OSTEOLOGY OF THE HYOPOTAMIDHS. 
89 
The phalanges of Hyopotamus found at Puy, where the didactyle Diplopus is not 
present, are, by this fact, already separated by nature. As seen in Plate XXX VII. 
tigs. 20 & 21, they strike us as being much longer than in most of the living genera, 
and considerably longer than in Anoplotherium. In Xiphodon and Entelodon, however, 
the first phalanges are also very long. 
The upper, or proximal, articular surface is not symmetrical, as the inner side of the 
first phalanx is considerably thicker than the outer, in correspondence with the same 
inequality of the distal extremities of the metacarpal and metatarsal bones. The same 
difference in the thickness of the inner side is also to be seen on the distal extremity. 
The proximal surface is concave, and the groove for the articular ridge of the metacarpal 
is limited to its posterior third only. This thickening of the inner side makes also the 
inferior end not completely symmetrical ; and this want of symmetry is much greater in 
the first phalanges of the didactyle Diplopus. 
The second phalanges. — The second phalanges of all Paridigitata (with the exception 
of Hippopotamus and Camelidas ) are very characteristic, as their distal extremity is shaped 
unsymmetrically in a peculiar manner, so as to cause the ungual phalanges to converge in 
treading on the ground. For this purpose, the outer half of the distal articular surface is 
not only much larger than the inner, but bends obliquely inwards, and the ungual pha- 
langes following this inner curve tend to converge. This arrangement is very strongly 
developed in the second phalanges of Anoplotherium (see De Blainville, Osteogr. 
Anoploth. pi. iii.) ; it may be seen in every Ruminant as well as in the Suidse. Hyopotamus 
and Diplopus also have second phalanges shaped on this pattern ; only this want of sym- 
metry is not so clearly developed as in the Suina or Ruminantia. 
The third phalanges. — These have a very peculiar shape and are quite identical in both 
genera. This strange shape I can compare to nothing better than to a very thickened 
and rounded human nail. Their proximal surfaces are unsymmetrical, to fit the unsym- 
metrical distal end of the second phalanges ; but the remaining part is much more symme- 
trical than in the Suina or Ruminantia, the inner side not being flattened at all, or very 
slightly. The palmar surface is quite flat. The lower and anterior margin shows the 
usual vascular foramina and a certain crispness to allow a firmer fitting of the horny hoof. 
With this I conclude my description of the long bones of the skeleton and the bones 
of the limbs ; the latter are all figured of the natural size, and the sections give a correct 
idea of their breadth and antero-posterior depth. Some exact dimensions which could 
be taken are given in the general Table (p. 90) I have taken the liberty of disposing 
right and left as best suited my purpose ; and while some bones from the collection 
of the British Museum were drawn directly from nature* and therefore in the Plates 
appear to belong to the opposite side, others have been reversed. 
