The<unk>  is one of the four connected fluid-filled cavities within the human brain. These cavities, known collectively as the ventricular system, consist of the left and right lateral<unk> s, the third<unk> , and the<unk> . The<unk>  extends from the cerebral aqueduct (aqueduct of Sylvius) to the obex, and is filled with cerebrospinal fluid (CSF).
The<unk>  has a characteristic diamond shape in cross-sections of the human brain. It is located within the pons or in the upper part of the medulla. CSF entering the<unk>  through the cerebral aqueduct can exit to the subarachnoid space of the spinal cord through two lateral foramina of Luschka (singular: foramen of Luschka) and a single, midline  foramen of Magendie (see List of human anatomical parts named after people).
Fourth ventricle
Cerebral peduncle
Vallecula of cerebellum
Uvula of cerebellum
Primitive ventricle
Lingula of cerebellum
Prosencephalon
Body of lateral ventricle