146 DINOCERATA. 



The Astragalus. 

 (Plate XLVII, Plate LIV, tigiire 2, a; ami woodcuts 139-142, below.) 



'i'lie astragalus in the D'mocerata considerably resembles that of the 

 elephant, the bone being, as in that animal, very short, along the axis of 

 the leg and foot. The articular faces are, moreover, but little cvirved, 

 indicating comparatively sliglit freedom of motion in the ankle joint. 



The superior, or proximal, face of the bone, articulating with the tibia, 

 is shown in Plate XLVII, figure 1. This surface is sub-quadrate in 

 general outline, with rounded angles, but is prolonged posteriorly on the 

 inner, or tibial, side into a large convex lobe. 



The surface of the tibial articulation is moderately convex from 

 before backward, and, in front, nearly flat from side to side, but, 

 posteriorly, it Ijecomes somewhat excavated, this being the only indication 

 of the conspicuous groove common in Ungulates. The tibial articular 

 surface is confluent, along the posterior part of its outer margin, with a 

 somewhat convex, rounded face for the fibula, as shown in figure 4. 



The inner surface of the bone (figure 2), or that which is presented 

 upon the tibial side of the foot, is excavated by a large, rounded 

 depression, encroaching above upon the margin of the tibial articular face. 



Below this depression, the bone is expanded, and presents a rounded 

 and convex articular surface, in close relation with the adjoining, and 

 nearly or quite confluent, tVice for articulation \\\\.\\ the navicular, as shown 

 in figiu'e 140, t' below. This convex facet apparently supported a separate 

 bone, as in the existing- H//ia.r (figure 155, C'hapter XIV). This bone, 

 as Baur has suggested, probablv represents the til)i;de, or inner tarsal of 

 tlie proximal row. The same bone exists also in Hi/sfrij., and many other 

 Rodents, and is regarded by Flower as a sesamoid. 



The inferior surface of the astragalus (Plate XLVII, figure 3) 

 articulated with three bcmes; below, Avith the upper faces of the 

 calcaneum, and, in front, with the navicular and the cuboid. All these 

 articular faces niay be confluent, as in the specimen figured on the Plate, 

 and the mode of union with the calcaneum is subject to con.siderable 

 variation. 



