9 o 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 withdrawn within the front aperture of its shell, and only 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, 



