SOME EXTINCT ARGENTINE MAMMALS 99 
the two-toed sloth they are reduced to two; in fact, the 
feet are reduced to the condition of little more than hooks, 
admirably adapted for suspending the animal back-down- 
wards from the boughs of trees, but forming poor instruments 
for terrestrial progression. Indeed, when on the ground 
sloths walk slowly and awkwardly, with the soles of the 
feet turned inwards, and the weight of the body supported 
on their outward edges. It is important to notice that 
in the skeleton of the feet the terminal bones, or those 
ensheathed in the long claws, are not longitudinally grooved 
on the upper surface. 
The South American, or true ant-eaters, one of which is 
terrestrial while the other two are more or less arboreal 
in their habits, are so unlike the sloths that it is difficult 
to believe they have any near relationship with the 
latter ; and, indeed, were it not for the extinct creatures 
now under discussion, it would have been very difficult 
to discover how close the connection between these two 
groups really is. In place of the short and rounded 
heads of the sloths, the ant-eaters have the head greatly 
elongated and very slender, while the thin jaws are totally 
devoid of teeth, and the tongue is long, cylindrical, and 
highly extensile. There is, however, some degree of 
variation in regard to the elongation of the skull, the 
maximum development occurring in that of the great 
ant-eater. If possible, a still greater difference obtains in 
the structure of the feet, the fore-foot of the great ant-eater 
having five toes, of which the middle one is vastly more 
powerful than either of the others, while all but the fifth 
have strong claws. In walking, the extreme outer side 
and part of the upper surface of the fore-foot are applied 
to the ground; but in the hind-foot, which has the fourth 
toe the largest and all the five digits furnished with claws, 
