Specialized area of phylogenetically old (three-layered) cortex; located in medial part of temporal lobe; part of hippocampal formation of limbic system.

The hippocampus proper refers to the actual structure of the hippocampus which is made up of four regions or subfields. The subfields CA1, CA2, CA3, and CA4 use the initials of cornu Ammonis, an earlier name of the hippocampus.