the great majority of which tracts pass through the corpus callosum
Commissural fiber The commissural fibers make up tracts that include the corpus callosum, the anterior commissure, and the posterior commissure.
Meninges The pia mater (Latin: tender mother[5]) is a very delicate membrane. It is the meningeal envelope that firmly adheres to the surface of the brain and spinal cord, following all of the brain's contours (the gyri and sulci). It is a very thin membrane composed of fibrous tissue covered on its outer surface by a sheet of flat cells thought to be impermeable to fluid. The pia mater is pierced by blood vessels to the brain and spinal cord, and its capillaries nourish the brain.