TEETH AND THEIR VARIATIONS. 205 



last teeth of a Mammal, two in Dogs and Civets (Fig. 

 64), but three in man, have, however, no such milk- 

 predecessors, and are hence called true grinders; the 

 teeth between these latter and the tusk, which are 

 only two in number in Man, against four in the Civet, 

 Dog, and Pig, being termed the false grinders. 



This single definite replacement of a certain number 

 of teeth it may be of only one, or it may be of seven 

 or eight on either side of each jaw is, therefore, a 

 peculiar feature of Mammals, and indicates the highest 

 and most nearly perfect phase of the development of 

 the tooth-series. 



Having thus acquired a general idea of some of the 

 more important characteristics distinguishing the teeth 

 of Mammals as a whole, we are in a position to enter 

 into the consideration of their structure in any par- 

 ticular group. Perhaps one of the most interesting of 





t~MW 



FIG. 65. The last three left upper cheek-teeth of an extinct Pi. 



all groups in regard to the gradual development of a 

 highly complex structure in the cheek-teeth of the 

 modern forms, is that of the Hoofed or Ungulate 

 Mammals; or that extensive order which includes 

 the three great groups of Pigs, Deer, Antelopes, and 



