The circle of Willis (CW) was first described 400 years ago by Thomas Willis as an important vascular ring at the base of the brain (Vrselja, Brkic, Mrdenovic, Radic, & Curic, 2014). It is named after Thomas Willis, an English physician. Circle of Willis is a very important anastomotic structure in the brain that provides blood supply to the fore-brain and hind-brain. ABSTRACT Aims and Objective: The blood supply of brain is of great importance because of the metabolic demands of the nervous tissue. Willis describes a number of cases that demonstrate the function of the arterial circle in providing compensatory collateral blood flow (Vrselja, Brkic, Mrdenovic, Radic, & Curic, 2014). The circle of Willis score of the patients with complete arterial occlusion was 1.33±1.52 in the fatal stroke group (n=3) and 3.20±1.64 in the asymptomatic group (n=6, p=0.099). The circle of Willis is a continuous loop of arteries in the brain that provides collateral circulation. The circle of Willis also allows blood to flow across the midline of the brain if an artery on one side is occluded. A significant anastomosis, the Circle of Willis exists between the carotid and vertebral arterial systems. In the process, they may become compressed, which restricts blood flow. the circle of Willis becomes important in ascertaining the effectiveness of the circulation of brain in surgeries like aneurysm coiling AVM embolisation, and also internal carotid artery ligation38. 2018;11(2): 43-45. The absence of some CoW elements may be fatal for patients with internal carotid artery stenosis39. -cerebral arterial circle-critically important anastomosis among the 4 major arteries feeding the brain. Variations of circle of Willis in human cadavers. This network of arteries provides blood to be distributed to both hemispheres from the internal carotid arteries or vertebral arteries. The Circle of Willis is a network of blood vessels that connects the two hemispheres. forms the Circle of Willis-anterior and posterior cerebral-anterior communicating … The circle of Willis (also called Willis' Circle, Loop of Willis, cerebral arterial circle, and Willis Polygon) is a circle of arteries at the base of brain that supply blood to the brain and surrounding structures. Int J Anat Var. When you turn your head from side-to-side or up and down, the arteries in your neck stretch and flex. It has a safety valve function in the brain. The circle of Willis thereby serves a safety valve function for the brain, allowing collateral circulation (or flow of blood through an alternate route) to take place if the flow is reduced to one area. Shubhangi Y. When performing the HD-X or HD-XG surgery in mice, it is important that the animal strain has a complete Circle of Willis. 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