408 NERVOUS SYSTEM. 
These nerves follow especially the arteries, forming plexuses 
over their surfaces, and passing with them to the organs which 
they supply. The cceliac plexus anastomoses with the pos- 
terior gastric plexus of the vagus. Parts of the cceliac plexus 
following the branches of the cceliac artery may be distin- 
guished as hepatic plexus, splenic plexus, etc. A dense 
plexus is formed on the surface of the suprarenal body (supra- 
renal plexus, 7), and a renal plexus (4) follows the renal artery 
to the kidneys (6). The superior mesenteric plexus (¢) forms 
a dense network over the superior mesenteric artery (5) and 
follows it to the intestine. A plexus passes caudad on the 
aorta (aortic plexus, %). This is a continuation of the cceliac 
and superior mesenteric plexuses; it receives a number of 
branches from the main sympathetic trunk, lying dorsad of the 
aorta. The aortic plexus contains a number of small ganglia. 
From the aortic plexus the smaller inferior mesenteric 
plexus (2) follows the inferior mesenteric artery (7) to the large 
intestine; in this lies a ganglion of considerable size, the 
inferior mesenteric ganglion. 
In the pelvic region small plexuses are formed in a similar 
manner, from branches given off by the main sympathetic 
trunk, together with branches from the plexuses of the 
abdominal cavity. These plexuses supply the various organs 
in the pelvis. 
The main sympathetic trunk (a) passes into the abdomen 
at the side of the crus of the diaphragm, lying dorsad of the 
great splanchnic nerve (4). In the abdomen it lies nearer the 
middle line than in the thorax, so that the two trunks of right 
and left side are separated by but a few millimeters as they lie 
on the ventral surface of the centra of the lumbar vertebra. 
There is a ganglion for each vertebra (Fig. 162, 2), and from 
each ganglion are given off one or more communicating 
branches to the spinal nerves,. and usually a branch which 
passes ventrad to join one of the plexuses among the viscera. 
The first three branches of this kind (Fig. 164, c) are larger 
and pass to the cceliac and superior mesenteric ganglia. The 
sympathetic may be traced into the pelvis, where it becomes 
smaller, and is lost as the caudal region is reached. 
