Summary Palmar interossei (3 muscles) Origin Palmar surfaces of 2nd, 4th and 5th metacarpals (3 unipennate muscles) Insertion Extensor expansions of digits and bases of proximal phalanges of digits 2, 4 and 5 Action Adduct digits toward axial line and assist lumbricals in flexing metacarpophalangeal joints and extending interphalangeal joints Innervation Deep branch of ulnar nerve (C8, T1) Arterial supply Palmar metacarpal arteries