The epidural space is an area immediately outside of a protective sac which contains the spinal cord. The spinal cord ends at the same level as the tip of your breast bone. Below this the spinal nerves to the lower abdomen and legs descend in this sac for a distance before leaving. The fluid in the sac allows them to move out of the way of any needle which penetrates the sac whether it be deliberate or inadvertent. The walls of the sac are formed by a thick membrane called the dura.