Perspective view of the base of the cerebrum. The base of the cerebrum consists of parts of the frontal, temporal and occipital lobes. From lateral to medial, the temporal lobes’ inferior temporal gyrus, fusiform gyrus, and parahippocampal gyrus (containing the medial uncus) form the inferior aspect of the temporal lobe. The uncus has a close relationship medially with the adjacent posterior cerebral artery, the oculomotor nerve, and the cerebral peduncle. Running along the length of the occipital and temporal lobes, the collateral sulcus (collateral fissure) separates the parahippocampal gyrus and the fusiform gyrus of the temporal lobes anteriorly and the lingual gyrus and the fusiform gyrus posteriorly. The isthmus of the cingulate gyrus is the portion of the cingulate gyrus that connects the cingulate gyrus dorsally with the parahippocampal gyrus ventrally. The calcarine sulcus separates the isthmus/parahippocampal gyrus from the lingual gyrus. Within the base of the frontal lobe, the gyrus rectus is most medial, separated from the orbital gyrus by the olfactory tracts & bulbs. Lateral to the orbital gyrus is the inferior frontal gyrus.  (Image courtesy of AL Rhoton, Jr.)