THE CESOPHAGUS AND STOMACH 



101 



Fig. 98. Muscular Coat of the Stomach. 



Middle layer of circular fibres. 



The circular muscular fibres at the intestinal end of the 

 stomach form a strong band which serves to keep the pylorus 

 closed. Such circular muscles are called sphincters (Gr. a tight 

 band). This sphincter remains at first firmly closed during digestion - r 

 but, as the process continues, it slowly relaxes, thus allowing the 

 digested portions to pass 

 through into the intestines; 

 and, towards the termina- 

 tion, it allows all the con- -^^ 

 tents of the stomach to 

 pass. 



The time during which 

 substances remain in the 

 stomach varies consider- 

 ably with the nature of 

 the food and the method 

 of cooking. Usually it is 

 not less than one hour, 

 and seldom more than five 

 hours. 



The mucous membrane of the stomach is smooth, level, and 

 soft, when the organ is moderately distended ; but is drawn up 

 into longitudinal folds when the stomach is empty. It consists 

 almost entirely of minute glands, which secrete mucus to keep 

 the surface moist, and, during digestion, a powerful fluid known 

 as the gastric juice or 

 gastric fluid. 



These glands are called 

 gastric glands or peptic 

 glands (Gr. pepto, I cook, 

 or digest). They are tubu- 

 lar glands, the openings 

 of which may be seen on 

 the surface of the mucous 

 membrane by the aid of a 

 lens. 



When the stomach con- 

 tains no food, the mucous 

 membrane is very pale in 

 colour, and is moistened 

 by mucus only ; but as soon as food is introduced, or even a non- 

 digestible substance, the supply of blood increases, the mucous 

 membrane becomes of a bright pink colour, and the secretion ot 

 the gastric fluid immediately commences. 



It is difficult to ascertain accurately the quantity of gastrio- 



99. Muscular Coat of the Stomach. 



Inner layer of oblique fibres. 



