THE OSTEOLOGY OF ELOTHERIUM. 315 



like that of Elotherium, 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 navicular 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-shajjed expansion, which has a broad, shallow tendinal sulcus on the 

 plantar face. From the free end the dorso-plantar diameter of the calcaneum increases 

 gradually to the fibular facet, where it reaches its maximum, and from which it contracts 

 rapidly toward the distal end. The sustentaculum is very 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. 



Kowalevsky does not describe the calcaneum of E. magnum and his description and 

 figures of Anthracotherium do not furnish data for comparison. The calcaneum of Sus 

 resembles that of Elotherium, but is broader and has a tuber of more uniform thickness, 

 not channeled on the outer side. The articular surface for the cuboid is very 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 concavities sepa- 

 rated by a broad, convex ridge, which on the dorsal side is marked by an elevation of the 

 proximal margin. The concavity on the tibial side is the larger of the two and its plantar 

 border rises ranch 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 vertically, 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. 



