4o8 hlERVOUS SYSTEM. 



These nerves follow especially the arteries, forming plexuses 

 over their surfaces, and passing with them to the organs which 

 they supply. The coeliac plexus anastomoses with the pos- 

 terior gastric plexus of the vagus. Parts of the coeliac plexus 

 following the branches of the coeliac 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, y), and a renal plexus {k) follows the renal artery 

 to the kidneys (g). The superior mesenteric plexus {g) 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, h). This is a continuation of the coeliac 

 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 (/) 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 (b). 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 vertebras. 

 There is a ganglion for each vertebra (Fig. 162, ;/), 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 coeliac 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. 



