608 



LAND MAMMALS IN THE WESTERN HEMISPHERE 



Despite innumerable variations of detail, the skeleton of the 

 Santa Cruz fground-sloths may be described without distinc- 

 tion of genera, though it should be added that the skeleton is 

 but partially known in many of the genera, and fuller knowledge 

 might require modification of some of the statements. The 

 neck was of moderate length, the body long, the tail long and 

 heavy and, in some instances, very mas- 

 sive. The sternal ribs were completely 

 ossified and already had the same elabo- 

 rate mode of articulation with the breast- 

 bone as in the great Pampean forms, 

 and the vertebrae the same intricate con- 

 nections. The shoulder-blade also had 

 the same characteristics as in the latter, 

 but the hip-bones had but a moderate 

 transverse expansion, having no huge 

 mass of viscera to support. 



The limbs were stout and short, fore 

 and hind legs of nearly equal length ; the 

 humerus had the epicondylar foramen 

 and the broad, flattened femur retained 

 the third trochanter. The radius had a 

 discoidal upper end, which rotated freely 

 upon the humerus ; the tibia and fibula 

 Owen). Cai, caicaneum. were always Separate. The feet were 

 tlvicu\T''^c!^% cn^'s, five-toed, all the digits complete and 

 middle and external cunei- functional and all provided with claws ; 



forms. C5., cuboid. • n i- ^ i^ j.i 



there was no coossmcation between tne 

 phalanges. The astragalus was little different from the 

 normal form, but in some genera {e.g. \Prepotherium) the 

 highly peculiar form of this bone characteristic of \Mylodon 

 and \Megatherium was distantly foreshadowed. The gait 

 must have been simply plantigrade, though some of the forms 

 had probably begun to throw the weight upon the outer edge of 

 the foot. 



Fig. 290. — Left pes of 

 \Mylodon, Pampean (after 



