Dorsal interossei of the hand


 * For the muscles of the foot, see Dorsal interossei muscles (foot).

The dorsal interossei of the hand are muscles that occupy the space between the metacarpals.

Structure
There are four dorsal interossei in each hand. They are specified as 'dorsal' to contrast them with the palmar interossei, which are located on the anterior side of the metacarpals.

The dorsal interosseous muscles are bipennate, with each muscle arising by two heads from the adjacent sides of the metacarpal bones, but more extensively from the metacarpal bone of the finger into which the muscle is inserted. They are inserted into the bases of the proximal phalanges and into the extensor expansion of the corresponding extensor digitorum tendon. The middle digit has two dorsal interossei insert onto it while the first digit (thumb) and the fifth digit (little finger) have none.

The first dorsal interosseous muscle is larger than the others. Between its two heads, the radial artery passes from the back of the hand into the palm.

Between the heads of dorsal interossei two, three, and four, a perforating branch from the deep palmar arch is transmitted. (The radial artery is transmitted between the heads of the first dorsal interosseous muscle.)

Innervation
All interosseous muscles of the hand are innervated by the deep branch of the ulnar nerve.

Actions
The dorsal interosseous muscles function to abduct the fingers away from the middle finger. This is in contrast to the palmar interossei, which adduct the fingers. This is often remembered by the mnemonic 'DAB PAD', short for "Dorsal ABducts, Palmar ADducts". The interossei also assist the lumbricals.