The Medial Temporal Region. A, Medial surface of the temporal lobe is formed by the parahippocampal and dentate gyri and the uncus. The calcarine sulcus intersects and divides the posterior part of the parahippocampal gyrus into an upper part that blends into the isthmus of the cingulate gyrus and a lower part that blends into the lingula. B, Enlarged view. The uncus, a medial projection at the anterior end of the parahippocampal gyrus, has an anterior and posterior segment and a medially directed apex. The collateral sulcus extends along the lateral margin of the parahippocampal gyrus, and the rhinal sulcus extends along the lateral margin of the uncus. The rhinal and collateral sulci frequently are not continuous, although they are in this case. The posterior segment of the uncus is divided by the uncal notch into an upper and lower part. The lower part is formed by the parahippocampal gyrus. The dentate gyrus, at its anterior end, blends into the upper part of the posterior segment, which is formed predominantly by the hippocampal head. The sylvian vallecula is the site where the middle cerebral artery exits the carotid cistern to enter the sylvian fissure. C, Medial part of the parahippocampal gyrus and the lower part of the posterior uncal segment have been removed to expose the dentate gyrus and the choroidal fissure. The beaded dentate gyrus blends into the posterior edge of the upper part of the posterior uncal segment and the medial side of the hippocampal head. The choroidal fissure is located between the fimbria of the fornix and the part of the thalamus from which the lateral geniculate body projects. D, Cross-section of the amygdala and globus pallidus. The anterior part of the roof of the temporal horn has been removed to expose the amygdala and head of the hippocampus. The amygdala, at its upper margin, blends into the globus pallidus. The combination of the globus pallidus and amygdala seem to wrap around the lateral aspect of the optic tract. The apex of the uncus protrudes medially toward the oculomotor nerve. The anterior uncal segment is located lateral to the carotid artery. The amygdala fills most of the anterior segment of the uncus, forms the anterior wall of the temporal horn, and tilts backward above the anterior part of the hippocampal head and roof of the temporal horn. The globus pallidus has a clearly defined inner and outer segment. E, Medial view of the uncus directed across the sella and tentorial edge. The carotid and middle cerebral arteries face the anterior segment of the uncus. The posterior cerebral artery courses along the medial side of the posterior segment. The anterior choroidal artery ascends as it passes backward across the anterior uncal segment to reach the upper part of the posterior segment. The anterior choroidal artery enters, and the inferior ventricular vein exits, the choroidal fissure by passing through the inferior choroidal point located just behind the head of the hippocampus and the posterior uncal segment. The inferior ventricular vein drains the optic radiations in the roof of the temporal horn and empties into the basal vein. F, Medial view of another uncus with the veins removed. The carotid and middle cerebral arteries face the anterior segment of the uncus. The posterior cerebral artery courses along the medial side of the posterior uncal segment. The anterior choroidal artery ascends as it passes backward across the anterior uncal segment to reach the upper part of the posterior segment. The anterior choroidal artery enters the choroidal fissure at the inferior choroidal point located just behind the head of the hippocampus and the posterior uncal segment. G, Another specimen. The anterior choroidal artery pursues an angulated course descending along the anterior uncal segment, but at the uncal apex it turns sharply upward, reaching the upper part of the posterior segment before entering the temporal horn. H, Superior view of the right temporal horn and basal cisterns. The posterior segment of the uncus faces the cerebral peduncle, across the crural cistern. The medial temporal lobe behind the posterior uncal segment faces the ambient cistern and is formed by the parahippocampal and dentate gyri and the fimbria. The posterior cerebral arteries course through the crural and ambient cisterns. The anterior segment of the uncus faces the carotid and middle cerebral arteries. The anterior choroidal artery arises from the internal carotid and passes around the anterior and posterior segments of the uncus to enter the temporal horn at the inferior choroidal point. The veins draining the temporal horn also exit the ventricle at the inferior choroidal point to enter the basal vein. (Images courtesy of AL Rhoton, Jr.)