Nerve fiber ( nerves (Herophilus, c335-280 BC) ) : An unmyelinated axon or a myelinated axon; literally accurate for the peripheral nervous system, but often applied (ambiguously) to the central nervous system as well. In the second century Galen (see translations by Duckworth, 1962, p. 254; Clarke, 1968, p. 124) recognized the fibrous nature of nerves (Herophilus, c335-280 BC). Leeuwenhoek (1718; see Van der Loos, 1967, pp. 10-16) identified the nerve fiber itself as the ultimate structure of nerves and called it a vessel, whereas Ehrenberg (1833, pp. 453-456) called it a nerve fiber.