MESOREODON 101 



former, less so than in the latter. The proximal end is much contracted and bears a single rounded articular 

 surface, part of which is for the ulna and part for the cuneiform. 



The trapezium is a small nodular bone which has but two facets, one for the trapezoid and, at an obtuse 

 angle with this, another for the second metacarpal. . . . This carpal enables us to state with entire confidence that 

 in Mesoreodon the pollex is not represented even by a rudiment. The trapezoid is a large bone both vertically 

 and transversely, but it has no great antero-posterior depth; proximally, it bears a large and simply convex facet 

 for the scaphoid and its radial side is occupied by a concave surface for the trapezium. Distally, there are two 

 facets, one of which is large and slightly concave, the other small, plane and inclined at an open angle to the 

 first; the former is the surface for the second metacarpal and the latter for the third. 



The magnum is a very characteristic bone. . . . Seen from the front, the magnum appears to be smaller 

 than the trapezoid, and is both lower and narrower, but its upper surface rises rapidly towards the palmar side, 

 forming the "head." Behind the anterior face the bone is deeply constricted by two concave facets, one on the 

 radial side for the trapezoid and the other on the ulnar side for the lunar. The trapezoid and magnum are very 

 closely interlocked and form a continuous saddle-shaped surface for the scaphoid, which in appearance resembles 

 the astragalar trochlea of a carnivore. The magnum ... is entirely beneath the scaphoid. . . . The lunar surface 

 is deeply concave . . . and almost entirely lateral in position, but on the palmar side is a small, shelf-like projec- 

 tion which extends somewhat beneath the lunar. This gradual displacement of the magnum towards the radial 

 side of the carpus is already indicated in the oldest known genus of the family, Protoreodon, and is more decidedly 

 marked in Oreodon and Eporeodon, though even in the latter it has by no means been carried to the same extent 

 as in Mesoreodon, in which it attains the extreme position found in Merychyus and Merycochcerus. The contact 

 between the magnum and the unciform is very slight and nearly or quite limited to the posterior or palmar margin, 

 the two bones being separated by the long beak of the lunar and the strong process which the third metacarpal 

 sends obliquely upward and outward to abut against the unciform. Distally, the magnum bears a single saddle- 

 shaped facet for mc. iii, which is reflected upward more upon the ulnar than on the radial side. This facet is 

 elongate and quite deeply concave in the dorso-palmar direction, contracting to a point behind, narrow and very 

 convex transversely. There is no facet for mc. ii, that bone being excluded from contact with the magnum by 

 the connection of mc. iii with the trapezoid. The posterior hook of the magnum is short, curved, blunt, depressed 

 and curved towards the radial side. The unciform is high and broad, with its proximal portion contracting 

 posteriorly. The upper surface bears an oblique facet for the lunar, which rests almost entirely upon the unci- 

 form, and somewhat larger convex facet for the cuneiform. The metacarpal surfaces form a nearly continuous 

 curve. On the radial side, though confined to the dorsal half of the bone, is a large oblique facet for the projec- 

 tion from mc. iii; distally, there is a larger facet for mc. iv and a smaller one for mc. v; the latter surface is 

 reflected up upon the ulnar side of the unciform. 



The four metacarpals are similar in proportions to those of Eporeodon but differ from them in 

 that Mc. II does not reach the magnum; Mc. IV descends somewhat below the end of Mc. Ill, and 

 yet it is the shorter of the two bones, and Mc. V is very similar to Mc. II. The proximal phalanges 

 are relatively shorter than those of earlier genera in this group; those of the middle row are 

 markedly shortened and broadened, and those of the distal row are "shaped like the half of a 

 slender and somewhat irregular cone." 



The hind limb closely resembles that of Eporeodon. Scott (1895, p. 143) says of the pelvis: 



The ilium has a shorter peduncle which expands more abruptly into a wider plate. The latter is less strongly 

 everted, especially at the antero-inferior angle, which is less prolonged. The iliac surface is broader and more 

 rounded, the acetabular border less prominent, and the pubic border more so. . . . The acetabulum is much larger 

 and relatively shallower and the articular surface is more reduced by the very large sulcus for the round ligament. 

 The ischium is more twisted upon itself, so that the posterior end is much more everted and depressed. The crest 

 above the acetabulum descends more abruptly in front and dies away behind without forming an ischiadic notch. 

 The pubis in its free portion is short and stout and the symphysis, in which the ischium shares, is elongate. 



The femur shows similar minor differences from that of Eporeodon. The tibise in the two 

 genera are much alike, except that the distal facet for the fibula has been better developed than that 

 of the earlier genus. The fibula is very much reduced. 



The pes departs almost none from the standard merycoidodont type of the earlier genera. The 

 ectocuneiform and mesocuneiform are ankylosed as usual. The metatarsals, when compared with 



