No. 3-] OSTEOLOGY OF MESOHIPPUS AND LEPTOMERYX. 323 



massive projection from the palmar face. The proximal surface 

 is small, slightly concave, and occupied by the ulna ; there is a 

 small facet also for the radius, but this is not apparent in all 

 specimens. Distally there is a concave facet for the unciform, 

 which is broader behind than in front. The pisiform facet is 

 narrow, but long, and but little oblique in position, presenting 

 nearly directly upwards. The cuneiform of the horse is rela- 

 tively broader and more massive, but lower ; the posterior pro- 

 jection is much less prominent, and the pisiform facet is nearly 

 vertical, presenting backward, and but very slightly upward. 



The pisiform is of entirely different shape from that seen in 

 the horse ; it is quite long and compressed, with a somewhat 

 contracted neck and expanded free end, which is slightly in- 

 flected at the tip. The cuneiform facet is long and narrow and 

 entirely on the inferior surface, forming nearly a right angle with 

 the ulnar facet, with which it is continuous (though in some 

 specimens it is separated from it by a short interval) ; the latter 

 is of triangular shape, and slightly concave. In the horse, the 

 pisiform has a much greater vertical diameter and no neck ; the 

 ulnar and cuneiform facets are both on the proximal end, on nearly 

 the same plane, and separated from each other by a deep notch. 



The trapezium is a very small nodular bone, with its vertical 

 diameter the principal one ; proximally it has a minute contact 

 with the scaphoid, and distally it presents an oblique facet for 

 the posterior side of the head of the second metacarpal, project- 

 ing below the level of the distal face of the trapezoid. 



The trapezoid is rather low, and very narrow in front, broader 

 behind. Its position is rather more lateral than in the horse, and 

 more of it is visible when the manus is viewed from the front. 

 The proximal surface is somewhat convex, the distal nearly 

 plane, and there is a small posterior facet for the trapezium. The 

 trapezoid supports only metacarpal II., and there is no separate 

 posterior facet for the magnum such as occurs in the horse. 



The magnum is relatively high and narrow, in correlation with 

 the moderate degree of expansion which the median digit has 

 undergone. The proximal surface is in front divided, nearly 

 equally, between the facets for the scaphoid and the lunar, the 

 former slightly the broader, the latter more oblique in position, 

 and the two meeting in an open angle, and forming a sharp 

 ridge. Posteriorly the magnum is covered only by the lunar, 



