FIG 3. A and B, Anatomic relationship of the opercula to the insula at earlier (A) and later (B) stages of dissection of the left cerebral hemisphere of a gross anatomic specimen from a 71-year-old man. The partes orbitalis (or), triangularis (tr), and opercularis (op) of the inferior frontal gyrus (I) overlie the anterior lobule of the insula. The anterior horizontal ramus (single open arrow) of the sylvian fissure leads to the anterior PS (APS). The anterior ascending ramus (dual open arrows) of the sylvian fissure leads to the superior PS (SPS) (8). The pars opercularis (op) joins with the inferior end of the precentral gyrus (4) to form most of the frontal operculum. In this specimen, they form a "bulky" union that invaginates into the convexity surface of the anterior lobule and depresses the MSG (m) slightly below the surface of the insula. Further posteriorly, the subcentral gyrus (11) and the anterior limb of the supramarginal gyrus (6) form the rest of the frontoparietal operculum that overlies the posterior lobule. The HG (H) overlies the PLG (P), so the anteromedial surface of HG abuts onto the lateral surface of the PLG. Deeper dissection (in B) shows the origin of the HG immediately posterior to the insula, posterosuperolateral to the PLG. In this specimen, the postcentral sulcus defines separate ALG (A) and PLG (P). PLG is dominant and forms the pole of the posterior lobule at the limen.