THORACIC LIMBS. 67 



fossa (;;/), receives a triangular facet on the proximal end of 

 the radius at the same time. Between the radial and coronoid- 

 foss;e on one side and the olecranon fossa on the other is only 

 a thin plate of bone. On the medial surface of the distal end 

 is a considerable roughened elevation, the medial epicondyle 

 (;/) (epitrochlea). It gives origin to flexor muscles and to the 

 ulnar collateral ligaments of the elbow-joint. Opposite the 

 medial epicondyle over the capitulum is the lateral epicondyle 

 {o) for the origin of extensor muscles of the forearm and of the 

 radial collateral ligaments of the elbow-joint. F"rom the lateral 

 epicondyle a ridge, the lateral supracondyloid ridge (/), con- 

 tinues proximad, curving onto the dorsal surface of the bone 

 and ending about opposite the junction of the deltoid and 

 pectoral ridges. 



Proximad of the medial epicondyle the bone is pierced near 

 its medial margin by an oblique oval foramen, the supracondy- 

 loid foramen {q). 



Radius (/, Figs. 49 and 50). — In the usual position the 

 radius lies with its proximal end on the lateral side of the arm, 

 articulating with the capitulum of the humerus. The proximal 

 end is thus laterad of the proximal end of the ulna. Its distal 

 end, however, lies on the medial side of the distal end of the 

 ulna, so that the radius in the natural position crosses ventrad 

 of the ulna. 



The radius is a curved bone slightly flattened dorsoven- 

 trally, with enlarged ends. It may be described as consisting 

 of a shaft and of a proximal and a distal end. Its proximal 

 end presents on the ventral surface a tuberosity, the bicipital 

 tuberosity (r), for the insertion of the tendon of the biceps 

 muscle. Proximad of this the bone is contracted to form a 

 neck (/^) which is surmounted by a head [a). The head has 

 on its proximal surface a depressed oval facet by which it 

 articulates with the capitulum, and on its ulnar border a long 

 narrow facet, the articular circumference {d), for articulation 

 with the radial notch of the ulna; also a triangular facet {c), 

 which fits into the radial fossa of the humerus. 



The shaft is convex dorsad and concave ventrad. The 

 distal end is somewhat pyramidal. From its medial or radial 



