This muscle lies deeply in the palm in contact with the metacarpals and interossei; it is not classified as part of the thenar eminence. The transverse head arises from the whole length of the palmar border of the third metacarpal whence the muscle converges, fan-shaped, to the ulnar sesamoid of the thumb, and so to the ulnar side of the base of the proximal phalanx and the tendon of extensor pollicis longus. There is an oblique head that arises from the bases of the second and third metacarpals and their adjoining carpal bones (trapezoid and capitate) by a crescentic origin that embraces the insertion of flexor carpi radialis. The fibers of this head run edge to edge with the transverse head and converge with it on the ulnar sesamoid.
Nerve supply of adductor pollicis:
By the deep branch of the ulnar nerve (T1).
Action of adductor pollicis:
To approximate the thumb to the index, whatever the original position of the thumb.