150 
I'OSSIL MAMMALIA. 
for the continual growth and firm fixture of the 
long and vertical molar teeth ; the extraordinary 
and strong process (b) descending from the zy- 
gomatic arch in the Megatherium, as well as i» 
the Sloths, seems intended to support the un- 
usual Aveight of the lower jaw consequent upon 
the peculiar form of the molar teeth. 
Hones of the 'Trunk. 
The vertebrae of the neck, though strong, am 
small in comparison with those towards th® 
opposite extremity of the body ; being duly 
proportioned to the size of a head, comparatively 
light, and without tusks. The dorsal portion 
of the vertebral column is of moderate size, but 
there is an enlargement of the vertebrae of th® 
loins, corresponding with the extraordinary buH^ 
of the pelvis and hind legs ; the summits of tb® 
spinous processes, (e,) are flattened like those in 
the Armadillo, as if by the pressure of a cuirasS- 
The sacral bone, (PI. 5, Fig. 2, a), is united tn 
the pelvis, (p), in a manner peculiar to itselb 
and calculated to produce extraordinary strength i 
its processes indicate the existence of very 
powerful muscles for the movement of the tail* 
The tail was long, and composed of vertebrae n 
enormous magnitude, (PI. 0, Fig. 2), the body nj 
the largest being seven inches in diameter, an 
