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1. a site of union of corresponding parts, such as the angle of the lips or eyelids.
2. the site of junction between adjacent cusps of a cardiac valve.
anterior commissure the band of fibers connecting the parts of the two cerebral hemispheres.
commissure of epithalamus a large fiber bundle that crosses the midline of the epithalamus just dorsal to the point where the cerebral aqueduct opens into the third ventricle.
middle commissure a band of gray matter joining the optic thalami; it develops as a secondary adhesion and may be absent.
posterior commissure commissure of epithalamus.
a thin band of white matter, crossing from side to side beneath the habenula of the pineal body and over the aditus ad aqueductum cerebri; it is largely composed of fibers interconnecting the left and right pretectal region and related cell groups of the midbrain; it marks the junction of the diencephalon and mesencephalon.
An axon tract running transversely through the gray matter that forms the roof of the cerebral aqueduct in the midbrain. This tract contains commissural axons interconnecting the right and left pretectal areas; it also contains decussating axons from each pretectal area to the contralateral Edinger-Westphal nucleus.
See also: commissure