The object of this report is to record observations on the innervation of the annulus fibrosus and the posterior longitudinal ligament at the fourth and fifth lumbar level. Recent reports in the literature concerning clinical cases of severe pain in the lower part of the back caused by herniation of the nucleus pulposus without peripheral disturbance aroused my interest in investigating the position and type of fibers involved in transmitting the pain impulse. Spurling and Bradford1reported that in many cases in which the herniation has remained in the midline, not sliding down along the dural sleeve of the nerve, there is localized pain of great intensity. The most frequent level at which such herniations occur is between the fourth and the fifth lumbar vertebra. Localization of pain may occur at any level at which such a herniation appears. The question whether the nerves involved are related directly to