[TA] a compact bundle of fibers arising in the habenula and passing anteriorly (ventrally) to the interpeduncular nucleus at the base of the midbrain; some of its fibers bypass this nucleus and terminate in the raphe nuclei of the caudal mesencephalic tegmentum. SYN: fasciculus retroflexus [TA], habenulointerpeduncular tract, habenulopeduncular tract [TA], tractus habenulointerpeduncularis [TA], fasciculus of Meynert, habenulopeduncular tract, retroflex bundle of Meynert.