3l4 THE OSTEOLOGY OF ELOTHERITJM. 



IX. The Pes. 



The tarsus has undergone little specialization, although the hind foot, like the fore 

 foot, is didactyl. 



The astragalus is elongate, though broad and massive as well. The proximal 

 trochlea is deeply but very broadly grooved and its two parts are unequal, the external 

 condyle rising much more, both proximally and dorsally, than the internal, but not pro- 

 duced so far distally. While the outer condyle is widely separated from the cuboidal 

 facet, the inner one is continued so far distally as to become confluent with the navicular 

 surface. A very large and deep pit occupies a great part of the dorsal surface between 

 the proximal and distal trochlea. The distal trochlea is broad and is unequally divided 

 into facets for the cuboid and navicular, the latter being much the wider and of a different 

 shape. The surface for the cuboid is strongly convex in the dorso-plantar direction, but 

 nearly plane transversely, while the navicular facet is hour-glass shaped, and on the fibular 

 side of the median line has a distinct, though wide and shallow groove for a corresponding- 

 ridge on the proximal side of the navicular. The junction of the two facets forms a sharp 

 but not prominent edge. 



The facets for the calcaneum somewhat resemble those which we find in Ancodus, 

 but they have not attained to such a degree of specialization as in the American species of 

 that genus. The proximal external facet is divided by a sulcus into two parts, both of 

 which are concave and present distally, as well as laterally. The proximal portion is set 

 on a conspicuous prominence of the fibular side of the astragalus, and is clearly visible 

 when the bone is seen from the dorsal side, while the distal portion is also prominent, but 

 is concealed when looked at from the same point of view. The sustentacular facet is very 

 large and is strongly convex in the proximo-distal direction, but almost plane trans- 

 versely; its external border projects as a shelf beyond the body of the astragalus, and 

 thus helps to enclose the large and deep sulcus which is found upon the external side of 

 the bone. The distal external facet fur the calcaneum is very small. The fibular facet 

 is well extended in the proximo-distal diameter, but is narrow in the dorso-plantar 

 direction. 



In Kowalevsky's specimen ('76, Taf. XXVII, Fig. 34) the astragalus, so far as it is 

 preserved, resembles that of the American species, but the external part of the proximal 

 trochlea is too much damaged to show the characteristic external calcaneal facet. In 

 Anthracotherium (Kowalevsky, '73, Taf. XI, Fig. 59, de Blainville, Osteographie, 

 Anthraco., PL II) the astragalus is proportionately much broader and lower than in 

 Motherium, the ridge on the distal trochlea, formed by the junction of the two facets, is 

 more prominent and pursues a more oblique course. The sustentacular facet is narrower 

 and shorter and the proximal calcaneal facet projects less. The astragalus of Sus is quite 



