E, The full length of the floor of the third ventricle has been exposed by removing the thalami bilaterally. The mamillary bodies are located at the junction of the anterior and middle thirds of the floor. The floor behind the mamillary bodies is formed by the upper midbrain. The floor in front of the mamillary bodies is very thin and serves as a suitable site for a third ventriculostomy. F, The floor of the third ventricle has been removed to expose the oculomotor nerves exiting the interpeduncular fossa below the posterior part of the floor of the third ventricle. The tentorial edge sweeps downward along the lateral margin of the midbrain. The upper pons is exposed behind the optic chiasm and between the oculomotor nerves. The crural cistern is located between the uncus and cerebral peduncle. G, Interior oblique view with the arteries preserved. The chiasm forms the upper margin of the chiasmatic cistern, which opens laterally into the carotid cistern surrounding the internal carotid arteries and upward around the optic chiasm to the cistern of the lamina terminalis. The anterior cerebral arteries ascend in front of the lamina terminalis. The anterior commissure crosses in the upper part of the anterior third ventricular wall. The columns of the fornix form the superior and anterior margins of the foramen of Monro. H, Anterosuperior view. The upper part of the left thalamus has been removed to expose the optic tract, which extends backward above the oculomotor nerve in the lateral part of the suprasellar area to reach the lateral geniculate body. The chiasm and posterior part of the optic nerves are located directly above the sella. The anterior cerebral arteries pass above the chiasm. The left anterior cerebral artery is hypoplastic. (Images courtesy of AL Rhoton, Jr.)