THE DIGESTIVE APPARATUS AND NUTRITION 221 



It has muscular walls, mostly of voluntary fibers, which 

 contract upon the food to push it into the esophagus, or 

 may force it back into the mouth if desired. Seven 

 passages open into this cavity: the mouth, the two nasal 

 passages, the two Eustachian tubes, the larynx, and the 

 esophagus. 



312. The Esophagus connects the pharynx with the stom- 

 ach (Figs. 108 and 110). It is a muscular tube lying 

 along the spinal column behind the trachea. The muscu- 

 lar coat of the wall of the esophagus contains an external 

 layer of fibers running lengthwise, while the second layer 

 is of circular fibers. They are mainly involuntary and 

 supplied by the vagus nerve, with fibers from sympathetic 

 ganglia also. 



313. The Stomach lies in the cavity of the abdomen 

 immediately below the diaphragm (Fig. 86, p. 153). 

 It is a large sac, formed by the dilation of the alimentary 

 canal (Fig. 110), and its walls have the three coats of 

 the rest of that canal, the inner mucous coat, the middle 

 connective tissue coat, and the external muscular coat, with 

 a fourth coat in addition, the peritoneum, which forms the 

 lining of the abdominal cavity and is reflected back over 

 the organs (or most of them) which it contains. The 

 peritoneum adheres to the walls of the abdominal cavity, 

 folds of it surround the blood vessels running to the 

 stomach, and a large pouch of the same forms a sling for 

 the stomach. From the lower side of the stomach another 

 large fold of the peritoneum, called the great omentum, 

 spreads over the rest of the abdomen. After middle life 

 it often holds a large accumulation of fat. 



The muscular coat of the stomach is composed of layers 

 of unstriped muscular fibers. Its mucous lining is inelas- 

 tic, and as it lines the organ smoothly when it is distended, 



MACY'S PHYS. 14 



