Right Cerebral Hemisphere. A, Right cerebral hemisphere. The cortical distribution of the MCA includes most of the lateral surface of the hemisphere and all the insular and opercular surfaces. The cortical branches anastomose with the terminal branches of the ACA approximately 1.5 cm lateral to the superior border. The M4, composed of the cortical branches of the MCA usually begins at the surface of the sylvian fissure and runs on the lateral surface commonly within the sulci. The cortical branches of the M4 segment, named based on their supply to 12 different areas, are as follows: orbitofrontal, prefrontal, central, anterior parietal, posterior parietal, angular, temporooccipital, posterior temporal, middle temporal, anterior temporal, and temporopolar. B, View of the M2, M3, and M4 segments. The bifurcation occurs just proximal to the genu. The M2 is constituted by the trunks that cross and supply the insula and end at the limiting sulci of the insula. The M3 segment starts at or near the limiting sulci where the M2 branches turn to course on the frontoparietal and temporal opercula. The M4 segment is formed by the cortical branches. In this hemisphere the inferior trunk gives rise to the temporopolar, anterior temporal, middle temporal, posterior temporal, temporooccipital, angular and posterior parietal branches. An early frontal branch gives origin to the orbitofrontal and prefrontal arteries. The superior trunk gives rises to the precentral, central, and anterior parietal branches. C, Enlarged view. The cortical arteries that supply the central lobe can be followed from their origin on the postbifurcation trunks on the insular surface to the cortex. The superior trunk gives rise to 3 stem arteries from which the cortical branches arise. The anterior stem artery bifurcates into the precentral arteries that supply the lower portion of the precentral gyrus, and the large stem artery bifurcates and gives rise to 2 central arteries in what was found to be a frequent pattern. Another stem artery arose from the superior trunk as a single branch to become the anterior parietal artery. D, The central artery arises at the outer edge of the sylvian fissure as a double artery and supplies most of the central lobe. The precentral artery supplies the lower part of the precentral gyrus. The anterior parietal artery supplies the middle third of the posterior portion of the postcentral gyrus. (Images courtesy of AL Rhoton, Jr.)