THORACIC LIMBS. 67 
fossa (7), receives a triangular facet on the proximal end of 
the radius at the same time. Between the radial and coronoid 
fossze 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 
(z) (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 
(0) for the origin of extensor muscles of the forearm and of the 
radial collateral ligaments of the elbow-joint. From the lateral 
epicondyle a ridge, the lateral supracondyloid ridge (f), 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 (¢). 
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 (c), for the insertion of the tendon of the biceps 
muscle. Proximad of this the bone is contracted to form a 
neck (4) 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 (7), for articulation 
with the radial notch of the ulna; also a triangular facet (e), 
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 
