Which artery originates from the internal carotid and is part of the circle of Willis, providing collateral flow to the opposite side via the anterior communicating artery?

• A. Internal Carotid Artery
• B. Anterior Cerebral Artery
• C. Posterior Communicating Artery
• D. Anterior Communicating Artery

Answer: (B)

The key idea is collateral flow within the circle of Willis. The anterior cerebral artery arises from the internal carotid and travels along the medial surface of the brain. Its left and right branches are connected by the anterior communicating artery, which creates a path for blood to cross from one hemisphere to the other if needed. This setup lets the anterior cerebral arteries provide collateral perfusion to the opposite side, which is why this vessel is the best answer. Other arteries may connect within the circle, but they don’t form this midline cross-flow via the anterior communicating artery.