The middle of three membranes covering the brain and spinal cord, which has a fine, almost cobweb-like, texture Between it and the pia mater within lies the subarachnoid space containing cerebrospinal fluid and large blood vessels; the membrane itself has no blood supply
The middle layer of the meninges. A membrane that protects the brain and spinal cord below the dura mater and above the subarachnoid space and the pia mater