GENERAL CHARACTERISTICS. 



197 



The bears are 



in 



general 



omnu'oroLis, 



delighting both in animal and vegetable food ; 

 but here also we meet with differences. 

 There are some which are entirely carnivorous, 

 lor 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 tendencv to the 

 omnivorous type, which is gradually de\-e- 

 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 obser\-e 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 lorm and broad grinding surface i 

 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 ha\-e . 

 thought of distinguishing a carnassial tooth 

 specially if the dentition of the bears had 

 been adopted as the general carnivorous tvpe. 

 The premolars present the lorm ordinariK" 

 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 



ng 



sharp, triangular, median lolje, while in the 

 large bears this part is thick and conical. 

 These premolars, moreover, ha\-e a tendencv 

 to disappear as age ad\ances, so that in some 

 large bears there is a wide inter\-al separati 

 the canine from the cheek teeth. 



I he canines and incisors preserve the 

 character of carnivores' teeth. But this 

 character is \-ery pronounced onl\' in the genus 

 Bassaris, in which the canines resemble those 

 ol the fox, while in the coatis they assume 

 the lorm of a strong triangular blade, sharp 

 on both edges, and in the true bears become 

 \-ery clumsy, ha\-ing only a slightly de\-eloped 

 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 ha\-e preserved the car- 

 nivorous type more strictly. 



Since the number of the premolars and 

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

 a few of the formulas for these teeth. 



Large Bears, Ailuropu 



pus : 



Procvon, Nasua, Bassaris: 



Ailurus: = :;S teeth. 



4-2 -' 



42 teeth. 



4 ■ ^ 



= 40 teeth. 



4-2 ^ 



Arctictis, Cercoleptes: "^ = 36 teeth. 



3 - 



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 lamih" we lorm 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. 



