The term retrochiasmatic area refers to an area at the base of the hypothalamus in which neurons are interspersed with fibers of the supraoptic decussations. Not to be confused with the larger, more medial retrochiasmatic part of the supraoptic nucleus, the area is located laterally on the ventral surface, just rostral to the anterior median eminence, at the boundary of the intermediate hypothalamic region with the anterior hypothalamic region. It is defined by Nissl stain in the human, macaque, rat and mouse. In the human the neurons are scattered along the base of the intermediate region between the ventromedial nucleus of the hypothalamus medially, the retrochiasmatic part of the supraoptic nucleus dorsolaterally, the optic tract laterally and the anterior median eminence caudally ( Mai-1997 ). In the macaque the area is located somewhat more rostrally, in the anterior hypothalamic region, dorsal to the optic chiasm, ventral to the anterior hypothalamic area and medial to the retrochiasmatic part of the supraoptic nucleus ( Paxinos-2009a ). In the rat it is located between the anterior hypothalamic nucleus dorsally, the supraoptic decussations ventrally, the optic tract laterally and the tuberal nucleus caudally ( Swanson-2004 ). In the mouse it is located ventral to the anterior hypothalamic nucleus and the ventromedial nucleus of the hypothalamus and dorsal to the optic tract ( Hof-2000 ). Some authors regard the retrochiasmatic area, which is relatively small in the human, to be a 'tuberal part' of the supraoptic nucleus rather than a distinct entity ( Mai-1997 ). The retrochiasmatic area is one of twenty six regions, zones, and nuclei that constitute the motor lateral hypothalamus in the rat. Functionally it belongs to the motor lateral hypothalamus of the subcortical motor system ( Swanson-2004 ).