Adductor pollicis muscle

The adductor pollicis muscle is a muscle in the hand that functions to adduct the thumb. It has two heads: transverse and oblique.

Oblique head
The oblique head (occasionally known as adductor obliquus pollicis) arises by several slips from the capitate bone, the bases of the second and third metacarpals, the intercarpal ligaments, and the sheath of the tendon of the flexor carpi radialis.

From this origin the greater number of fibers pass obliquely downward and converge to a tendon, which, uniting with the tendons of the medial portion of the flexor pollicis brevis and the transverse head of the adductor pollicis, is inserted into the ulnar side of the base of the proximal phalanx of the thumb, a sesamoid bone being present in the tendon.

A considerable fasciculus, however, passes more obliquely beneath the tendon of the flexor pollicis longus to join the lateral portion of the flexor pollicis brevis and the abductor pollicis brevis.

Transverse head
The transverse head (also known as adductor transversus pollicis) is deeply seated.

It is triangular, arising by a broad base from the lower two-thirds of the palmar surface of the third metacarpal bone; the fibers converge, to be inserted with the medial part of the flexor pollicis brevis and the oblique head into the ulnar side of the base of the proximal phalanx of the thumb.

Relations
The radial artery passes between the two heads, travelling from the back of the hand into the palm, where it forms the deep palmar arch.

Innervation
The adductor pollicis is innervated by the deep branch of the ulnar nerve.

Actions
Adduction of the thumb is bringing it back into the plane of the palm of the hand from its previously abducted position. This muscle, however, also brings the thumb to the side of the palm and index finger.

Froment's Sign is used to test for a compromised adductor pollicis muscle.