The general layout or body plan of the pallium is already clearly defined in animals with relatively simple brains, including lampreys, sharks and amphibians.

The medial pallium is the progenitor of the mammalian hippocampus, and is thought to be involved in spatial cognitive mapping and memory formation across a broad range of species.

Situated ventral to the pallium in the basic vertebrate forebrain plan (though representing a topologically rostral field in neural plate fate maps) is another region of telencephalic gray matter known as the subpallium, which is the progenitor area for the basal ganglia, a set of structures that play a crucial role in the executive control of behavior.

The subpallium region has distinct striatal, pallidal, diagonal and preoptic subregions, which are stretched obliquely between the septal midline and the amygdala at the posterior pole of the telencephalon.

The amygdala thus encompasses an heterogeneous group of subpallial nuclei and hypopallial olfactory and amygdalohippocampal corticonuclear cell masses which are on the whole heavily involved in emotion and motivation.

In contrast, the superfial periglomerulary neurons, various intermediate interneurons and the deep granule cells are all of subpallial origin and migrate tangentially out of the striatal part of the subpallium (apparently from a dorsal subsector of this domain) through the so-called rostral migratory stream into the olfactory bulb.

The olfactory bulb is thus singularly formed by a minority of autochthonous pallial neurons and a majority of immigrated inhibitory subpallial cells (it is nevertheless classified as a part of the ventral pallium).

There is also a modified accessory olfactory bulb at the base of the principal one, which is associated specifically to incoming afferents from Jacobson's organ found at the nasal septum.

Reptiles developed a distinct three-layered structure of medial and dorsal portions of their pallium, a morphological schema referred to with the concept of allocortex.

In contrast, the lateral and ventral pallium sectors of reptiles adopted hypopallial structure (superficial olfactory cortex, covering deep pallial nuclei).

[4] Birds essentially show much increased cellularity, keeping within the reptilian morphological schema, which leads to the apparent disappearance of layering within its medial and dorsal pallial sectors.