DIGESTION 



165 



both connected with successive portions of the esophagus. The first mechan- 

 ism is temporarily suspended during deep anesthesia while the second per- 

 sists. (Meltzer.) 



Though the peristalsis of the esophagus is excited by nerve impulses 

 coming through the vagus nerves and is abolished by their division, Cannon 

 has shown by means of the Rontgen rays that this effect for the lower portion 

 of the esophagus, at least in the cat and monkey, is of a temporary duration 

 only, lasting from one to several days, after which a peristalsis again develops 

 with sufficient vigor to force food through the cardiac orifice into the stom- 

 ach. The muscle coat of this portion of the esophagus is composed of non- 

 striated muscle-fibers, is supplied with a myenteric nerve plexus and resem- 

 bles lower portions of the alimentary canal. It is capable of developing a 

 peristalsis merely in response to the pressure of food within and independent 

 of extrinsic nerves. 



GASTRIC DIGESTION 



After the food has passed through the esophagus it is received by the 

 stomach, where it is retained for a variable length of time, during which 



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Sulcus intermedius 

 Gastro duodenal cotisfrictio?i Vestibule 



FIG. 69. DIAGRAM SHOWING THE ANATOMIC FEATURES OP THE STOMACH. 



important changes are induced in its physical structure and chemic 

 composition. The disintegration of the food inaugurated by mastication 

 and insalivation is still further carried on in the stomach by the solvent 

 action of the acid fluid there present, until the entire mass is reduced to 

 a liquid or semi-liquid condition. 



The Stomach. The stomach is the dilated and highly specialized por- 

 tion of the alimentary canal intervening between the esophagus and small 

 intestine. When moderately distended with food, it is somewhat conical or 

 pyriform in shape and slightly curved on itself. It is situated obliquely and 

 in some individuals almost vertically in the upper part of the abdominal 

 cavity, extending from the left hypochondrium to the right of the epigastrium. 

 The dimensions and capacity of the stomach undergo considerable periodic 

 variation according to the extent to which it is distended by food. In the 

 average condition it measures in its long diameter from 25 to 35 centimeters, 



