The meninges comprise the dura, pia and arachnoid mater. The cerebrospinal fluid is produced in the choroid plexuses of the lateral, 3rd and 4th ventricles of the brain and leaves through the three foramina in the roof of the 3rd ventricle. It passes into the subarachnoid space between the arachnoid and pia and serves to protect the brain and spinal cord.
• The dura mater (Fig. 68.1): the fibrous layer is closely adherent to the bone but the serous layer separates from the fibrous layer in places to form the dural venous sinuses which are lined by endothelium. It also forms two large sheets—the falx cerebri and the tentorium cere-belli (see below).
• The arachnoid mater: deep to the dura. Bridges over the sulci and fissures of the brain. The subarachnoid space contains the cerebrospinal fluid.
• The pia mater: follows the contours of the brain, dipping into the sulci.
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