262 



ELEMENTAR Y ANA TO MY. 



[LESS. 



exceeded by what we find in certain of the Hog tribe, e.g. in 

 the Babyrussa (Porcus), where the upper canines first mount 

 vertically and then curve over backwards and downwards, 

 whence its native name, which signifies Deer-Hog. 



Undoubted canines attain their 

 maximum in the upper jaw of the 

 Walrus, which develops a pair of enor- 

 mous descending tusks growing from 

 permanent pulps, and which are said 

 to aid the animal in its locomotion 

 amongst the ice. 



The longest tooth developed in the 

 whole animal kingdom is the tusk of the 

 Narwhal. It may be doubted, indeed, 

 whether this tooth represents a canine or a molar, yet, as it is 

 embedded entirely in the maxilla, it cannot be an incisor. 

 In the female Narwhal these teeth remain undeveloped and 

 in the bone. In the male the tooth of one side is generally 

 developed, but sometimes both are so. The pulp cavity 

 extends nearly the whole extent of the enormous tooth, 

 which is said to attain a length of ten feet. Though straight, 

 its surface has a spirally-twisted appearance, and formerly 

 was sometimes exhibited as the horn of the Unicorn. 



Upper canines may be present though upper incisors are 

 wanting, as in the case of the Musk Deer and Muntjac. 

 Lower canines may be closely approximated to and shaped 



FIG. 233. SKUI.I. AND 



TUSKS OF THE BABYRUSSA 



(Porcus). 



FIG. 234. DENTITION OP A SHEEP. (TYPICAL RUMINANT DENTITION.) 



mx, maxilla ; px, pre-maxilln, which is edentulous, there being no upper in- 

 cisors ; i 1 , z' 2 , z 3 , three lower incisors of left side ; c, lower canine ; pm, pre- 

 molars ; m, molars. 



like the incisors adjacent to and between them, as in the 

 Lemurs and in the Ox and Sheep tribes. 



Lower canines may be altogether wanting, though both in- 

 cisors and molars are present in each jaw, as is the case in 



