The blood supply to the brain is extremely rich and comes mainly from the carotid artery and the vertebral basilar artery system on both sides. The carotid artery system supplies blood to the first 3/5 of the cerebral hemisphere mainly through the internal carotid artery, middle cerebral artery and anterior cerebral artery. The vertebrobasilar system supplies blood to the posterior 2/5 of the cerebral hemisphere, the posterior half of the cerebrum, the brainstem and the cerebellum mainly through the vertebral arteries on both sides, the basilar artery, the superior cerebellar artery, the anterior inferior and posterior inferior cerebellar arteries and the posterior cerebellar artery. The two anterior cerebral arteries communicate with each other by the anterior communicating artery, and the middle cerebral artery and the posterior cerebral artery communicate with each other by the posterior communicating artery, forming a ring of arteries at the base of the brain. The arterial anastomosis of this ring in the brain is extremely important for the regulation and balance of the blood supply between the two major blood supply systems of the carotid artery and the vertebral basilar artery, especially the blood supply to both cerebral hemispheres and the formation of collateral circulation in pathological conditions. Since the internal carotid artery, the vertebral basilar artery and the basilar artery ring composed of their trunks and branches are located on the ventral side of the brain, the arteries supplying the brain are wound from the ventral side of the brain to the dorsal side. They are called deep penetrating arteries. Although there is a structural anastomosis between the central branches, they often do not function as a collateral circulation because of functional closure, and are therefore considered to be a functional terminal artery. When the -branch of these fine arteries is blocked, infarct softening is imminent in its distribution area. The cortical branches form an extensive network of vascular anastomoses as they enter the soft meninges, and then send small arterial branches that enter the brain vertically and are distributed in the cerebral cortex and white matter. Because the anastomosis between cortical branches is extremely extensive and their function is developed quickly, when a small artery is blocked, the blood of its neighboring branches can compensate to some extent, so the scope of focal neurological damage is smaller than that of the damaged arterial supply area.