A, Basal surface of the temporal and occipital lobes from two different brains. The collateral sulcus separates the parahippocampal and occipitotemporal gyri and extends backward onto the occipital lobe. The parahippocampal gyrus is broken up into several segments on both hemispheres by sulci crossing it from medial to lateral. The occipitotemporal gyri that 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 hemispheres. The rhinal sulci that extend along the lateral margin of the uncus are in continuity with the collateral sulci. B, Another cerebrum. The rhinal sulcus on both sides extends along the lateral uncal margin, but is not continuous with the collateral sulcus as in A. The parahippocampal, occipitotemporal, and the inferior temporal gyri are broken up into multiple segments. C, Enlarged view. Dark pins outline the position of the lateral ventricle above the basal surface. The frontal horn is located above the posteromedial part of the basal surface of the frontal lobe. The body of the ventricle is located above the midbrain and thalamus. The temporal horn is located above the collateral sulcus and parahippocampal gyrus. There are prominences, the collateral eminence, in the floor of the temporal horn and the collateral trigone, in the floor of the atrium, that overlie the deep end of the collateral sulcus. D, Basal surface of another 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 medial part of the parahippocampal gyrus faces the ambient cistern located between the lateral side of the midbrain and the parahippocampal gyrus. The rhinal sulcus courses along the lateral margin of the anterior part 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. (Images courtesy of AL Rhoton, Jr.)