344 THE HARMONIES OF NATURE. 



well adapted for plucking or nibbling the herbage. The canines are 

 inconstant, and the molars, usually six on each side of both j awe, 

 have flattened crowns surmounted by two double and irregularly 

 crescentic folds of enamel, formed for affording the greatest pos- 

 sible extent of triturating surface. The lower jaw of the ruminants 

 is not so broad as the upper one (as we see in the accompanying 

 illustration), so that the surfaces of the upper molars project on 

 both sides beyond those of the corresponding inferior rows ; but 

 both have been made to cover each other by the alternating 

 lateral movements of the lower jaw to the right or to the left, a 

 motion as admirably calculated for assisting the grinding or 

 triturating process, as the hingelike and vertical motion of the 

 lower jaw of the carnivora for shearing or cutting. 



Several mammals are distinguished by the enormous develop 

 ment of their canine teeth. Thus in the walrus they constitute 

 formidable weapons of defence, and no less useful levers with 

 which the unwieldy animal raises his huge body upon the ice- 

 blocks and precipitous shores where he loves to bask in the sun. 

 The long curved and sharp tusks of the wild-boar are capable 

 of inflicting the most severe and painful wounds, and serve 

 likewise for the digging-up of roots. In the narwhal only one 

 of the upper canines projects in the shape of a formidable horn, 



while the other remains in a 

 rudimentary condition. This 

 horn, which is harder and 

 whiter than ivory, is from six 

 to ten feet long, spirally 

 striated throughout its whole 

 length, and tapering to a point. 

 We know but little of the habits of the narwhal, 

 but have no reason to doubt that this power- 

 ful horn, which is restricted to the males, is 

 an admirable weapon of defence. The upper 

 incisors of the elephant, developed to an extra- 

 ordinary size, form the tusks of this wonder- 

 ful animal, and not only surpass other teeth in 

 size, as belonging to a quadruped so enormous, 

 Tusks of wahus. h llt are fa e largest of all teeth, in proportion to 

 the size of the body. Their possessor uses them for plough- 

 ing up the earth in quest of nutritious roots, or as a protection 



