AIISINOITJIERIUM. 
39 
of the bone widens out to a broad surface, so that the lower end of the bone 
immediately above the articulation is quadrate in section. The articular surface 
is marked off from the shaft by a roughened groove {g.) ; the surface itself is concave 
both from before backwards and from side to side in front, but posteriorly it is 
strongly convex from before backwards, and forms a sort of trochlear surface which 
extends slightly on to the posterior face of the bone. Nearly the whole of this 
articular surface (text-fig. 18, D) is for the cuneiform {cu.), with perhaps a slight 
posterior contact with the pisiform ; but adjoining it and on its inner side there 
is another comparatively small surface [1.) looking inwards and downwards, which 
articulates with a facet of the lunar. This distal articulation is much like that 
of the elephant ulna, but, as in the case of the j’adius, it is more extended antero- 
posteriorly, apparently indicating that the foot was more mobile in that direction 
than in the modern Proboscidea. The radius is closely applied to the inner 
face of the lower end of the ulna, which also bears a small facet (r.s/) for that 
bone along its lower edge. 
This nlna differs from that of Eleplias in being much shorter and stouter, in 
having its distal articulation wider from before backwards, and in forming a larger 
proportion of the carpal joint compared with the radius. 
It differs from the ulna of Uintatheriuin in being stouter, in not articulating 
with the radius across the whole width of the humeral joint, in having an olecranon 
process which projects farther back but rises less above the articulation, in widening 
towards the distal end, and in forming a very much larger share of the carpal 
articulation. 
The structure of the carpus (text-figs. 19-24) is very difficult to determine with 
certainty, owing to the want of associated series of bones and the great variability in 
size of the individuals to which isolated specimens belonged. Moreover, the similarity 
of the feet to those of the Proboscidea introduces another element of doubt into the 
determination of scattered carpal and tarsal bones ; at the same time the extreme 
rarity of any bones that can be definitely referred to Palceomastodon (for instance, 
only a single specimen of the calcaneum has yet been found) makes it highly probable 
that by far the larger number of the carpals and tarsals found belong to Arsinoitherium, 
and in any case the larger and more massive specimens may be referred to that animal 
with a considerable degree of confidence. Further assistance is derived from the 
fact that in a few cases carpals have been found under such circumstances as to 
leave no doubt that they are those of Arsinoitherium. The best of these associated 
series (M. 8470) is one which includes the distal epiphysis of the ulna, a scaphoid, 
an unciform and a fourth metacarpal of the left side, and the distal half of the 
radius and the os magnum from the right. These all show signs of having belonged 
to a young animal, and were, in fact, found associated with portions of a young skull 
with milk-teeth in situ, no remains of Palceomastodon occurring in the neighbourhood. 
