radius

Bones of the Forearm
The forearm contains two bones: the radius and the ulna.
Radius
The radius is the lateral bone of the forearm (Fig. 9.49).
Its proximal end articulates with the humerus at the elbow
joint and with the ulna at the proximal radioulnar joint. Its
distal end articulates with the scaphoid and lunate bones
of the hand at the wrist joint and with the ulna at the distal
radioulnar joint.
At the proximal end of the radius is the small circular
head (Fig. 9.49). The upper surface of the head is concave
and articulates with the convex capitulum of the humerus.
The circumference of the head articulates with the radial
notch of the ulna. Below the head, the bone is constricted
to form the neck. Below the neck is the bicipital tuberosity
for the insertion of the biceps muscle.
The shaft of the radius, in contradistinction to that
of the ulna, is wider below than above (Fig. 9.49). It
has a sharp interosseous border medially for the attachment
of the interosseous membrane that binds the radius
and ulna together. The pronator tubercle, for the insertion
of the pronator teres muscle, lies halfway down on
its lateral side.
At the distal end of the radius is the styloid process; this
projects distally from its lateral margin (Fig. 9.49). On the
medial surface is the ulnar notch, which articulates with
the round head of the ulna. The inferior articular surface
articulates with the scaphoid and lunate bones. On the posterior
aspect of the distal end is a small tubercle, the dorsal
tubercle, which is grooved on its medial side by the tendon
of the extensor pollicis longus