Origin Oblique head: bases of 2nd and 3rd metacarpals, capitate, and adjacent carpals; Transverse head: anterior surface of body of 3rd metacarpal Insertion Medial side of base of proximal phalanx of thumb Action Draws 1st metacarpal laterally to oppose thumb toward center of palm and rotates it medially Innervation Deep branch of ulnar nerve (C8 and T1) (C8, T1) Arterial Supply Deep palmar arterial arch