Much work is being done on the circulation, origin and final destination of the cerebrospinal fluid (Weed,1 Dixon and Halliburton,2 Dandy and Blackfan,3 Cushing,4 Hill,5 Petitt and Girard6), yet little or no attention has been given to the types of obstruction or partial obstruction existing in the course of the fluid through the ventricular outlets. Special consideration is here given to the foramina in view of the fact that some authorities consider the ependymal foramina of the fourth ventricle as normally closed and as playing no important rôle in the circulation of the cerebrospinal fluid. If correct, such views would mean that there are two entirely separate fluid areas; one in the ventricular systems and one in the subarachnoidal spaces, completely separated except for the tissue spaces by means of which the ventricular fluid seeps through the brain substance. Since such views (von Monakow