THE TEETH OF MAMMALS 161 



nine, and the presence or absence of the other two 

 varies much. The type of the molar is seleno- 

 dont. The non-ruminant, even-toed Ungulates 

 include the Pig (Fig. 66), Hippopotamus, etc. 

 The formula of the Pig is, — 



. 3-3 1-1 4-1 3-3 AA 



l - 3=3 C - lH P ' m - U m - 3-3 = 41 



The Wart Hog has but thirty-four and Dicotyles 

 thirty-eight. The incisors are well developed, 

 and increase in size from center to sides. The 

 canines are sometimes enormously developed, as 

 in the Wild Boar. This development is arrested 

 in the domestic hog by castration, showing that 

 the excessive growth is due to sexual influence. 

 The canines are small in the female. In the Wild 

 Boar they curve outward and upward into hooks 

 to make formidable weapons for ripping up an 

 adversary. They sometimes pierce the upper 

 lip, are triangular in section, and are deeply 

 ridged on the anterior surface, the enamel being 

 rough and irregular. The lower canines are 

 much smaller. The molar series increase in size 

 from front to back, and present sharp, high crests 

 which usually remain unworn in the domestic hog. 

 When worn the crests present a characteristic tri- 

 angular form. The Wild Hog of Mexico (Fig. 

 67) has long, sharp canines for warfare (Fig. 68). 

 The Hippopotamus is much like the pig as re- 

 gards its dentition, but has four incisors less. 



