A, The branches from the internal carotid artery to the anterior perforated substance arise from the posterior wall above the anterior choroidal artery, and course upward behind the carotid bifurcation. Inset: lateral view of the carotid artery. Eighty-one percent of the branches to the anterior perforated substance arise from the posterior wall below the bifurcation and 18% arise from the posterosuperior surface of the wall, at or near the level of the bifurcation. B, Internal carotid zone and territory in the anterior perforated substance. Most of the branches of the internal carotid artery enter the posterior and middle zones of the medial territory of the anterior perforated substance. C, A branch to the anterior perforated substance arises in common with the origin of the anterior choroidal artery. D, The superior branch of the anterior choroidal artery gives rise to branches to the anterior perforated substance. E, The main trunk of the anterior choroidal artery gives off branches to the anterior perforated substance along its course to the choroid plexus in the temporal horn. F, The anterior choroidal branches enter the posterior and middle zones near the junction of the medial and lateral territories of the anterior perforated substance. (Images courtesy of AL Rhoton, Jr.)