A, Lateral view, right cerebrum. The inferior frontal gyrus is formed by the pars orbitalis, tri-angularis, and opercularis. The pre- and postcentral gyri are located between the pars opercularis anteriorly and supramarginal gyrus posteriorly. The precentral gyrus is broken into two gyral strips. B, The pars opercularis, triangularis, and orbitalis, and the superior temporal gyrus and part of the supramarginal gyrus have been removed to expose the insula. A number of pins have been placed on the cortical surface to identify the deep location of various structures: the green pin indicates the foramen of Monro; the red pin, the massa intermedia; yellow pin, the pineal gland; white pin, the lamina terminalis. The ovoid group of dark pins identifies the outer margin of the corpus callosum. The arrows along the posterior half of the superior margin identify the site at which sulci on the medial surface intersect the superior margin as follows: white arrow, the ascending (marginal) ramus of cingulate sulcus that marks the posterior edge of the paracentral lobule; red arrow, the parieto-occipital sulcus; and yellow arrow, the calcarine sulcus. C, Red pins have been placed on the convexity directly lateral to the course of the calcarine and parieto-occipital sulci and the cingulate sulcus and its ascending ramus on the medial surface. The ascending ramus of the cingulate sulcus extends along the posterior edge of the paracentral lobule formed by the upper end of the pre- and postcentral gyrus overlapping onto the medial surface of the hemisphere. The parieto-occipital and calcarine sulci on the medial surface converge and join in a Y-shaped configuration. Small black pins outline the thalamus. The yellow pins outline the outer margin of the caudate nucleus. The large blue pinhead is located at the level of the pineal, and the green pin is located directly lateral to the foramen of Monro. D, Medial surface of the same hemisphere. The yellow pins mark the location of the central sulcus. The lower end of the central sulcus is located just behind the foramen of Monro as is also shown in B and C. The dark pins outline the circular sulcus of the insula. The green pin is positioned at the sylvian point where the last branch of the middle cerebral artery turns laterally from the surface of the insula to reach the cortical surface. (Images courtesy of AL Rhoton, Jr.)