Today's mini been is here! An Overview of the Ventricular System of Brain The ventricular system is a set of four interconnected cavities (ventricles) in the brain. Within each ventricle is a region of choroid plexus, a network of ependymal cells involved in the production of CSF. The cranial cavity has two lateral ventricles, 3rd ventricle, and fourth ventricle. Lateral ventricles open into the 3rd ventricle by foramen of Monro and then to 4th ventricle by the cerebral aqueduct. 4th ventricle o