THE ORGANS OF DIGESTION. 



Apparatus for the Digestion of the Food consists of the alimentary canal 

 _L and of certain accessory organs. 



The alimentary canal is a musculo-membranous tube, about thirty feet in 

 length, extending from the mouth to the anus, and lined throughout its entire 

 extent by mucous membrane. It has received different names in the various parts 

 of its course : at its commencement, the mouth, we find provision made for the 

 mechanical division of the food (mastication), and for its admixture with a fluid 

 secreted by the salivary glands (insalivatioii) ; beyond this are the organs of 

 deglutition, the pharynx and the oesophagus, which convey the food into that part 

 of the alimentary canal (the stomach) in which the principal chemical changes 

 occur, and in which the reduction and solution of the food take place ; in the small 

 intestines the nutritive principles of the food (the chyle) are separated, by its 

 admixture with the bile and pancreatic fluid, from that portion which passes into 

 the large intestine, most of which is expelled from the system. 



Alimentary Canal. 



f Duodenum. 



Mouth. Small intestines Jejunum. 



Pharynx. ( Ileum. 



(Esophagus. T Caecum. 



Stomach. Large intestines Colon. 



( Rectum. 



Accessory Organs. 

 Teeth. 



( Parotid. 

 Salivary glands < Submaxillary. 



( Sublingual. 



Liver. 



Pancreas. 



Spleen. 



THE MOUTH. 



The mouth (oral or buccal cavity) (Fig. 552) is the vestibule to the alimentary 

 canal. It is a nearly oval-shaped cavity, bounded in front by the lips, upon the 

 sides by the cheeks, behind by the soft palate and fauces. The upper and lower 

 dental arches, together with their alveolar processes, subdivide the general cavity 

 into a lingual and a buccal cavity. The latter has as its inner wall the external 

 faces of the teeth and gums of both jaws ; its external wall is formed by the lips 

 and cheeks. The lingual cavity is bounded anteriorly and laterally by the lingual 

 surfaces of both dental arches ; above, by the hard and the soft palates ; below, by 

 the floor of the mouth and the tongue. 



The mucous membrane lining the mouth is continuous with the integument at 

 the free margin of the lips and with the mucous lining of the fauces behind ; it is 

 of a rose-pink tinge during life, and very thick where it covers the hard parts 

 bounding the cavity. It is covered by stratified epithelium. 



The lips are two fleshy folds which surround the orifice of the mouth, formed 

 externally of integument and internally of mucous membrane, between which are 

 found the Orbicularis oris, muscle, the coronary vessels, some nerves, areolar tissue, 

 and fat, and numerous small labial glands. The inner surface of each lip is con- 



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