white matter, the tissue of the central nervous system and much of the part of the cerebrum, consisting mainly of myelinated nerve fibers, but with some unmyelinated nerve fibers, embedded in a spongy network of neuroglia. It is subdivided in each half of the spinal cord into three funiculi: the anterior, the posterior, and the lateral white column. Each column subdivides into tracts that are closely associated in function. The anterior column divides into two ascending tracts and five descending tracts. The posterior column divides into two large ascending tracts, one small descending tract, and one intersegmental tract. The lateral column divides into six ascending tracts and four descending tracts. Also called white substance. Compare gray matter. See also cerebrum, spinal cord, spinal tract.
