Inferior Perspective of Third Ventricle. Anterior is towards the top of the figure and posterior towards the bottom.  The crus cerebri have been retracted laterally to permit optimal visualization of the third ventricle. The roof of the third ventricle, seen between the posterior commissure and massa intermedia, is formed by velum interpositum. The columns of the fornices sweep posterior to the anterior commissure and anterior to the interventricular foramina of Monro; they then sweep posteriorly and laterally to end in the mammillary bodies, which are visible just medial to the oculomotor nerves.  Near the top of the image, the optic chiasm and optic tracts surround the pituitary stalk and supraoptic recess.  (Image courtesy of AL Rhoton, Jr.)