INTRODUCTION There is a growing appreciation of the significance of the intervertebral disk in its relationship to spinal disease. When it is remembered that the disks make up a full quarter of the total length of the presacral portion of the spinal column, it is evident that these structures constitute an extensive organ. In point of fact it may be said that the greater majority of conditions resulting in spinal deformity or in derangement of spinal function are primarily the outcome of involvement of the intervertebral disks. For a clear appreciation of the pathologic pictures and notably for the interpretation of pathologic processes and their genesis, a thorough acquaintance with the structure and function of the disks is essential. From decade to decade there are considerable variations in both the anatomic character and the physiologic competence of the disks; hence it is necessary to consider their developmental history. Nonetheless a