224 ANIMAL LIFE PAST AND PRESENT. 



required the retention of a type of limb constructed on 

 principles of strength rather than elegance. Hence 

 there has been no inducement for any alteration in 

 the structure of the feet of these ponderous brutes as 

 time rolled on ; and so that while it requires the aid 

 of the man of science to trace the relationship existing 

 between the tooth of the ancient Mastodon and that 

 of the modern Indian Elephant, the veriest tyro would 

 not hesitate to declare that the skeletons of the same 

 two creatures indicated the closest relationship. 



To sum up the results of this brief survey of some 

 of the more striking features connected with the 

 cheek-teeth of the Ungulate Mammals, we may say 

 that all the .Ungulates of the lower Tertiary deposits 

 had low-crowned teeth of comparatively simple struc- 

 ture ; and that those of all the three groups into which 

 the order is divided can be derived from a type of 

 tooth not far removed from that possessed by the 

 ancestors of the Pigs, the latter type being itself a 

 modification from the still more primitive triangular 

 type. In all the three groups of Ungulates, the crowns 

 of the teeth have tended to increase in height and in 

 complexity of structure with the advance of time ; 

 those Ungulates with the tallest crowned teeth being 

 characteristic of the most recent period of the earth's 

 history. Finally, that while in the groups containing 

 the Ruminants and the Horses the structure of the 

 feet has been modified pari passu with that of the 

 teeth, to produce limbs capable of carrying their 

 owners at an extremely rapid rate, in the Elephants, 



