OSTEOLOGY OF THE HYOPOTAMIDJE. 
79 
teeth ; but fortunately we have still a living form which stands to the typical Rumi- 
nantia nearly in the same relation as our Dicotyles would stand to the Post-quaternary 
Suinte with a cannonbone. The parallel is really complete, with the exception of 
some small points*. This living form is the Hyomoschus aquaticus, hardly distinguish- 
able from its fossil congener of the Middle Miocene. If we examine the manus of this 
animal (Plate XXXV II. fig. 8), from the inner side, we shall meet with characters 
common to all Paridigitata. The interlocking of the two middle metacarpals is 
effected in the usual way ; the inner, or radial, margin of the third is enlarged in the 
same way as we saw it in Dicotyles — only the two carpal bones which support this 
enlarged third metacarpal, the magnum and trapezoid, are already confluent (fig. 8, 
m & td ) ; the reduced, but still complete, second digit has a small facet on the back part 
of the coalesced trapezoideo-magnum. On the outer side of the manus, the large fourth 
metacarpal is supported by the unciform, and the distal surface of this bone gives also 
a small facet to the reduced and thin, but still complete, metacarpal of the fifth digit. 
The pes of Hyomoschus will show us something similar to what we have seen in the 
manus. As seen in fig. 14, Plate XXXVII., the inner side of the third metatarsal is 
enlarged, and has taken the whole of the second cuneiform, the second metatarsal being- 
supported entirely by the first cuneiform, which is distinct, while both the others have 
coalesced mutually and with the navicular (c 3 +c 2 -f-w, fig. 14). 
On the outer side of the pes we find that the large fourth metatarsal has taken nearly 
the whole distal surface of the cuboid ; however, it leaves a very small facet for the 
articulation of the complete fifth digit. The length of the lateral metacarpals and 
metatarsals nearly equals that of the middle ones, though, owing to their thinness and 
the want of direct firm support from the carpals and tarsals, they are, as it seems, not 
subservient to locomotion. The middle metatarsals are confluent in the adult. 
In the Traguliclse (Plate XXXVII. figs. 7 & 15) the middle metacarpals and meta- 
tarsals are distinct in the young, even after their complete ossification ; in this state we 
may ascertain that their mutual interlocking is effected as in all other Paridigitata. 
The inner margins of the third metacarpal and metatarsal are enlarged even more than 
in Hyomoschus, and their relation to the trapezoid and second cuneiform is altogether 
the same. The lateral digits persist during the whole of life as filiform bones on both 
sides of the middle cannonbone. Although of the same length as the cannonbone, they 
are useless for locomotive purposes, owing to their extreme thinness. At last, in the 
typical Ruminantia, the two middle metacarpals and metatarsals coalesce into the cannon- 
bone during the process of ossification. All particulars we have remarked in the Tragulinae 
* The chief are these : — the trapezoid is confluent with the magnum, while it is only preparing to become so 
in the anomalous Dicotyles ; the navicular of the pes is confluent with the coalesced second and third cuneiforms 
(as in all the Tragulidte) ; the fifth digit of the pes is completely developed, not lost, as in Dicotyles. The 
articular ridge of the distal end of the metacarpals and metatarsals is confined only to the palmar side, and 
the first phalanges are modified accordingly. If we remember that some of the ancient Pigs, as Chceromorus, 
show just the same smoothness of the distal ends of the metapodium, the parallelism of both groups of 
Paridigitata appears to hold good, even in the slighter details. 
