A step has been taken toward the clarification of the arterial circulation in the spine, particularly the intrinsic circulation of the vertebral body. Twenty-four foetal and infant spines were used. Twelve were preserved in formalin and dissected. Twelve were injected with vinyl acetate and cleared with potassium hydroxide. Selected sections of the vertebral bodies were made and stained.

The pedicles, transverse processes, articular facets, and laminae have a good arterial blood supply through the anastomosing branches of the posterior rami from the paired segmental arteries of the thoracic and abdominal aortae. The only arteries to the vertebral body worthy of the name are: a fairly prominent branch of the anastomosis in the floor of the spinal canal, which enters the mid-dorsal surface of the centrum; and two small anterolateral branches which emerge from the segmental arteries soon after they leave the aorta (Fig. 7). The main dorsal vertebral-body artery and the right and left anterolateral arteries appear to end in the middle of the developing osseous spongiosa. No arterial branches could be demonstrated beyond the center of the vertebral body. Irregular vascular canals were seen in the spongiosa, and a diffuse network of thin-walled channels was seen in the surrounding cartilaginous zone (Fig. 8). Very small vessels appeared to perforate the cartilaginous plate, and tiny capillary channels to permeate the annulus fibrosus.

The intervertebral-disc tissues still appear to offer an important focus for degeneration, as they are always the farthest from the arterial blood supply.

Further investigation is needed to explain the circulation, physiology, and pathology of the spine segments.