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George E. Carvell, PhD, PT   University of Pittsburgh
The adult spinal cord begins at the medulla-spinal cord transition at the foramen magnum and ends as the conus medullaris at the L1- L2 vertebral level. Below the conus, spinal roots continue caudally as the cauda equina. Lumbar and sacral roots of the cauda equina exit at the appropriate orthopedic level. Like the Brain in the cranial vault, the spinal cord and the cauda equina are surrounded by three meninges (dura mater, arachnoid, and pia mater) & cerebrospinal fluid (CSF) in the subarachnoid space. A spinal tap at the L4-5 level is used to measure the pressure and constituents of the CSF. There are 8 cervical, 12 thoracic, 5 lumbar, and 5 sacral segments in the human spinal cord.
C&S  fig 1-5 p 7
C&S  fig 9-5 p 237
Note the differences in the shape and relative proportions of gray and white matter at different spinal cord levels (fig 9-5). The spinal cord is partially suspended by the denticulate ligament at each segment of the cord (fig 1-5).