The amygdaloid body, one of the most prominent member of the so-called limbic system, is generally described as a large subcortical collection of gray matter located just in front of the Ammon's horn, that surfaces in the anterior medial side of the temporal lobe to become intercalated between the temporal allocortex, on one side, and other basal forebrain structures, on the other. However, in contradiction with this restricted definition, recent and continuously accumulating data with source in different branches of the neurosciences, favor to change this view by one that also includes a deep lying extra temporal gray formation, the extended amygdala (EXA).

On purely topographical grounds, the amygdaloid nuclear grisea can be divided into deep and superficial cell groups. The laterobasal nuclear complex (LBNC), most of the grisea conforming the EXA, the intercalar masses (IC), the intramedullary grisea (IMG), and a transitional field, the amygdalo striatal zone (ASZ) constitute the deep group. The cortical amygdaloid gray matter (CO), the amygdalohipocampal area (AHI) and a transitional cortical field, the amygdalopiriform transition area (APIR) conform the superficial group. The nucleus of the lateral olfactory tract (NLOT), and even perhaps a putative nucleus of the accessory olfactory tract (NAOT), would be additional members of the superficial group, provided their existence is unequivocally demonstrated in the human and other apes. Furthermore, although both the medial amygdaloid nucleus (MEA) and the anterior amygdaloid area (AAA) are located superficially, their direct structural continuity with the gray continuum represented by the EXA, of which they are just its expanded posterior surfacing end, would justify their exclusion from the superficial groups of amygdaloid nuclei.

The EXA also includes other traditionally recognized amygdaloid nuclei such as the central (CEA) amygdaloid nucleus, and the intraamygdaloid continuation of the bed nucleus of the stria terminalis (BSTIA).These areas together with the MEA and AAA ( i.e., the centromedial amygdaloid group for many authors,) contribute to the formation of gray continuum that includes deep lying forebrain structures such as the sublenticular substantia innominata (here named as the sublenticular extended amygdala, SLEA), the interstitial nucleus of the posterior limb of the anterior commissure (IPAC), the supracapsular extension of the bed nucleus of the stria terminalis (BSTS) and the main paraseptal expansion which is the bed nucleus of the stria terminalis (BST).

The LBNC, as its name suggest, is composed by four gray masses, the lateral (LA), basolateral (BL), basomedial (BM) and paralaminar (PL) nuclei. Each of these nuclei possess many distinguishing morphological, chemoarchitectonical and connectional features that distinguish them apart.

Within the so-called cortical amygdala, two well defined divisions can be recognized, anterior sulcal (ACO) and ventral uncal (VCO). Although the existence in the human Co of a third division, the posterior cortical amygdaloid nucleus (PCO), has been suggested as a probable homologous of an equally named structure in macrosmatic mammals, such existence is highly controversial and waits for further documentation in order to accept or deny it.

Subdivisions can be recognized in almost every one of the above listed amygdaloid nuclei. Although most of them were originally recognized on purely cytoarchitectonical grounds, which has given origin in the past to many controversies, today they find firm support in an abundant documentation provided by modern histochemical and immunohistochemical procedures as well as by experimental connectional tracing studies carried out in monkeys, and also subprimates mammals like the rat. Their soundness is even more dramatized by physiological, pharmacological and behavioral investigations that have provided further and continuous support to the segregation of the aforementioned subdivisions once viewed as purely academic.