Anatomy

Origin

First—medial side of base of first metacarpal bone Second, third, and fourth—anterior surfaces of second, fourth, and fifth metacarpal bones

Insertion

First—medial side of base of proximal phalanx of thumb Second—medial side of base of proximal phalanx of index finger Third and fourth—lateral side of proximal phalanges of ring finger and fifth finger

Nerve

Ulnar nerve (C8, T1)

Actions

Adduct fingers toward center of third finger at metacarpophalangeal joints, assist in flexion of fingers at metacarpophalangeal joints