'20 



TUSKS AND THEIR USES. 



used for purposes of attack, or for procuring food. 

 Doubtless, however, the narwhal's tusk is of some use to 

 its owner ; but in another cetacean, known as Layard's 

 mesoplodon, the tusks appear not only useless, but actually 

 harmful. In the whale in question, which is a rare species 

 from the southern seas, there is but one large strap-like 

 tusk on each side of the middle of the lower jaw, both of 

 these curving upwards and inwards over the snout, so as 

 actually to prevent the mouth from opening to its full 

 extent. The only possible use we could suggest of such a 

 structure would be to prevent the creature dislocating its 

 jaw by yawning ; but as other animals manage to get on 

 without such an arrangement, this is scarcely likely to be 

 a solution of the problem. It is more probable, indeed, 

 that we have here to do with another instance of ultra, or 

 monstrous development. 



Other examples of hollow or permanently-growing tusks 

 occur among the hoofed mam- 

 mals, other than the pigs, in all 

 of which these teeth are found 

 only in the upper jaw. and are 

 developed chiefly or solely in 

 the males. Among recent forms 

 these tusks attain their greatest 

 development in the little musk- 

 deer of the Himalaya, where 

 they are frequently over three 

 inches in length, and project 

 considerably below the lower 

 FIG. 10. Extremity of the jaw. In form they are sabre- 

 Skull of a young Chinese like, and recall the upper tusks 

 Water-Deer, with the base 



of the Tusk exposed. 

 (After Sir Y. Brooke.) 



of the feline carnivores, only 

 being more slender, and grow- 

 ing permanently. Similar but 

 smaller tusks are met with in the Chinese water- deer 

 (Fig. 10), in the Indian niuntjac, and the little deer-like 

 animals known as chevrotains. The latter belonging 

 to a totally distinct group from the others, it is 

 evident that these scimitar-like tusks have been inde- 

 pendently acquired in the two groups ; while it is quite 



