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refers classically to the combination of gray and white matter components that make up a seahorse-shaped structure revealed by dissection on the floor of the lateral ventricle in the human ( Shaw-1997 ) and the macaque ( Martin-2000 ). (\'Hippocampus\' in Latin means \'seahorse\' in English.) Part of the cerebral cortex, the hippocampal formation is an infolding of archicortex of the ventral part of the limbic lobe into the lateral ventricle. It consists of three predominantly gray matter structures: the dentate gyrus, CA fields, and subiculum, and two predominantly white matter structures: the alveus and fimbria ( Carpenter-1983 ).
In primates it is a relatively flat structure the rostral end of which abuts the amygdala and curves medially to form the uncus. In rodents, where it constitutes a much greater portion of the cerebral cortex it curves up caudally into a C-shaped structure. With increasing knowledge of the region the term has come to be used for a broader set of predominantly gray structures in adjacent cortex. See hippocampal formation (Insausti) and hippocampal formation (functional).
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