Triceps definition

Part of the upper arm, the triceps include the medial and lateral heads that join to the posterior surface of the humerus. The long head joins to the lower border of the scapula, nearby to the arm socket.    All the heads connect to the triceps tendon that is positioned at the base of the ulna on its posterior side (the point is called the olecranon).    The triceps are responsible for extending the arm at elbow.