300 THE OSTEOLOGY OF ELOTHERIUM. 



external border, while in Elotherium this difference is decidedly less marked. In Sus 

 the humerus resembles that of the White River genus in form, but is proportionately 

 very much shorter ; the deltoid ridge is shorter and less prominent, while the supinator 

 ridge and the epicondyles are more so. 



The radius and ulna (PL XVIII, Fig. 10) are firmly coossified in all the known 

 species of Elotherium, though the suture between them is clearly marked, even in old 

 animals. The radius is relatively very long, but rather slender ; the head is quite thick, 

 but of only moderate breadth, projecting most toward the external side. The humeral 

 surface is composed f three connected facets, of which the internal one is much the 

 largest and bears an elevated ridge for the corresponding depression on the humeral 

 trochlea. The groove for the intercondylar ridge of the latter is quite broad and notches 

 the anterior border of the radius. The shaft is rather narrow transversely, but quite 

 thick and heavy, and arches forward but moderately ; the distal portion is broadened and 

 thickened and bears upon its dorsal face a deep tendinal sulcus, bounded by very promi- 

 nent ridges. The. distal face is quite broad, but without much dorso-palmar extension, 

 and carries two well-distinguished carpal facets, which pursue an oblique course, from 

 before backward and inward. The scaphoidal facet, which is the smaller of the two, is 

 concave in front, saddle-shaped behind, and is reflected up upon the posterior face of the 

 bone. The facet fur the lunar is much larger than that for the scaphoid, and has a 

 somewhat similar shape, but the anterior concavity is not so deep, and the articular 

 surface is carried much farther up upon the palmar side of the radius. The radius has 

 no contact with the pyramidal. 



In Hippopotamus the forearm bones are ankylosed, though somewhat less intimately 

 than in Elotherium. The radius is very short, broad and thick, and is almost straight. 

 The external facet for the humerus is larger and more concave and the carpal facets are of 

 more nearly equal size, while that for the lunar rises much more steeply toward the ulnar 

 side. In Sus the two bones are separate, and the radius is short, very heavy and arched 

 forward; its distal end is much more thickened than in Elotherium, the facet for the 

 scaphoid is relatively larger, while that for the lunar is smaller and is extensively 

 reflected upon the palmar face of the radius. In Dieotyhs the ulna and radius have 

 coalesced even more completely than in Elotherium. 



The ulna has a very long, thick and prominent olecranon, which projects far behind 

 the plane of the shaft. The process is convex on the outer side and concave on the inner, 

 thickened and club-shaped at the free end, which displays a broad, shallow sulcus for the 

 extensor tendons. The sigmoid notch is deep and the coronoid process prominent, as is 

 required by the great depth of the anconeal fossa on the humerus. The articulation of 

 the ulna with the latter is confined to the posterior and superior aspects of the humeral 



