MEGATHERIDA 187 
backwards from the extremity of the upper surface of the pre- 
maxille. 
The vertebral column consists of seven cervical, sixteen dorsal, 
three lumbar, five sacral, and eighteen caudal vertebre. The 
spinous processes are much better developed than in the Sloths, 
and are all directed backwards, there being no reversing of the 
inclination near the posterior end of the dorsal series, as in most 
active-bodied mammals. In the lumbar region, the accessory zyga- 
pophyses, rudimentary in Sloths, are fully developed, as in the 
Anteaters. 
The tail is large, and its basal vertebrae have strong lateral and 
spinous processes and chevron bones, indicating great muscular 
development. The scapula resembles that of the Sloths in the 
union of the acromion with the coracoid, and in the bridging over 
of the supra-scapular notch. The clavicle is complete and very 
large, much resembling that of man on a large scale. The fore 
limbs are longer than the hind limbs. The humerus has no ent- 
epicondylar foramen. The radius and ulna are both well developed, 
and have a considerable amount of freedom of movement. The 
hand is singularly modified. The pollex is represented only by a 
rudimentary metacarpal, but the next three digits are large, and 
terminate in phalanges adapted for the support of immense claws, 
the middle one being especially large. The outer or fifth digit has 
no claw, and it may be considered as certain that the weight of the 
foot was, in standing and walking, chiefly thrown upon this one, 
which was protected by a callous pad below, as in the existing 
great Anteater, while the other toes were curved inwards towards 
the palm, and only came in contact with the ground by their outer 
surfaces. The mechanical arrangements by which the weight of the 
body was thrown entirely upon the outer side of the foot are very 
curious, and are fully described in Owen’s memoir. The pelvis is 
remarkably wide, even more so than that of the Elephant, but it is 
formed on the same principle as in the Sloths. The femur is 
extremely broad and flattened; the tibia and fibula are short and 
strong, and united together at each end. The hind foot, contrary 
to the usual rule in the Edentata, is even more singularly modified 
than the hand. Thus the ankle-joint is formed upon a peculiar 
plan, quite unlike that of the Sloths, or of any other mammal, except 
the Megatherium’s nearest allies ; and the caleaneum projects nearly 
as far backwards as the fore part of the foot does forwards. There 
is no trace of great toe or hallux, or of its corresponding cuneiform 
bone ; the second toe is rudimentary ; while the third has an enor- 
mous ungual phalanx, which, as in those of the hand, is remarkable 
for the immense development of the bony sheath reflected from 
its proximal end around the base of the claw. The two outer toes 
have large and very peculiarly-shaped metatarsals, but only small 
