A study of the blood supply to the intervertebral discs in the adult dog

The (mainly lumbar) intervertebral discs of 21 recently euthanatized dogs (aged 3 days to 14 years) were examined grossly, under the dissection microscope and by light microscopy. The findings of the adult animals and the salient differences from the younger ones are reported. A few capillaries were observed in the outer 2-4 layers of the anulus fibrosus; these arose from segmental arteries that lay directly on the intervertebral discs. The principal supply of all intervertebral discs occurs by diffusion emanating from capillary loops. These are visible at 10-30 times enlargement in both unstained and benzidin stained preparations. They pass through the end plate of the vertebral body to where the bone gives way to the softer tissue of the disc. The capillary loops have wider lumina and are more numerous opposite the nucleus pulposus and in the adjacent perinuclear zone than more peripherally where the annular fibers attach to the bone.