90 MOSTLY MAMMALS 
somewhat limited. The observer will not fail to notice 
also the great strength and upright position of the haunch- 
bones and the powerful build of the legs and feet, the 
latter terminating in five toes armed with broad, flattened 
nails. As an illustration of the various modifications of 
the same general plan of structure in use in the animal 
kingdom, it may be well to point out how essentially the 
arrangement of the armour of a glyptodon differs from 
that of an ordinary tortoise or turtle. In the latter the 
carapace is completely welded to the ribs, which are situated 
externally to the haunch- and shoulder-bones, whereas in 
a glyptodon there is no sort of connection between the 
carapace and the ribs, while the latter are internal to 
the haunch- and shoulder-bones. In these respects the 
leathery turtle holds a somewhat intermediate position 
: between ordinary turtles and the glyptodons, the carapace 
: being composed of polygonal plates totally unconnected 
with the ribs, while the latter are situated externally to 
the bones of the shoulder and haunch. 
Not less remarkable are the modifications of the vertebrae 
of the tail for the support of the rings or tube with which 
the latter is encased. In the first place, most of the ver- 
tebrae of this region are welded together so as to form 
a hollow, tapering rod, while from each segment are given 
off radiating processes upon which the bony plates are 
borne, and as the whole of the latter are firmly welded 
together, the entire structure is of great strength. 
When standing with the edges of its impenetrable cara- 
pace resting on the ground, its mail-crowned head partially 
withdrawn within the front aperture of its shell, and only 
the lower portions of the limbs exposed, a glyptodon must 
have been safe from all foes save savage man, and even 
he must have had a tough job to slaughter the monster, 
