THE OSTEOLOGY OF ELOTHERIUM. 299 
The humerus is relatively long, but is, at the same time, a massively constructed 
bone. The head is large and very strongly convex, especially from above downward, 
although it is not set upon a very distinct neck, nor does it project far behind the plane 
of the shaft. The external tuberosity is very large, forming a massive and roughened 
ridge, which runs across the whole anterior face of the head and rises toward the internal 
side, where it terminates in a high, thick and recuryed hook, overhanging the bicipital 
groove. The internal tuberosity is very much smaller, but is, nevertheless, quite promi- 
nent; it likewise projects over the bicipital groove, which is very broad and deeply 
incised into the bone. The great transverse breadth of the external tuberosity displaces 
the groove far toward the internal side of the humerus. The shaft is long and heavy ; 
its proximal portion has a great antero-posterior diameter, and its transverse thickness, 
though less, is still very considerable. The fore-and-aft diameter gradually diminishes 
downward, until the shaft assumes an almost cylindrical shape, below which point it 
begins to expand transversely. The deltoid ridge is rugose and prominent, and runs far 
down upon the shaft, but forms no deltoid hook. The distal end of the shaft is very 
heavy, being both broad and thick. The supratrochlear fossa is low, wide and shallow, 
while the anconeal fossa is very high, narrow and deep, its depth being much increased 
by the great production of the posterior angles of the distal end. The supinator ridge is 
rough, heayy and prominent. The trochlea, which is very completely modernized, in 
correspondence with the advanced differentiation of the ulna and radius, is somewhat 
obliquely placed with reference to the long axis of the shaft, descending toward the ulnar 
side. The trochlea differs very markedly from that of such primitive artiodactyls as 
Oreodon and Anoplotherium ; it is high, full and rounded and is divided into two unequal 
radial facets, of which the inner one is decidedly the larger. The intercondylar ridge, 
which, in most primitive artiodactyls, forms a broad and rounded protuberance, is, in 
Klotherium, compressed into a sharp and prominent ridge, and shifted well toward the 
external side. The internal epicondyle, which is so largely developed in Oreodon and 
other early artiodactyls, has practically disappeared. 
The humerus of Hippopotamus is relatively much shorter and more massive than 
that of Hlotherium ; the external tuberosity is not extended so far across the anterior 
face of the bone and the bicipital groove is, in consequence, not shifted so far toward the 
inner side; the deltoid ridge is much better developed and gives rise to a prominent 
deltoid hook. In the existing species of Hippopotamus the intercondylar ridge is 
narrower and less conspicuous, but in a Pliocene species from the Val d’Arno it has 
quite the same appearance as in H/otherium (see de Blainyille, Ostéographie, Hippopot- 
amus, Pl. V). The epicondyles are much more prominent than in the latter, and 
the postero-internal border of the anconeal fossa projects much more than does the 
