SOME EXTINCT ARGENTINE MAMMALS 81 



while the huckle-bone, or astragalus, of the ankle articulates 

 with the leg-bone by a flat surface. On the other hand, 

 in both the odd-toed or perissodactyle ungulates, as repre- 

 sented by the rhinoceros and horse, and the even-toed or 

 artiodactyle group of the order, of which we have familiar 

 examples in the pig and the deer, the toes are never more 

 than four in number, the bones of the wrist and ankle 

 interlock or alternate, and the huckle-bone has a pulley- 

 like surface for articulation with the large bone of the leg. 

 Whereas, however, in the former of these two groups the 

 middle toe is larger than either of the others and sym- 

 metrical in itself, in the second group it is the two toes 

 corresponding to the second and third of the human foot 

 which are larger than the others, while they are also 

 symmetrical to a line drawn between them. There is like- 

 wise a well-marked difference between the huckle-bones of 

 the two groups. The fourth group, represented only by 

 the various species of hyrax the coney of Scripture need 

 not detain us here. 



Turning to the proper subject of this article, I com- 

 mence my notice with one of the largest of the Argentine 

 mammals, which derives its name of Toxodon from the 

 peculiarly curved or bow-like form of its long molar-teeth. 

 This gigantic animal, which rivalled the large Indian 

 rhinoceros in size, is remarkable for the peculiar lowness 

 of the forequarters, in consequence of which the enormous 

 head is carried much below the line of the back. Since 

 the creature has much the general appearance of a rhino- 

 ceros, as shown by its relatively short and stout neck and 

 limbs, while the number of toes to each limb is three, of 

 which the middle one is symmetrical in itself, an observer 

 might, at first sight, be disposed to place the toxodon 

 among the odd-toed ungulates. A closer examination 



6 



