3C 
TEETIAliT VEIiTEBEATA OE THE FATtlM. 
In its general form the radius (text-figs. 17, 18, 19) is much like that of Elephas, 
hut is shorter and stouter. The proximal articulation is an elongated oval in 
outline, its transverse diameter being to the antero-posterior diameter as 3 to 1. The 
surface is slightly concave from before backwards, and for the outer two-thirds (o.), 
which help to form the articulation for the outer half of the humeral trochlea, it is 
(concave from side to side also. The inner third (/.), which forms a small part of the 
surface for the inner half of the trochlea of the humerus, is nearly flat, and this 
))ortion is bent downwards so as to look upwards and inwards. The articulation 
Text-fig. 17. 
A B 
o. 
Left radius of ArsinoiiJierium zitteli : A, from front ; B, from bade. 
a.^)., anterior prominence; 6.C, bicipital tuberosity ; 7, inner portion of proximal articulation ; 7, .articulation 
for lunar; o., outer portion of proximal articuLation ; posterior prominence; r., anterior ridge; 
r.', posterior ridge; u.s., proximal surface for ulna; u.s.', dist.al surface for ulna. ^ mat. size. 
of the radius with the humerus does not extend across the whole width of the ulnar 
surface as in Uintatherium, but the relations of tlie two bones in this resjtcct arc 
almost exactly as in Eleplias. 
On the outer side of the posterior face of the bone, immediately beneath the 
enter portion of the humeral surface, there is an elongated facet («.6'.) for articulation 
with the ulna, and beneath this the surface of the bone is greatly roughened for 
some centimetres down, showing that its union with the ulna was very close and 
