Superior dissection of the third ventricle and associated midline structures. The corpus callosum has been mostly removed in this dissection in order to expose the III ventricle, hypothalamus, thalamus, and midbrain.  The floor of the third ventricle is formed posteriorly by the mammillary bodies and anteriorly by the tuber cinerium of the hypothalamus.  The anterior commissure crosses the midline immediately anterior to the third ventricle. Immediately posterior to the anterior commissure, the columns of the fornices diverge from one another in V-like fashion to terminate in the mammillary bodies.  At the diencephalon/midbrain transition zone are the posterior commissure and pineal gland.  Several midbrain structures are also visible, including the superior colliculus, red nucleus and oculomotor nerve.  (Image courtesy of AL Rhoton, Jr.)