SIMPLICITY OF THEIR STRUCTURE. 77 



"The root of the tusk, more curved than the free 

 portion, bears internally a cavity analogous to that of 

 the root of the incisors, and, like it, diminishes in size 

 and finally disappears as age advances ; but it is always 

 relatively larger, because of the absence of the infun- 

 dibulum in the canine teeth. 



" The structure of these teeth is much simpler than 

 that of the incisors, consisting, as they do, of a central 

 mass of dentine, hollowed by the pulp cavity, and cov- 

 ered by an external layer of enamel, on which is de- 

 posited a little cement." 



As there is more or less mystery about the tushes, 

 and as they are important factors in the consideration 

 of the problem of the evolution of the horse as well as 

 other animals, a few extracts from the works of well- 

 known scientific men, giving their views on the sub- 

 ject, will prove interesting if not instructive. 



Mr. Charles R Darwin gives the following interest- 

 ing account of tushes and their uses in certain animals, 

 among them the horse (" Descent of Man," vol. ii, pp. 

 245-G-7) : 



" Male quadrupeds which are furnished with tusks 

 use tliem in various ways, as in the case of horns. 

 The boar strikes laterally and upward, the musk-deer 

 with serious effect downward. The walrus, though 

 having a short neck and unwieldy body, ^can strike 

 upward, downward, or sideways with equal dexterity.' 

 The Indian elephant fights, as I was informed by the 

 late Dr. Falconer, in a difi'erent manner according to 

 the position and curvature of his tusks. When they 

 are directed forward and upward, he is able to fling a 

 tio-er to a p-reat distance — it is said to even thirty feet; 



