Stepwise Dissection of Right Cerebral Hemisphere. A, The natural upward retraction of the apex of the pars triangularis creates the largest natural opening in the sylvian fissure. The posterior ramus, the longest ramus of the sylvian fissure, extends backward and upward to its termination in the inferior parietal lobule, where the supramarginal gyrus wraps around its posterior end. The Heschl gyrus, the most anterior of the transverse temporal gyri, extends obliquely backward and medially across the temporal operculum from the cortical surface. The frontoorbital ramus of the sylvian fissure crosses the basal surface of the frontal lobe medial to the pars orbitalis. B, The lower and upper portions of the frontal and temporal opercula, respectively, have been removed to show the relation-ship between opercular and insular structures. The central insular sulcus courses superficial to, and almost parallel with, the central sulcus on the convexity. In this hemisphere, the frontoorbital ramus (red dotted arrow) is differentiated from a superficial orbital sulcus (white arrow)—which is located on the orbital surface of the frontal lobe between the anterior horizontal and frontoorbital rami of the sylvian fissure—by the fact that the deep end of the frontoorbital ramus opens into the sylvian fissure at the level of the anterior limiting sulcus, but the orbital sulcus above it does not open into the sylvian fissure. The mean length of the frontoorbital ramus of the sylvian fissure is 10 mm. Opening the frontoorbital ramus, when present, provides access to the most anteroinferior portion of the insula. C, The remaining part of the frontoparietal operculum has been removed. The anterior limiting sulcus is directed upward and anterior, to form the anterior border of the insula. The insular apex is the most prominent laterally projecting point on the insular convexity. D, Enlarged view of the insula. The middle short gyrus is the widest of the short gyri in this specimen. The short gyri have a radiating pattern that converges on the anteroinferior edge of the insula. The accessory and transverse gyri connect the anterior edge of the insula to the adjacent gyri on the orbital surface of the frontal lobe. E, The frontoparietal and temporal opercula and the upper portion of the central core of the hemisphere have been removed using transverse cuts that extend along the superior and inferior limiting sulcus to show the relationship between the insula and the deeper structures. The central core of the hemisphere, which contains the caudate and lentiform nuclei, thalamus, and internal capsule, is located deep to the insula. The foramen of Monro is located deep to the middle portion of the posterior short gyrus. The posterior end of the insula and the junction of superior and inferior limiting sulci are located superficial to the anterior edge of the atrium. F, Enlarged superolateral view of the same specimen featured in E. The central insular sulcus ascends superficial to the posterior third of the lentiform nucleus. The axial cut extends through the superior limiting sulcus. The lentiform nucleus is positioned deep to the insula and extends from the midportion of the middle short gyrus to the middle part of the posterior long gyrus in this cut. The genu of the internal capsule is positioned deep to the posterior short gyrus. (Images courtesy of AL Rhoton, Jr.)