Within the brain are five fluid filled cavities, the walls of which are lined with ependymal cells.  Roughly 400 cc's of cerebrospinal fluid  (CSF) are produced daily by the choroid plexus (small vascular structures which project into the ventricles).  The CSF passes from the lateral ventricles, through the foramen of Monro, to the third ventricle.  From there, it passes through the aqueduct of Sylvius (in the brainstem) to enter the fourth ventricle.  From the fourth ventrticle, the CSF leaves through the foramen of Luschka and the foramen of Magendie, to percolate around the brain and pass around the spinal cord.