A 28-year-old pregnant woman is admitted to the obstetrics department for delivery. In the final stages of labor a caudal anesthetic is administered via the sacral hiatus. Into which of the following spaces in the sacral canal is the anesthetic placed?

The vertebral canal is the longitudinal canal that extends through the vertebrae, containing the meninges, spinal cord, and associated ligaments. The vertebral venous plexus is the valveless network of veins extending longitudinally along the vertebral canal. Neither of these answer choices describes a specific space. The epidural space is found superficially to the dura mater. It is a fat-filled space extending from C1 to the coccyx. The subarachnoid space is a true space containing CSF. It is found within the CNS and extends to the level of S2. The subdural space is a potential space between the dura and the arachnoid mater. Normally these two layers are fused due to the pressure of CSF in the subarachnoid space.