Abductor pollicis longus

The abductor pollicis longus lies in the deep part of the posterior compartment of the forearm. It extends from the radius and ulna toward the thumb. It is an extrinsic hand muscle, and its main function is the abduction and extension of the thumb at the first carpometacarpal joint. It also assists in abduction of the hand (radial deviation) at the wrist joint and midcarpal joint.