14. A Remarkable Ground Sloth 



is abraded, which may have been due in part to the fall into the pit and the subsequent 

 struggle to escape. 



To summarize: The chief additions to Stock's description are the presence of 

 functional digits I and V. Digit V has about the same degree of reduction as in the 

 Miocene Hafalop, with which it also agrees in having the metacarpal the longest of 

 the five. The movement of this digit on the metacarpal is directed toward the axis of 

 the hand, rather than toward the palm. 



In the only known instance from the Rancho la Brea the trapezium is fused with 

 metacarpal I . I n the Yale specimen there is complete fusion in the left manus but not 

 in the right, for, while the line of articulation shows distinctly, there was no move- 

 ment between the elements. There is also a single metacarpal I from the Rancho with- 

 out trapezium. It is evident, therefore, that this fusion is a variable feature, as with the 

 Pleistocene genus Mylodon. 



Pelvis.— The pelvis (Plate VIII) is preserved entire, save for the outer rim, 

 which is absent except along the dorsal outline of the right ilium. This makes the ilia 

 appear somewhat smaller than they should. The right ilium bears a portion of the 

 hide with hair, the underlying tissue being much shrunken. 



There is nothing to add to Stock's description. 



PELVIC MEASUREMENTS 



Greatest transverse diameter across the ilia 



Width of ilial wing measured parallel to posterior border 



Length of posterior descending process of ischium from superior 



border to ventral symphysis 

 Dorso-ventral diameter of pelvic opening 

 Transverse diameter of pelvic opening 

 Width across posterior ends of ischia 

 Length of fused sacrals 

 Greatest transverse width of sacrum 

 Length of crest of fused dorsal spines 

 Height of dorsal crest, anterior end, from base of centrum 



Femur. — The description of the femur also agrees in detail. Stock mentions a 

 facet for the fabella. In our specimen the fabellae are both present, and in addition an- 

 other flattened bone lies in the articulation between the outer condyle and the tibia, the 

 outlines of which are obscured by tissue. These ossicles are both present in the existing 

 tree sloth Choloefus. The knees of the Yale specimen are flexed at an angle of about 

 90 , and no attempt was made to straighten them in mounting the animal, as they are 

 held rigid by the ligaments. The pose of the Rancho la Brea specimen differs from 

 ours in this regard, but the Yale pose cannot be far from the habitual one. 



