of the lower jaw, when the mouth is 

 closed, advancing before those of the upper : to these succeed, on each 

 side, thirdly, the molars, or grinding teeth. 



With respect to the names, by which the teeth are designated, it must 

 be confessed, that they are not of strictly universal application; for the 

 trenchant back teeth of the Felidae cannot be called molars, or grinders 

 (mola, a mill ; molo, to grind) ; nor is the term incisor better adapted to 

 the front teeth of the insectivorous animals : still, however, as these 

 terms are universally adopted, and as none of a comprehensive significa- 

 tion can be well devised, their use becomes a matter as much of necessity 

 as convenience. The incisor teeth vary, in form and character, almost 

 ad infinitum. In Man, and the Simiae, they are broad and com- 

 pressed, with a flat edge ; and the upper 

 and lower incisors are opposed to each 

 other vertically, or nearly so ; though less 

 truly in the Simiae than in Man : in both 

 they are large and important : in the Orang 

 their strength and thickness are very re- 

 markable (fig. 111). In the Bats they vary 

 in shape and importance ; and (as in the 

 genus Edostoma), those of the upper jaw 

 often differ, both in form and number, from 

 those of the lower jaw. In the Carnivora their number is six in each 

 jaw ; but they are small, feeble, and comparatively unimportant. In the 

 Insectivora they also vary, assuming, in many species, as the Shrews 

 (fig. 112), a prehensile character ; and are adapted, by their 

 length, and subulate, or awl-shaped form, for seizing small 

 objects of prey. Where the incisors are long, the canines 

 are little distinguishable from the lateral incisors, or from 

 the false molars ; but, where the canines are large, all the inci- 

 sors are small. In the Ruminantia there are no incisors in the 

 upper jaw ; and those of the lower jaw are flat, broad, and 

 oblique, so as to oppose their upper surface to the callous 

 gum of the upper jaw. The Pachydermata present great variation in the 

 character of the incisors. In the Horse we find them large and strong, 



Incisors of 

 Shrew. 



