242 THE DIGESTIVE SYSTEM 



clinicians have taught that, although the visceral peritoneum 

 is insensitive to stimuli which produce painful impressions 

 when applied to the skin, the parietal peritoneum is a highly 

 sensitive membrane. Mackenzie believes that the parietal 

 peritoneum is in no way different from the visceral layer, and 

 that the pain which is apparently referable to the parietal 

 peritoneum is in reality due to stimulation of the numer- 

 ous sensory nerve-endings which abound in the extra-peri- 

 toneal fat. 



Little is known with regard to the particular segments of 

 the spinal medulla which innervate the peritoneum, bat it is 

 probable that they are identical with the segments which 

 innervate the abdominal wall. Abnormal stimulation of the 

 nerves supplying the peritoneum gives rise to both viscero- 

 sensory and viscero motor reflexes (p. 192). This condition 

 is well shown when stomach contents escape into the peritoneal 

 cavity following the perforation of a gastric ulcer. Pain is 

 referred to the whole of the anterior abdominal wall, and the 

 muscles of the wall, which are innervated by the same nerves, 

 become contracted and board-like. 



THE STOMACH 



The Stomach is situated chiefly in the left hypochondriac 

 and the epigastric regions, but it also descends for a variable 

 distance below the subcostal plane (p. 233). At its proximal 

 end, or cardiac orifice, which lies immediately below the 

 diaphragm, i inch to the left of the median plane, the stomach 

 becomes continuous with the oesophagus ; at its distal end or 

 pylorus, which lies at a lower level and slightly to the right of 

 the median plane, it becomes continuous with the duodenum. 

 The stomach possesses anterior and posterior surfaces, which 

 are separated from one another by two borders, termed the 

 lesser and greater curvatures. To the left side of the cardiac 

 orifice, the stomach bulges upwards into the left cupola of 

 the diaphragm, and this dilatation is referred to as the fundus. 



