The abductor pollicis longus is a long skeletal muscle located in the posterior compartment of forearm. Flat and bipennate, it originates from the posterior surface of radius and ulna bone, underneath the supinator muscle. Then it travels obliquely and downwards, with its long tendon going around the distal end of radius and under the extensor retinaculum to be inserted into the base of the first metacarpal bone.
Action
The abductor pollicis longus abducts the thumb, drawing it anteriorly (backwards) away from the palm, reinforcing the extensor pollicis brevis muscle to extend the thumb.
Nerve and blood supply
It is innervated by fibers of the posterior interosseous nerve, which is a branch of the radial. It is supplied by the posterior interosseous artery, which is a branch of the common interosseous (and this latter springs from the ulnar artery).
Below, the image of forearm showing the abductor pollicis longus
