M. polycern abductor (abductor pollicis) - m. polymorus, Latin musculus abductor pollicus, pterygoid muscle of the thumb. Pulls the thumb away from the rest and raises it. Ends in the digital fossa. Located lateral to the flexor carpi radialis and the superficial radial nerve, it is supplied by the vessels of the ulnar nerve: it is innervated by the superficial radial nerve.
The muscle abducts the thumb, extends the wrist joint, and stabilizes the position of the wrist joint. It is also responsible for the range of motion when placing your hands behind your back.