G, The medial lenticulostriate arteries arise from the proximal part of the M1 segment. Inset: these arteries arise predominantly from the posterior and superior wall of the artery. H, They enter the middle and posterior zones of the medial part of the lateral territory of the anterior perforated substance. I, These arteries arise from the M1 segment and, because of a complex branching, form a candelabra appearance as they approach the anterior perforated substance. Inset: they arise predominantly from the posterior, superior, and posterosuperior aspects of the wall. J, The arteries enter predominantly the middle and posterior zones of the central part of the lateral territory of the anterior perforated substance. K, Lateral lenticulostriate arteries. These arteries arise in closer proximity to the bifurcation of the middle cerebral artery, from the M1 and M2 segments, and have an S-shaped course. First, they pass posterior, medial, and superior, then turn laterally, and finally complete an S-curve by turning medially just before entering the anterior perforated substance. Approximately half arise proximal and half arise distal to the bifurcation of the middle cerebral artery. Inset: site of origin. These arteries arise from the posterior, superior, or posterosuperior aspect of the parent trunk. L, The lateral lenticulostriate arteries enter predominantly the middle and posterior zones of the lateral territory of the anterior perforated substance. (Images courtesy of AL Rhoton, Jr.)