The skeleton of the forearm is
formed by two parallel long bones: the ulna and the radius.
Their proximal articulation is with the humerus
and their distal
articulation is with the bones of the wrist.
The radius and the ulna articulate also with each other proximally and distally at the
radioulnar joints. They are also connected throughout their entire lenght by an
interosseous membrane (a tough, flexible fibrous membrane).
The Ulna is the longer of the two bones in the forearm.
Its proximal end looks like a hook: identify the 2 proeminent processes, the olecranon process and the coronoid process separated by a deep concavity: the trochlear notch. This concavity articulates with the trochlea of the humerus and allows only flexion and extension of the forearm. The Olecranon process forms your elbow. Palpate the olecranon process at your elbow and trace the course of the ulna to the wrist.
The ulna approaches the wrist on the side of the little finger. Distally, the ulna does not articulate with the wrist directly, but it does articulate with the radius.
The Radius is the shorter bone of the forearm, and lies on the lateral (thumb) side.
The lozenge shaped head has a smooth circular band running around it. This is the surface for articulation with the ulna. As the hand is pronated (turned palm down), the proximal end of the radius rotates, and the distal end pivots around the ulna. Observe this movement in your own arm as you change the position of the hand. The radius articulates with the capitulum of the humerus.
The distal end of the radius articulates with the carpal
bones of the wrist and with the ulna.