88 
DR. W. KOWALEVSKY ON THE 
Hyopotamidse and the living genera of Paridigitates, which, as it seems to me, have 
descended from a branch given off by the tetradactyle Hyopotamidae of the Eocene epoch. 
The proximal articular surfaces of the two middle metatarsals of Diplopus (Plate 
XXXVIII. fig. 4") may be compared with the corresponding proximal surfaces, of the 
tetradactyle Hyopotamus (Plate XXXVIII. fig. 2'), when the differences are seen at a 
glance. The facet ( cb.f ) is intended to meet a like facet on the inner side of the beak- 
like posterior projection of the cuboid (fig. 11, f.my) ; it is wanting in Hyopotamus , as 
well as the cuneiform facet (fig. 4 ,, ,/b 1 ) for the first cuneiform, which was wedged in 
between this posterior projection of the third metatarsal and the rudiment of the second 
digit (fig. 4", nr). This rudiment was confluent with the third metatarsal in one of 
the figured specimens (fig. 4 and 4", nr), but it was absent (because not so coalesced) 
from all the other specimens of the third metatarsals in the British-Museum collection — 
for instance, from the third metatarsal represented in Plate XXXVIII. fig. 12. On the 
free (outer and inner) sides of both metatarsals are longitudinal facets to which the 
rudiments were articulated ; these last, however, I could not find, save the one of the 
second metatarsal ankylosed to the third represented in fig. 4, Plate XXXVIII. 
The interlocking of the two middle metatarsals was effected by a very prominent tubercle 
of the fourth entering a deep pit on the fibular side of the third, as seen in the figures ; 
besides there is an oval facet on the inner faces of the posterior projection of each meta- 
tarsal. The beak-like downward process of the cuboid and the wedge of the first cunei- 
form pressing laterally from the inner and outer sides upon these posterior projections of 
the two middle digits held them firmly together. This close fitting of the two metatarsals 
(and metacarpals) together was further assisted by the mode of metatarso-phalangeal 
articulations universal among Paricligitata — namely, by the outer halves of the distal 
surface being a little shorter than the inner (as is clearly seen in Plate XXXVIII. 
fig. 6) : in the phalanges the relation is inverse, and therefore in treading on the ground 
their upper ends are made to converge and to press the two metatarsals and metacarpals 
together ; the two separate metatarsals, compressed in this way, approach as near as 
possible to the cannonbone of modern Ruminantia. 
Phalanges. 
The first phalanges. — In a set of mixed phalanges belonging to both Diplopus and 
Hyopotamus it would be utterly impossible to distinguish the bones belonging to each 
genus : as difficult is it to separate those of the rnanus from the phalanges of the pes ; 
their relative height and thickness present no good constant characters. One of the 
best authorities, Professor Hensel, in his memoir on Ilipp avion, printed in the Transac- 
tions of the Berlin Academy for 1861, tells us that it is even impossible to distinguish 
the fore and aft phalanges of living Ungulata in the case of several individuals being- 
mixed together. This may serve as an excuse for my not trying to do it among the 
fossils ; and 1 therefore intend to give only a general description, which will apply to 
both the fore and hind limb. 
