Extensor muscles of right forearm

(A) In this image, the superficial layer of extensor muscles is shown. The distal extensor tendons have been removed from the dorsum of the hand without disturbing the arteries because they lie on the skeletal plane. The fascia on the posterior aspect of the forearm is thickened to form the extensor retinaculum, which is anchored on its deep aspect to the radius and ulna. (B) Here, the deep layer of extensor muscles is shown. Three outcropping muscles of the thumb* emerge between the extensor carpi radialis brevis and the extensor digitorum: abductor pollicis longus, extensor pollicis brevis, and extensor pollicis longus. The furrow from which the three muscles emerge has been opened proximally to the lateral epicondyle, exposing the supinator muscle. (C) This transverse section of the forearm shows the superficial and deep layers of muscles in the posterior compartment (pink), supplied by the radial nerve, and the anterior compartment (gold), supplied by the ulnar and median nerves.