Structurally, each cerebral hemisphere is divided into four major anatomical lobes: frontal, parietal, occipital, and temporal (eFig. 9.9A). The frontal lobes are located anteriorly and are separated from the more posterior parietal lobe by the central sulcus (sulcus of Rolando) (eFig. 9.9A). Laterally, the frontal lobe is separated from the temporal lobe by the lateral sulcus (fissure of Sylvius). Although there is no specific demarcation between the parietal and occipital lobe laterally, along the medial aspect of the hemispheres the two lobes are separated by the parieto-occipital sulcus (eFig. 9.9B). Along the midline, the cerebral hemispheres are separated from one another by the longitudinal fissure (interhemispheric fissure, sagittal fissure). Concealing a small area of cortex called the insula laterally are portions of the frontal, parietal, and temporal lobes collectively referred to as the operculum (Latin for “lid”) (eFig. 9.10). The insula represents fusion of the telencephalon and diencephalon and can be seen by gently prying open the lateral sulcus.