THE OSTEOLOGY OF SINOPA— MATTHEW. 



223 



distal end, the internal and external condyles almost equally developed, 

 the trochlea very wide and shallow, the inferior end of the deltoid crest 

 very high and situate far down on the shaft. 



Radius and ulna. — The shafts of these bones are nearly straight, 

 with the olecranon in line with the ulnar shaft, as in the viverrines. In 

 the cats and in Daphanus, as also in the opossum, the shafts are 

 slightly convex forward; in Caw^s they are 

 considerably bowed. The olecranon is 

 rather long, and expanded anteroposteri- 

 orly, as in Daiyhjunus and the viverrines; 

 in the cats it is a little shorter and pro- 

 jects more anteriorly; in the opossum it 

 projects more anteriorly and is much less 

 expanded in an anteroposterior direction. 

 The ulnar and radial shafts arc about 

 equally robust, as in Daphcenus and the 

 viverrines; the ulna is somewhat larger 

 proportionately than in either, but not so 

 robust as in DldelpJiys^ and is expanded 

 on the antero-internal side, next the radius, 

 in a broad flat plate, thin distally, but with 

 thickened margin toward the proximal 

 part. This plate lies in the position of 

 the interosseous membrane, and probably 

 gave a rigid attachment for strong pro- 

 nator muscles. It is not present in other 

 carnivora, which I have examined, nor in 

 Didelphys. In Tlycenodon it has become 

 narrower and much thicker, forming an 

 integral part of the very robust ulnar 

 shaft, but it is clearl}^ indicated \)y the 

 broad deep groove extending down the 

 anterior face of the shaft. 



The distal end of the ulna resembles that 

 of Ilyxnodon and the viverrines, and 

 allowing for the great reduction in size 

 in Canu^ it resembles that genus, while 

 it difl'ers notably from Daphcenus and the 

 cats in the position of the cuneiform facet, which faces more distally 

 (but not so much so as in Hysenodon)., and is nearly continuous with 

 the radial facet, while in Daphoenus and the Felidse, it faces almost 

 internally and stands on the end of a stout hooked process, separated 

 by a deep groove from the radial facet. 



The head of the radius has the same oval form as in Hysenodon., the 

 ulnar facet being comparative^ flat, permitting of but a limited 



Fig. 16.— Sinopa grangeri, raduis 

 and ulna, anterior and poste- 

 rior views, nat. size. 



