The mesencephalic duct, also known as the<unk>  of Sylvius or the<unk> , contains cerebrospinal fluid (CSF), is within the mesencephalon (or midbrain) and connects the third ventricle in the diencephalon to the fourth ventricle, which is between the pons and cerebellum.
Cerebral aqueduct
Arachnoid mater
Primitive ventricle
Subarachnoid space
Fourth ventricle
Carotid sinus
Epidural space
Hypophysial fossa