Which arterial ring at the base of the brain forms a circular anastomosis connecting the brain's anterior and posterior circulations?

• A. Circle of Willis
• B. Circle of Arteries
• C. Vertebral Venous Plexus
• D. Superior Sagittal Sinus

Answer: (A)

The structure is the Circle of Willis, a circular arterial junction at the base of the brain. It is formed by the internal carotid arteries giving rise to the anterior cerebral arteries, which are connected by the anterior communicating artery, and by the posterior communicating arteries linking the internal carotid system to the posterior cerebral arteries coming off the basilar artery. This arrangement ties together the brain’s anterior (carotid) circulation with its posterior (vertebrobasilar) circulation, allowing collateral blood flow if one pathway narrows or blocks. The other options are venous channels or an incorrect term, not this arterial ring that enables communication between the two major cerebral supplies.