Cerebral aqueduct

The cerebral aqueduct, also known as the aqueductus mesencephali, mesencephalic duct, or the aqueduct of Sylvius is within the mesencephalon (or midbrain), contains cerebrospinal fluid (CSF), and connects the third ventricle in the diencephalon to the fourth ventricle within the region of the mesencephalon and metencephalon, located dorsal to the pons and ventral to the cerebellum.