Fenestration of the epithelium lining the roof of the fourth cerebral ventricle in amphibia.

Scanning electron microscopy of the caudal end of the roof of the fourth cerebral ventricle in four amphibian species shows that numerous pores occur between the ependymal cells. These pores have diameters ranging from 5--100 micron; they permit bluk flow of cerebrospinal fluid out of the ventricular system into the subarachnoid space.