- A dictionary of medical eponyms

Willis' circle

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The circle of anastomosed arteries (roughly pentagonal in outline) at the base of the brain, with the posterior communicating artery on either side joining posterior cerebral (branches of the basilar artery) to the anterior cerebral (branches of the internal carotid artery) arteries. By this full circulation to all parts of the brain can be maintained even when the carotid or vertebral arteries are blocked.

Thomas Willis was not the first to describe the circle, but he was the first to do so completely and with an illustration of the vascular network at the base of the brain. Gabriel Fallopius (1523-1563) gave an incomplete description in 1561, Giulio Casserio (1552-1616) was the first to draw the circle, Johann Vesling (1598-1649) decribed it in a treatise in 1653, and the Swiss physician Johann Jakob Wepfer (1620-1695) in 1658.


  • Gabriel Fallopius:
    Observationes anatomicae. Venice 1561.
  • Giulio Casserio:
    Tabulae Anatomicae lxxiix.
    Venetiis, apud E. Deuchinum, 1627.
    First publication of the very beautiful copperplates engraved by Francesco Valesio after Odoardo Fialett, a pupil of Titian.
  • J. J. Wepfer:
    Observationes anatomicae, ex cadaveribus eorum, quos sustolit apoplexia. Schaffhusii, J. C. Suteri, 1658.
    Partial English translation in Ruskin, Classics in arterial hypertension, 1956.
  • T. Willis:
    Cerebri anatome: cui accessit nervorum descriptio et usus.
    London, 1664.

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