aqueductus cerebri

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The cerebral aqueduct (aqueductus mesencephali, mesencephalic duct, sylvian aqueduct or aqueduct of Sylvius) is within the midbrain. It contains cerebrospinal fluid (CSF) and connects the third ventricle to the fourth ventricle, located dorsal to the pons and ventral to the cerebellum. The cerebral aqueduct is surrounded by an enclosing area of gray matter called the periaqueductal gray, or central gray. It was first named after Franciscus Sylvius https://en.wikipedia.org/wiki/Cerebral_aqueduct