Like the brain, the spinal cord is surrounded by three concentric meninges: the dura mater, arachnoid mater, and pia mater. The spinal dura mater is continuous with the inner meningeal layer of the cranial dura mater and extends inferiorly to the posterior surface of the vertebral body of S2 (eFig. 9.45). It is separated from the bony vertebral canal by the epidural/extradural space (eFig. 9.45). In addition, unlike in the cranial cavity, the underlying arachnoid mater is not tightly adherent to the dura mater, and instead has a theoretical plane or potential space called the subdural space.