GENERAL CHARACTERISTICS. 



197 



The bears are in general omnivorous, 

 delighting both in animal and vegetable food; 

 but here also we meet with differences. 

 There are some which are entirely carnivorous, 

 for example, the polar bear; while other 

 species are almost purely vegetarian. In 

 this family we can point to a series of 

 transitions between these two opposite kinds 

 of diet, transitions which are also recognizable 

 in the dentition. 



The dentition of the Ursida is, in fact, 

 distinguished from that of all the other 

 Carnivora by the marked tendency to the 

 omnivorous type, which is gradually deve- 

 loped (in different species) from behind 

 forwards, and is manifested partly in the 

 structure of the teeth, partly in the loss of 

 premolars originally formed on the carnivorous 

 type. 



In all bears we observe in each jaw at least 

 two small tubercled molars, to which in the 

 large bears a third is added in the lower jaw. 

 In some American genera the tubercles of 

 these true molars still appear in the form of 

 low but sharp cones, but in the true bears 

 they are so blunt that an isolated specimen 

 of one of these molars might, on account of 

 its massive form and broad grinding surface 

 studded with only insignificant inequalities, 

 be ascribed to a pig. 



The carnassial, which in the upper jaw is 

 a premolar, in the lower a true molar, is 

 scarcely distinguishable in form from the 

 other molars, though it is somewhat longer 

 and flattened at the sides, and has rather 

 sharper tubercles. Only in the American 

 genus Bassaris can it be at once recognized 

 as a carnassial by its two sharp external cusps 

 and its internal heel. No one would have 

 thought of distinguishing a carnassial tooth 

 specially if the dentition of the bears had 

 been adopted as the general carnivorous type. 



The premolars present the form ordinarily 

 met with in Carnivora, but here again it is 

 found that the premolars of the small Ameri- 

 can bears (coatis, raccoons, &c.) have a rather 



sharp, triangular, median lobe, while in the 

 large bears this part is thick and conical. 

 These premolars, moreover, have a tendency 

 to disappear as age advances, so that in some 

 large bears there is a wide interval separating 

 the canine from the cheek teeth. 



The canines and incisors preserve the 

 character of carnivores' teeth. But this 

 character is very pronounced only in the genus 

 Bassaris, in which the canines resemble those 

 of the fox, while in the coatis they assume 

 the form of a strong triangular blade, sharp 

 on both edges, and in the true bears become 

 very clumsy, having only a slightly developed 

 conical crown with an enormous root. 



The bears of the Old World are, in general, 

 to be described rather as omnivorous than 

 carnivorous in their diet, while most of the 

 American bears have preserved the car- 

 nivorous type more strictly. 



Since the number of the premolars and 

 molars varies a little, it will be as well to give 

 a few of the formulas for these teeth. 



Large Bears, Ailuropus: ^-7- = 42 teeth. 

 Procyon, Nasua, Bassaris: = 40 teeth. 

 Ailurus: ~ 38 teeth. 



^ ' 2 



Arctictis, Cercoleptes: = 36 teeth. 



In the milk-dentition of the true bears, the 

 bassaris, and the coatis, there are four pre- 

 molars with rather blunt tubercles, both in 

 the upper and the lower jaw. 



In this family we form two large groups: 

 the Subursida or Small Bears, with 36-40 

 teeth and a long tail ; and the True or Large 

 Bears (Ursida), with 42 teeth and short tail. 

 The two groups are equally represented in 

 both hemispheres. 



