138 THE MAMMALIA. 



lesser importance, in America simply by the 

 Peccary, Dicotyles. From Sus we can most directly 

 follow the series in its earlier forms, whereas the 

 hog-deer of Celebes (Babirussa) and the African wart- 

 hog (Phacochoerus) show peculiarities of dentition 

 which, in the Babirussa, have proceeded from new 

 and special adaptations ; and the Phacochoerus 

 seems to owe its existence to an unknown lateral 

 branch. 



FIG. 15. Eepresentation of a Tuberculate Tooth and of a 

 Crescentic Tooth. 



The head of the Pig is remarkably long. Its 

 mode of life has played a great part in forming 

 this elongated shape. This is evident from a com- 

 parison of the Wild Boar with the Domestic Pig, or 

 of an animal kept in a sty with an individual even 

 of the same litter that has had to seek its food 

 in meadows. The more the pig has to work with 

 its head, by burrowing, the more it stretches the 



