This plexus (Fig. 451) results substantially from the union of the
ventral branches of the last three lumbar and the first two sacral
nerves, but it derives a small root from the third lumbar nerve also.
The anterior part of the plexus lies in front of the internal iliac
artery between the lumbar transverse processes and the psoas minor. The
posterior part lies partly upon and partly in the texture of the
sacro-sciatic ligament. From the plexus are derived the nerves of the
pelvic limb, which are now to be described.