Spinal Cord
The spinal cord ( Gross Anatomy: Spinal Cord) starts at the level of the foramen magnum.
The spinal cord consists of a peripheral portion of white matter dominated by fibers, a central portion of grey matter dominated by neurons surrounding the central canal.
The grey matter are arranged in three columns on each half side of the spinal cord.
The central canal is lined with ependymal cells and filled with cerebrospinal fluid. It opens upward into the inferior portion of the fourth ventricle.
The spinal cord terminates at the L1 vertebral level in adults. Therefore, the lumbar and sacral nerve roots descending in the vertebral canal below the L1 vertebral level form a mass of nerve roots that resembles the tail of a horse; hence, the name cauda equina. Because the cauda equina floats in the CSF, a needle introduced into the subarachnoid space will displace the roots with little possibility of puncture damage.