OSTEOLOGY OF THE HY OPOT AMIDiE. 
59 
specimens of Hyopotamus from Puy the posterior prolongation of the fourth metatarsal 
is not well preserved (Plate XXXVIII. fig. 2', iv.) ; but as there is no downward pro- 
longation in the cuboid and no facet, the cuboid seems not to have articulated with this 
posterior prolongation of the fourth metatarsal, and it does not so articulate in Anoplo- 
therium and Hippopotamus. In the Hog the relations are just the same as in the 
didactyle Diplopus ; only this beak has on its outer side another small facet, for the 
posterior prolongation of the outer or fifth metatarsal — which is wanting in Diplopus , 
and, though present in Hyopotamus , has no such posterior prolongation as in the Hog. 
A glance at a hog’s tarsus will make all this much clearer. 
The distal surface of the cuboid in Diplopus (Plate XXXVIII. fig. 11) is entirely taken 
up by a single large facet for the fourth metatarsal, leaving no place at all for an additional 
digit as in fig. 10, though a rudiment of such fifth digit certainly existed, as is proved by 
a small facet on the outer border of the fourth metatarsal, to which this rudiment was 
undoubtedly attached, without ascending, however, so far as to touch the cuboid. 
All these differences clearly indicate that the Plyopotamoid form to which this cuboid 
(fig. 11) belonged had no fifth metatarsal, but only a rudiment of it ; we have seen the 
same thing in the manus, where the unciform, instead of supporting two toes, is shown 
by the distal articular facets to have supported only one (the fourth) while a rudiment 
of the fifth, indicated by an external facet of the upper border of the fourth metacarpal, 
did not reach the unciform and left no trace upon it. 
Dimensions of the Cuboid. 
Hyopotamus, 
from Puy 
(Plate XXXVIII. 
figs. 1 , 10). 
Hyopotamus, 
from Hempstead. 
Diplopus, 
from Hordwell 
(Plate XXXVIII. 
figs. 3, 11). 
Height, anterior 
26 
19, 31 
23 
Breadth, upper part ............ 
21 
17, 24 
19 
Breadth, inferior, on the distal surface. ....... 
18 
15, 21 
16i 
Antero-posterior depth 
25 
25, 28i 
25 
The navicular (Plate XXXVIII. figs. 1-4, n). — This bone is nearly identical in both 
genera, and has the same general shape as in all Paridigitata, in which the navicular is 
separate from the cuboid. The upper or proximal surface is entirely the same as in the 
Hog, except that the middle rising which fits into the groove of the distal pulley of the 
astragalus is more rounded. The inner (fibular) surface has, on the anterior and 
posterior part, facets corresponding with those already described on the tibial side of 
the cuboid. The posterior termination is rounded and only moderately produced 
downwards (as seen in figs. 2 and 4), without such large beak-like prolongation as is 
seen on the posterior side of the navicular of a hog (Plate XXXVII. fig. 12, n) or 
Dicotyles (fig. 13, n). 
The distal surface is the most important one, as it supports the three cuneiform bones, 
which carry the digits. All the anterior part of the distal surface of the navicular is 
HDCCCLXXIII. k 
