The Ventricles CSF is produced mainly by a structure called the choroid plexus in the lateral, third and fourth ventricles. CSF flows from the lateral ventricle to the third ventricle through the interventricular foramen (also called the foramen of Monro).SF then flows into the subarachnoid space through the foramina of Luschka (there are two of these) and the foramen of Magendie (only one of these). Absorption of the CSF into the blood stream takes place in the superior sagittal sinus through structures called arachnoid villi.