The first lumbar dorsal nerve roots contain afferent somatic and visceral nerve fibers corresponding to the first lumbar spinal cord segment.  They emerge as two or three rows of rootlets from the postero-lateral sulci of the spinal cord.  Rootlets of adjacent dorsal roots may communicate via thin branches.

The roots pass infero-laterally to their exit through the intervertebral foramina between the pedicles of L1 and L2.  They are larger in diameter, obliquity and length than the dorsal roots above.  They pass over the superior surfaces of the transverse processes of L2 to join with the first lumbar ventral roots to form the first lumbar spinal nerves.  On each side, the first lumbar dorsal roots possess an ovoid spinal ganglion (dorsal root ganglion) proximal to where they join the first dorsal ventral roots.  They are covered by a sleeve of pia mater, which is continuous with that of the spinal cord, and loosely invested by a prolongation of dura and arachnoid mater (the dural sleeve) almost as far as the spinal nerves.

Cauda Equina
The cauda equina is formed from the most caudal spinal roots.  As the spinal cord terminates before the vertebral column, the lower spinal roots descend inferior to the cord, as a divergent sheath, to reach their corresponding foramina.