908 THE ORGANS OF DIGESTION. 



viscera. Variations according to Age. In an early period of development the stomach is verti- 

 cal, and in the newborn child it is more vertical than later on in life, as owing to the large size 

 of the liver it is more pushed over to the left side of the abdomen, and the whole of the anterior 

 surface is covered by the left lobe of this organ. 



On looking into the pyloric end of the stomach, the mucous membrane is 

 found projecting inward in the form of a circular fold, the pyloric valve, leaving 

 a narrow circular aperture, about half an inch in diameter, by which the stomach 

 communicates with the duodenum. 



The pyloric valve is formed by a reduplication of the mucous membrane of the 

 stomach, containing numerous circular fibres, which are aggregated into a thick 

 circular ring ; the longitudinal fibres and serous membrane being continued over 

 the fold without assisting in its formation. 



Structure. The wall of the stomach consists of four coats : serous, muscular, 

 areolar, and mucous, together with vessels and nerves. 



The serous coat is derived from the peritoneum, and covers the entire surface 

 of the organ, excepting along the greater or lesser curvatures, at the points of 

 attachment of the greater and lesser omenta ; here the two layers of peritoneum 

 leave a small triangular space, along which the nutrient vessels and nerves pass. 

 On the posterior surface of the stomach, close to the cardiac orifice, there is also a 

 small area uncovered by peritoneum, where the organ is in contact with the under 

 surfaces of the Diaphragm. 



The muscular coat (Fig. 493) is situated immediately beneath the serous cover- 

 ing, to which it is closely connected. It consists of three sets of fibres longi- 

 tudinal, circular, and oblique. 



FIG. 493. The muscular coat of the stomach. 



The longitudinal fibres are most superficial ; they are continuous with the 

 longitudinal fibres of the oesophagus, radiating in a stellate manner from the cardiac 

 orifice. They are most distinct along the curvatures, especially the lesser, but are 

 very thinly distributed over the surfaces. At the pyloric end they are more thickly 

 distributed, and continuous with the longitudinal fibres of the small intestine. 



The circular fibres form a uniform layer over the whole extent of the stomach 

 beneath the longitudinal fibres. At the pylorus they are most abundant, and are 

 aggregated into a circular ring, which projects into the cavity, and forms, with the 

 fold of mucous membrane covering its surface, the pyloric valve. They are con- 

 tinuous with the circular fibres of the oesophagus. 



