The Insula and Deep Nuclei. M, frontal view. A coronal cut has been made at the level of the bifurcation of the internal carotid artery (anterior perforated substance). 1, insula; 2, internal capsule; 3, thalamus; 4, claustrum, external and extreme capsules; 5, lentiform nucleus; 6, thalamostriate vein, column of the fornix, and anterior commissure; 7, hypothalamus; 8, lateral lenticulostriate arteries and insular pole; 9, lamina terminalis and anterior cerebral artery (A1 segment); 10, middle cerebral artery (MCA) (M2 segment); 11, internal carotid artery (supraclinoid segment); 12, olfactory tract and optic nerve. The arrowheads indicate the extent of the M1 segment of the MCA from the carotid bifurcation to the limen insulae. N, Basal view of the right hemisphere. A coronal section, followed by an axial section, has been performed at the level of the anterior perforated substance. 1, frontal horn; 2, accessory gyrus of the insula; 3, lentiform nucleus and the internal capsule; 4, head of the caudate nucleus; 5, genu of the MCA; 6, insular pole; 7, anterior perforated substance; 8, amygdala; 9, head of the hippocampus. (Images courtesy of AL Rhoton, Jr.)