Abductor pollicis longus muscle Abductor pollicis longus muscle In human anatomy, the abductor pollicis longus (APL) is one of the extrinsic muscles of the hand. As the name implies, its major function is to abduct the thumb at the wrist. Its tendon forms the anterior border of the anatomical snuffbox. The abductor pollicis longus lies immediately below the supinator and is sometimes united with it. It arises from the lateral part of the dorsal surface of the body of the ulna below the insertion of the anconeus, from the interosseous membrane, and from the middle third of the dorsal surface of the body of
Standard anatomical position Standard anatomical position Because animals can change orientation with respect to their environment, and because appendages (arms, legs, tentacles, "etc.") can change position with respect to the main body, it is important that anatomical terms of location refer to the organism when it is in its standard anatomical position. Thus, "all descriptions are with respect to the organism in its standard anatomical position", even when the organism in question has appendages in another position. However, a straight position is assumed when describing the proximo-distal axis. This helps avoid confusion in terminology when referring to the same organism in different postures.