84 
DR. W. KOWALEVSKY ON THE 
surface is very prominent, in order to enter into the deep pit on the ulnar side of the 
third and bring about a firm interlocking of the two digits. On the outer and posterior 
side, we see an excavation for the nodular rudiment of the fifth metacarpal, which, as it 
seems, did not touch the unciform, at least had no facet on it. The posterior surface 
is very nearly flat, and the section of the hone is a rounded triangle instead of being a 
fiat trapezium as in the Hyopotamus. I have seen a complete specimen of only this single 
metacarpal ; fortunately this gives us the length of the metacarpus in the didactyle 
genus ; it is considerably longer than the metacarpus of Hyopotamus , as may be seen 
by comparing figs. 5 and 6 of Plate XXXVIII. 
As we have no means of distinguishing with complete certainty the phalanges of the 
fore from those of the hind foot, they will be noticed after the description of the meta- 
tarsals. 
The Metatarsals of Hyopotamus and Diplopus. 
My materials for the hind foot are fortunately more complete than those for the fore 
limb, and the striking dissimilarity we noticed between Diplopus and Hyopotamus in 
considering the manus, is still more confirmed by the study of the pes. According to 
the order adopted by me, I shall describe at first the middle metatarsals, as they always 
exhibit the fundamental features of the pes, and consider the lateral digits afterwards. 
I begin with the tetradactyle Hyopotamus. 
The third metatarsal (Plate XXXVIII. fig. 1, m.). — As in all Paridigitata, this meta 
tarsal is distinguished at once by the presence, on its fibular side, of a deep pit, into 
which fits the corresponding projection of the tibial side of the fourth (fig. 1, iv.), 
giving rise to the characteristic interlocking of the middle digits. The proximal 
surface of the third metatarsal (fig. 2', in.) is of a rounded triangular outline, and 
slightly concave to meet the slight convexity of the distal surface of the third cunei- 
form (fig. 1, c 3 ). The third metatarsal is supported entirely by the third cuneiform ; 
and as the lateral internal (tibial) side of this third cuneiform descends a little lower 
than the second cuneiform, the second metatarsal going to meet its typical second 
cuneiform, may lean also against the third cuneiform (fig. 2, ii.), a constant feature in all 
unreduced Ungulata. The posterior projection of the metatarsals is very long, and pressed 
against a similar projection of the fourth metatarsal (fig. 2', hi., iv.) ; on the inner (tibial) 
side of this projection we see no trace of a facet for the first cuneiform, such as is 
presented by Diplopus (fig. 4 and the recent Suina. The inner or tibial edge of the 
proximal surface is slightly elevated, though not enough to exclude the second meta- 
tarsal from its facet on the third cuneiform, as it may be seen also in Hippopotamus 
and Anthracotherium. The outer, or fibular, side of the third metatarsal is flattened 
(section, fig. 1) in correspondence with the adjoining side of the fourth; besides the 
deep pit mentioned before, we see, on this side, a long narrow facet on the posterior 
projection (fig. 2'), articulated to a similar facet of the posterior projection of the 
fourth. (As the fourth metatarsal was slightly defective in my specimen, the posterior 
