Gray matter nucleus : A term applied to many gray matter regions in the cerebrospinal axis (Meckel, 1817), usually though not always (e.g., the human dorsal lateral geniculate nucleus) when they have relatively clear borders and are nonlaminated. The first use of the term in this way was by Ludwig (1779, Fig. 2b, p. 36); the cell nucleus, a cytological feature, was named by Brown (1833, p. 710).