The calcar avis, previously known as the hippocampus minor, is an involution of the wall of the

lateral ventricle The lateral ventricles are the two largest ventricles of the brain and contain cerebrospinal fluid (CSF). Each cerebral hemisphere contains a lateral ventricle, known as the left or right ventricle, respectively. Each lateral ventricle resemble ...

's posterior cornu produced by the

calcarine fissure The calcarine sulcus (or calcarine fissure) is an anatomical landmark located at the caudal end of the medial surface of the brain of humans and other primates. Its name comes from the Latin "calcar" meaning "spur". It is very deep, and known as ...

. It is sometimes visible on

ultrasonogram Medical ultrasound includes diagnostic techniques (mainly imaging techniques) using ultrasound, as well as therapeutic applications of ultrasound. In diagnosis, it is used to create an image of internal body structures such as tendons, muscles ...

and can resemble a

clot A thrombus (plural thrombi), colloquially called a blood clot, is the final product of the blood coagulation step in hemostasis. There are two components to a thrombus: aggregated platelets and red blood cells that form a plug, and a mesh of c ...

Name

The ridge was originally described by anatomists as the ''calcar avis'', while the ridge running along the floor of the

temporal horn of the lateral ventricle The lateral ventricles are the two largest ventricles of the brain and contain cerebrospinal fluid (CSF). Each cerebral hemisphere contains a lateral ventricle, known as the left or right ventricle, respectively. Each lateral ventricle resemble ...

was described by various names, in particular as the

hippocampus The hippocampus (via Latin from Greek , ' seahorse') is a major component of the brain of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus is part of the limbic system, ...

. A classical allusion was introduced later with the term ''pes hippocampi'', which may date back to Diemerbroeck in 1672, introducing a comparison with the shape of the folded back forelimbs and webbed feet of the Classical

hippocamp The hippocampus or hippocamp, also ''hippokampos'' (plural: hippocampi or hippocamps; grc, ἱππόκαμπος, from , "horse" and , "sea monster"

us (Greek: ἱππόκαμπος), a sea monster with a horse's forequarters and a fish's tail. At a subsequent stage the hippocampus was described as ''pes hippocampi major'', with the calcar avis being named ''pes hippocampi minor''. The renaming of the hippocampus as hippocampus major, and the calcar avis as hippocampus minor, has been attributed to

Félix Vicq-d'Azyr Félix Vicq d'Azyr (; 23 April 1748 – 20 June 1794) was a French physician and anatomist, the originator of comparative anatomy and discoverer of the theory of homology in biology. Biography Vicq d'Azyr was born in Valognes, Normandy, the son ...

systematising nomenclature of parts of the brain in 1786. While "hippocampus minor" was used interchangeably with "calcar avis" for much of the 19th century, for a few years after 1861 the former name was subjected to publicity and ridicule when the hippocampus minor became the centre of a dispute over

human evolution Human evolution is the evolutionary process within the history of primates that led to the emergence of ''Homo sapiens'' as a distinct species of the hominid family, which includes the great apes. This process involved the gradual development o ...

between

Thomas Henry Huxley Thomas Henry Huxley (4 May 1825 – 29 June 1895) was an English biologist and anthropologist specialising in comparative anatomy. He has become known as "Darwin's Bulldog" for his advocacy of Charles Darwin's theory of evolution. The stor ...

and

Richard Owen Sir Richard Owen (20 July 1804 – 18 December 1892) was an English biologist, comparative anatomist and paleontologist. Owen is generally considered to have been an outstanding naturalist with a remarkable gift for interpreting fossils. Ow ...

, satirised as the

Great Hippocampus Question The Great Hippocampus Question was a 19th-century scientific controversy about the anatomy of ape and human uniqueness. The dispute between Thomas Henry Huxley and Richard Owen became central to the scientific debate on human evolution that followe ...

. The term hippocampus minor fell from use in anatomy textbooks, and was officially removed in the

Nomina Anatomica ''Nomina Anatomica'' (''NA'') was the international standard on human anatomic terminology from 1895 until it was replaced by ''Terminologia Anatomica'' in 1998. In the late nineteenth century some 30,000 terms for various body parts were in use ...

of 1895, but still featured in the ''

Encyclopædia Britannica The ( Latin for "British Encyclopædia") is a general knowledge English-language encyclopaedia. It is published by Encyclopædia Britannica, Inc.; the company has existed since the 18th century, although it has changed ownership various ...

'' of 1926, and appeared in general dictionaries as late as 1957.

Additional images

File:Human brain right dissected lateral view description.JPG, Human brain right dissected lateral view

References

* * {{DEFAULTSORT:Calcar Avis Hippocampus (brain)