MAY, 1921. AMERICAN MARSUPIAL, C^ENOLESTES OSGOOD. 91 



Nevertheless, I have been unable to find a case of a similar extension in 

 any other marsupial or in other mammals. Its effect is a much wider 

 articulation with the ulna than usual and, as described below, there is a 

 corresponding increase of the articular surfaces of the ulna. Func- 

 tionally it may have some correlation with the distinctness of the 

 median head of the triceps muscle, and although it might not be re- 

 markable in an animal of fossorial habits, it seems quite incompatible 

 with the distal elements of the arm and leg which are adapted to cur- 

 sorial life. 



A small oval epicondylar foramen is present and the ridge bounding 

 it has a smooth rounded surface directed with a spiral curvature toward 

 the distal end of the deltoid crest but widely separated from it by the 

 smooth shaft. The outer epicondylar ridge is similarly twisted and 

 gradually merges with the surface of the shaft without any abrupt angle 

 or hooked process. Its edge distally is broadly curled so that it presents 

 a relatively broad flattened lateral aspect instead of the sharp edge of 

 most other marsupials. The external epicondyle is little more than the 

 extremity of this ridge. It has a decidedly concave surface for the seat 

 of the sesamoid of the tendon of the supinator brews muscle. This 

 sesamoid, as mentioned elsewhere, is not present in other marsupials. 

 It is sufficiently distinct to be obvious to the preparator and is usually 

 found in situ in first class ligamentary skeletons. 



The ulna is broad, heavy and compressed proximally but rapidly 

 tapers to its distal third which is subcylindrical and scarcely half the 

 diameter of the radius. The outer side of its proximal half is deeply 

 channelled. Its inner side is smooth and convex except an excavated 

 area on the side of the olecranon. The upper lip of the greater sigmoid ' 

 cavity is unusually broad, especially its inner division which extends 

 well beyond the inner base of the olecranon from which it stands out 

 prominently. Its inner division has the usual position opposite the 

 lesser sigmoid cavity. This broad upper lip articulates with the whole 

 of the posterior articular surface of the humerus and in doing so brings 

 the ulna into a very oblique or nearly transverse position with its 

 broad grooved outer side directed nearly forward. Except at its distal 

 end the ulna is caudad of the radius. The olecranon is relatively thick 

 and heavy with a rhomboidal roughened extremity for various muscle 

 attachments. 



The radius has a rounded ovoid head supported on a distinct neck 

 below which is a prominent tubercle having a rounded roughened face 

 quite two-thirds as large as that of the head. The proximal third of the 

 radius is rather abruptly flexed forward leaving a considerable space 

 between it and the ulna. For the remainder of its length it is in close 



