Ventricles are cavities within the brain derived from the original lumen of the neural tube. They exist in each cerebral hemisphere (the lateral ventricles), between the hemispheres (the third ventricle), and beside the cerebellum (the fourth ventricle). Canals connect these ventricles together. The interventricular foramen connects the lateral with the third ventricle, the cerebral aqueduct connects the third and fourth ventricles. The fourth ventricle connects to the central canal of the spinal cord, and other canals, called apertures, lead to the subarachnoid space of the meninges.