Decussates

Decussation is used in biological contexts to describe a crossing (Latin: the roman numeral for ten, deca, is an uppercase 'X'). (In Latin anatomical terms the form decussatio is used, e.g. decussatio pyramidum.) Similarly, the anatomical term chiasma is named after the Greek uppercase 'Χ', chi).

Examples include:

The origin of the contralateral organization, the optic chiasm and the major decussations on the nervous system of vertebrates has been a long standing puzzle to scientists. For long the visual map theory of Ramón y Cajal has been the most popular theory., see also for an english summary. More recently, scientists have realized that this theory has some severe flaws. According to the current theory, the decussations are caused by an axial twist which makes that the anterior head, along with the forebrain is turned by 180° with respect to the rest of the body.

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