60 
DE. W. KOWALEVSKY ON THE 
occupied by a broad facet for the great or third cuneiform, which supports the third 
metatarsal. I have not figured the distal extemity of the navicular ; but, by looking 
at the distal surface of the Anoplotherium navicular (Plate XXXVII. fig. 17) or that of 
a hog, the reader may form a correct idea of it. This facet is much narrowed in its 
posterior part, and then expands slightly again, forming a small facet for the second 
cuneiform ; behind this there is a slight sharp ridge, which is seen tolerably well in 
the side view, fig. 4, Plate XXXVIII., as well as on a navicular of the Hog (Plate 
XXXVII. figs. 12, 13, n) ; behind this ridge is the facet for the first cuneiform. This 
last facet is concave on some of the naviculars of Hyopotamus , and convex on the two 
others belonging undoubtedly to the two-toed Diplopus ; whether the difference was 
constant I cannot tell without ampler materials. I find no essential differences in the 
shape of the navicular bone in the two genera ; and my description, made from good 
specimens of the Diplopus, may apply to the Hyopotamus also ; of this last I had only 
one, not quite perfect, specimen of navicular from Puy. 
Navicular of the Tarsus. 
Hyopotamus. 
from Puy. 
Diplopus, 
from Hordwell. 
Anterior height 
11 
121, 14 
Breadth, proximal face 
151 
15, 17 
Depth, antero-posterior 
24 
26, 30 
Breadth, distal surface 
14 
141, 20 
The cuneiforms (Plate XXXVIII. figs. 1-4, c 3 ). — These are small but very important 
bones, on account of their relation to the digits which they have to support. The second 
row of the tarsus, containing the three cuneiforms and the cuboid, exhibits very clearly 
the complete homology of the fore and hind limbs. As in the complete manus we have 
in the second row of the carpus three distinct bones (the trapezium, trapezoideum, and 
magnum), each supporting a separate toe, and one external bone, the unciforme, 
giving support to the two outer digits (the fourth and fifth), so in the pes we perceive 
also an entirely homologous set of three cuneiforms (first, second, and third), each 
supporting a separate toe, and one external bone, the cuboid, giving support to the two 
outer digits of the pes (the fourth and fifth). Where all the five digits are completely 
developed this rule admits of no exception whatever in the whole range of Mammalia ; but 
where, as in Ungulata, the number of the digits becomes sometimes greatly reduced, the 
relation of the carpal and tarsal bones to the remaining digits is slightly changed, though 
all the three cuneiforms are still retained, and I know of no instance where one of 
them is wanting. This persistence of cuneiforms is a strange fact ; for in the carpus, 
which is generally less reduced than the tarsus, the trapezium (homologue of the 
first cuneiform) is certainly lost in Horses and Ruminants, while its homologue in the 
tarsus is still retained in a recognizable state. These relations, slight as they may 
seem, are important; we must know all the details and the true homology of the 
