66 DISSECTION OF THE DOG 



the plexus follow the lesser curvature of the stomach almost as far as the 

 pylorus. Some hepatic filaments reach the liver. 



Tbttncus (esophagbtjs doesalis. — The fusion of the dorsal branches of 

 the vagus nerves has been seen to produce the dorsal oesophageal nerve trunk. 

 Like the ventral trunk, this enters the abdomen and forms a plexus. The 

 fine filaments of the plexus lie mainly along the lesser curvature and caudal 

 surface of the stomach : and many of them are connected with the cceliac plexus. 



The two great plexuses formed by the oesophageal trunks are connected 

 with each other in the region of the cardia of the stomach. 



Ganglia cceliaca. — The cceliac ganglia, right and left, are placed ventral 

 to the aorta, between the origins of the cceliac and cranial mesenteric arteries. 

 The right ganglion is the larger. Radiating from the gangha are anastomosing 

 filaments constituting the cceliac plexus (plexus cceliacus) with which gastric, 

 hepatic, and splenic plexuses are associated. 



Ganglion mesentericum. — A ganglion of fair size, connected by filaments 

 with the much larger cceliac ganglion, should be found about the root of the 

 cranial mesenteric artery. Numerous filaments from the mesenteric ganglion 

 follow the branches of the artery and form the mesenteric plexus (plexus 

 mesentericus). 



Connected with both the cceliac and mesenteric ganglia is another small 

 ganglion, or possibly more than one, related to the adrenal gland. 



Dissection. — Remove the stomach and duodenum from the abdomen and 

 examine their structure and the interior of their cavities. In the first 

 place they should be moderately distended with water. 



Structure of the stomach. — Like the other parts of the alimentary 

 tract within the abdomen, the wall of the stomach is composed of four layers : 

 (1) An external serous tunic derived from the peritoneum ; (2) a muscular 

 tunic ; (3) submucous tissue ; and (4) a mucous membrane. 



The serous covering is complete except along those narrow areas following 

 the curvatures by which vessels and nerves gain access to or egress from the 

 wall of the organ. The muscular tissue is disposed in three strata. When 

 the serous membrane has been removed, longitudinal fibres, most numerous 

 along the curvatures, are exposed. Over the surface of the right half of 

 the sac the fibres are oblique rather than longitudinal. 



The superficial fibres should now be carefully removed and a stratum of 

 circular fibres displayed. The circular stratum is more or less complete over 

 the whole stomach, but near the pylorus it is thicker than it is towards the 

 right. At the pylorus a double sphincter is produced by a marked thickening 

 of the circular fibres. The two sphincters are separated on each side by a 

 thin area in the middle of which is a large vein proceeding from the underlying 



