POSITION AND STRUCTURE OF HORSE 39 



of their crowns ; in which respect, as will be shown 

 in the sequel, they differ from the corresponding 

 teeth of the horse's early ancestors, which had 

 quite short crowns. Now, if surrounding con- 

 ditions be the same, tall-crowned teeth indicate 

 the potentiality of much longer life on the part of 

 their owner than is afforded by low-crowned ones ; 

 as it is obvious that a tall tooth will take much 

 longer to wear down than will a low one. In this 

 particular instance it has, however, to be borne 

 in mind that the early ancestors of the horse were 

 swamp-dwelling animals living on soft, luscious 

 vegetation which could be masticated without having 

 much effect on their teeth. The horse and its 

 relatives, on the other hand, when in a state of 

 nature, live on open plains where the grass is often 

 more or less hard and wiry, and thus calculated 

 to wear away the teeth at a relatively rapid rate. 

 In the case of domesticated horses the rate of wear 

 is probably still further accelerated by the nature 

 of the food. */ 



Still, after making due allowance for all this, 

 there can be little doubt that the existing members 

 of the horse tribe are longer-lived animals than 

 were their early forerunners. And, as animals 

 go, the domesticated horse may be considered to 

 have a considerable pre-eminence in the matter 

 of longevity, although in this respect it does not 

 equal its distant cousins the rhinoceroses, some of 



