Hypothalamus ( HY ; Kuhlenbeck, 1927 ) : The ventral (Schulze, 1893) topographic division of the interbrain (Baer, 1837): the dorsal (Barclay, 1803) topographic division is the thalamus (His, 1893a). The first adequate description of the hypothalamus as a layer of gray matter surrounding the lower half of the third ventricle (Galen, c173) was provided by Wharton (1656, see 1966 translation, p. 170); His (1893a, pp. 159-162) introduced the term but assigned the preoptic region (Swanson, 1976b, pp. 229-235) of the hypothalamus (Kuhlenbeck, 1927) to the telencephalon (His, 1893b). The definition here was introduced for vertebrates by Kuhlenbeck (1927, p. 67, Ch. 9); also see Christ (1969, p. 23), Nauta & Haymaker (1969, Tab. 4-1).