THE CIRCLE OF WILLIS AS SIMULATED BY AN ENGINEERING MODEL.

Abstract

THE FUNCTION and purpose of the arterial circle at the base of the brain have been the subjects of inquiry since Willis first described it in 1664.¹Many physiologists have believed that the circle can serve as an effective equalizer of flow and pressure in the brain while others looked on it as purely an anastomosis between the vertebral and carotid supply arteries which functions poorly and only under conditions of extreme stress. The anatomic position of the circle, well protected by the skull, makes it inaccessible to direct measurements of pressure and flow. For this reason, the phenomena occurring in the cerebral arterial circulation must be viewed from a distance and experimenters are faced with the problem of demonstrating the applicability of their data to the conditions in the circle per se. Only within the last few years have flow and pressure measurements been made simultaneously