Caudal Perspective of the Medial Temporal Region. I, Basal surface of the temporal lobe. The anterior segment of the medial temporal lobe is formed by the uncus, which has an anterior segment that faces forward toward the carotid cistern and entrance into the sylvian cistern and a posterior segment that faces posteromedially toward the cerebral peduncle and crural cistern. The posterior segment of the uncus is divided into upper and lower parts by the uncal sulcus. The part above the uncal sulcus is formed by the medially folded head of the hippocampus. The uncinate gyrus is exposed above the uncal sulcus. The part below the uncal sulcus is formed by the parahippocampal gyrus. The uncal apex, at the junction of the anterior and posterior segment, is positioned lateral to the oculomotor nerve. The cortical component of the middle segment of the MTR is formed by the part of the parahippocampal gyrus that faces the midbrain across the ambient cistern. The rhinal sulcus courses along the lateral margin of the uncus and is continuous posteriorly with the collateral sulcus. J, The part of the posterior uncal segment located below the uncal notch and formed by the medial part of the parahippocampal gyrus has been removed to expose the lower surface of the upper half of the posterior uncal segment formed by the extraventricular head of the hippocampus. The fimbria is exposed above the dentate gyrus. The head of the hippocampus that folds into the upper part of the posterior segment of the uncus is related, from posterior to anterior, to the intralimbic gyrus, band of Giacomini, and the uncinate gyrus. The choroidal fissure, located between the thalamus and fimbria, extends along the lateral edge of the lateral geniculate body and pulvinar. K, The hippocampus and dentate gyrus have been removed while preserving the fimbria and attachment of the choroid plexus along the choroidal fissure. The choroid plexus is attached on one side 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, located at the lower end of the attachment of the choroid plexus in the temporal horn, is positioned behind the head of the hippocampus, anterior to the lateral geniculate body and lateral to the posterior edge of the cerebral peduncle. L, The 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 amygdala. The tapetum fibers in the roof of the temporal horn have been K removed to expose the fibers of the optic radiation arising from the lateral geniculate body and passing across the roof and around the lateral wall of the temporal horn. Only a thin layer of tapetal fibers separate the optic radiations from the temporal horn and atrium as they pass posteriorly to reach the borders of the calcarine sulcus. The cuneus forms the upper bank and the lingula forms the lower bank of the calcarine sulcus. (Images courtesy of AL Rhoton, Jr.)