Combined with the |abductor pollicis longus|, the |extensor pollicis brevis| (thumb muscle) creates a narrow, triangular muscle form which wraps around the lower end of the |radius| (the bone of the forearm on the thumb side). The |extensor pollicis brevis| originates from the back side of the |radius| and inserts in the base of the first phalanx of the thumb. This muscle extends the thumb and continued action rotates the hand. The combination of the |abductor pollicis longus| and the |extensor pollicis brevis| forms the oblique carpal muscle group, which produces a small but important convexity three-fourths of the way down the forearm on its outer (radial) profile.
