A schematic diagram showing the direction of the CSF bulk flow in the mammalian brain based on a midsagittal section of the rat brain, kindly provided by Prof. L.W. Swanson. The following regions are indicated: telencephalon (pink shades); diencephalon (interbrain) and brainstem areas (yellow shades); cerebellum dorsal to the brainstem (light blue); sectioned fiber tracts (black). CSF (blue arrows) flows from the lateral ventricles to the third ventricle via the interventricular foramen (IVF), and flows caudally along the dorsal and ventral side of thalamic adhesion, to the cerebral aqueduct (AQ) and fourth ventricle (V4). Some CSF may continue flowing caudally through the central canal of the spinal cord (CC), but most leaves the ventricular system via the lateral apertures and flows through the subarachnoid space, surrounding the brain. This external flow is indicated here along the dorsal and ventral side of the brain but occurs also along all other external brain surfaces. The destination of the subarachnoid flow is the cribriform plate of the ethmoidal bone, containing the penetrating olfactory fibers, where CSF is released in small lymphatic vessels. Additional abbreviations: V3(p, h, m, t, pi): regions and recesses of the third ventricle; Circumventricular organs: 1: subfornical organ; 2: organum vasculosum of the lamina terminalis; 3: median eminence; 4: subcommissural organ; 5: pineal organ; 6: area postrema; AL, IL and NL: different lobes of pituitary; Fiber bundles crossing the midline, coloured black, are not relevant for the present review.