From Wikipedia, the free encyclopedia. In human anatomy, the left and right posterior communicating arteries are arteries at the base of the brain that form part of the circle of Willis. Each posterior communicating artery connects the three cerebral arteries of the same side.he brain is supplied with blood by the internal carotid arteries and also by the posterior cerebral arteries; the posterior communicating arteries connects the two systems. This provides redundancies or collaterals in the cerebral circulation so that, if one system is blocked or narrowed, the other can take over.