Myelinated axon : An axon (Kölliker, 1896) with a myelin sheath, which is formed by types of glia (Virchow, 1846): oligodendrocyes in the vertebrate central nervous system (Meckel, 1817), and Schwann cells in the vertebrate peripheral nervous system (Meckel, 1817). Axons above a threshold diameter characteristic of particular species become myelinated, thus forming the set of thicker axons; see Williams (1995, pp. 951-954). The myelinated axon was probably discovered by Remak (1837) who described a primitive band-the axon-within a very thin-walled tube (see Van der Loos, 1967, p. 19).