52 
DE. W. KOWALEVSKY ON THE 
higher, reminding one precisely of what is seen in Sus, and even more so in Hyomoschus. 
The distal surface (Plate XXXVIII. fig. 8') is also very different. The facet for the 
third metacarpal, instead of being oblique as in the bone figs. 5 & 7, u, Plate XXXVIII. 
(where it forms an oblique truncature of the inferior radial angle on the unciform), has 
gone over to the inner or radial vertical wall of the bone, forming a facet homologous 
to that of the Hog, composed of the facets of the Anoplotherium (Cuvier, pi. 102. 
fig. ii. A 5). In consequence of this the beak-like projection of the third metacarpal in 
the two-toed form is more horizontal (Plate XXXVIII. fig. G, in.) than in the four-toed 
form (fig. 5, hi.), approaching what is presented by the Suidce. The distal surface (fig. 8') 
shows no trace of the outer facet for the fifth metacarpal, and is entirely taken up by 
the greatly enlarged facet of the fourth ; and the margin of this facet is so sharp that it is 
evident that the rudiment of the fifth metacarpal (whose existence is proved by a facet 
on the outer side of the fourth metacarpal) did not touch the unciform, confining itself 
to the lateral upper facet of the fourth metacarpal. 
The posterior projection of the unciform (fig. 8') is very much broadened, so that the 
whole distal surface acquires a somewhat square outline ; but what is more interesting, 
the inner or radial inferior margin of this projection has a large round facet* by which 
it articulated posteriorly with the os magnum. We never meet with such an enlargement 
of the posterior par tof the unciform in the true Saidce , as in these the posterior and 
inferior parts of the unciform and magnum do not articulate together. Such an enlarge- 
ment, however, is seen in Dicotyles , where the unciform sometimes touches the magnum, 
while in Hyomoschus we see, on the inner side of the same posterior enlargement of the 
unciform, a round facet for the magnum ; this facet is also very characteristic of the 
unciform of all true ruminants. The reason of this closer articulation between the 
magnum and unciform seems to lie in the reduction of the lateral metacarpals, which 
caused the carpal bones to concentrate more towards the central part of the carpus. 
The proximal, or upper, surface of this unciform is also much broader and flatter than 
in the four-toed form, both facets for the lunar and pyramidal being more on one plane. 
These two facets are very nearly equal in size, not as in the Pig, where the lunar facet is 
much longer and broader than the facet for the pyramidal. 
Dimensions. 
Unciform of 
Diplopus, from Hordwell. 
Transverse breadth 21-| 
Antero-posterior depth 21 
Height 19 
Tarsus of Diplopus and Hyopotamus. 
The general structure of the tarsus in the Hyopotamidae is quite conformable to the 
typical structure shown by all Paridigitata ; and, in considering the shape of each of its 
constituent bones, I shall point out the features in which it resembles, or differs from, 
* This facet is seen in fig. 8' from below, as a projection of the posterior and inner margin of the bone. 
