36 



TEETIAET VEETEBEATA OE THE EATtTM. 



In its general form the radius (text-figs. 17, 18, 19) is much like that of Mephas, 

 but 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 

 portion is bent downwards so as to look upwards and inwards. The articulation 



Text-fig. 17. 



Left radius of Arsinoitherium zitteli : A, from front ; B, from back. 



a.p., anterior prominence ; h.t., bicipital tuberosity, i., inner portion of proximal articulation ; I., articulation 

 for lunar; o., outer portion of proximal articulation; p.p., posterior prominence; r., anterior ridge; 

 r.', posterior ridge ; u.s., proximal surface for ulna ; u.s.', distal surface for ulna, j nat. 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 the two bones in this respect are 

 almost exactly as in Elephas. 



On the outer side of the posterior face of the bone, immediately beneath the 

 outer portion of the humeral surface, there is an elongated facet {u.s.) 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 



