68 MAMMALIA. 



The anterior molars are the most trenchant; next comes a molar, 

 larger than the others, usually furnished with a larger or smaller 

 tuberculous heel; then follow one or two small teeth, that are per- 

 fectly flat. It is with these small teeth in the back part of the 

 mouth that the Dog chews the grass he sometimes swallows. We 

 will call, with M. Fr. Cuvier, this large upper molar, and its cor- 

 responding one below, carnivorous teeth; the anterior pointed ones, 

 false molars; and the posterior blunted ones, tuberculous teeth. 



It is easy to conceive that those genera which have the fewest 

 false molars, and whose jaws are the shortest, are those best adapted 

 for biting. 



It is upon these differences that the genera can be most surely 

 established. 



It is necessary, however, that the consideration of the hind foot 

 should be added to them. 



Several genera, like those of the two preceding families, in walk- 

 ing, or when they stand erect, place the whole sole of the foot on 

 the ground, a fact proved by the total want of hair on that part of it. 



Others, and by far the greater number, walk on the ends of the 

 toes, by raising up the tarsus. They are much swifter, and to this 

 first difference are added many others of habits, and even of inter- 

 nal conformation. In both the clavicle is a mere bony rudiment 

 suspended in the muscles. The 



PLANTIGRADA 



Form this first tribe, in which the whole sole of the foot is placed 

 on the ground in walking, a circumstance which gives them a 

 greater facility in standing vertically upon their hinder feet. They 

 partake of the slowness and nocturnal life of the Insectivora; most 

 of those that inhabit cold countries pass the winter in a state of tor- 

 por. They all have five toes to each foot. 



URSUS, Lin. 



Bears have three large molars on each side in each jaw, altogether tuber- 

 culous, and of which the posterior upper, and anterior lower are the 

 longest. They are preceded by a tooth a little more trenchant, which is 

 one of the carnivorous teeth of this genus, and by a variable number of very 

 small false molars, which are sometimes shed at a very early period. This 

 almost frugivorous sort of dentition is the reason why, notwithstanding 

 their great strength, they seldom eat flesh unless from necessity. 



They are large, stout-bodied animals, with thick limbs, and a very short 

 tail: the cartilage of the nose is elongated and movable. They excavate 



