SCOTT CAMAZINE / SCIENCE PHOTO LIBRARY SCOTT CAMAZINE / SCIENCE PHOTO LIBRARY
Angiogram of a 34-year-old male, showing a normal Circle of Willis, the arteries at the base of the brain that supply it with blood. It is named after Thomas Willis, an English physician. The arrangement of the brain's arteries into the Circle of Willis creates redundancies in the cerebral circulation. If one part of the circle becomes blocked or narrowed (stenosed) or one of the arteries supplying the circle is blocked or narrowed, blood flow from the other blood vessels can often guarantee continued cerebral perfusion.
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