The venous system of the brain is responsible for draining all the blood in the brain, and sending it to the internal jugular veins, to return to the heart, from where it is pumped through the lungs and reoxygenated.  Fine veins form in the pial venous plexuses (on the surface of the brain).  These in turn drain into larger cerebral veins, which empty into the venous sinuses (formed by leaves of dura).  The venous sinuses eventually drain into the sigmoid sinus, which empties into the jugular veins.