In human anatomy, the palmar or volar interossei (interossei volares in older literature) are three small, unipennate muscles in the hand that lie between the metacarpal bones and are attached to the index, ring, and little fingers. They are smaller than the dorsal interossei of the hand. Structure All palmar interossei originate along the shaft of the metacarpal bone of the digit on which they act. They are inserted into the base of the proximal phalanx and the extensor expansion of the extensor digitorum of the same digit. Pollical palmar interosseous The first palmar interosseous is located at the thumb's medial side. Passing between the first dorsal interosseous and the oblique head of adductor pollicis, it is inserted on the base of the thumb's proximal phalanx together with adductor pollicis. The "pollical" palmar interosseous muscle (PPIM), is present in more than 80% of individuals and was first described by . Its presence has been verified by numerous anatomists since, but others have either failed to mention it or considered it part of either adductor pollicis or flexor pollicis brevis. However, the deep head of the flexor pollicis brevis originates on the thumb's ulnar sesamoid bone and the oblique portion of the adductor pollicis on several carpal bones, as well as the bases of the second and third metacarpal bones and not on the first metacarpal. Central palmar interossei The other three palmar interossei originate on the side of the metacarpal facing the hand's midline (ray of long finger); the second is attached to the medial side of the index finger; the third to the lateral side of the ring finger; and the fourth to the lateral side of the little finger. The tendons of these three muscles pass posterior to the deep transverse ligament before being inserted onto the extensor expansion. Innervation All of the interosseous muscles of the hand are innervated by the deep branch of the ulnar nerve. Blood supply The palmar interossei are supplied by the palmar metacarpal artery of the deep palmar arch. Function 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. In addition (like dorsal interossei) they flex the finger at the metacarpo-phalangeal joint and extend the finger at the interphalangeal joint and thus assist the lumbricals. The palmar interossei, together with the dorsal interossei