After the brain tissue has taken up the oxygen and nutrients, the blood drains into superficial cerebral veins, or bridging veins, that also sit in the subarachnoid space.
After the fourth ventricle, the cerebrospinal fluid enters the subarachnoid space, which is the space between the arachnoid and pia mater, two of the inner linings of the meninges which cover and protect both the brain and the spine.