1. The intercalary bone of the intervertebral disc is an osseous formation completely surrounded by the tissue of the intervertebral disc,—that is, it is interposed between the two intervertebral bodies.
2. Considering the high incidence of spondylosis, these formations provide a rare accidental finding of only secondary importance.
3. Symptoms, if any are present, are not characteristic of the condition; particular symptoms definitely connected with the presence of intercalary bones do not exist. The intercalary bones do not occur as a sequel to an accident. Intercalary bones, as well as calcification and ossification of the nucleus pulposus, are encountered in connection with spondylosis, providing that a certain degree of wear and tear of the intervertebral disc has occurred. They represent the ultimate stage of a curative process in a lesion of the outer portion of the intervertebral disc and of the nucleus pulposus, which had occurred a considerable time before.