1. The work of Kellgren (1939) and Lewis and Kellgren (1939) on the production of segmental pain by stimulation of structures near the mid-line of the back has been reviewed, and! a number of experiments have been carried out with the object of testing the validity of their conclusions.

2. On both anatomical and experimental grounds there is reason to believe that pain produced in this manner does not arise, as was assumed by Lewis and Kellgren, from irritation of the interspinous ligaments, but is rather due to the stimulation of nerve trunks in the vicinity. The views of Kellgren (1941, 1942) on the etiology of pain in certain cases of sciatica, and on the part played by intervertebral ligaments in the production of pain in the back, have been discussed. They have been shown to rest on an inadequate foundation.

3. The importance in investigations of this kind of a detailed anatomical survey has been emphasized.