What is the band of nerve fibres in the centre of the brain called?

The callosal commissure, also known as the corpus callosum (Latin for "tough body"), is a flat bundle of commissural fibres that runs beneath the cerebral cortex of the brain. Only mammals that give birth to live young have the corpus callosum. It connects the left and right cerebral hemispheres over a portion of the longitudinal fissure, allowing for communication between them. With 200–300 million axonal projections and a length of around 10 centimetres, it is the biggest white matter structure in the human brain.