The circle of Willis is a circulatory anastomosis in the brain comprised of the anterior cerebral arteries, the anterior communicating artery, the internal carotid arteries, the posterior cerebral arteries, and the posterior communicating arteries.

http://purl.obolibrary.org/obo/HP_0012518

The circle of Willis is a circulatory anastomosis in the brain comprised of the anterior cerebral arteries, the anterior communicating artery, the internal carotid arteries, the posterior cerebral arteries, and the posterior communicating arteries.

Abnormal circle of Willis morphology

HP:0012518

Abnormal circle of Willis morphology

http://purl.obolibrary.org/obo/HP_0009145