338 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



epaxial muscles. To see them, turn the animal dorsal side up and carefully 

 cut down through the mass of epaxial muscles close to the vertebrae. The 

 dorsal rami will then be seen emerging from the vertebral column and penetrat- 

 ing the epaxial mass, accompanied by blood vessels. There are twelve or thirteen 

 pairs of thoracic nerves. 



f) The abdominal portions of the vagus and the sympathetic: Trace the vagi 

 into the peritoneal cavity, removing the liver if not already done. In the rabbit 

 the left vagus crosses the ventral surface of the esophagus obliquely to the right 

 and is distributed to the lesser curvature and ventral surface of the stomach. 

 The right vagus crosses the dorsal surface of the esophagus obliquely to the left 

 and is distributed to the dorsal surface of the stomach. In the cat the ventral 

 division of the vagus passes to the lesser curvature, the dorsal division to the 

 greater curvature. In both cases the vagi form plexi on the stomach called the 

 ventral and dorsal gastric plexi, which also connect with the nearby sympathetic 

 plexi, described in the next paragraph. 



Locate again the posterior part of the thoracic portion of the sympathetic 

 trunk. Expose it and note the nerve, the greater splanchnic nerve, which arises 

 from the sympathetic trunk on each side and passes obliquely ventrally toward 

 the diaphragm. In the cat this nerve is accompanied by additional smaller 

 nerves, the lesser splanchnic nerves, arising from the sympathetic shortly posterior 

 to the origin of the greater splanchnic nerve. The splanchnic nerves pass to 

 either side of the crura of the diaphragm into the peritoneal cavity. (The crura 

 of the diaphragm are the muscular cords which fasten the diaphragm to the 

 lumbar vertebrae.) Turn the abdominal viscera to the right and look on the 

 left surface of the superior mesenteric artery near its origin from the aorta. 

 Two prominent sympathetic ganglia will be found lying on the superior mesenteric 

 artery. These are the coeliac and superior mesenteric ganglia; the former lies in 

 front of or on the left surface of the artery; the latter behind or on the ventral 

 surface of the vessel. The two ganglia are bound together by a strong connec- 

 tion. The splanchnic nerves of both sides may be traced into the coeliac gang- 

 lion. From this ganglion a prominent coeliac plexus will be seen extending 

 toward the stomach, where it connects with the gastric plexi of the vagi. This 

 great sympathetic plexus formed around and dorsal to the stomach is often 

 called the solar plexus. From the coeliac and superior mesenteric ganglia and 

 adjacent plexi also arise plexi for the liver, spleen, adrenal glands, gonads, and 

 the great blood vessels. Some of these will probably be seen. The inferior 

 mesenteric ganglion of the sympathetic system lies in the mesocolon alongside 

 the inferior mesenteric artery. It is situated in the inferior mesenteric plexus 

 from which networks extend to adjacent structures. 



The main sympathetic trunk of the abdominal region should now be traced 

 caudad from the place of origin of the splanchnic nerves. The two trunks 

 descend deep dorsally lying in the groove between two muscle masses. At 

 segmental intervals they have ganglionic enlargements from which nerves pass 



