Spinal Cord

The spinal cord is a long, slender, cylindrical extension of nervous tissue that continues on from the brain stem, running down inside the bony vertebral canal and, like the brain, wrapped by the same three meningeal layers. It does not run the full length of the vertebral column — it typically ends around the first or second lumbar vertebra — so the nerve roots below that point have to stretch further down before exiting through their own vertebral space, forming a thick bundle of elongated roots called the cauda equina ('horse's tail') because of its appearance. In cross-section, the cord shows two surface indentations — the anterior median fissure and the posterior median sulcus — and, unusually for the CNS, its grey matter sits on the inside, forming a butterfly-shaped region surrounded by white matter (the reverse of the arrangement seen in the brain). …