Dominant Hemispheric Landmarks. A, Lateral view of the left cerebral hemisphere. 1, pars triangularis of the inferior frontal gyrus; 2, precentral gyrus; 3, postcentral gyrus; 4, supramarginal gyrus; 5, pars orbitalis; 6, pars opercularis; 7, junction between the superior temporal gyrus and the Heschl’s gyrus; 8, external acoustic meatus. Asterisk, at this point, the planum polare starts to deviate medially. Note the large space in the sylvian fissure between the structures 1, 5, and 6. B, Sagittal magnetic resonance imaging (MRI) scan at the surface of the left hemisphere. 1, postcentral gyrus. Asterisk, projection of the external acoustic meatus over the petrous temporal bone. Heschl’s gyrus (arrow). C, Sagittal MRI scan at the opercular level of the left hemisphere. 1, postcentral gyrus. Asterisk, projection of the external acoustic meatus over the petrous temporal bone. Heschl’s gyrus (arrow). D, Anterobasal view of the cerebrum. 1, pars triangularis; 2, pars orbitalis; 3, pars opercularis; 4, precentral gyrus. The large arrow indicates where the medial deviation of the planum polare begins. The small arrow indicates where the medial deviation of the planum polare intensifies. (Images courtesy of AL Rhoton, Jr.)