Transsylvian view of the temporal horn and insula. The temporal lobe is being retracted inferiorly and the insula and frontal lobes superiorly to reveal the temporal horn of the lateral ventricle, the hippocampus, choroid plexus, and choroidal fissure. Through the choroidal fissure, the ambient cistern can be reached containing the posterior cerebral arteries and the basal veins of Rosenthal. The limen insula demarcates the starting point of the insular cortex and the transition point from the M1 to the M2 branches of the middle cerebral artery. (Image courtesy of AL Rhoton, Jr.)