Palmar interossei muscles

The palmar interossei (interossei volares) are small muscles in the hand that lie on the anterior aspect of the metacarpals. They are smaller than the dorsal interossei of the hand, which lie between the metacarpals.

Structure
Each palmar interosseous muscle arises from the entire length of the metacarpal bone of one finger, and is inserted into the side of the base of the proximal phalanx and extensor expansion of the extensor digitorum tendon to the same finger.

There are three palmar interossei:

The palmar interossei are unipennate.

From this account it may be seen that each finger is provided with two interossei, with the exception of the little finger, in which the abductor digiti minimi muscle takes the place of one of the pair.

Some texts consider the medial head of the flexor pollicis brevis to be a palmar interosseous muscle. This muscle would then be considered the first palmar interosseous muscle, and the total number of palmar interosseous muscles in the hand would be four.

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

Actions
The palmar interosseous muscles adduct the fingers towards the middle finger. This is in contrast to the dorsal interossei, which abduct the fingers away from the middle finger. The interossei also assist the lumbricals.