E, The cross section of another third ventricle extends through the anterior commissure. The body of the fornix sits in the floor of the body of the ventricle. The columns of the fornix pass around the superior and anterior margins of the foramen of Monro and behind the anterior commissure. The lamina terminalis extends upward from the chiasm. F, Enlarged view. The lamina terminalis has been opened. The chiasmatic recess is located between the lower part of the lamina terminalis and the posterior part of the optic chiasm. The nucleus basalis is located below the lateral part of the anterior commissure. G, Another third ventricle. The lamina terminalis ex-tends upward from the optic chiasm and blends into the rostrum of the corpus callosum. H, The lamina terminalis has been opened. The posterior margin of the chiasm is exposed behind the anterior communicating artery. The anterior commissure is ex-posed behind the upper edge of the lamina terminalis. The incision has been extended upward through the rostrum of the corpus callosum be-tween the columns of the for-nix. This exposes the roof of the third ventricle above the anterior commissure. The choroid plexus hangs down from the tela into the roof of the third ventricle. The mamillary bodies are exposed in the floor. (Images courtesy of AL Rhoton, Jr.)