316 FOOD AND DIGESTION 



motor fibers concerned are branches of the fifth, supplying part of the digastric 

 and mylo-hyoid muscles and the muscles of mastication; the facial, supplying 

 the levator palati; the glosso-pharyngeal, supplying the muscles of the 

 pharynx; the vagus, supplying the muscles of the larynx through the in- 

 ferior laryngeal branch; and the hypoglossal, the muscles of the tongue. The 

 nerve center by which the muscles are harmonized in their action is situated 

 in the medulla oblongata. It cannot be definitely circumscribed, but is in 

 the general level of the vagus origin. The movements of the esophagus are 

 coordinated by the complex of sensory and motor fibers of the fifth and the 

 ninth to twelfth cranial nerves, which all take some part in this complicated 

 reflex. 



DIGESTION IN THE STOMACH. 



The stomach in man and those mammalia which are provided with a 

 single stomach consists of a dilatation of the alimentary canal placed between 

 and continuous with the esophagus, which enters its larger or cardiac end on 

 the one hand, and the small intestine, which commences at its narrowed end 

 or pylorus, on the other. It varies in shape and size according to its state of 

 distention. It is supplied with nerves from the vagus and from the sympa- 

 thetic and receives a special artery, the gastric artery. 



Structure of the Stomach. The stomach is composed of four 

 coats, called respectively, the external or peritoneal, the muscular, the sub- 

 mucous, and the mucous coat. Blood-vessels, lymphatics, and nerves are 

 distributed in and between them. 



The muscular coat consists of three separate layers of fibers which, accord- 

 ing to their several directions, are named the longitudinal, circular, and 

 oblique. The longitudinal set are the most superficial and are continuous 

 with the longitudinal fibers of the esophagus and spread out in a diverging 

 manner over the cardiac end and sides of the stomach to the pylorus. The 

 circular or transverse coat more or less completely encircles all parts of the 

 stomach; this coat is thickest at the middle and in the pyloric portion of the 

 organ, and forms the chief part of the thick ring of the pylorus. The next 

 and consequently deepest coat, the oblique, is continuous with the circular 

 muscular fibers of the esophagus at the cardiac orifice of the stomach. This 

 coat is quite interrupted and more or less incomplete. The muscular fibers 

 of the stomach and intestinal canal are unstriated. 



The mucous membrane of the stomach, which rests upon a layer of loose 

 cellular membrane, or submucous tissue, is smooth, soft, and velvety. It is 

 of a pale pink color during life, and in the contracted state is thrown into 

 numerous longitudinal folds or rugae, which disappear when the organ is 

 distended. It is composed of a mass of short tubular secreting glands. 



The Gastric Glands. The glands of the mucous membrane of the 

 stomach are of two varieties, Cardiac and Pyloric. 



