commissure

n. Site where two elements are joined. In anatomy it is used to refer to the nerve pathways crossing from one side to the other in the brain (and also the spinal cord) as well as to the site or point where two parts join, for example, in the lips. The brain commisures are the corpus callosum, the anterior commissure, and the posterior commissure. The corpus callosum (the largest white matter structure in the human brain) is situated ventral to the cortex, connects the right and left hemispheres, and contains about 250 million axons. The anterior commissure is a neural pathway connecting the cerebral hemispheres across the middle line, at the level of the fornix. The posterior commissure crosses the midline at the upper end of the cerebral aqueduct.      

- aa

► See also corpus CALLOSUM