Fig. 25.Organization of the hypothalamic neurohypophysial tract (arrows). Note arching fibers emanating from magnocellular neurons in the paraventricular nucleus (PVN) as they descend toward and join fibers emanating from the supraoptic nucleus (SON). The fiber tract converges in the midline at the base of the hypothalamus in the retrochiasmatic area (arrowheads) before entering the internal zone of the median eminence. III = third ventricle, F = fornix, OC = optic chiasm.