The spinal cord lies within a bony canal formed by adjacent vertebrae and soft tissue elements (the vertebral canal):
Within the vertebral canal, the spinal cord is surrounded by a series of three connective tissue membranes (the meninges):
a. the pia mater is the innermost membrane and is intimately associated with the surface of the spinal cord;
b. the second membrane, the arachnoid mater, is separated from the pia by the subarachnoid space, which contains cerebrospinal fluid;
c. the thickest and most external of the membranes, the dura mater, lies directly against, but is not attached to, the arachnoid mater.