A Remarkable Ground Sloth 1 3 



One generic distinction in N othrotherium is the presence of an entepicondylar 

 foramen which, while a characteristic of the Santa Cruz ground sloths, has been lost 

 in all other Pleistocene genera. It is a primitive character. 



Ulna and Radius (Plate II).— The distal end of our ulna differs from Stock's 

 figures in having a distinct concavity for the reception of the cuneiform bone. It 

 agrees, however, with his description. 



There is no complete radius in the Rancho la Brea collection, so that the length 

 as compared with ours is conjectural. 



ULNAR MEASUREMENTS 



Manus (Pis. II, IV, V). — The manus in the Yale N othrotherium are complete 

 and add to our knowledge of this element, Stock's very accurate restoration erring in 

 a perfectly understandable way. The very perfection of the manus and pes, in which 

 the tendons, ligaments, and claws are in situ, obscures some details and makes detailed 

 study of the individual bones impossible. X-ray photographs kindly taken by Dr. 

 C. R. Scott of the Yale Medical School and here reproduced (Plate V) will aid in 

 supplementing the description. 



The manus has five digits of which the first and fifth, while complete and possess- 

 ing claws, did not bear the creature's weight in walking on the knuckles. In the right 

 manus of the Yale specimen, however, the outermost claw had apparently been lost 

 during life, and the second phalanx is rounded off distally, having lost about half of 

 its normal length. The digit is complete on the left hand but, were the right only 

 known, one would be justified in the belief that the fifth digit was vestigial. Sesa- 

 moids are borne on digits II, III, and IV but not on I and V. The second claw is 

 lighter and straighter than the third. The unguals are flexed at an angle of about 90 

 in the left manus with comparatively little flexion of the other articulations. The 

 digits are united by the skin to about half the length of the second phalanx, so that 

 little more than the claws are free. In their present condition the claws tend to con- 

 verge toward their tips, a feature yet more marked in the pes. To what extent this is 

 due to shrinkage of the soft tissue is not clear, but, in the foot at any rate, this con- 

 vergence seems to be natural, not postmortem. The tip of the middle claw of the manus 



