The triceps brachii is a muscle in the posterior compartment of the upper arm. It is a large horseshoe-shaped muscle, which forms the majority of the muscle bulk of the upper arm. Attachments: Long head originates from the infraglenoid tubercle of the scapula. Lateral head originates from the humerus (superior to the radial groove). Medial head originates from the humerus (inferior to the radial groove). Distally, the heads converge into one tendon which inserts onto the olecranon of the ulna. Function: Extension of the arm at the elbow. Blood Supply: Deep bracial (profunda brachii) artery Innervation: Radial nerve By TeachMeSeries Ltd (2025) Fig 1The long and lateral heads of the triceps brachii. Pro Feature - 3D Model You've Discovered a Pro Feature Access our 3D Model Library Explore, cut, dissect, annotate and manipulate our 3D models to visualise anatomy in a dynamic, interactive way. Learn More Print Article Rate This Article