triceps brachii /trī″seps brak″ē·ī/ [L, three-headed, brachium, arm] , a large muscle that extends the entire length of the posterior surface of the humerus. Proximally it has a long head, a lateral head, and a medial head. The three parts of the muscle converge in a long tendon and insert in the posterior aspect of the olecranon. It functions to extend the forearm and to adduct and extend the arm. Also called triceps. Compare biceps brachii.
