[TA] the left limb or branch of the atrioventricular bundle that separates from the atrioventricular bundle just below the membranous portion of the interventricular septum to descend the septal wall of the left ventricle and begins to ramify subendocardially. SYN: crus sinistrum fasciculi atrioventricularis [TA], left crus of atrioventricular bundle, left limb of atrioventricular bundle.