The spinal canal becomes progressively narrower from its superior opening at the foramen magnum to its inferior opening at the sacral hiatus . The canal itself is primarily formed by the vertebral foramen of adjacent vertebrae. Allowing for variation, the spinal cord occupies the superior two-thirds of the spinal canal and terminates at approximately the middle of the L1 vertebral body .
The canal has a typical shape depending on it's level:
- anterior: vertebral bodies, intervertebral discs, posterior longitudinal ligament
- posterior: ligamentum flavum lining the laminae
- lateral: vertebral pedicles
- spinal meninges
- spinal cord with its associated nerve roots and vessels (see blood supply of the spinal cord)
- epidural space