STOMACH. 



G65 



stomach is distended the Diaphragm is forced upwards, contracting the cavity of the chest ; 

 hence the dyspnoea complained of, from inspiration being impeded. The heart is also displaced 

 upwards ; hence the oppression in this region, and the palpitation experienced in extreme disten- 

 sion of the stomach. Pressure from without, as in the pernicious practice of tight lacing, pushes 

 the stomach down towards the pelvis. In disease, also, the position and connections of the 

 organ may be greatly changed, from the accumulation of fluid in the chest or abdomen, or when 

 the size of any of the surrounding riscera undergoes alteration. 



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

 projecting inwards in the form of a circular fold, the pylorus, leaving a narrow 

 circular aperture, about half an inch in diameter, by which the stomach commu- 

 nicates with the duodenum. 



The pylorus is formed by a reduplication of the mucous membrane of the 

 stomach, containing numerous muscular 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. The aperture is occasionally oval. 

 Sometimes, the circular fold is replaced by two crescentic folds, placed, one above, 

 and the other below, the pyloric orifice ; and, more rarely, there is only one. 



Structure. The stomach consists of four coats ; a serous, a muscular, a cellular, 

 and a mucous coat, 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 and lesser curvature, 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. 



The muscular coat is situated immediately beneath the serous covering. It con 

 sists of three sets of fibres, the longitudinal, circular, and oblique (fig. 334). 



Fig. 334. The Muscular Coat of the Stomach. 



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

 tudinal 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. 



