HOLLAND AND PETERSON: OSTEOLOGY OF THE CHALICOTHEROIDEA. 365 
dactyla the distal articulation is generally divided into two portions, for the navic- 
ular and cuboid respectively. The astragalus is on the whole quite rhinocerotic, 
excepting the features above mentioned. In proportion it is higher and narrower 
than the astragalus of Titanotherium. The trochlea is also more deeply grooved 
and the external and internal condyles are more nearly uniform in size and less 
oblique than in the latter genus. A characteristic feature not usually found in 
the Perissodactyla is the downward projection of the external condyle, so that the 
articulation for the tibia on that side projects below the articular facet for the 
navicular (Fig. 98, 1). The tibial condyle has the usual backward projection met 
with in the Perissodactyla. The sustentacular facets are well formed and strongly 
interlocked. Distally there is, as previously stated, but a single large facet for 
the navicular which is very slightly convex transversely and concave antero- 
posteriorly especially near the tibial face. 
In Macrotherium the astragalus is relatively broader and much lower than in 
the American form. Furthermore, its distal face is divided, having a larger facet 
for the navicular and a smaller for the cuboid as in other Perissodactyla (see Fig. 
98, 5). The external condyle of the trochlea does not extend so low (see Fig. 98, 3) 
al ) 
iy 
“WM 
Fie. 98. Astragalus. 1, anterior view of right astragulus of M. elatus (No. 1706A). XX. 2, lateral 
view of do. 3, anterior view of astragalus of Macrotherium. +4. 4, inferior view of left astragalus of M. 
elatus (No. 1710). 4. 5, inferior view of left astragalus of Macrotherium. +4. 
nor does the tibia touch the caleaneum on its extreme backward flexure as in the 
American genus. The fibula, however, apparently came in contact with the lateral 
face of the caleaneum. 
Judging from the sustentacular facets of the caleaneum and the facets on the 
cuboid in Nestoritherium it may be clearly inferred that the astragalus of this 
large form was perhaps more nearly like that in Moropus, 7. e., the distal face 
articulated with the navicular only. 
