After these initial expansions, a series of further developments occurs to form some of the major landmarks in the brain. The mesencephalon narrows prior to the proencephalon resulting in the formation of the 'Foramen of Munro' and the 'Cerebral Aqueduct'. The proencephalon develops two further pouches in the cranial lateral aspect which are the foundations of the 'Lateral Ventricles' and the 'Third Ventricle'.