NATURE OF TUSKS. 15 



carnivorous mammal, such as a lion or a wolf, the upper 

 tusks are considerably larger than the lower, although 

 neither project beyond the edges of the muzzle when the 

 jaws are closed. If we examine such tusks in a dried 

 skull we shall find that their roots (which, as in all tusks, 



FIG. 7. Skeleton of Missouri Mastodon. 



are simple) are completely closed ; thus indicating that 

 their growth ceased at a certain period of life. Moreover, 

 we may notice that the upper and lower pairs of tusks do 

 not abrade against one another to any marked extent, and 

 that consequently their summits are only subject to the 

 ordinary wear and tear necessarily undergone during use. 

 In many other mammals the form and structure of these 

 tusks is, however, very different. Take, for instance, a 

 wild boar, in which the upper tusks are short and curved 



