The humeroulnar joint, is part of the elbow-joint or the Olecron Joint, between the ulna and humerus bones is the simple hinge-joint, which allows for movements of flexion, extension and circumduction. The Humero-Ulnar Joint is the junction of trochlear notch of the ulna and the trochlea of the humerus. Owing to the obliquity of the trochlea of the humerus, this movement does not take place in the antero-posterior plane of the body of the humerus. When the forearm is extended and supinated, the axis of the arm and forearm are not in the same line; the arm forms an obtuse angle with the forearm. During flexion, however, the forearm and the hand tend to approach the middle line of the body, and thus enable the hand to be easily carried to the face. The accurate adaptation of the trochlea of the humerus, with its prominences and depressions, to the semilunar notch of the ulna, prevents any lateral movement. Flexion is produced by the action of the Biceps brachii and Brachialis, assisted by the Brachioradialis, with a tiny contribution from the muscles arising from the medial epicondyle of the humerus. Extension is produced by the Triceps brachii and AnconC&us, with a tiny contribution from the muscles arising from the lateral epicondyle of the humerus, such as the Extensor digitorum communis. [ http://en.wikipedia.org/wiki/Humeroulnar_joint ]