The neurohypophysis, an extension of the ventral hypothalamus, attaches to the dorsal and caudal surface of the adenohypophysis1 (Fig. 25-1). In adult men and women, it weighs ˜100 mg. It is divided by the diaphragma sellae into an upper part, called the infundibulum or median eminence, and a lower part, known as the infundibular process or pars nervosa. The two parts are supplied with blood by branches from the superior and inferior hypophyseal arteries. In the pars nervosa, the arterioles break up into localized capillary networks that drain directly into the jugular vein through the sellar, cavernous, and lateral venous sinuses. In the infundibulum, the primary capillary networks coalesce into another system, the portal veins, which perfuse the adenohypo-physis before discharging into the systemic circulation.