Abstract
Topics discussed include EM of intraependymal and intraventricular nerve fibers; ultrastructure of nerve fibers reaching the 3rd ventricle and cavities other than the 3rd ventricle and fibers associated with the ependyma but which do not reach the ventricular cavities; ependymal specializations [subcommissural organ, pineal], biologically active principles in the CSF [cerebrospinal fluid] [pituitary hormones]; neurotransmitters and their metabolites; and the probable integrative role of the CSF.