[3] The specific regions of the brain usually described as belonging to the allocortex are the olfactory system and the hippocampus.
Allocortex is termed heterogenetic cortex, because during development it never has the six-layered architecture of homogenetic neocortex.
[6][7] The two granular layers II and IV of neocortex are absent in paleocortex.
Archicortex is a type of cortical tissue that consists of four laminae (layers of neuronal cell bodies).
Because the number of laminae that compose a type of cortical tissue seems to be directly proportional [citation needed] to both the information-processing capabilities of that tissue and its phylogenetic age, and also because olfaction is a major sensory modality in phylogenetically early animals, paleocortex is thought to be the most primitive form of cortex.