# Commissure

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{{Short description|Anatomical location where two things cross or are joined}}
A '''commissure''' ({{IPAc-en|ˈ|k|ɒ|m|ə|ʃ|ər}}) is the location at which two objects abut or are joined. The term is used especially in the fields of anatomy and biology.

* The most common usage of the term refers to the brain's commissures, of which there are at least nine. Such a commissure is a bundle of [commissural fiber](/source/commissural_fiber)s as a [tract](/source/nerve_tract) that crosses the midline at its level of origin or entry (as opposed to a [decussation](/source/decussation) of fibers that cross obliquely). The nine are the [anterior commissure](/source/anterior_commissure), [posterior commissure](/source/posterior_commissure), [corpus callosum](/source/corpus_callosum), [commissure of fornix](/source/Fornix_(neuroanatomy)) (hippocampal commissure), [habenular commissure](/source/habenular_commissure), [ventral supraoptic decussation](/source/ventral_supraoptic_decussation), Meynert's commissure, anterior hypothalamic commissure of Gasner, and the [interthalamic adhesion](/source/interthalamic_adhesion). They consist of fibre [tract](/source/Neural_pathway)s that connect the two [cerebral hemisphere](/source/cerebral_hemisphere)s and span the [longitudinal fissure](/source/longitudinal_fissure). In the spinal cord, there are the [anterior white commissure](/source/anterior_white_commissure), and the [gray commissure](/source/gray_commissure). ''Commissural neurons'' refer to [neuronal cells](/source/neuron) that grow their [axons](/source/axon) across the midline of the nervous system within the brain and the spinal cord.
* ''Commissure'' also often refers to cardiac anatomy of [heart valve](/source/heart_valve)s. In the heart, a commissure is the area where the valve leaflets abut. When such an abutment is abnormally stiffened or even fused, [valvular stenosis](/source/stenosis) results, sometimes requiring [commissurotomy](/source/commissurotomy).
* The term may also refer to the junction of the upper and lower [lip](/source/lip)s (see [labial commissure of mouth](/source/labial_commissure_of_mouth)).
* It may refer to the junction of the upper and lower mandibles of a [bird's beak](/source/beak),<ref>{{cite book |title=Handbook of Field and General Ornithology |first=Elliott |last=Coues |year=1890 |publisher=Macmillan and Co |location=London |page=155 |url=https://books.google.com/books?id=yU8aAAAAYAAJ&q=Handbook+of+Field+and+General+Ornithology&pg=PA1 |oclc=263166207}}</ref> or alternately, to the full-length apposition of the closed mandibles, from the corners of the mouth to the tip of the beak.<ref>{{cite book |editor-last= Campbell |editor-first= Bruce |editor2-last= Lack |editor2-first= Elizabeth |title=A Dictionary of Birds |year=1985 |publisher=T and A D Poyser |location=Carlton, England |page=105 |isbn=0-85661-039-9}}</ref>
* It may refer to the nasal and temporal meeting points of the upper and lower [eyelid](/source/eyelid)s (the medial and lateral [canthi](/source/canthi)).
* In the [vulva](/source/vulva), the joining points of the two folds of the [labia majora](/source/labia_majora) create two commissures—the anterior commissure just anterior to the prepuce of the clitoris, and the posterior commissure of the labia majora, directly posterior to the frenulum of the labia minora and anterior to the perineal raphe.

In [biology](/source/biology), the meeting of the two valves of a [brachiopod](/source/brachiopod) or [clam](/source/clam) is a commissure; in [botany](/source/botany), the term is used to denote the place where a [fern](/source/fern)'s laterally expanded vein endings come together in a continuous marginal [sorus](/source/sorus).

==See also==
* [Decussation](/source/Decussation)

==References==
{{Reflist}}

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Category:Anatomy
Category:Anatomical terminology
Category:Parts of a bird beak

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Adapted from the Wikipedia article [Commissure](https://en.wikipedia.org/wiki/Commissure) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Commissure?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.