Origin Palmar 1 - 3: Palmar surfaces of 2nd, 4th and 5th metacarpals (unipennate muscles) Insertion Palmar 1 - 3: Extensor expansions of digits and bases of proximal phalanges of digits 2, 4 and 5 Action Palmar 1 - 3: Adduct digits toward axial line and assist lumbricals in flexing metacarpophalangeal joints and extending interphalangeal joints Innervation Deep branch of ulnar nerve (C8 and T1) (C8, T1) Arterial Supply Palmar 1 - 3: Palmar metacarpal arteries