The fourth ventricle is one of a system of four communicating cavities within the brain that are continuous with the central canal of the spinal cord.
Four ventricles consist of the two lateral ventricles, the third ventricle and the fourth ventricle.

The fourth ventricle is the most inferior (lowest) of the four ventricles of the brain. It extends from the aqueduct of the midbrain to the central canal of the upper end of the spinal cord with which it communicates by the two foramina (openings) of Luschka and the foramen (opening) of Magendie.

The ventricles are filled with cerebrospinal fluid, which is formed by structures called choroid plexuses located in the walls and roofs of the ventricles.