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Ammon's horn and the hippocampus
  1. J M S PEARCE
  1. 304 Beverly Road, Anlaby, Hull HU10 7BG, UK

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    The word hippocampus comes from late Latin: hippocampus, derived from the Greek words for a horse+sea monster. In mythology it was a sea horse, having two forefeet, with the body ending in a dolphin's or fish's tail, represented as drawing the vehicle of Neptune the sea God. The earliest use (Oxford English Dictionary) was in 1606, cited as “Drummond of Hawthornden” Let. Wks. (1711) 232. “Stately pageants. that of Cheapside was of Neptune on a hippocampus, with his Tritons and Nêreides”.

    Neurologists recognise it as each of two elongated eminences (hippocampus major and minor) on the floor of each lateral ventricle of the brain; so called from their supposed resemblance to the fish.

    With its base in ancient classical history, neuroanatomy provides several metaphors that relate the gods and the brain. One is Ammon's horn. The term Cornu Ammonis, or Ammon's horn, is a well known description of the whorled chambered shells of a fossil genus of Cephalopods. They were once supposed to be coiled snakes petrified, and hence called “snake-stones” from their resemblance to the involuted horn of Jupiter Ammon.

    The hippocampus received its name from the Italian Julius Caesar Arantius in the late 16th century.1 Less than two centuries later, the hippocampus was called Ammon's horn.2 3 An early, anatomical use is in the 1742 book of a felicitously named surgeon René Jacques Croissant de Garengeot.4 In 1732 Jacques Bénigne Winslow used the term ram's horn. Thus Ammon's horn was probably not in use at this date. Albrecht von Haller, the anatomist, indicated that the term Ammon's horn was already used in a paper of the Oeconomische Abhandlung of 1755 (Haller, 1774–7, vol 2 p 507).

    The term Ammon's horn is a metaphor that refers to the ram shaped horns5 on the head representing the Egyptian God Amun who protected the Pharaoh Taharqa in the temple of Kawa.6 Many temples were dedicated to Amun. The Greek form of the name was Ammon, the Libyan Jupiter whom the Greeks identified with Zeus. King David conquered a Jordanian tribe, the Ammonites, who were descendants of Lot, by the son of his younger daughter.

    It is of interest that the related hippocampal commissure together with the crura of the fornix, is sometimes termed the “psalterium” or “lyra Davidis”. Psalterium and lyra are both harps.

    To add to the confusion, French neuroanatomists refer to the horn shaped lateral part of the fourth ventricle with its choroid plexus leaving the foramen like a posy of flowers as the “corne d'abondance” (horn of plenty, or cornucopia).

    jmspearce{at}freenet.co.uk

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