Superior view of the right mesiotemporal lobe and diencephalomesencephalic junction. The floor of the third ventricle is visible from the tuber cinereum anteriorly to the Sylvian (mesencephalic or cerebral) aqueduct posteriorly (the latter located directly under the posterior commissure). The impressions of the mammillary bodies are seen posterior to the tuber cinereum in the floor of the third ventricle. The optic chiasm forms part of the anterior wall of the third ventricle. The lateral walls of the third ventricle are formed by the thalami posteriorly and the hypothalamus anteriorly.T he medial temporal region is divided into three parts: anterior, middle, and posterior. The anterior part (blue brackets) extends posteriorly from the anterior end of the rhinal sulcus and uncus to a transverse line at the level of the inferior choroidal point. The middle part (red brackets) extends posteriorly from the inferior choroidal point to a transverse line passing at the level of the quadrigeminal plate. The posterior part (green brackets) extends from the quadrigeminal plate to the level of the basal parietotemporal line, which connects the preoccipital notch to the lower end of the parieto-occipital sulcus.  One can think of the medial temporal lobe as a "ladder" with the following "steps" going from medial to lateral: the parahippocampal gyrus, the dentate gyrus (or teeth-like, as it is shaped like a denture by the impressions of small transverse crossing vessels), the fimbria, and the hippocampus. The anterior parahippocampal gyrus forms a "hook" know as the uncus. The uncus has an anterior and posterior surface. The apex of the uncus projects medially and is in close proximity to the oculomotor nerve and mesencephalon (midbrain). The uncal recess separates the hippocampus from the amygdala. (Image courtesy of AL Rhoton, Jr.)