THE DIGESTIVE APPARATUS AND NUTRITION 223 



by a thick ring of circular muscular fiber, forming a 

 sphincter muscle, which keeps the opening closed except 

 when food is ready to pass from the stomach. 



314. Nervous Supply of the Stomach. Nerve fibers from 

 many centers reach the different coats, glands, and blood 

 vessels of the stomach and those of the large and small 

 intestines. They are gathered in large tangles of nervous 

 matter, called plexuses, which contain branches from the 

 vagus nerves, from many of the spinal nerves, and from 

 the ganglia of the sympathetic chain. The great solar 

 plexus, or epigastric plexus, is placed at the pit of the 

 stomach ( Fig. 22, p. 31) ; the hypogastric plexus lies 

 before the last of the lumbar vertebrae, and divides into 

 two parts, one lying on each side of the rectum. These 

 plexuses give rise to innumerable branches which control 

 the complicated processes of digestion, the precise path of 

 each different sort of nervous influence not having been 

 yet made out. It is easy to see, however, that this close 

 nervous connection of the digestive organs with all parts 

 of the system implies important relations between them. 



Vagus nerve fibers appear to stimulate the peristaltic 

 or wavelike movement of the stomach and bowels, which 

 by the progressive narrowing of the tube forces on its 

 contents, while the sympathetic fibers are inhibitory and 

 bring the movements to an end. It is believed that the 

 walls of these organs possess some power of spontaneous 

 action such as appears in the walls of the heart. 



315. The Small Intestine ( Fig. Ill ) is a tube with many 

 curves, about twenty feet in length, two inches in diameter 

 at its upper end and somewhat smaller in its lower por- 

 tion. Its coats are the same as those of the stomach, but 

 the peritoneum, a fold of .which forms the outer coat, does 

 not entirely surround the tube, but runs off to form a sup- 



