• A. At the base of the brain ✓
  • B. In the spinal column
  • C. Within the dura mater
  • D. Within the pia mater


The circle of Willis is located at the base of the brain within the interpeduncular cistern of the subarachnoid space. It encircles various structures within the interpeduncular fossa, including the optic chiasm and infundibulum of the pituitary gland. This location allows it to provide collateral blood flow between the anterior and posterior arterial systems of the brain, protecting against ischemia and stroke in cases of vascular obstruction or damage.

In other words, it is a circulatory anastomosis that supplies blood to the brain and surrounding structures. The circle of Willis is formed by the joining of several major arteries at the base of the brain, creating a circular network that helps ensure a constant blood supply to the brain even if one of the arteries becomes blocked or compromised.

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