The medial head originates from the extensive area on the posterior surface of the shaft of the humerus inferior to the radial groove.
The lateral head originates from a linear roughening superior to the radial groove of the humerus.
The three heads converge to form a large tendon, which inserts on the superior surface of the olecranon of the ulna.
The triceps brachii muscle extends the forearm at the elbow joint.