Interosseous muscles of the hand

The interosseous muscles of the hand are muscles found near the metacarpal bones that help to control the fingers. They are considered voluntary muscles.
They are generally divided into two sets:

4 Dorsal interossei - Abduct the digits away from the 3rd digit and are bipennate.
3 Palmar interossei - Adduct the digits towards the 3rd digit and are unipennate.

This is often remembered by the mnemonic PAD-DAB, as the Palmar interosseous muscles ADduct, and the Dorsal interosseous muscles ABduct. The axial line goes down the middle of the 3rd digit, towards the palm of the hand.
Both sets of muscles are innervated by the deep branch of the ulnar nerve.