Three sets of nerves reach the bladder itself, its sphincter
apparatus and the posterior urethra. Two of these sets belong to
the autonomic system, a pathway derived from the thoracicolumbar
outflow of the autonomic system, and a pathway derived from its
sacral outflow. The former is usually termed sympathetic; the
latter, parasympathetic. The remaining set (pudic nerves)
belongs to the somatic system, and arises from sacral segments
of the spinal cord. —The origins of the fibers forming the
thoracicolumbar outflow are shown in figure 1. They are finally
concentrated in the presacral nerve, or superior hypogastric
plexus, which has a superficial position under the peritoneum in
front of the last lumbar vertebra. More than half of the total
number of fibers in the presacral nerve are medullated
preganglionic fibers, which are chiefly the downward
continuations of mesially directed branches from the lumbar
sympathetic ganglions; the nonmedullated fibers appear