196 



DIGESTION. 



the pharynx, where, by the successive action of the constrictor muscles, it is forced 

 into the oesophagus. This tube leads from the pharynx to the stomach and is provided 

 with thick muscular walls, by the contraction of which the food is passed into this cavity, 

 which serves at once as a receptacle for the food and an important active organ in 

 digestion. 



FIG. 47. Stomach, liver, small intestine, etc. (Sappey.) 



1, inferior surface of the liver ; 2, round ligament of the liver; 8, gall-bladder; 4, superior surface of the right 

 lobe of tlie liver ; 5, diaphragm; 6, lower portion of the oesophagus; 7, stomach; 8, gastro-hepatic omentum; 9, 

 spleen; 10, gastro-splenic omentum ; 11, duodenum ; 12,12,8mallintestine; IS, caecum; 14, appendix ve,r~ 

 miformis ; 15, 15, transverse colon ; 16, sigmoid flexure of the colon; 17, urinary bladder. 



The stomach is covered externally by the general peritoneal covering of the abdominal 

 organs. It is provided with a mucous membrane, which secretes the gastric juice and 

 absorbs the water with inorganic and other principles in solution. The stomach also has 

 muscular walls, composed of unstriped muscular fibres arranged in two principal layers. 

 Nearly all the principles contained in food are modified by the gastric juice, and some are 

 completely liquefied and absorbed in the stomach. By the action of the gastric juice, the 

 food, comminuted and incorporated with the fluids of the mouth, is farther reduced to a 

 pultaceous mass, which was formerly called the chyme, the muscular movements of the 

 stomach turning it over and over, so that it becomes thoroughly incorporated with the 

 fluids. These movements have a tendency to force the food, as it becomes sufficiently 

 liquefied, into the small intestine ; and a collection of circular muscular fibres, called 

 sometimes the pyloric muscle, stands at the pylorus as a guard, allowing the liquid por- 

 tions to pass gradually through, but sending back the larger masses to be farther acted 

 upon in the stomach. By these movements, a great portion of the food, prepared by the 



