Milhorat, a long-time worker in the field of cerebrospinal fluid formation and circulation, has chosen in this monograph to emphasize the lymphatic-like arrangement of the cerebrospinal fluid pathways. With this, he reverts to Harvey Cushing's concept of "The Third Circulation," with emphasis on the fluid as a closely regulated internal milieu, and as a vehicle for intracerebral transport.
This fluid is formed in the ventricles by the choroid plexuses and by passage into these chambers of interstitial fluid filtering through the blood-brain barrier, having taken up metabolic products and secretions. Milhorat repeatedly describes (and pictures in simplified diagrams) the "other" route that the fluid may take to end up in the cerebrospinal fluid proper; that is, by filtering through the pial surfaces (eg, Figures 13 and 30). This raises the immediate intriguing question, unfortunately not answered: Why does this pial route not take care of the excess fluid in the