E, Both P1s are smaller than the PComAs, but both P1s give rise to thalamoperforating arteries. The smaller, or left, P1 gives rise to more and larger perforating arteries than the larger, right, P1. F, The dissector holds up two perforating branches that arise from the origin of the superior cerebellar artery and enter the brain through the same area as the thalamoperforating arteries. G, The left PCA has a fetal origin of the PComA. A series of perforating arteries arises from the PComA and enters the diencephalon medial to the optic tract in the region of the mamillary bodies and floor of the third ventricle. The P1 pursues a tortuous course to its junction with the P2. H, Inferior view. The lateral parts of the P1s give rise to thalamoperforating arteries. Perforating branches also arise from the PComA. (Images courtesy of AL Rhoton, Jr.)