Section of the medulla oblongata at the level of the decussation of the pyramids.

Decussation is used in biological contexts to describe a crossing. (In Latin anatomical terms the form decussatio is used, e.g. decussatio pyramidum.) In anatomy the term chiasma or chiasm means nearly the same as decussation.

Examples include:

In this "true bug", Dysdercus decussatus, in the family Pyrrhocoridae, the specific epithet refers to the bandolier-like markings on the back.

Evolutionary significance

After the origin of the nervous system, in the course of evolution from invertebrate to vertebrate, the nerve cord moved from the ventral side (side towards the belly) to the dorsal side (side towards the back). It is believed that in this process, the decussation arose with a 180° shift with respect to the brain.[2][3]

See also


  1. Jaeger, Edmund Carroll (1959). A source-book of biological names and terms. Springfield, Ill: Thomas. ISBN 0-398-06179-3.
  2. Kinsbourne, M (Sep 2013). "Somatic twist: a model for the evolution of decussation.". Neuropsychology. 27 (5): 511–5. doi:10.1037/a0033662. PMID 24040928.
  3. Dixon, A. Francis (31 May 2014). "Why are the great motor and sensory tracts of the central nervous system crossed?". The Dublin Journal of Medical Science. 124 (1): 1–4. doi:10.1007/BF02972358.

Further reading

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