OSTEOLOGY OP THE HYOPOTAMIM. 
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typical relation ; and, besides, a rudiment of the second digit pressed against the upper 
margin of the third digit. To prove this, I have figured the pes of the Anoplotherium 
from Yaucluse, where this rudimentary digit is completely developed (Plate XXXVII. 
fig. 11), we see in this foot the three typical cuneiforms nearly in the same relation as 
in Hippopotamus-, the third cuneiform articulated to the third metatarsal, the second 
cuneiform to the metatarsal of the short second digit ; the first cuneiform, seen behind, 
aids to support this short second digit. I have represented in Plate XXXVII. fig. 19 
the distal surface of the navicular of this Anoplotherium tridactylum ; and we distinctly 
see the three facets for the three cuneiforms, which all articulated with the navicular 
bone. Together with these navicular bones from the tridactyle form, we have from 
Vaucluse some naviculars of the didactyle species (fig. 18): the complete second digit is 
reduced in this species to a mere rudiment; and we see a corresponding diminution of the 
facet for the second cuneiform which supported this rudiment, the facet for the third 
remaining nearly of the same size. Now in the Anoplotherium from the Paris gypsum, 
as I see by a navicular in the British Museum (fig. 17), this facet for the second cunei- 
form is even smaller, but it exists still. As far as I can judge by a cast of another 
Anoplotherian pes in the Museum, the facet for the second cuneiform is absent from 
it ; but still we see a trace where this very reduced second cuneiform leaned against the 
third, perhaps not touching the navicular ; the posterior navicular facet for the first 
cuneiform remains very large. The reduction of metacarpal and metatarsal bones 
always precedes that of the carpals and tarsals ; and when a rudiment of the former still 
lingers, we may be sure to find the corresponding tarsal or carpal ; and so it is in 
Anoplotherium , which possessed besides its three typical cuneiforms a rudiment of the 
second metatarsal. 
Proceeding now to the Ilyopotamus , we find that it, as well as the Dipl opus, had 
three cuneiforms to its tarsus ; but unfortunately the first is absent from all collec- 
tions examined by me ; the second is preserved, thanks to its tendency to coalesce 
with the third or great cuneiform. The shape of the third cuneiform is very like 
that of the same bone in the Hog or Anoplotherium ; it is articulated to the third 
metatarsal below (Plate XXXVIII. figs. 1-4) ; and its tibial or inner border gives additional 
support to the second metatarsal *, as its homologue, the magnum, does in the carpus. 
The second cuneiform is a small nearly cubic bone. I have never seen it separately, as it 
is always lost owing to its small size ; but it is represented in fig. 2, having coalesced with 
the third cuneiform, and giving support to the second metatarsal. The third cuneiform 
of Diplopus , figured in the nearly complete tarsus (Plate XXXVIII. figs. 3 and 4), is in 
all respects similar to that of Ilyopotamus ; only, as seen in fig. 4, it did not give any 
attachment to the rudiment of the second metatarsal, as it does to the complete 
second metatarsal in Ilyopotamus-, nay, more, the tibial upper margin of the third 
* In fig. 2, Plate XXXVIII., the second metatarsal rises a little higher than the third, and touches the 
internal side of the third cuneiform. The same is to be seen in Hippopotamus (Plate XXXVII. fig. 10) and 
Anihracotherium. This relation is essential in an unreduced tarsus. 
