It has earlier been demonstrated (BREIG 1960) that when the head and spinal column are bent in different directions, the continuous tissue tract consisting of the hind brain, spinal cord, and the associated cerebral and spinal nerves change in form and tension. In ventroflexion, the increase in tension is mainly a result of the lengthening of the spinal canal and the subsequent stretching of the cord which is anchored at its extremities. In dorsal extension, on the other hand, the spinal canal is shortened and the tissue tract slackens. By taking account of this behaviour it is possible to predict the state of tension in the cord for any position of the head and spinal column. Knowing the mechanism whereby the normal deformation of, and the change oftension in, the tissue tract are caused by the normal lengthening and shortening of the spinal canal, it can be deduced how pathologic tension is set up in the tissue tract by skeletal alterations which increase the length of the canal, and by pathologic changes in the soft tissues which alter their normal adaptability. These basic phenomena were analysed on autopsy specimens and on spinal cords exposed at neurosurgical operations. Hitherto, the application of radiography in this field has been limited to a study of the influence of head posture on the configuration of the fourth ven-