Basal Surface of the Temporal Lobe. A, Collateral sulcus separates the parahippocampal and occipitotemporal gyri and extends backward onto the occipital lobe. The parahippocampal gyrus is broken up into several segments by sulci crossing it from medial to lateral. The occipitotemporal gyri, which form the middle strip along the long axis of the basal surfaces, are discontinuous, as are the inferior temporal gyri that fold from the convexity around the lower margin of the hemisphere. The rhinal sulci that extend along the lateral margin of the uncus are not in continuity with the collateral sulci, as exists in some hemisphere and as shown in B. B, Basal surface of another left temporal lobe. The uncus has an anterior segment that faces forward toward the carotid cistern and entrance into the sylvian cistern and a posterior segment that faces posteriorly toward the cerebral peduncle and crural cistern. The apex between the anterior and posterior segment is located lateral to the oculomotor nerve. The posterior segment of the uncus faces the cerebral peduncle and crural cistern. The ambient cistern is located behind the uncus between the lateral side of the midbrain and the parahippocampal gyrus. The rhinal sulcus courses along the lateral edge of the uncus and is continuous with the collateral sulcus. The posterior segment of the uncus is divided into an upper and lower part by the uncal notch. C, Part of the posterior segment of the uncus below the uncal notch and the medial part of the parahippocampal gyrus have been removed to expose the lower surface of the upper half of the posterior segment that blends posteriorly into the beaded dentate gyrus. The fimbria of the fornix is exposed above the dentate gyrus. The head of the hippocampus folds into the upper part of the posterior segment of the uncus. The choroidal fissure, located between the thalamus and fimbria, extends along the lateral edge of the lateral geniculate body. D, Hippocampus and dentate gyrus have been removed while preserving the fimbria and choroid plexus. The choroid plexus is attached on one side of the choroidal fissure to the fimbria and on the opposite side to the lower margin of the thalamus. The amygdala forms the anterior wall of the temporal horn and fills most of the anterior segment of the uncus. The inferior choroidal point, the lower end of the choroidal fissure and the choroid plexus, is located behind the posterior segment of the uncus. E, Fimbria and choroid plexus have been removed to expose the roof of the temporal horn. The lower part of the anterior uncal segment has been removed to expose the upper part of the amygdala. A small portion of the posterior uncal segment setting below the optic tract has been preserved. The inferior choroidal point, the most anterior attachment of the choroid plexus in the temporal horn and the lower end of the choroidal fissure, is located behind the head of the hippocampus, anterior to the lateral geniculate body, and at the posterior edge of the cerebral peduncle. A thin layer of tapetal fibers from the corpus callosum forms the roof and lateral wall of the temporal horn and atrium. The thin layer of tapetal fibers is all that separates the roof of the temporal horn from the optic radiations. F, Thin layer of tapetal fibers in the roof and lateral wall of the temporal horn has been removed to expose the fibers of the optic radiation arising from the lateral geniculate body and passing across the roof of the temporal horn and around the lateral wall of the temporal horn and atrium. Meyer’s loop of the optic radiations extends forward to the anterior tip of the roof of the temporal horn. The cuneus forms the upper bank and the lingula forms the lower bank of the calcarine sulcus. (Images courtesy of AL Rhoton, Jr.)