The triceps brachii is composed of three heads: lateral, medial, and long. Only the long head crosses the glenohumeral joint.
- The triceps brachii attaches from the infraglenoid tubercle of the scapula (long head) and the posterior shaft of the humerus (lateral and medial heads) to the olecranon process of the ulna.
- Extends the forearm at the elbow joint (entire muscle)
- Extends the arm at the glenohumeral joint (long head only)
- The medial head of the triceps brachii is sometimes referred to as the deep head.