36 
DK. W. KOWALEVSKY ON THE 
Dimensions of the Ulna. 
• 
Diplopus 
(%• 1, 
Plate XXXVL). 
Hyopotamus. 
Puy (Plate XXXVI. fig. 2). 
Hempstead. 
Total length along the curvature 
270 
Posterior chord 
254 
Greatest breadth at the radial facets 
32 
30 
26 
25 
30 
Breadth at the middle 
33 
18 
17 
Antero-posterior diameter (at radial facets). . 
22 
24 
23 
25 
30 
Antero-posterior diameter (middle) 
12 
19 
. . 
20 
Transverse breadth, inferior extremity 
16 
Antero-posterior diameter, inferior extremity 
n i 
Antero-posterior diameter from the point 1 
43 
• 
Aa 
of olecranon to the posterior surface . . . . J 
The distal end of the ulna of Diplopus is triangular, with a slightly excavated tri- 
angular facet for the pyramidale of the carpus. I have not the pisiform bone; but as 
there is no facet on the posterior side of the distal end of the ulna, this bone probably 
did not articulate with the ulna, but exclusively with the pyramidale. 
The great difference in the horizontal sections of the ulnse of both genera (fig. 1" and 
fig. 2', Plate XXXVI.) is produced by the great flattening of the ulna of the didactyle 
Diplopus. The section of the ulna of a hog taken in the middle will give nearly the 
same figure as the section of the Hyojyotamus ulna (fig. 2'). The same letters mark the 
corresponding parts in both sections. As an instance of a greatly compressed ulna, I 
may adduce the ulna of Hyomoschus ; it is so compressed laterally that its antero- 
posterior depth is ten times as large as the transverse breadth ; and the whole bone, from 
its radial articulation downwards, looks like a knife-blade with its sharp edge turned 
forwards towards the radius. 
The Radius (Plate XXXVI. fig. 3). — I was not fortunate with this bone, as I have not 
a single complete specimen ; even fragments are rare.. I found, however, in the collection 
of the British Museum an upper half and a distal extremity of a radius from Hempstead 
which belonged undoubtedly to Hyopotamus. I possess also the same parts from Puy, 
and they entirely agree with the English specimens. 
The proximal extremity of the radius is always shaped so as to fit the distal end of 
the humerus, and their variations are always correlative. For this reason the radius of 
Anoplotherium, constructed to fit the very peculiar distal end of its humerus, is made on a 
pattern exceedingly different from that of all other Ungulata, and shows a striking likeness 
to the proximal extremity of the radius of a carnivore, especially the Dog ; but in ITyo- 
potamus we find a more Ungulate-like radius. Instead of the great oblique middle 
fossa of the Anopl other ium, we see in Hyopotamus a shallow and broad groove (fig. 3, a')l 
made to fit the middle bulging (fig. 4, a) of the distal extremity of the humerus. The 
inner part of the proximal surface is a plane (Plate XXXVI. fig. 3, h') less inclined than 
in Anoplotlierium (Blainv. Ost. Anopl. pi. iii.), but much more so than in Pigs, owing to 
the greater downward production of the inner condyle of the humerus (Plate XXXVI. 
