280 MAMMALIA. 



Y-shaped as usual. The acromion process of the scapula unites with 

 the coracoid process, completing a foramen as in the modern sloths. 

 The clavicle is relatively large and sigrnoidally bent. The fore limb is 

 longer than the hind limb, and is shown to have been remarkably mobile. 

 There is no entepicondylar foramen in the humerus. In the hand, the 

 first digit or pollex is represented merely by a rudimentary metacarpal ; 

 nos. ii to iv are complete and well-developed, with enormous claws, 

 which bear a reflected bony sheath at the base ; no. v, or the outermost 

 digit, exhibits only two small phalanges without a claw. The pelvis is 

 very wide, and the short and stout hind limbs with the tail form a tripod 

 on which the whole weight of the body would easily rest. The femur is 

 extremely broad and flattened antero-posteriorly ; the short tibia and 

 fibula are fused together at each end. The tarsus is peculiar, and the 

 calcaneum projects backwards almost as far as the toes extend forwards. 

 The first or inner digit is entirely wanting, and the second digit is quite 

 rudimentary ; the third or middle digit is very large, and bears a great 

 claw with its characteristic basal sheath ; while the two outer digits are 

 furnished only with relatively small phalanges and no claw. No dermal 

 armour has been observed. The genus Megatherium occurs typically in 

 the Pampa Formation (Pleistocene) of the Argentine Republic, but has 

 also been found in superficial deposits in Chili and Brazil. No undoubted 

 remains have hitherto been met with in North America, though similar 

 teeth occur in the phosphates of South Carolina. 



Megatherium seems to have been entirely destitute of 

 dermal armour, and the only one of its allies in which bony 

 plates have hitherto been found is Mylodon, while these are 

 very small and not fused together. The species of Mylodon do 

 not attain quite so large a size as the typical Megatherium. 

 The skull in this genus is comparatively short, with the teeth 

 more or less ovate in section, like those of the modern sloths, 

 and the series extending almost to the anterior end of the jaws. 

 The three inner digits of the fore foot bear claws, while the 

 two outer digits are reduced and without claws. As in Mega- 

 therium the hind foot wants digit no. I, but both no. II and 

 no: in bear claws. The typical species is Mylodon harlani, 

 about as large as a rhinoceros, from the Pleistocene of Kentucky 

 and other southern parts of North America ; but the genus is 

 still better represented in the Pliocene and Pleistocene of 

 South America. In the South American Scelidotherium 

 (fig. 161) the skull is comparatively elongated, its shape more 

 like that of the anteater than any of the others. 



