MAMMALIA. 



73 



feeding. The original bones and teeth of Megatherium, other Stand X. 

 remains of Mylodon, and numerous parts of the skeleton of Case Y - 

 Scelidotherium (Fig. 68) are arranged in Wall-case. 26. The 

 bones bear conspicuous crests and ridges, which indicate the 

 muscular power of these animals. The feet are twisted, 

 so that their side rather than their palm would be used when 

 walking; and one, two, or three of the toes on each foot 

 terminate in a great claw. The fore quarters are arranged 

 for the easy motion of the grasping arms. The front of the 

 mandible is spout-shaped (see Figs. 68, 69), evidently adapted 

 to a long protrusible tongue, which could be used like that 

 of a giraffe for pulling leaves off the trees. The few grinding 

 teeth would continually grow as they were worn down 

 throughout life, and those of Megatherium (Fig. 69) are made stand X. 



Pig. 69. — Lower jaw of Megatherium americanum, showing double- 

 ridged molar teeth and long spout-shaped symphysis (d), from the 

 Pampa Formation of Buenos Aires, Argentine Republic ; one-eighth 

 nat. size. (Wall-case 26.) 



extremely powerful by consisting of alternate soft and hard 



plates of tooth-substance, which produce cross-ridges on the 



crown. 



The skeletons of the ground-sloths are wonderfully well 



preserved in the Pampa Formation of the Argentine 



Eepublic, and it is the rule rather than the exception to find 



them whole. Most of them are discovered on the borders 



of old lakes and rivers, evidently in the position in which 



the animals suddenly died. They are supposed to have 



perished in the mud and soft ground when attempting to 



reach the water to drink during dry seasons ; for droughts 



are common even at the present day in the country where 



they formerly lived. In the time of the ground-sloths, 



however, the pampa can scarcely have been the bare plain 



that it is now ; it must have borne forest vegetation. 



Both human bones and stone implements have occasionally Table-ease 



15a. 



