The left and right cerebral hemispheres are connected to each other by about 10 cm long bundles of nerve fibres (about 200 million). The bundles of nerve fibres inside the central nervous system (brain and spinal cord) are called the tracts. Hence, the left and right cerebral hemispheres are connected to each other by a tract of nerve fibres. This tract of nerve fibres which connects the two cerebral hemispheres is called the corpus callosum.