The Humerus 

The bone of the arm is the humerus. It is the longest and largest bone of the upper limb.

Its proximal extremity has a hemispherical head. The anatomical neck separates the head from two large bony prominences. The greater tubercle, situated on the lateral aspect, and the lesser tubercle, situated on the anterior surface. Between the two tubercles is the bicipital, or intertubercular groove. The surgical neck below the tuberosity is frequently the site of fractures.

Proximally, the shaft is almost cylindrical, but it becomes flat distally. Approximately in the middle lateral third of the shaft is the deltoid tuberosity.

The broad distal extremity consists laterally of the capitulum and medially of the trochlea. The capitulum articulates with the fovea on the head of the radius and the trochlea with the trochlear notch on the ulna. Proximal to these two eminences on the anterior aspect are the radial and the coronoid fossa (which receive the head of the radius) and the coronoid process of the ulna, respectively, when the forearm is flexed. Posterior to the trochlea is the olecranon fossa, which receives the olecranon process of the ulna when the forearm is extended. On the sides of the distal end are two prominences, the lateral and medial epicondyles.

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