THE SYMPATHETIC SYSTE:\I 495 



corpora albicantia, and behind these again tlie third pair of nerves, supply- 

 ing the muscles of the eye. Still further back is a square eminence, the 

 pons varolii, from the sides of which the fourth and fifth pairs of nerves 

 arise, while its posterior border gives origin to the sixth pair in the middle 

 and the seventh externally to these. The eighth and ninth nerves have 

 ah'cady been alluded to, as arising from the medulla oblongata. 



THE SYMPATHETIC SYSTEM 



This division of the nerves consists of a series of ganglia, lying on each 

 side the spine, from the head to the coccyx, communicating with the cranial 

 and spinal nerves, and distributing branches to all the internal organs of 

 digestion, circulation, depuration, and generation. The branches of dis- 

 tribution accompany the arteries, forming a plexus, or series of meshes, 

 around each of them. In the head there are four small ganglia, in the neck 

 three, and posteriorly a small ganglion lies opposite each vertebra. The 

 posterior cervical ganglion communicates with the spinal nerves of that 

 region by a branch which accompanies the vertebral artery, and sends 

 forward filaments to form the bronchial and cardiac plexus, the former 

 being largely supplied also with branches from the pneumogastric nerve. 

 From the dorsal ganglia a large nerve is formed, the greater splanchnic nerve, 

 and also the lesser splanchnic, which enter the abdomen close beneath the 

 crus of the diaphragm, where they give off a number of branches which, 

 together with filaments of the pneumogastric nerve, unite on both sides to 

 form the semilunar ganglion, or collection of ganglia arranged somewhat in 

 that shape. They lie close to the posterior aorta, and surround the root of 

 the coeliac artery, supplying branches to form the phrenic and the splenic 

 plexus, the gastric plexus, the hepatic plexus, the anterior and posterior 

 mesenteric plexus, the renal plexus, and the spermatic plexus, all surrounding 

 the corresponding arteries and supplying the important organs whose names 

 they bear. 



