<prompt> Which of the following is not considered a part of Circle of Willis?Anterior cerebral arteryMiddle cerebral arteryPosterior communicating arteryPosterior cerebral artery  <response>: Circle of Willis is formed by:-In front: anterior communicating artery.Anterolaterally: two anterior cerebral artery.Laterally: proximal segments of both internal carotid arteries.Postero-laterally: two posterior communicating arteries.Behind: proximal segments of both posterior cerebral arteries, arising at bifurcating terminal of the basilar artery. 