[TA] that portion of the arachnoid that lies within the vertebral canal and surrounds the spinal cord and the vertebral portion of the subarachnoid space. It extends from the foramen magnum above to the S2 vertebral level. Because the spinal cord ends at the L2 vertebral level, a wide separation occurs between the arachnoid and pia mater, the lumbar cistern, filled with cerebrospinal fluid in which the cauda equina is suspended. SYN: arachnoidea mater spinalis [TA], arachnoid of spinal cord, arachnoidea spinalis, spinal part of arachnoid.