CHAPTER XIII 

 THE DIGESTIVE SYSTEM 



The digestive system includes the cavities of the mouth,, pharynx, 

 esophagus, stomach, and intestines, together with the accessory glands 

 the salivary glands, pancreas, and liver. Associated with the mouth 

 and cooperating in the function of the essential organs of digestion are 

 also the teeth and the tongue. 



THE MOUTH 



The walls of the oral cavity comprise a mucous membrane, a sub- 

 mucous layer of connective tissue, and a muscular or bony paries. 



The mucous membrane (mucosa) is clothed with a layer of strati- 

 fied squamous epithelium which presents, at the margin of the lips, 

 a gradual transition to the epidermis of the skin, and at the fauces is 

 continuous with the lining epithelium of the faucial isthmus and the 

 pharynx. 



The tunica propria (corium, stratum proprium) upon which the 

 epithelium rests, consists of dense areolar tissue, the superficial portion 

 of which specially abounds in elastic fibers. This portion of the corium 

 consists of rather delicate connective tissue bundles which at frequent 

 intervals are prolonged into the epithelial coat in the form of minute 

 conical papillae, similar to those of the skin, whose height varies with 

 the location. The tallest papilla are found on the gums and at the 

 margins of the lips, the lowest on the inner surface of the cheeks and 

 the soft palate. 



The papillary layer of the corium contains a plexus of capillary blood- 

 vessels which is connected with a network of small arteries and veins in 

 the deeper part of the tunica propria. 



The submucosa consists of looser connective tissue which blends 

 insensibly with that of the mucosa, and unites the mucous membrane 

 to the subjacent muscles and bones forming the wall of the oral cavity. 

 In most portions the buccal mucous membrane is but loosely connected 



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