356 



ABDOMEN 



closed, except during digestion, when it opens intermittently, 

 and at irregular intervals, to allow material to be squirted 

 from the stomach into the duodenum. 



The muscular coat of the pyloric canal is modified to 

 adapt it to its function. It is provided with a powerful 

 sphincteric apparatus. Both the circular and longitudinal 

 muscular fibres are present in greater mass than in any other 

 part of the organ. The circular fibres are disposed in the 

 form of a thick sphincteric muscular cylinder which surrounds 

 the entire length of the pyloric canal. At the duodeno- 



FlG. 1 66. Anterior Wall of a Slightly Distended Stomach. Showing the 



folds of the mucous membrane. 



A, QEsophagus ; B, Pylorus. 



pyloric constriction the margin of this cylinder becomes 

 increased in thickness, forming thereby the strong muscular 

 ring which encircles the pyloric orifice and constitutes the 

 pyloric sphincteric ring. The knob -like appearance presented 

 by the extremity of the pyloric region, when viewed from the 

 interior of the duodenum, is produced by the presence 

 of the muscular ring beneath the mucous membrane. The 

 sphincteric cylinder which surrounds the pyloric canal varies 

 much in its thickness in accordance with different degrees of 

 contraction of the canal. 



The longitudinal muscle fibres likewise form a thick layer 

 on the superficial aspect of the sphincteric cylinder and ring. 

 They are uniformly disposed around the pyloric canal, but 



