154 FOSSIL MAMMALIA. 
toes.* The ulna (1) is extremely broad and 
powerful at its upper extremity, affording large 
space for the origin of muscles, concerned in the 
movements of the foot. The radius (m) revolves 
freely on the ulna, as in the Sloths and Ant- 
eaters, both of which make much use of the 
fore-leg, though for different purposes ; it has a 
cavity at its upper end, which turns upon a 
spherical portion of the lower part of the hu- 
merus, and a large apophysis (n), projecting from 
its longitudinal crest, indicates great power in 
the muscles that gave rotatory motion. 
The entire fore-foot must have been about a 
yard in length, and more than twelve inches 
wide ; forming a most efficient instrument for 
moving the earth, from that depth within which 
succulent roots are usually most abundant. This 
great length of the fore- foot, when resting upon 
the ground, though unfavourable to progressive 
motion, must have enabled one fore-leg, when 
acting in conjunction with the two hind legs and 
tail, to support the entire weight of the body ; 
leaving the other fore-leg at liberty to be em- 
ployed exclusively in the operation of digging 
food. I 
* There is a similar expansion of the lower part of the 
Humerus in the Ant-eater, which employs its fore-feet in digging 
up the solid hills of the Termite Ants. 
f At PI. 5, beneath Fig. 1, are represented the fore-foot of an 
Armadillo (Dasypus Peba), and the fore-foot of the Chlamy- 
phorus, each eidapted, like that of the Megatherium, to form an 
