The term refers to the functional unit formed by:
1/ Ammon's horn (cornu ammonis)(the structure commonly referred to when referring to the hippocampus)
2/ The toothed windling (gyrus dentatus).
3/ Seahorse support (subiculum) and sometimes also
4/ the vault band/arch fringe (taenia/fimbria fornicis), i.e. the backwards increasingly thick bundle of wire that arises on the inside/top of the seahorse and which, when it reaches the lower posterior part of the brain beam, passes into the actual vault (fornix).