OSTEOLOGY OF THE HYOPOTAMID2E. 
47 
lunar bones of different sizes from English deposits as well as from Puy. Those from the 
latter place agree entirely with smaller lunars from Hempstead ; and we may safely 
infer that they belonged to the Hyopotamus . 
In general shape the lunar has the same character as the same bone in other Pari- 
digitata, especially the Suina — with this difference, that it is relatively much thinner 
and higher in Hyopotamus, as might be expected from the form of all the bones of 
the skeleton, showing that the Hyopotamidse had a much more elegant and higher 
skeleton than our recent Suina. The proximal or upper surface of the lunar, which 
articulates with the outer half of the distal extremity of the radius, has a considerable 
rising in the fore part and an excavation behind ; this upper surface, looking on it 
from above, has a very oblique direction inwards ; this is effected in such a way that 
the radial upper margin of the lunar is pressed closely to the scaphoid, while there 
is a great interval between its upper ulnar margin and the pyramidale : a glance at the 
proximal surface of a pig’s carpus will explain this disposition much better than long 
descriptions. 
The distal surface of the lunar is prolonged into a prominent beak inserted between 
the os magnum and unciforme. This insertion of the lunar between the two principal 
bones of the lower row is a feature common to all Paridigitata ; only in Hippopotamus 
(Plate XXXVII. fig. 1, l) the beak, owing to the squareness of all the bones, is much 
blunted ; but it is very well seen in Anoplotherium , Xipliodon (Plate XXXVII. figs. 
2 & 3, l ), the Suina and Ruminantia. The beak is limited on both sides by two oblique 
facets, one radial for the os magnum, the other ulnar for the unciforme ; a ridge running 
from the anterior point of the beak through the whole antero-posterior depth of the 
bone separates the two facets from one another. On the anterior half of the distal 
surface of the lunar, the ulnar facet for the unciforme is larger than the radial or 
os-magnum facet ; but on the posterior half this relation of the two facets is inverse : 
this disposition is obviously an adaptation for the better interlocking of the carpals. 
The posterior termination of the lunar is very like that of the lunar of the Suidse : 
the lateral facets for the two adjoining bones show nothing particular; only the upper 
radial facet covers the whole upper and inner margin of the lunar, while the ulnar is 
only developed on the fore part, the ulnar side not touching the pyramidal in its 
middle and posterior part. I have, from Hempstead, a lunar bone much larger than 
the one described and figured by me in the restoration of the carpus (Plate XXXVIII. 
fig. 5) ; it may have belonged to the largest species, called Hyopotamus bovinus , although 
it looks too large for it ; there is no difference in shape whatever. 
