The origin of the triceps brachii lateral head is from which region?

• A. Infraglenoid tubercle of the scapula.
• B. Posterior humerus above the radial groove.
• C. Lateral epicondyle.
• D. Olecranon.

Answer: (B)

The triceps brachii has three heads, each with its own proximal attachment along the humerus (and one from the scapula for the long head). The lateral head originates from the posterior surface of the humerus above the radial groove, which places it on the upper, lateral portion of the posterior arm. The long head comes from the infraglenoid tubercle, and the medial head from the posterior humerus below the radial groove; all three converge to insert on the olecranon. The other options point to different sites: the infraglenoid tubercle is for the long head, the olecranon is where the muscle inserts, and the lateral epicondyle is not an origin for the triceps. So the region above the radial groove on the posterior humerus is the correct origin for the lateral head.