

DIGESTION. 27 



and viscid ; division of the sympathetic does not, however, completely 

 dilate the vessels. There is evidence of the existence of a local vaso- 

 motor mechanism, which is inhibited by the chorda tympani ; exalted by 

 the sympathetic. 



Deglutition is the act of transferring food from the mouth into the 

 stomach, and may be divided into three stages : 



1. The passage of the bolus from the mouth into the pharynx. 



2. From the pharynx into the oesophagus. 



3. From the oesophagus into the stomach. 



In the ist stage, which is entirely voluntary, the mouth is closed and 

 respiration momentarily suspended; the tongue, placed against the roof 

 of the mouth, arches upward and backward, and forces the bolus into the 

 fauces. 



In the sd stage, which is entirely reflex, the palate is made tense and 

 directed upward and backward by the levatores-palati and tensores-palati 

 muscles ; the bolus is grasped by the superior constrictor muscle of the 

 pharynx and rapidly forced into the oesophagus. 



The food is prevented from entering the posterior nares by the uvula 

 and the closure of the posterior half-arches (the palato-pharyngei muscles); 

 from entering the larynx by its ascent under the base of the tongue and the 

 action of the epiglottis. 



In the $d stage, the longitudinal and circular muscular fibres, contracting 

 from above downward, strip the bolus into the stomach. [For nervous 

 mechanism of Deglutition, see Medulla Oblongata.] 



Gastric Digestion. The stomach is a dilation of the alimentary canal, 

 13 inches long, 5 inches deep, having a capacity of about 5 pints ; there ' 

 can be distinguished a cardiac and pyloric orifice, a greater and lesser curva- 

 ture, a greater and lesser pouch. 



It possesses three coats : 



1. Serous, a reflection of the peritoneum. 



2. Muscular, the fibres of which are arranged longitudinally, transversely 

 and obliquely. 



3. Mucous, thrown into folds, forming the rugae. 



Imbedded in the mucous coat are immense numbers of mucous and 

 true gastric glands. In the pyloric end of the stomach are found the 

 mucous glands, which are lined with columnar epithelium throughout 

 their extent. In the cardiac end are found the true peptic glands (Fig. 3), 

 the ducts of which are also lined with columnar cells, while the secretory 

 parts are lined with two distinct -varieties of cells. Oije variety consists ot 



