an artery that arises from the internal carotid artery and passes just ventral to the optic tract to merge with the posterior cerebral artery, thus completing the circle of Willis at the base of the brain. Branches of the posterior communicating artery supply the optic tract and part of the optic chiasm, the genu of the corpus callosum, the posterior hypothalamus, parts of the internal capsule, the third ventricle, and anterior and ventral nuclei of the thalamus.