The term anterior part of the medial amygdalar nucleus (MEAa) refers to the more rostral component of the medial amygdalar nucleus as identified by Nissl stain in the human ( Mai-1997 ) and the macaque ( Amaral-1992 ). The other is the posterior part of the medial amygdalar nucleus (MEAp). The MEAa is located deep to the entorhinal sulcus on the medial aspect of the temporal lobe. It is bounded laterally by the anterior amygdalar area, ventrally by the basomedial nucleus of the amygdala and, in the human, medially by the periamygdalar cortex. In the macaque it is located similarly relative to the anterior amygdalar area, but is bounded ventrally by the periamygdalar cortex, or by the nucleus of the olfactory tract by authors who identify that structure in the primate ( Amaral-1992 ). In the rat ( Swanson-2004; Paxinos-2009b ) its rostral portion extends from the endorhinal groove medially; it is bounded dorsomedially by the lateral hypothalamic area, dorsolaterally, laterally and ventrally by the anterior amygdalar area and the nucleus of the olfactory tract. More caudally the bed nucleus of the accessory olfactory tract intervenes between it and the sulcal surface and the optic tract intervenes between it and the lateral hypothalamic area; it is bounded dorsolaterally by the central amygdalar nucleus, laterally by the basomedial nucleus of the amygdala and ventrolaterally by the periamygdalar cortex. Its topology in the mouse is similar to that in the rat except that it is partially bounded dorsally by the substantia innominata ( Hof-2000; Franklin-2008 ). In the rat and mouse the anterior part of the nucleus is further subdivided into two parts: the anterodorsal part of the medial amygdalar nucleus and the anteroventral part of the medial amygdalar nucleus.