n. In anatomy, the body-axis; the mesal, longitudinal, skeletal axis of the body, represented in Branchiostoma and embryos by a membranogelatinous notochord, and in most adult vertebrates by the cartilaginous or osseous centra of the vertebræ and the base of the skull. Wilder, N. Y. Med. Jour., Aug. 2, 1884, p. 113. Also called axis.n. The efferent or axis-cylinder process of a nerve-cell. Also spelled axone.