5 10 



ABDOMEN 



stitutes the pyloric sphincteric ring. The knob -like appear- 

 ance presented by the extremity of the pyloric canal, when 

 viewed from the interior of the duodenum, is produced by the 

 presence, beneath the mucous membrane, of this muscular 

 ring. 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 



Sphincteric cylinde 



Duodeno-pyloric constriction 



Sphincteric ring 

 Orifice of pyloric canal 



Interior of duodenum 



Sphincteric ring 

 Duodeno-pyloric constriction 



Sphincteric cylinder 



Pyloric vestibule 



FIG. 196. Pyloric Canal and Pyloric Vestibule of the Stomach opened up 

 by section in the plane of the two curvatures. 



'comparatively few of these fibres pass superficially over the 

 duodeno-pyloric constriction to become continuous with the 

 corresponding fibres of the muscular coat of the duodenum. 

 As they approach the duodenum the deeper longitudinal 

 fibres of the pyloric canal leave the surface and penetrate the 

 substance of the pyloric sphincteric ring. There can be little 

 doubt that by this arrangement an effective apparatus, 

 antagonistic to the pyloric sphincteric ring, is provided, by 

 means of which, when the sphincter relaxes, the pyloric 

 orifice may be dilated. There is thus a constrictor and a 

 dilator of the pylorus. 



In suitable specimens this arrangement of the muscle 



