BOG THE OSTEOLOGY OF ELOTHERIUM. 



The magnum figured by Kowalevsky ('76, Taf. XXVI, Figs. 21, 32) is of the same 

 general type as in the American species, but with some differences of detail. Thus, the 

 bone is of relatively greater antero-posterior thickness ; the palmar face is narrower and 

 the palmar hook very much more prominent ; the sulcus which, on the ulnar side, 

 separates the two arms of the lunar facet is much narrower, and, in consequence, the 

 arms themselves are broader ; the head of the magnum rises less abruptly toward the 

 palmar side. The magnum of AnthracotJierium is not sufficiently well known for com- 

 parison. That of Hippopotami/* is low and broad, and differs from the magnum of 

 Elotherium in that the dorsal portion of the lunar facet is proximal in position. In Stts 

 also the magnum is low and wide ; its lunar facet is relatively larger than in Hippopota- 

 mus, and it lias no articulation with the second metacarpal, from which it is excluded by 

 the contact of the third metacarpal with the trapezoid; the head is low. 



The unciform is the largest and most massive bone of the carpus ; in shape it is low, 

 broad and thick, with its principal diameter directed transversely, and has on the palmar 

 side a hook-shaped process, which is not very prominent, but broad and heavy. The 

 proximal end is occupied by the facets for the lunar and pyramidal, of which the latter 

 is much the wider: the junction of the two forms a prominent ridge which curves across 

 the proximal end, from the dorsal to the palmar side. These two facets are both slightly 

 concave transversely, hut very strongly convex antero-posteriorly, being reflected far 

 down upon the palmar face. On the radial side are two vertical articular bands, 

 separated by a wide and deep sulcus. The dorsal hand, which is much the wider of the 

 two, is composed of two very obscurely separated facets, a minute proximal one for the 

 magnum and a very large distal one for the unciform process of the third metacarpal. 

 The palmar hand is a high and narrow facet for the magnum only, and is much more 

 extended vertically than the corresponding surface on that hone. The distal end. carries 

 a large facet for the head of the fourth metacarpal, and on the ulnar side is a minute facet 

 lor the rudimentary fifth metacarpal. 



The unciform of Kowalevsky's specimen docs not differ in any significant way from 

 that of the American species. In AnthracotJierium this bone is much wider and lower 

 than in Elotherium and the facet for the fifth metacarpal is more distal than lateral. In 

 Hippopotamus the unciform is exceedingly large, and its dorsal face is of a low, wide. 

 rectangular outline, and its great breadth corresponds to the large size and functional 

 importance of the fifth metacarpal. The proximal end is divided almost equally between 

 the lunar and pyramidal facets, and the absence of a distal beak on the lunar allows a 

 larger contact between the unciform and magnum. In Sus, which has much reduced 

 lateral digits, the unciform is narrower than in Hippopotamus, hut broader than in 

 Elotherium, and the facet for the fifth metacarpal is not so completely displaced toward 

 the ulnar side as in the latter. 



