lvon] the hares and their allies 377 



In the upper part of the forearm, the radius lies in front of the 

 uhia, while at the distal extremity the radius is found toward the 

 inner side. 



The radius in general is flattened antero-posteriorly, presenting a 

 rather flattened posterior surface and a convex anterior one. The 

 upper extremity of the radius forms the inferior portion of the sig- 

 moid notch for articulating with the double trachlear surface of the 

 lower end of the humerus. The lower extremity of the radius is 

 rather enlarged and its distal surface is concave, the concavity in- 

 clining to be double for articulating with the scaphoid and semilunar 

 bones of the wrist. 



The ulna in general lies behind the radius and toward the outer 

 side. In some cases the shaft of the ulna is more heavily built than 

 the shaft of the radius, while in other cases it is very much reduced. 

 The outer part of the lower end of the ulna is prolonged downward 

 into a convex articular surface which fits into a corresponding con- 

 cavity formed jointly by the cuneiform and pisiform bones. This 

 projecting part of the ulna is the only part of that bone which 

 articulates with the carpus in the case of the Leporidse. In the case 

 of the Ochotonidas, however, there is a concave facet internal to this 

 projection which articulates with a corresponding convexity on the 

 cuneiform. A condition approaching this is found in Pcntalagus, 

 Roincrolagits, Brachylagus, and in some skeletons of Sylvilagus and 

 Lcpiis. 



In the genus Lcpus the ulna is much reduced in size along the 

 middle of the shaft, and except at the lower extremity it is placed 

 almost entirely behind the radius. The radius itself is rather long 

 and slender. The humerus and radius are usually subequal in 

 length. In the subgenus Macrotolagus, at least so far as the limited 

 material shows, the radius is slenderer than it is in the two other 

 subgenera, Lepiis and Po:cUolagns, and it is decidedly longer than the 

 humerus. 



In the genera Syh'Uagus, Pronolagiis, and Limnolagus the radius 

 and ulna are subequal in size, the ulna not being reduced in the 

 middle part of the shaft. The ulna is situated external to the 

 radius rather than behind it as in Lcpus. Both radius and ulna as a 

 rule are moderately slender. The radius equals the humerus in 

 length. 



The condition of the bones of the forearm in Brachylagus is very 

 similar to that just described, but the humerus is distinctly longer 

 than the radius. 



