CHAPTER XIV 



THE DIGESTIVE SYSTEM: ALIMENTARY CANAL AND ACCESSORY 



ORGANS 



Digestion is the process by means of wliich the food we take 

 into our mouths is transformed into a condition of solution or 

 emulsion suitable for absorption into the blood. The organs in 

 which the food is contained while undergoing digestion as well as 

 the organs which assist in the process are grouped together and 

 called the digestive system. 



THE DIGESTIVE SYSTEM 



The digestive system consists of the alimentary canal and 

 the accessory organs : (1) the salivary glands, (2) the tongue, 

 (3) the teeth, (4) the pancreas, and (5) the liver. 



ALIMENTARY CANAL 



The alimentary canal is a musculo-membranous tube extending 

 from the mouth to the anus. It is about twenty-eight feet long 

 and the greater part of it is coiled up in the cavity of the abdomen. 

 The diameter of the tube is by no means uniform, being consider- 

 ably dilated in certain parts of its course. It is composed of three 

 coats, the serous coat being absent from the mouth, to where it 

 passes through the diaphragm, and of four coats in the abdominal 

 cavity. These coats are : — 



(1) The mucous j Both described 



(2) The areolar, or sub-mucous [ in Chapter VIII. 



(3) The muscular coat is composed for the most part of un- 

 striped muscular fibres, the layers of which are disposed in various 

 ways, the most general arrangement being in a longitudinal and 

 circular direction. By the alternate contraction and relaxation 

 of fibres arranged in this fashion (the contractions starting from 

 above), the contents of the tube are propelled from above dowTi- 

 ward. 



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