DIGESTION. 69 



To accomplish this aim both chemical and mechanical changes are 

 closely interwoven. In the stomach, as one of the principal organs, 

 is performed a large and important share of the whole digestive 

 process; as it were, it is one of the large departments of a me- 

 chanical and chemical laboratory or establishment in which every 

 department is working toward a definite end: the digestion of the 

 food. Unlike the amylolytic changes of the saliva, which best occur 

 in an alkaline solution, stomachic digestion is an acid digestion. 



The stomach is the first organ into which the food passes as it 

 leaves the oesophagus. It is the most enlarged or dilated portion of 

 the entire alimentary canal, being located in the left hypochondriac, 

 epigastric, and right hypochondriac regions. It is a large muscular 

 pouch, and extends from the oesophagus to the small intestine. The 

 greater extremity of the stomach is to the left and communicates 

 with the oesophagus by the cardiac orifice. The pyloric end is the 

 lesser extremity, and at the right communicates with the small 

 intestine by the pyloric orifice. 



The fundus is the greater extremity of the stomach, and 

 projects several inches to the left of the oesophagus. The lesser 

 extremity for about two inches of its length is slightly constricted, 

 and is called- the pyloric antrum. The pyloric orifice is the entrance 

 to the duodenum, and is about a half-inch in diameter. It contains 

 the pyloric sphincter, or valve. 



STRUCTURE OF THE STOMACH. 



The stomach has four coats: from the outside, serous, mus- 

 cular, fibrous, and mucous. The serous coat is derived from the 

 peritoneum. The muscular coat contains three layers of unstriped 

 muscular fibers. The layer of longitudinal fibers is continuous with 

 that of the oesophagus, from which it radiates over the stomach. 



The middle layer is composed of circular fibers. These circular 

 fibers gradually accumulate toward the pyloric extremity and form 

 a thick band known as the pyloric sphincter. The internal layer 

 consists of oblique fibers. The submucous coat is made up of 

 areolar tissue and forms an extensible layer upon which the strength 

 of the stomach mainly depends. The mucous membrane of the 

 stomach is soft to the touch and of a pale-pinkish color. Under 

 excitement it becomes reddened. During digestion and when 

 inflamed it has a deep-red hue. It is thin at the fundus and 

 gradually thickens toward the pyloric extremity. In this place it 

 ordinarily is in a state of wrinkles or ruga?, which are longitudinal 



