The term hippocampus (HPP) refers to a composite substructure of the limbic lobe defined on the basis of dissection and internal structure. It is a C-shaped structure circling the diencephalon (IBR) and corpus callosum (cc) in humans, macaque, rat and mouse. It is synonymous with archicortex ( Stephan-1975 ). From 1995 to 2025, the NeuroNames Standard term for the structure was 'archicortex' ( Bowden-1995 ). During a thorough review of NeuroNames three decades later, it was found that the use of the term 'hippocampus' in English publications had risen from ~50 times that of 'archicortex' to ~1000 times more frequent than 'archicortex ( Ngram ). A major consideration in selecting standard terms is familiarity as measured by frequency of use. Thus, in 2025, the NeuroNames Standard was changed to 'hippocampus'. In the humans ( Mai-1997 ) and, the macaque ( Paxinos-2009a ) the HPP consists of the hippocampal complex (HPC), which lies horizontal deep to the parahippocampal gyrus (PHG) of the limbic lobe (LLB). It narrows posteriorly to become the fasciolar gyrus (FSG), which curves around the splenium of the corpus callosum (scc) and narrows further to become the very thin supracallosal gyrus (SCG). The SCG continues on the dorsal surface of the body of the corpus callosum (bcc) and ventrally around the genu of the corpus callosum (gcc) to become the paraterminal gyrus ( Stephan-1975 ). In humans, the HPP constitutes 3.5% of the surface area of the cerebral cortex (CCX) ( Zilles-1990 ). In the rodent, the substructures are the same except that the subiculum (SUB), a key component of the HPC in the primate, is not assigned to the otherwise HPC equivalent in the rodent, the hippocampal region (HIP) ( Functional CNS Model - Rat ( Swanson-2004 ). Instead it is considered part of the retrohippocampal region (RHP). Also, the FSG, SCG and PTG equivalents, are not topologically separate structures in the rodent but are embedded successively in the RHP, retrosplenial area (RSP), anterior cingulate cortex (ACC), and cerebral cortex (CCX) abutting the septal nuclei (SPN) (Swanson-2004 ). Updated 21 Jul 2026.