OF DIGESTION. 



107 



as the moles and bats, have the molars terminated by several 



Fig. 74. 



Fig. 76. Fig. 75. 



sharp, conical points, (Fig. 74,) so arranged that the eleva- 

 tions of one tooth fit exactly into the depressions of the tooth 

 opposite to it. In the true Carnivora, (Fig. 75,) on the con- 

 trary, the molars are compressed laterally, so as to have 

 sharp, cutting edges, as in the bats ; and they shut by the 

 side of each other, like the blades of scissors, thereby di- 

 viding the food with great facility. 



220. The same adaptation is observed in the teeth of her- 

 bivorous animals. Those which chew the cud, (ruminants,) 

 many of the thick-skinned animals, (pachydermata,) like the 

 elephant, and some of the gnawers, (rodentia,) like the hare, 

 (Fig. 76,) have the summits of the molars flat, like mill-stones, 

 with more or less prominent ridges, for grinding the grass 

 and leaves on which they subsist. Finally, the omnivora, 

 those which feed on both flesh and fruit, like man and the 

 monkeys, have the molars terminating in several rounded 

 tubercles, being thus adapted to the mixed nature of their 

 food. 



221. Again, the mode in which the molars are combined 

 with the canines and incisors furnishes excellent means of 

 characterizing families and genera. Even the internal struc- 

 ture of the teeth is so peculiar in each group of animals, and 

 yet subject to such invariable rules, that it is possible to 

 determine with precision the general structure of an animal, 



