34-O PATAGONIAN EXPEDITIONS! PALAEONTOLOGY. 



It may be asserted with confidence that the manus was pentadactyl and 

 that all the digits carried claws. Metacarpal I is short and very heavy 

 and has a rugged, massive appearance, quite unlike the smooth, subcylin- 

 drical form seen in Hapalops ; the facet for the trapezium is very large 

 and oblique, forming a sharp edge with the facet for metacarpal -II ; the 

 shaft is short, heavy and rugose ; the distal trochlea is well developed 

 and has a distinct carina. 



Metacarpal II is very much longer, but relatively slender ; the proximal 

 end has a curiously warped surface for the trapezoid ; dorsally there is no 

 contact with the magnum, but on the palmar side there is an articulation 

 of considerable extent ; on the radial side of the head is a very large 

 and slightly concave facet for the first metacarpal, and on the ulnar side 

 a still larger facet for the third. The shaft is of very irregularly trihedral 

 shape, increasing in diameter distally ; it receives a somewhat twisted 

 appearance from the presence of a prominent, oblique rugosity upon the 

 dorsal face and from the obliquity of the carina ; on the ulnar side, below 

 the facet for III is a prominent rugosity, which may represent an incipient 

 stage of the extensive connection between the second and third meta- 

 carpals, which characterizes Megatherium. The distal trochlea resembles 

 that of Hapalops, except for the obliquity of the carina and the narrow- 

 ness of the lateral facets. 



Of metacarpal III only the distal end is preserved ; the broken end of 

 the shaft has an almost square section, of a diameter much exceeding that 

 of metacarpal II. The carina is less extended palmo-dorsally and pro- 

 jects less in front of and behind the shaft than in Hapalops, and its free 

 border is much less curved. 



Metacarpal IV much exceeds II in length, though not nearly so much 

 as in Megatherium; the proximal end must have been extensively over- 

 lapped by III, the facet for which is much -more oblique than in Hapalops, 

 leaving but a narrow surface for the unciform, while the facet for V 

 resembles that in the latter genus, and there was evidently no such artic- 

 ulation between metacarpals III, IV and V, as in Megatherium. The 

 shaft is much compressed laterally, but thick palmo-dorsally, the dorsal 

 face being a narrow ridge. The trochlea is quite different from that of 

 Hapalops, the carina being less prominent and having a straighter edge, 

 while on the palmar side are small, but well defined and prominent facets, 

 probably for the sesamoids. 



