A, Left side. The cortical branches of the MCA, which form the M4, spread out from the sylvian fissure to supply the majority of the lateral convexity. Branches of the ACA (yellow arrows) spread over the superior hemispheric border to reach the lateral hemispheric surface, and branches of the PCA pass around the occipital pole and adjacent part of the temporal lobe to supply the adjacent part of the convexity (red arrows). B, The frontoparietal operculum that covers the upper part of the insula has been removed to show the M2 crossing the insula, the M3 curving around the opercular lips, and the M4 on the lateral cortical surface. C, Enlarged view. The sylvian vallecula is the opening between the lips of the sylvian at the limen insula where the MCA turns posteriorly to form the M2 segment. D, Another specimen with the lips of the sylvian fissure retracted. This shows a large dominant inferior trunk that gives rise to multiple branches that supply the majority of the lateral convexity. E, Another hemisphere with the lips of the sylvian fissure retracted to expose the branches forming the M2, M3, and M4 crossing the insula and passing around the opercular lips to reach the cortical surface. F, The upper part of the hemisphere and the frontal and parietal operculum have been removed to expose the M2 branches crossing the insula. The posterior M3 branches cross the transverse temporal gyri, the most anterior of which forms Heschl’s gyrus, to reach the cortical surface. (Images courtesy of AL Rhoton, Jr.)