The space between the arachnoid and pia mater in the spine that is continuous with the intracranial subarachnoid space via the foramen magnum. The spinal subarachnoid space extends from the foramen magnum to the S2 vertebra. It contains approximately half the volume of the total cerebrospinal fluid in the body. L2 is the location where most lumbar punctures are taken to sample and assess cerebrospinal fluid. Epidural anesthesia is also often delivered to this space.