Fouh Ventricle * Roof of the fouh ventricle -Formed by thin laminae of white matter. The lower has a median apeure (foramen of Magendie); cerebrospinal fluid escapes through this opening and lateral apeures into the subarachnoid space. Because these are the only communications between the ventricular and subarachnoid spaces, their blockage can produce one type of hydrocephalus. * The floor of the fouh ventricle, also known as rhomboid fossa, is formed by the dorsal surfaces of the pons and medulla oblongata. Fouh Ventricle and Cerebellum Posterior View ref : BD CHAURASIA