Chap. XIV] THE DIGESTIVE SYSTEM 265 



(3) The submucous, also called the areolar coat, is loose and 

 vascular. It carries the nerves and vessels which go to and 

 from the muscular and mucous coats. 



(4) The mucous coat is very soft and thick, the thickness being 

 mainly due to the fact that it is densely packed with small tubular 

 glands. It is covered with columnar epithelium, and in its undis- 

 tended condition is thrown into folds or rugae. The surface is 

 honeycombed by tiny, shallow pits, into which the ducts or mouths 

 of the tubular glands open. The glands are of two kinds : (1) pep- 

 tic, (2) pyloric. During digestion they secrete the gastric juice. 



Nerves and blood-vessels. — The stomach is supplied with 

 nerves from the sympathetic system, and also with branches 

 from the pneumogastric nerve, which comes from the cerebro- 

 spinal system. The blood-vessels are derived from the three 

 divisions of the coeliac axis. 



Function. — The functions of the stomach are (1) to connect 

 the oesophagus with the intestine, (2) to hold the food while it 

 undergoes gastric digestion, and (3) to secrete mucus and gastric 

 juice. 



THE SMALL OR THIN INTESTINE^ 



The small intestine extends from the stomach (pyloric valve) 

 above to the large intestine (valve of the colon) below. It is 

 a convoluted tube about twenty feet (6.0 m.) in length, and fills 

 the greater part of the front abdominal cavity. Its diameter at 

 the beginning is about two inches (5 cm.), but it gradually dimin- 

 ishes in size and is hardly an inch (2.5 cm.) in diameter at its lower 

 end. The small intestine is divided by anatomists into three 

 portions : — 



The duodenum. 



The jejunum. 



The ileum. 



The duodenum. — The duodenum is twelve fingers' breadth 

 in length (eight inches or 20 cm.), and is the widest part of the 

 small intestine. It extends from the pyloric end of the stomach 

 to the jejunum. 



Beginning at the pylorus, the duodenum at first passes in a 

 direction upward and backward to the under surface of the liver ; 

 it then makes a complete bend and passes in a direction downward 



