This area has a few medium sized neurons scattered among the fibres of the dorso-medial division of the medial forebrain bundle (Gurdjian, 1927, Swanson, 1976a, Bleier et al., 1979) The central part of this area contains mainly fibres and is termed as para preoptic of medial forebrain bundle (MFB) The medial part, termed the preoptic nucleus contains fibres and many neurons (Gurdjian, 1927, Jacobwitz and Palkovits, 1974, Swanson, 1976a, Bleier et al .. 1979) The magnocellular preoptic nucleus has been identified by Loo ( 193 1 ), Krieg (1932), Papez and Aronson (1934), Humphrey (1936), Atlas and Ingram (1937) and Fox (1940) It has also been called the nucleus interstitialis septo-hypothalamicus (Gurdjian, 1927) and "nucleus of the horizontal limb of the diagonal band" (Price and Powell, 1970) The lateral preoptic zone merges medially with the rnPOA and caudally with the lateral hypothalamic area Rostrally, it 1s delineated by the diagonal band of Broca and the nucleus accumbens Dorsally, it is separated from the bed nucleus of stria terminalis by a thin layer of relatively cell free zone (Swanson, 197 6a).