OSTEOLOGY OE THE HYOPOTAMIDAL 
57 
nterval between the distal surface of the navicular and proximal of the great or third 
cuneiform ; the rising was very slight on our specimen, and is only imperfectly seen in 
the drawing. On the posterior part of the inner wall we see two facets divided by a groove 
for the external and posterior part of the navicular (in the Hog these two facets have 
coalesced into an elongated single facet on the posterior border of the inner wall of the 
cuboid). This posterior margin of the internal wall shows in Ilyopotamus a considerable 
bulging inwards, into the middle of the tarsus (seen in Plate XXXVIII. fig. 10), which 
makes this cuboid much broader than the corresponding bone of the Diplopus (fig. 11), 
where this bulging is mucli less, nearly identical with that of a hog’s cuboid. 
The outer surface of the cuboid is rounded. If we look at the external surface of the 
cuboid of a hog we shall see a deep sulcus for the peronseus tendon situated between the 
posterior prolongation of the cuboid and the distal articular facet ; this sulcus is absent in 
Hyopotamus, owing to the fact that the posterior part of the cuboid is not produced 
downwards, as we shall immediately see. The posterior surface of the cuboid is con- 
siderably broader than the anterior, as is to be seen in fig. 10, while in Diplopus (fig. 11), 
and especially in the Hog, the converse is the case. Besides, looking at the cuboid from 
the posterior aspect, we perceive a very broad and rough transverse ridge for muscular 
and ligamentous attachment, running through the whole breadth of the bone as it is seen 
in fig. 10 from below. The Anoplotherium and the Hippopotamus have nearly the same 
transverse ridge on the back part of the cuboid ; only it descends lower down, while 
in Hyopotamus this ridge does not reach the level of the distal articular surface of the 
cuboid, which is the lowest point of the bone ; we shall by-and-by indicate the difference 
presented in this respect by the cuboid of Diplopus. 
The distal surface (Plate XXXVIII. fig. 10) is the most important, as it presents the 
articular facets for the two outer metatarsals. Not only in Ungulates but in all recent 
and fossil Mammalia the cuboid of the tarsus, as well as its homologue (the unciform) in 
the carpus, gives an attachment to the two outer metatarsals and metacarpals of the 
foot (the fourth and fifth) if they are not entirely reduced. In looking at the distal 
surface of the cuboid in Hippopotamus , we shall perceive a large central facet for the 
fourth metatarsal, and outwards from this another good-sized facet for the well-developed 
fifth metatarsal. In the common Hog, nearly the whole distal surface of the cuboid is 
taken up by the much developed fourth metatarsal ; but still there exists at the 
outer part of this large facet a smaller and oblique facet for the still functionally developed 
fifth digit. In Dicotyles , where the fifth digit is lost, or only a short rudimental 
metatarsal of it remains, the whole distal surface of the cuboid is taken up by the 
fourth metatarsal, the rudiment of the fifth being only attached to the outer side of the 
fourth metatarsal, without touching the cuboid (De Blainville, Sus, plate vii. Dicot . 
labiatus , lowest left figure). In the Anoplotherium commune , as well as in A. tridactylum , 
there is not the slightest trace of a facet for a rudimentary fifth digit ; but in Xiphodon , 
which also has only two developed metatarsals, we have on the distal surface of the 
cuboid a large facet for the fourth metatarsal, and an outer small facet for the rudi- 
ment of the fifth, which certainly existed, as the outer border of the fourth metatarsal 
