The extensor pollicis brevis is a muscle within the deep compartment of the posterior forearm. The tendon of the extensor pollicis brevis passes through the 1st extensor compartment at the wrist, where it contributes to the radial border of the anatomical snuffbox. Attachments: Originates from the posterior surface of the radius and interosseous membrane. It attaches to the base of the proximal phalanx of the thumb. Actions: Extension at the metacarpophalangeal and carpometacarpal joints of the thumb. Innervation: Radial nerve (posterior interosseous branch). Blood supply: Ulnar artery. By TeachMeSeries Ltd (2025) Fig 1Muscles in the deep layer of the posterior forearm. 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