A, Identification of the pre- and postcentral gyri and variations in the frontal and temporal lobe. Right frontotemporal area adjoining the sylvian fissure. This is the area that would be exposed in a sizable frontotemporal craniotomy. The limited exposure may make it difficult to determine the site of the central sulcus and the precentral and postcentral gyri. Usually, the pre- and postcentral gyri can be located by examining the gyral pattern along the upper lip of the sylvian fissure. From anteriorly, the pars orbitalis, triangularis, and opercularis can be identified. The precentral gyrus is usually located at the posterior margin of the pars opercularis. The sylvian fissure also can be followed backward to its upturned posterior end that is capped by the supramarginal gyrus. Usually, the postcentral gyrus is the next gyrus along the sylvian fissure anterior to the supramarginal gyrus. B, Overview of the right hemisphere shown in A. The central sulcus can be followed to the superior margin of the hemisphere. The precentral gyrus is broken up into several segments by crossing sulci. The relationships of the pars opercularis to the precentral gyrus and the supramarginal gyrus to the postcentral gyrus are quite consistent and are helpful in identifying the central sulcus and the pre- and postcentral gyri during the limited operative exposures along the sylvian fissure. The anterior horizontal ramus of the sylvian fissure separates the pars orbitalis and triangularis and the anterior ascending ramus separates the pars triangularis and opercularis. C, Another right hemisphere. The lower end of the precentral gyrus is located behind a somewhat lobulated pars opercularis. The postcentral gyrus is located at the anterior edge of the supramarginal gyrus, which wraps around the upturned posterior end of the sylvian fissure. D, The part of the right frontal and parietal lobes in front of and behind the pre- and postcentral gyri and central sulcus has been removed. The precentral gyrus is located lateral to the posterior part of the body of the ventricle. The postcentral gyrus is located lateral to the anterior part of the atrium. Both gyri adjoining the sylvian fissure are positioned lateral to the splenium of the corpus callosum. E, Superolateral view of the left frontal lobe. The frontal lobe is often depicted as being split into three gyri, superior, middle, and inferior, by two sulci, superior and inferior. Often, as shown, the superior frontal gyrus is split into medial and lateral segments by irregular sulci and gyri. The middle frontal gyrus does not have a smooth, unbroken surface, but is broken up into multiple, tortuous segments. On the inferior frontal gyrus, formed by the pars orbitalis, triangularis, and opercularis, there can be multiple variations in the size and shape of the contributions from each part. The precentral gyrus, in this case, is broken up into several segments by limbs of the precentral sulcus. F, Anterior view. A portion of the right superior frontal gyrus is broken into two longitudinal gyral strips. The left superior frontal gyrus is composed of multiple gyri that extend medially and laterally across the superior frontal area. The superior frontal sulci are continuous along both frontal lobes. The middle frontal gyri on both hemispheres are made up of numerous worm-like gyral segments. (Images courtesy of AL Rhoton, Jr.)