THE C (ELI AC PLEXUS 1043 



are the so-called inhibitory, the latter motor. The inhibitory impulses leave the central 

 nervous system by the spinal accessory and vagus nerves. The motor fibres leave the spinal 

 cord by the ventral roots and white rami communicantes of the thoracic nerves and terminate 

 about the cells of the intervening sympathetic ganglia. From the cells of these gangha arise 

 the non-meduUated (grey) fibres of the plexus. These fibres terminate directly upon the fibres 

 of cardiac muscle or about the cells of the minute intrinsic. cardiac ganglia which in their turn 

 give axones to the muscle. 



2. The Pulmonary Plexuses 



The pulmonary plexuses are a continuation of the cardiac plexuses. The 

 two are so intimately joined that it is difficult to distinguish them as separate 

 plexuses. The pulmonary are formed by fibres from both the vagus and sympa- 

 thetic nerves. The anterior and posterior pulmonary branches of the vagus 

 unite, dorsal to the bifurcation of the trachea, with fibres from the second, third 

 and fourth ganglia of the thoracic portion of the sympathetic trunk to form the 

 anterior and posterior pulmonary plexuses that lie ventral and dorsal to the 

 bifurcation of the trachea. Here the pulmonary plexuses of both sides connect 

 with each other freely. Leaving the trachea, the plexuses pass into the lungs 

 along the pulmonary arteries (figs. 744, 789) . The parts of the plexus of each side 

 are named according to their position anterior or posterior to the right and left 

 pulmonary arteries; thus, there is a right anterior and a right posterior, a left 

 anterior and a left posterior pulmonary plexus. 



3. The Cceliac Plexus 



The coeliac (solar or epigastric) plexus is the largest of the prevertebral 

 plexuses. It is unpaired, and is continuous above with the aortic plexus of the 

 thorax and below with the abdominal aortic and superior mesenteric plexuses. 

 It lies in the epigastric region of the abdomen behind the bursa omentalis (lesser 

 sac of the peritoneum) and the pancreas, upon the crura of the diaphragm and over 

 the abdominal aorta, and around the origin of the coeliac and the superior mesen- 

 teric arteries. It occupies the interval between the suprarenal bodies and extends 

 downward as far as the renal arteries. It is formed by the great and the lesser 

 splanchnic nerves of both sides, by coeliac branches of the right vagus, and by 

 filaments from the upper lumbar ganglia of the sympathetic trunk. It sometimes 

 receives coeliac branches from the left vagus. It contains two large ganglia, the 

 right and left cceliac (semilunar) ganglia (fig. 790). 



The cceliac (semilunar) ganglia are two large, flat, irregularly shaped masses, 

 separable into a varying number of ganglia. These two masses, or rather the 

 smaller ganglia which compose them, are associated by a varying number of com- 

 municating branches. Each mass, right and left, lies upon the corresponding crus 

 of the diaphragm, at the medial border of the corresponding suprarenal body, 

 being sometimes overlapped by this body. The right mass lies behind the inferior 

 vena cava. Each coeliac ganglion receives at its upper border the greater 

 splanchnic nerve, and, near its lower border, lying over the origin of the renal 

 artery, is a more or less detached part, known as the aortico-renal ganglion. 

 This ganglion receives the lesser splanchnic nerve and may seemingly give origin 

 to the greater part of the renal plexus. Another part of the cceliac ganglion, often 

 found dorsal to the origin of the superior mesenteric artery, is known as the 

 superior mesenteric ganglion (fig. 790) . 



From the coeliac plexus and its ganglia subordinate plexuses are continued 

 upon the aorta and its branches. These comprise both paired and unpaired 

 plexuses. The paired plexuses are the phrenic, suprarenal and renal, the sper- 

 matic in the male, and, in the female, the ovarian plexuses. The unpaired plex- 

 uses are the aortic, hepatic, splenic, superior gastric, inferior gastric, superior mesen- 

 teric, and inferior mesenteric. 



That part of the coeliac plexus surrounding the coeliac artery was formerly 

 described as the coeliac plexus. It is better considered as an unnamed part of the 

 larger coeliac (solar) plexus. This part of the plexus receives fibres from both 

 vagus nerves, and gives filaments that form plexuses around the branches of the 

 coeliac artery and their ramifications. 



