324 SCOTT. [Vol. V. 



into a concave facet of which the narrow, elevated "head" of 

 the magnum fits. The distal surface of the magnum is nearly- 

 plane, broad in front and narrow behind, and is occupied entirely 

 by the third metacarpal, but on the radial side is a small facet 

 for metacarpal II. The magnum of AnchWierium, as figured by 

 Kowalevsky (No. 25, PI. II., Fig. 1), is very different from that 

 of Mesohippus, being low and very broad, and the lunar facet 

 is relatively very wide ; on the ulnar face there is in front but a 

 single facet for the unciform, which occupies the whole height of 

 the magnum, while in the horse this facet is divided into supe- 

 rior and inferior portions. Some specimens of Mesoliippus agree 

 with Anchitherium in this respect, others with Eqinis. In the 

 latter genus, the magnum has become extremely broad and low, 

 which especially affects the radial side, so that the scaphoidal 

 facet is now much broader than the lunar. In particular, the 

 posterior portion of the magnum, which is very narrow in Anchi- 

 therium, and still more so in Mesohippus, has become very wide 

 in the horse. 



The unciform is narrow and compressed, but very high, having 

 nearly twice the vertical diameter of the magnum, and in conse- 

 quence projecting far below the distal face of the latter. The 

 proximal end exhibits a small facet for the lunar, and a much 

 larger one for the cuneiform, which is reflected well down upon 

 the postero-external face. Distally there is a large facet for meta- 

 carpal IV. and a much smaller one for metacarpal V. The facet 

 for metacarpal III. is vertical and entirely lateral in position, 

 being placed upon the radial side of the bone, and not at all dis- 

 tal. In Anchitherium (Kowalevsky, PL II., Figs. 1 and 9), the un- 

 ciform is lower, and the distal portion much more produced pos- 

 teriorly ; the facet for metacarpal III. is very oblique in position. 

 The unciform of the horse is very different from that of the 

 Miocene genera ; it is much lower, hardly projecting at all below 

 the level of the magnum, which it exceeds but little in height ; 

 the lunar facet has become somewhat broader, and the facet for 

 metacarpal III. almost entirely distal in position, forming a 

 gently curved outline with the facet for metacarpal IV. ; of 

 course, there is no facet for a fifth digit ; posteriorly the unci- 

 form is seen to rest upon the third metacarpal : in Mesohippus 

 this is not the case. 



The metacarpus (PI. XXIII., Figs. 26-28, 30) consists of three 



