OSTEOLOGY OF THE HYOPOTAMIM. 
61 
smallest bones to establish clear lines of descent. I shall be obliged to discuss the 
question of the cuneiforms again when I come to describe the metatarsals, and 
will confine myself in this place to a general review of them in the Paridigitata, and 
a special description of these bones in Hyopotamus and Diplopus. As the Hippo- 
potamus is the most complete of the living Paridigitata, we see in the side view 
of its tarsus (Plate XXXVII. fig. 10) all the three bones (c\ c 2 , c 3 ) fully developed; 
but as the first digit is aborted, its typical tarsal bone, the first cuneiform (c y ), gives 
additional support to the second digit. Each of the two inner digits (the third 
and second) are supported by a separate cuneiform. We see besides, in this side view 
of the tarsus, that the second digit (fig. 10, il), besides its own tarsal bone (the second 
cuneiform), seeks additional support from the large third cuneiform : we shall discuss this 
relation when we come to the metatarsals ; and I will merely observe here that it seems 
to be a very ancient one, which existed perhaps in the progenitor of the whole class of 
Mammalia. In the Hog (Plate XXXVII. fig. 12) we find the three cuneiforms 
quite distinct ; but there is a great change in their relative position : instead of the 
third cuneiform giving additional support to the second digit, it is now not only 
entirely occupied by the enlarged third digit, but even the greater part of the second 
cuneiform leaves the reduced second digit to give additional support to the enlarged third. 
The first cuneiform is also peculiar in the Hog ; it is thrust like a wedge between 
the posterior beak-like prolongation of the navicular, the head of the second metatar- 
sal, and a posterior process of the third metatarsal, to which it gives an articular facet. 
Remembering what we have said in reference to an analogous beak-like prolongation 
of the cuboid in hogs, and looking at a hog’s tarsus in naturd , we shall see that the 
wedge-shaped first cuneiform, together with the cuboid, press from within and 
without on the posterior processes of the third and fourth metatarsals, and make the 
two middle metatarsals act like a single undivided bone : this is moreover aided by 
a special provision in the articulation of the distal extremities of these metatarsals 
with the first phalanges ; namely, the outer borders of the combined distal extremities of 
the two metatarsals are produced down less than the inner, so that the digits, being 
expanded in treading on the ground, tend to meet by their proximal ends and compress 
both metatarsals firmly together, thus materially aiding the compression of their upper 
extremities by the beak-like prolongation of the cuboid and the wedge-like first 
cuneiform. There is nothing of the sort in Hippopotamus ; but the same provision 
existed in the two-toed Diplopus. 
Dicotyles (Plate XXXVII. fig. 13) presents nearly the same relations ; only the second 
cuneiform (c 2 ) has gone entirely over to the third digit ; and after this there was no 
assignable reason why these two bones, giving support to a single metatarsal, should 
not coalesce : and this they have done in Hyomoschus and Tragulus (figs. 14 and 15, 
c 3 , (?), where the navicular has also coalesced with the two cuneiforms, the first cuneiform 
(c 1 ) remaining entirely distinct in both. In a Miocene ruminant from Auvergne, 
fig. 16 (Amphitragulus 1), with a rudimentary second metatarsal, we may also clearly 
K 2 
