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LESSON XXVIII. 



THE STRUCTURE OF THE STOMACH. 



1. SECTIONS of the cardiac region of the dog's stomach, cut perpendicularly 

 to the surface of the mucous membrane. The tissue is to be stained with log- 

 wood or borax-carmine, and the sections are to be mounted in Canada balsam. 



In these sections the general arrangement of the coats of the stomach is to 

 be studied and sketches are to be made under a low power illustrating this 

 arrangement, and others under a high power showing the structure of the 

 glands of the mucous membrane. 



Measure the whole thickness of the mucous membrane, the thickness of 

 the muscular coat, the size of the columnar epithelium-cells of the surface, 

 and that of the cells in the deeper parts of the glands. 



2. Sections of the mucous membrane of the same region, cut parallel 

 to the surface. 



These sections will show better than the others the arrangement of the 

 cells in the glands. 



3. Vertical sections of the mucous membrane from the pyloric region 

 of the dog's stomach. Make a sketch under a low power of one of the glands 

 in its whole length, filling up some of the details with the high power. 



4. Study the arrangement of the blood-vessels of the stomach in vertical 

 sections of the wall of an organ the vessels of which have been injected. 



The wall of the stomach consists of four coats, which, enumerated 

 from without in, are as follows, viz.: serous, muscular, areolar or sub- 

 mucous, and mucous membrane. 



The serous coat is a layer which is derived from the peritoneum. 

 It is deficient only along the lines of the lesser and greater curvatures. 



The muscular coat consists of three layers of plain muscular fibres. 

 Of these the bundles of the outer layer run longitudinally, those of the 

 middle layer circularly, and those of the inner layer obliquely. The 

 longitudinal and circular bundles become thicker and stronger towards 

 the pylorus, at which they pass into the corresponding layers of the 

 small intestine ; at the pylorus itself the circular layer is greatly 

 thickened to form the sphincter muscle. The oblique fibres are only 

 present in the left or cardiac part of the stomach. 



The areolar or submucous coat is a layer of areolar tissue, which 

 serves to unite the mucous membrane loosely to the muscular coat ; 

 in it ramify the larger branches of the blood-vessels and lymphatics. 



