S, A retractor has been placed between thalamus and crus fornix to open choroidal fissure. Opening choroidal fissure in body ventricle exposes third ventricle. Opening choroidal fissure between pulvinar and crus fornix exposes quadrigeminal cistern, and opening fissure between lower surface thalamus and fimbria fornix exposes ambient cistern. T,  remaining insula has been removed to expose thalamus forming inner rim choroidal fissure. lateral geniculate body is exposed at lower margin thalamus. optic radiations pass laterally above hippocampus in ro temporal horn and posteriorly around lateral margin at atrium to reach calcarine sulcus. anterior wall temporal horn is formed by amygdala, which tilts backward above, but is separated from hippocampal head by temporal horn. U,  thalamus has been removed to expose third ventricle. body, crus, and fimbria fornix, forming outer margin choroidal fissure, have been preserved. Opening choroidal fissure in front crus fornix exposes pineal region and quadrigeminal cistern. Opening choroidal fissure adjacent to body fornix exposes third ventricle. Opening choroidal fissure in temporal horn exposes ambient cistern and posterior arteries. medial posterior choroidal arteries are exposed in quadrigeminal cistern. striae medullaris thalami marks lower edge velum interpositum, in which internal veins course. V,  half body fornix has been folded downward to expose right half body and medial aspect contralateral choroidal fissure located between body fornix and upper surface thalamus. pineal gland and posterior commissure are exposed at posterior margin and anterior commissure and columns fornix are exposed at anterior margin third ventricle. (Images courtesy AL Rhoton, Jr.)