Figure 28. Original depiction of the arterial circle (or “polygon”) surrounding the hypothalamic infundibulum at the base of the brain, as shown in the Cerebri Anatome (1664) by Thomas Willis and drawn by the British architect, Cristopher Wren. Note the presence of branches to the mammillary bodies but absence of vessels to the infundibulum. (Courtesy of the Library of the Department of Human Anatomy of the University of Parma, Italy.)