An intrinsic hand muscle that closes the web between the thumb and first finger. The adductor pollicis has two origins: the oblique head begins along the bases of the second and third metacarpals and their adjacent carpals, the transverse head begins on the front (anterior) surface of the shaft of the third metacarpal. Both heads attach to the base of the proximal phalanx of the thumb. The adductor pollicis adducts the thumb. The muscle is innervated by a deep branch of the ulnar nerve (C8, Tl).