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, 1 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 
