Origin Proximal 3/4 of medial and anterior surfaces of ulna and interosseous membrane Insertion Base of the distal phalanx of digits 2 - 5 Action Flexes distal phalanges at distal interphalangeal joints of medial four digits; assists with flexion of hand Innervation Medial part: ulnar nerve (C8 and T1); Lateral part: anterior interosseous branch of median nerve (C8 and T1) (C8, T1) Arterial Supply Ulnar and anterior interosseous arteries