440 PROFESSOK OWEN ON MACBOPUS. 



or fibular border (2), but more definitely bounded by a ridge (a) on the inner side, 

 over which the articular surface passes, at almost a right angle, to form the flattened 

 one (ib. d, & fig. 5, d a) adapted to the inner malleolus. Beyond this surface a 

 depressed non-articular part of the bone (fig. 3, e) extends a short way inward and 

 forward, where it is terminated by the narrow anterior oblong convexity (fig. 5,/) for 

 the naviculare. The inner non-articular part of the astragalus terminates in a 

 tuberosity (ib. g). The posterior non-articular part, forming the apex of the triangle 

 (ib. h), applies itself to the hind part of the inner articular expansion of the calcaneum, 

 to which it is ligamentously attached. 



On the under surface of the astragalus (fig. 4) is the antero-posteriorly concave 

 surface (^), articulating with the convex one on the outer half of the upper expanded 

 articular part of the calcaneum (fig. 6, i). Internal to this, at the middle of the under 

 surface of the astragalus, is the oblong flattened articulation (fig. 4, ^j for the fiattened 

 surface on the inner division of the upper articular part of the calcaneum (fig. 6, k). 

 Anterior and internal to this is a smaller facet (fig. 4, I), continuous with the navicular 

 one (/), but articulating with the inner side of the anterior calcaneal surface for the 

 cuboid. No part of the surface (/, I) is extended to the tibio-malleolar articulation 

 as in Phascolomys. 



The astragalar characters are well marked, and could not fail to be recognized in a 

 fossil bone of the Macropodal family. 



The calcaneum of a Kangaroo is equally well characterized (PI. LXXXIII. figs. 1 & 2, 

 r, b, figs. 6 & 7). The fulcral portion [a b, a c) is long and triedral, the narrowest, 

 roughest, flattened side, or " sole," being below (fig. 7 c) ; the two broader, smoother, 

 concave sides convei'ge to the superior or anterior rounded angle (fig. 6, b) : the free end 

 is due to a tuberous epiphysis (a) with an upper smooth bursal surface on the terminal 

 facet. 



The upper angle (fig. 6, b) expands to the anterior articular or tarsal portion of the 

 bone, which is more abruptly enlarged, and especially to the outer side : this supports 

 the subconvex articular surface {d) for the external malleolus formed by the distal 

 epiphysis of the fibula (PI. LXXXII. fig. 8, b). The upper surface of the expansion 

 supports the convex surface (?') for the articulation (?') of the astragalus (fig. 4). The 

 upper and inner rising is divided into a small anterior smooth articular surface (fig. 6, 

 k) for that marked k in the astragalus (fig. 4), and a posterior, chiefly roughened, 

 surface {h) for syndesmosis with the apical part of the astragalus (fig. 4, h). In advance 

 of the astragalar expansion the calcaneum, somewhat contracted, extends, and terminates 

 in the large subtriangular vertical surface for the " cuboides." The outer half of this 

 surface (fig. 8, e) is more produced than the inner one (ib. /), and is continued into 

 the lower or apical part (ib. g) of the cuboidal facet. The astragalar expansion (figs.6, 

 7, d, n, e) overhangs the lateral concave surface on both sides of the bone, but most so 

 on the outer one (fig. 2), which develops two tuberosities (fig. 7, n, «'). 



