# Hippocampus and cornu ammonis: mythonyms that prevail in Terminologia Anatomica, Terminologia Neuroanatomica, and Terminologia Histologica

## TL;DR

This paper examines the use and meaning of the terms 'hippocampus' and 'cornu ammonis' in anatomical terminology, highlighting inconsistencies and their mythological origins.

## Contribution

The paper identifies discrepancies in terminology and clarifies the mythological etymology of hippocampus and cornu ammonis.

## Key findings

- The terms hippocampus and cornu ammonis have mythological origins and are inconsistently used across anatomical terminologies.
- Etymological analysis shows hippocampus refers to a sea horse and cornu ammonis to the horns of an Egyptian god.
- The terminologies fail to meet FIPAT requirements for describing these structures.

## Abstract

Julius Caesar Arantius first described the hippocampus and proposed the term hippocampum. Years later, French anatomists called the structure ram’s horns, and a decade later, it was named cornu ammonis. Although both concepts were first associated with the same structure, their use has expanded to include different but related structures. This situation can make understanding and applying the terminology more difficult. The objective of this work was to determine the presence of the terms hippocampus, cornu ammonis and their variants in Terminologia Anatomica, Terminologia Neuroanatomica, and Terminologia Histologica, evaluating their congruence in said terminologies, in addition to examining the etymology of both terms. We searched Terminologia Anatomica, Terminologia Neuroanatomica, and Terminologia Histologica for terms containing the concepts hippocampus, cornu ammonis, and their derivatives. We analyzed the terms hippocampus and cornu ammonis from their etymology by examining several Latin texts. This analysis included the dissection of the hippocampus and fornix and a review of the RAT rules. The etymological analysis indicated that the hippocampus refers to a sea horse; however, the term also has a mythological background. Cornu ammonis, on the other hand, refers to the horns of an Egyptian god. The terminologies present discrepancies regarding the terms derived from hippocampus and cornu ammonis. Although both terms appear in various terminologies, they are mythonyms that fail to describe the structure they refer to or meet the requirements set by FIPAT.