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CHAPTER XV 

 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. These 

 latter organs will form the subjects of subsequent chapters. 



THE MOUTH 



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

 submucous layer of connective tissue, and a muscular or bony 

 paries. 



The mucous membrane (mucosa} is clothed with a layer of stra- 

 tified 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 propia (corium, stratum proprium) upon which 

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

 portion of which specially abounds in elastic fibres. 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 papillae 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 mem- 

 brane to the subjacent muscles and bones forming the wall of the 

 oral cavity. In most portions the buccal mucous membrane is but 

 loosely connected with the underlying parts, but in the hard 

 palate and the gums this union is verv firm. 



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