This is a continuation of the dorsal sympathetic, and has upon it ganglia corresponding to the number of lumbar nerves from the inferior division of which it receives its afferent branches. Behind, it is continued by the sacral sympathetic.

Its efferent branches consist of short filaments to the lumbo-aortic plexus. The small mesenteric artery receives others, which surround the vessel and form the posterior mesenteric plexus, in the centre of which is a ganglion of some size. This ganglion supplies in addition branches to the posterior mesenteric vein, and others to the spermatic arteries and the rectum.

Two or three long divisions from each side pass beneath the peritoneum, and on reaching the lateral part of the rectum blend with others from the inferior sacral nerves, forming the plexus from which all the pelvic organs are supplied.