Superior view of the lateral and third ventricles through the velum interpositum after partial resection of the fornices. The choroid plexus of both lateral ventricles is visible entering the foramina of Monro. At this level, the paired septal veins merge with the thalamostriate veins to form both internal cerebral veins, which course posteriorly along the roof of the third ventricle. Choroidal veins and arteries are visible. (Image courtesy of AL Rhoton, Jr.)