It is now recognized that the cerebrospinal venous system represents not only a route for dissemination of metastases, but also a route for dissemination of infection throughout the cerebrospinal axis, in both directions.

Amongst these ducts or nadis, three are of the utmost importance: the Medullar Sushumna, which interpenetrates the cerebrospinal axis from the perineum to the juncture of the lamboid and sagittal suture of the cranium, and it is associated with both nostrils being open and free to the passage of air.