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(FRAME-INFO (STRING "Spinal Cord Segments. \(Image modified from H.D. Patton et al., Introduction to Basic Neurology, with permission of W.B. Saunders Co., 1976\). The spinal cord develops as a segmental structure, as do the myotomes. From the left and right sides of each cord segment emerges an anterior \(ventral\) and posterior \(dorsal\) root; these combine to form a single spinal nerve at each segmental level \(one on each side\). The roots are in the subarachnoid space. The nerves arise in the intervertebral foramina. Early in development the spinal cord segments and corresponding vertebrae are side-by-side, but the vertebrae grow at a faster rate, with the result that the cord ends at approximately lumbar vertebra L2 \(or the disc above or below\). For this reason spinal taps are done well below this level, to avoid puncturing the cord. The lumbar and sacral roots that are present caudally are pushed aside by the entering needle and not injured. Note that the roots, from rostral to caudal, progressively travel longer distances caudally before exiting the vertebral canal. This is due to the cord ending at vertebral level L2. It accounts for the fact that a patient may present with symptoms of root damage that are caudal to the level of the injured vertebra, especially in the lumbar vertebral region, where, for example, a slipped disc can injure sacral roots causing pain referred to the sacral distribution in the leg."))