Hippocampus and inferior horn/atrium of lateral ventricle.  In this dissection, the lateral portions of the temporal and parietal lobes have been removed to expose the atrium and inferior horn of the lateral ventricle.  The hippocampus is a prominent ridge of tissue that lies in the ventromedial wall of the inferior horn of the ventricle. Its anterior region, the head of the hippocampus, is bulbous and resembles morphologically the dorsal surface of an animal's paw, hence, early neuroanatomists often referr to it as the "pes hippocampus."  The more caudal portion of the hippocampus is curvilinear and roughly columnar in shape and tapers to a conical point at the level of the atrium.  The fimbria, the proximal portion of the fornix, attaches to the dorsomedial surface of the hippocampus.   At the level of the atrium, the fimbria detaches from the hippocampus and arches dorsomedially to continue as the crus of the fornix.  The dentate gryus, not visible from this lateral perspective, lies on the medial surface of the hippocampal formation, between the fimbria and the parahippocampal gyrus. (Image courtesy of AL Rhoton, Jr.)