[TA] rostrocaudally oriented regions of the hypothalamus characterized by their position and cell groups. The periventricular zone [TA] (zona periventricularis [TA]) is a thin sheet of small neurons located in the wall of the third ventricle. The medial zone [TA] (zona medialis [TA]) lies between the periventricular zone and a rostrocaudal line drawn between the mammillothalamic tract and the postcommissural fornix, and consists of supraoptic, tuberal, and mammillary regions. The lateral zone [TA] (zona lateralis [TA]) is lateral to the medial zone, and contains the tuberal nuclei and the fibers of the medial forebrain bundle. SYN: zonae hypothalamicae [TA].