THE STUDY of the innervation of the choroid plexus is attended with great technical difficulties, explaining the paucity of investigations on this subject. Isolated notes on the nerve supply of the choroid plexus are found in the works of older authors. As far back as 1874 Benedikt1identified nerve fibers in the choroid plexus of the fourth ventricle. He used carmine staining. These fibers were rami of the tenth nerve and originated in the cells of the nucleus ambiguus. Benedikt named these fibers "the thirteenth nerve." His observations were confirmed by Bokhdallek and Purkinje. Bkhnenek described nerve plexuses around the vessels of the "paraphysis" of the frog. He was able to trace the course of the fibers from these plexuses to the choroid plexus of the lateral ventricles. Findley drew attention to the presence of sympathetic nerve fibers in the choroid plexus of man and cattle. Together with Studnitska,