INTRODUCTION
The vertebral column forms part of the axis of the human body, extending in the midline from the base of the skull to the pelvis. Its four primary functions are protection of the spinal cord, support of the head, provision of an attachment point for the upper extremities, and transmission of weight from the trunk to the lower extremities. Pertinent to regional anesthesia, the vertebral column serves as the landmark for a wide variety of regional anesthesia techniques. It is important, therefore, that the anesthesiologist be able to develop a three-dimensional mental image of the structures comprising the vertebral column.