The evolution of our understanding of CSF production and pathway in relation to brain spaces. A. Cladius Galenus' (Galen, 129 - 219AD) concept of the CSF pathway. In his writings Galen describes a lateral ventricular choroidal origin (1) and exit through the fourth ventricle to the spinal canal (2). He also erroneously describes movement of the fluid across the cribriform plate into the nasal cavity (3) and across the infundibulum to the palate (4). B. Albrecht von Haller's (1708 - 1777AD) CSF pathway correctly stated the origin of CSF from the ventricles (1), with exit from the fourth ventricle (2) and down the spinal canal for venous absorption. This early description was essentially correct. C. François Magendie's (1783 - 1855AD) concept of the CSF pathway was exactly opposite to the system of both von Haller and Galen. D. The modern description of the CSF pathway. CSF is produced by the choroid plexuses (1) from where it moves from the lateral ventricles into the third and fourth ventricles (2). It then flows across the surface of the brain (3) and down the spinal canal (moving from the back to front (3) of the canal). CSF is then reabsorbed by the arachnoid granulations (4) back into the blood stream. The arachnoid villi are projections from the arachnoid layer of the meninges that connect with veins via the venous sinus. Absorption into lymphatics also occurs (not shown). Abbreviations: 3V, third ventricle; 4V, fourth ventricle; LV, lateral ventricle.