Ventricular Circulation. The fluid flows from the lateral ventricles through the foramen of Monro to the third ventricle, where it combines with fluid secreted into the third ventricle. From there CSF flows through the aqueduct of Sylvius into the fourth ventricle, where more fluid is formed; it then leaves the fourth ventricle by way of the lateral foramen of Luschka and the midline foramen of Magendie and flows into the cisterna magna. From there CSF flows to the cerebral and cerebellar subarachnoid spaces, where it is absorbed. A large portion is absorbed through the arachnoid villi, but the sinuses, veins, brain substance, and dura also participate in absorption.