THE ORGANS OF DIGESTION. 



m HE 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 (insalivation) ; 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, pancreatic and intestinal fluids, from that portion which 

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



Alimentary Canal. 



( Duodenum. 



Mouth. Small intestine^ Jejunum. 



Pharynx. [ Ileum. 



(Esophagus. ( Csecum. 



Stomach. Large intestine < Colon. 



( Rectum. 



Accessory Organs. 

 Teeth. 



( Parotid. Liver. 



Salivary glands < Submaxillary. Pancreas. 



( Sublingual. Spleen. 



THE MOUTH. 



The mouth (oral or buccal caviiy) is placed at the commencement of the ali- 

 mentary canal ; it is a nearly oval-shaped cavity, in which the mastication of the 

 food takes place (Fig. 466). It consists of two parts ; an outer, smaller portion, 

 the vestibule (vestibulum oris), and an inner, larger part, the cavity proper of the 

 mouth (cavum oris proprium). 



The vestibulum oris is a slit-like aperture, bounded in front and laterally by 

 the lips and cheeks ; behind and internally by the gums and teeth. Above and 

 below it is limited by the reflection of the mucous membrane from the lips and 

 cheeks to the gum covering the upper and lower alveolar arch respectively. It 

 receives the secretion from the parotid glands, and communicates, when the jaws 

 are closed, with the cavum oris by an aperture on each side behind the wisdom teeth. 



The cavum oris proprium is bounded laterally and in front by the alveolar 

 arches with their contained teeth ; behind it communicates with the pharynx by a 

 constricted aperture termed the isthmus faucium. It is roofed in by the hard and 

 soft palate, while the greater part of the floor is formed by the tongue, the remainder 

 being completed by the reflection of the mucous membrane from the sides and 

 under surface of the tongue to the gum lining the inner aspect of the mandible. 

 It receives the secretion from the submaxillary and sublingual glands. 



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 pharynx 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 



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