THE OSTEOLOGY OF ELOTHEKIUM. 30? 



The metacarpus consists of four members, two functional, the third and fourth, and 

 two mere rudimentary nodules, the second and fifth. 



Metacarpal Ilia not preserved in any of the specimens which I have seen, though it 

 is figured by Marsh ('93, PI. VIII, Fig. 4), but the facets on the neighboring bones show 

 that it was carried by the trapezoid and retained a lateral connection with the magnum, 

 excluding mc. iii from any contact with the trapezoid. The manus of Elotheriwm is thus 

 a typical example of what Kowalevsky has called the "inadaptive mode" of digital 

 reduction. 



Metacarpal III is long and massive. The head is heavy, enlarged in both dimensions, 

 and has a stout prominence upon the palmar side ; it bears a broad, saddle-shaped surface 

 for the magnum. On the radial side is a depression for mc. ii, at the proximal end of 

 which are two small facets for that bone. The unciform process is very large, prominent 

 and heavy, and projects far over the head of mc. iv, but is, as usual, confined to the 

 dorsal half of the head. On the distal side of this process and on the ulnar side of the 

 shaft is a continuous, concave facet for the head of mc. iv. A second facet for the same 

 metacarpal is borne upon the palmar projection from the head. The shaft of mc. iii is 

 broad, but much compressed and flattened antero-posteriorly ; both width and thickness 

 are nearly uniform throughout, but increase slightly toward the distal end. The distal 

 trochlea is broad and rather low, but is reflected well up upon the palmar face; on the 

 dorsal side it is demarcated from the shaft only by an obscure ridge, with no deep 

 depression above it. The carina is very prominent, but is confined entirely to the palmar 

 face. The lateral pit on the ulnar side is large and deep, but that on the radial side is 

 faintly marked. 



In Kowalevsky's specimen ('76, Taf. XXVI, Fig. 21) the third metacarpal does not 

 differ in any important way from that of the American species, though the magnum 

 facet is somewhat more concave transversely and the shaft is rather more slender. In 

 Anthracotherium (Kowalevsky, '73, Taf. XIII, Fig. 80) mc. iii is very similar to that of 

 Elotherium, but is relatively heavier ; at the proximal end the tubercle for the insertion 

 of the extensor carpi radialis muscle is more conspicuous, and the palmar projection of 

 the head more prominent. 



Metacarpal IV is a little shorter and narrower than mc. iii, with which it articulates 

 by two large facets, separated by a wide and deep groove ; of these facets the dorsal one. 

 which is overlapped by the unciform process of mc. iii, is strongly convex, while the 

 palmar facet is flat and borne upon the palmar projection. The ulnar side has a shallow 

 groove, in which lies the nodular mc. v ; the articulation with the latter is by means 

 of a single, small, triangular facet. The shaft is somewhat narrower transversely than 

 that of mc. iii, but is otherwise like it, as is also the distal trochlea. 



