View of the basal surface of the brain showing a long circumflex artery. The artery borders the midbrain medially to the posterior cerebral artery and inferomedially to the posteromedial choroid artery. It travels through the crural, ambient, and quadrigeminal cisterns, and ends in the quadrigeminal plate to irrigate the superior colliculi. In the quadrigeminal plate it anastomoses with branches of the superior cerebellar artery that irrigate the inferior colliculi. 1, Internal carotid artery; 2, posterior communicating artery; 3, P1 segment; 4, long circumflex arteries origin; 5, posteromedial choroid artery; 6, P2A segment; 7, trochlear nerve; 8, anterior temporal artery; 9, hippocampal artery originating from P2A; 10, posterolateral choroidal artery; 11, uncinate gyrus; 12, band of Giacomini; 13, intralimbic gyrus; 14, dentate gyrus. (Image courtesy of E de Oliveira)