Abstract: Introduction & Objective: The circulus arteriosus, exist between the internal carotid arteries and two vertebral arteries, that supplies the remainder. It slows down the blood before it reaches the brain and helps in collateral circulation. The knowledge of the CirculusArteriosus and its variations is essential in clinico –pathological conditions such as surgical hemorrhage, encephalomalacia, infarction of the brain and intra cranial aneurysms as it is one of the major collateral circulations ensuring the complete perfusion of the brain