A STUDY OF BLOOD MANUFACTURE 



87 



6. THE ESOPHAGUS 



Structure of the Esophagus. The esophagus traverses the 

 length of the chest cavity, and as it nears the stomach it 

 goes through the diaphragm. In a cross section of this tube 

 the following tissues appear. Like all other parts of the 

 alimentary canal, it is lined with mucous membrane, which 

 furnishes a soft, 

 moist surface for 

 the passage of food. 

 Outside the mu- 

 cous membrane are 

 rings of circular 

 muscle running 

 around the esopha- 

 gus, and a longi- 

 tudinal layer of 

 muscle is found 

 outside the circu- 

 lar muscles. 



Functions of the 

 Esophagus. The 

 food is pushed 

 slowly down this = esophagus. 



6 = cardiac region of stomach. 



c = upper wall of stomach. 



d = pyloric region of stomach. 



e bile duct from liver. 



/= gall bladder. 



g = duct from pancreas. 

 h, i = small intestine showing ridges. 



FIG. 30. Longitudinal Section of Stomach and 

 Small Intestine. 



straight tube by the 

 successive contrac- 

 tion of the rings 

 of muscle described 

 above. Swallowing 

 is, therefore, not a 

 mere dropping of the food into the stomach, for the walls of 

 the esophagus are pressed together by surrounding organs, 

 except when the tube is opened by the passing food. In 

 fact, after practice one can swallow when standing on one's 

 head, and most quadrupeds (horse, dog, cow) when feeding 

 hold the head below the level of the stomach. 



