Surface Anatomy of Sylvian Region. A, Superolateral view of the left hemisphere. 1, precentral gyrus; 2, postcentral gyrus; 3, supramarginal gyrus; 4, inferior frontal sulcus; 5, pars opercularis of the inferior frontal gyrus; 6, superior temporal gyrus; 7, pars triangularis of the inferior frontal gyrus. The arrows indicate the ascending and descending terminal branches of the posterior ramus of the sylvian fissure. The arrowhead indicates posterior ramus of the sylvian fissure. The largest transverse diameter of the cerebrum usually corresponds to the level of postcentral gyrus and to the middle and the superior temporal gyri (at the level of the postcentral gyrus). B, Superolateral view of the same specimen shown in A. A transverse cut has been made by following a line drawn from the base of the pars triangularis of the inferior frontal gyrus to the supramarginal gyrus, immediately above the posterior ramus of the sylvian fissure. 1, frontal horn; 2, head of the caudate nucleus; 3, atrium; 4, pars triangularis; 5, pars opercularis; 6, precentral gyrus; 7, postcentral gyrus; 8, supramarginal gyrus; 9, superior temporal gyrus. C, The operculum of the supramarginal gyrus has been removed to display the middle and posterior transverse temporal gyri and the medial end of the Heschl’s gyrus. 1, medial part of the Heschl’s gyrus (anterior transverse temporal gyrus); 2, middle transverse temporal gyrus; 3, posterior transverse temporal gyrus; 4, precentral gyrus; 5, postcentral gyrus; 6, posterior end of the superior temporal gyrus turning around the descending branch of the posterior ramus of the sylvian fissure to become the supramarginal gyrus; 7, superior temporal gyrus. The supramarginal gyrus constitutes the posterior wall of the posterior ramus of the sylvian fissure. D, The operculum of the postcentral gyrus has been removed to display the Heschl’s gyrus and posterior end of the insula. 1, posterior long gyrus of the insula; 2, Heschl’s gyrus; 3, middle transverse temporal gyrus; 4, posterior transverse temporal gyrus; 5, pars opercularis; 6, precentral gyrus; 7, supramarginal gyrus; 8, superior temporal gyrus. E, The operculum of the precentral gyrus has been removed to display the posterior part of the planum polare, located immediately anterior to the Heschl’s gyrus, and also to display the posterior half of the insula. 1, posterior insula; 2, pars triangularis; 3, pars opercularis; 4, Heschl’s gyrus; 5, middle transverse temporal gyrus; 6, posterior transverse temporal gyrus; 7, planum polare; 8, superior temporal gyrus. F, The pars opercularis of the inferior frontal gyrus has been removed to display the anterior portion of the planum polare and the anterior portion of the insula. 1, insula; 2, pars triangularis; 3, Heschl’s gyrus; 4, planum polare. G, Frontal view of the cerebrum. The largest transverse diameter of the brain in the suprasylvian region corresponds to the postcentral gyrus (large arrows). The largest transverse diameter of the brain in the infrasylvian region corresponds to the superior or middle temporal gyrus, in the coronal plane of the postcentral gyrus (small arrows). (Images courtesy of AL Rhoton, Jr.)