Also known as the great cerebral commissure (where a commissure is a band of fibers of tissues connecting bilateral structures), it is the large midline band or collection of commissural fibers connecting the right and left hemispheres of the cerebral cortex, with an area of about 6.2 cm² (mid-saggital section) in the adult human (see figure below). The number of fibers in the human corpus callosum has been estimated at 250,000,000. Its function is to transfer information from the cerebral cortex on one side of the brain to the same region on the other side. At about 9 weeks gestational age, the two cerebral hemispheres fuse in the midline just above the two foramina of Monro to form a commissural plate. Axons that will connect a given area of cerebral cortex on one side with the corresponding area on the other side grow into this plate, and in doing so form the corpus callosum and a smaller, separate anterior commissure.
