20 



TUSKS AND THEIK rSES. 



\ised fuv purposes of attaclc, 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 ouly useless, but actually 

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

 from the southern seas, there is but one large strajj-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 ouly possible irse 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 siicli an arrangement, this is scarcely likely to he 

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

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

 monstrous development. 



Other examples of hollow or ;[>ermanently-growing tusks 

 occiu' among the hoofed mam- 

 mals, other than the pigs, in all 

 of which these teeth are found 

 only in the ujjper 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 i>roject 

 considerably below the lower 

 jaw. In form they are sabre- 

 like, and recall the ixpper tusks 

 of the feline carnivores, only 

 lieing more slender, and grow- 

 ing permanently. Similar but 

 smaller tusks are met with in the Chinese water-deer 

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

 animals known as chevrotains. The latter belongino- 

 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 



Fig. 10.— Extremity of the 

 Slfull of a TOUiis Chinese 

 "Water-Deer, ^vitli the haso 

 of the Tusli exposed, 

 (Aftei- Sir V. Brool^e.) 



