MOVEMENTS OF THE STOMACH. 309 



As in the intestine, there are two plexuses of nerves with ganglia; 

 one in the sub-mucous coat and the other between the two muscular 

 coats. Blood-vessels and numerous lymphatics lie in the mucous and 

 sub-mucous coats.] 



157. Movements of the Stomach. 



When the stomach is empty, the great curvature is directed down- 

 wards and the lesser upwards ; but when the stomach is full, it rotates on 

 an axis running horizontally through the pylorus and cardia, so that the 

 great curvature appears to be directed to the front and the lesser back- 

 wards. 



Arrangement of the Muscular Fibres. The non-striped muscular 

 fibres of the stomach are arranged in three directions or layers, an outer 

 longitudinal continuous with those of the oesophagus. This layer is 

 best developed along the curvatures, especially the lesser. At the 

 pylorus the fibres form a thick layer, and become continuous with the 

 longitudinal fibres of the duodenum. The circular fibres form a com- 

 plete layer, but at the pylorus they are well marked and constitute 

 the pyloric sphincter-muscle, or valve ; whilst at the cardia (inlet), 

 such a muscular ring is absent (Gianuzzi). The innermost oblique or 

 diagonal layer is incomplete. 



The movements of the stomach are of two kinds : (1.) The rotatory 

 or churning movements, whereby the parts of the wall of the stomach 

 lying in contact with the contents or ingesta glide to and fro with a 

 slow rubbing movement. Such movements seem to occur periodically, 

 every period lasting several minutes (Beaumont). By these move- 

 ments the contents are moistened with the gastric juice, while the 

 masses of food are partly broken down. The formation of hair-balls in 

 the stomach of dogs and oxen indicates that such rotatory movements 

 of the contents of the stomach take place. (2.) The other kind of 

 movement consists in a periodically occurring peristalsis, whereby, as 

 with a push, the portions of the contents of the stomach first dissolved 

 are forced into the duodenum. They begin after a quarter of an hour 

 (Busch), and recur until about five hours after a meal (Beaumont). 

 This peristalsis is most pronounced towards the pyloric end, and the 

 muscles of the pyloric sphincter relax to allow the contents to pass 

 into the duodenum. According to Riidinger, the longitudinal mus- 

 cular fibres, when they contract, especially when the pyloric end is 

 filled, may act so as to dilate the pylorus. 



The strongly muscular walls of the stomach of grain-eating birds effect a tritura- 

 tion of the food. The mechauical force thereby exerted was often experimented 



