A, Midsagittal section of the sella, pituitary gland, sphenoid sinus and third ventricle. The anterior part of the third ventricle is located above the sella. The columns of the fornix descend along the superior and anterior margins of the foramen of Monro to reach the mamillary bodies. The optic chiasm and stalk are located above the sella. The internal cerebral veins course in the roof of the third ventricle. B, Enlarged view. The suprachiasmatic recess of the third ventricle is located between the lamina terminalis and the chiasm. The infundibular recess extends into the stalk in the area behind the chiasm. The lamina terminalis extends upward and is continuous with the rostrum of the corpus callosum. The thin part of the third ventricular floor between the chiasm and the mamillary bodies is suitable for a third ventriculostomy. The anterior commissure crosses the wall of the third ventricle in front of the columns of the fornix. The massa intermedium crosses the midportion of the third ventricle. C, The anterior part of the hemisphere has been removed to expose the lateral ventricles and suprasellar area. The optic nerve and chiasm are located above the sella. The chiasmatic cistern is located below the optic chiasm and opens upward between the optic nerves to the area in front of the lamina terminalis. The anterior commissure crosses the anterior wall of the third ventricle above the lamina terminalis. The anterior part of the third ventricle is located above the sella. The body of the lateral ventricle is situated above the third ventricle. The columns of the fornix form the superior and anterior margins of the foramen of Monro. The olfactory tracts pass above the optic nerves and the optic tracts pass above the oculomotor nerves. D, The cross section on the right hemisphere has been extended backward to the midportion of the temporal horn and thalamus. This exposes the oculomotor nerve arising on the medial surface of the cerebral peduncle and passing below the floor of the third ventricle and lateral to the sella. The crural cistern is located between the uncus and the cerebral peduncle. The mamillary bodies are positioned in the floor of the third ventricle. The posterior commissure sits above the aqueduct. (Images courtesy of AL Rhoton, Jr.)