THE OSTEOLOGY OF ELOTHERIUM. 315 
like that of Hlotherium, especially in the proportions of the distal trochlea. In Hippopo- 
tamus the astragalus is remarkable for its extreme shortness, for the asymmetry of its 
proximal trochlea, the outer condyle much exceeding the inner in size, and for the almost 
equal division of its distal trochlea between the nayicular and cuboid facets. 
The calcaneum has a long tuber, which is deeply channeled on the external side and 
for most of its length is compressed and rather slender, but swells at the free end into a 
massive, club-shaped expansion, which has a broad, shallow tendinal. sulcus on the 
plantar face. From the free end the dorgo-plantar diameter of the caleaneum increases 
gradually to the fibular facet, where it reaches its maximum, and from which it contracts 
rapidly toward the distal end. The sustentaculum is yery prominent and bears a wide, 
slightly concave facet for the astragalus. The distal astragalar facet is much more 
extended in the dorso-plantar direction than is the corresponding surface on the astragalus 
and indicates an unusual amount of movement between the two bones. The cuboidal 
facet is narrow transversely, but much extended antero-posteriorly ; it is divided, though 
very obscurely, into dorsal and plantar parts, of which the former is the larger and has 
something of a saddle-like shape, while the latter is smaller and concave. 
Kowaleysky does not describe the caleaneum of 2. magnum and his description and 
figures of Anthracotherium do not furnish data for comparison. The caleaneum of Sus 
resembles that of Hlotherium, but is broader and has a tuber of more uniform thickness, 
not channeled on the outer side. The articular surface for the cuboid is yery distinctly 
divided into two facets, the junction of which forms a sharp ridge. In Hippopotamus the 
calcaneum has an exceedingly long and massive tuber, which is greatly swollen at the 
free end. 
The navicular is a large bone, not very broad, but of considerable dorso-plantar 
diameter. The surface for the astragalus is hour-glass shaped, with two coneayities sepa- 
rated by a broad, convex ridge, which on the dorsal side is marked by an eleyation of the 
proximal margin. The concavity on the tibial side is the larger of the two and its plantar 
border rises much higher than that of the external concavity. There are three facets for 
the cuboid on the fibular side of the bone, one plantar and two dorsal; the former is very 
strongly convex, projecting well outward, and is high yertically, but narrow antero- 
posteriorly. The two dorsal facets are both small and plane, and are placed at the 
proximal and distal margins of the navicular. The plantar hook is very much reduced, 
forming hardly more than a roughened ridge. The distal end is occupied principally by 
the large facet for the ectocuneiform, which extends across the whole dorsal side and 
much of the tibial side also. Partially separated from this is a minute surface for the 
mesocuneiform. The facet for the entocuneiform is much larger than the latter ; it stands 
isolated at the postero-internal angle of the distal end and is somewhat saddle-shaped, 
