156 THE MAMMALIA OF THE DEEP RIVER BEDS. 



with slightly opisthoccelous faces which is commonly found among the larger artio- 

 dactyls. In the middle and hinder parts of the region the spines become lower and 

 more slender. The transverse processes in the middle region rise high above the 

 centra and project conspicuously outward. 



The lumbar vertebras number at least five, since that many are preserved in one 

 specimen. These vertebras have long, depressed and arched centra, which are quite 

 sharply contracted in the middle. As in the other vertebral regions, the neural canal 

 is notably small, especially in the vertical diameter. The spines are very thin and 

 compressed, but extended antero-posteriorly, and the transverse processes are long 

 and wide but also very thin and depressed. The zygapophyses are of the usual 

 interlocking character, and, in the anterior region at least, the metapophyses are 

 conspicuous. Little is preserved of the sacrum, but enough to show that the pleura- 

 pophyses were massive and apparently confined to the first vertebra. No caudals 

 are represented in any of the specimens-. 



The ribs are known only from a few fragments. It is obvious, however, that 

 the anterior ribs were broader and more flattened than in the other oreodont genera, 

 in which they are remarkably slender for hoofed animals, though probably Merycliyus 

 should be excepted from this statement. 



The humerus is rather short but of massive construction, which is merely an 

 exaggeration of the structure which occurs in the smaller and lighter genera of the 

 family. The head is large, projecting strongly backward, and is very convex in both 

 directions, so as to be of almost hemispherical shape. The external tuberosity is 

 greatly enlarged and extends across the entire anterior face of the bone, and is 

 strongly curved so as to follow the shape of the head; its free border rises steeply 

 towards the inner side and is wider than the base, projecting at both ends, especially 

 internally, where it is drawn out into a massive hook. The inner tuberosity is small 

 and the bicipital groove very deep. The proximal portion of the shaft is compressed, 

 but of great antero-posterior depth ; the deltoid ridge is not very prominent, but 

 extends far down the shaft. The distal end of the humerus is broad and the trochlea 

 is characteristically like that of the other oreodont genera, as is especially seen in 

 the broad, low and rounded intercondylar ridge and in the very prominent and mas- 

 sive internal epicondyle. 



The ulna is heavy and altogether unreduced, being larger than the radius, except 

 at the distal end. The olecranon is extremely high and deep antero-posteriorly and 

 is thickened and grooved by a tendinal sulcus at the free end. The upper part of the 

 articular surface for the humeral trochlea is broad, but then abruptly contracts and 

 is continued downward only upon the internal side, and the radial facets are distinctly 



