A, The frontal lobe and the anterior carotid arteries have been elevated to expose the optic chiasm and lamina terminalis. The pituitary stalk extends downward from the floor of the third ventricle. The optic tracts pass along the lateral margin of the floor of the third ventricle. The lamina terminalis blends above into the rostrum of the corpus callosum. The olfactory tracts pass backward above the optic nerves. B, The lamina terminalis has been opened to expose the chiasmatic recess, mamillary bodies, and aqueduct. The pituitary stalk is exposed below the infundibular recess located behind the optic chiasm and in front of the mamillary bodies. Superior hypophyseal arteries pass medially from the carotid artery. C, Another third ventricle. The anterior communicating artery commonly passes in front of the lamina terminalis. Perforating arteries arise from a precallosal branch of the anterior communicating artery and penetrate the anterior wall of the third ventricle to reach the columns of the fornix. D, Anterior view of a cross section through the anterior part of the third ventricle and body of the lateral ventricle. The lamina terminalis, which has been opened, extends upward in front of the anterior commissure and blends into the rostrum of the corpus callosum. The anterior cerebral arteries have been folded forward. The choroid plexus extends through the foramen of Monro into the roof of the third ventricle below and the body of the lateral ventricle above. (Images courtesy of AL Rhoton, Jr.)