The spinal canal extends from the foramen magnum to the coccyx. The spinal intradural and subarachnoid compartments containing the neural elements end at the level of S2. The cord lies within these meningeal sleeves and in a normal adult, the conus medullaris tapers to an end at the L1/L2 intervertebral disc level. Below this the subarachnoid space is occupied by the filum terminale and the lumbosacral roots forming the cauda equina. (Fig. 23.1). At birth the cord terminates at L3 level, but due to differential growth rates of the cord and spinal column, the cord ascends to the adult position.