172 



PATAGONIAN EXPEDITIONS '. PALEONTOLOGY. 



(14) The radius has a discoidal or transversely oval head and a remark- 

 ably limited proximal facet for the ulna, the position of which seems to 

 indicate that the radius was habitually carried in front of rather than in- 

 ternal to the ulna ; the proximal portion of the shaft is slender and of 

 transversely oval section, while, for the distal two thirds, it is very much 

 broader and of trihedral shape. In Megatherium the radius is very similar. 



a 



FIG. 24. 

 Hapalops longiceps, left manus, x \. 



FIG. 23. 



Hapalops longiceps, a, left ulna, x \. b, left 

 radius, x \. 



(15) The manus is most like that of Megalonyx and Nothrotherium, 

 though considerably less specialized ; all its parts are free and no element 

 has been lost. The proximal line of the carpus is transverse and not 

 oblique to the axis of the limb ; the scaphoid rests upon the trapezium 

 and trapezoid, but not upon the magnum, while the lunar rests upon the 

 latter, but not on the narrow unciform. Five digits are present, all 

 functional and provided with claws, though the median three digits, 

 II, III, IV, are considerably longer and heavier than the laterals, 

 I and V. None of the phalanges are coossified, and they are present 

 in unreduced number in all the digits. In the Afegalonyc hides the 

 ungual phalanges are very long and sharp, much compressed and de- 

 curved, and more or less deeply cleft at the distal end, while in the 

 manus of the Planopsidce they are of a quite different shape, being much 

 broader, more strongly decurved and depressed, more bluntly pointed and 

 with shallow distal cleft ; in both groups the subungual processes are very 

 large and the bony hood or lamina at the base of the claw is well devel- 

 oped, though less extensively than in the Pleistocene genera. 



So far as the manus itself is concerned, there is little in its structure to 

 indicate that the gait was other than simply plantigrade, but the articular 



