Once the vertebral bodies and neural arches are formed, the spinal nerves leave the spinal canal through the intervertebral foramina at the level of each segment (beginning of the fetal period). Thereafter, the spinal column undergoes more rapid growth than the spinal cord, the caudal end of which is moved more and more cranially (ascent of the spinal cord). During month 6, the caudal end of the spinal cord is situated at the S1 segment; at birth it is at L3; in the adult it is at approximately L2. As a consequence of this differential growth, the ventral and dorsal roots of spinal nerves in the caudal spinal segments descend at a more acute angle than those originating from segments higher up. The conus medullaris and the filum terminale reflect the ascent of the spinal cord.