Here, the dura has been removed and the arachnoid, a delicate, filmy layer, can be seen lying on the surface of the brain like a wet sheet. When the dura was pulled away, the arachnoid granulations "popped out" of the superior sagittal sinus and can be seen on the left. In life, the space just underneath the arachnoid (the subarachnoid space) is filled with cerebrospinal fluid (CSF) which lifts the arachnoid off the surface of the brain and presses it against the dura.