CHAPTER X. 

 THE ALIMENTARY SYSTEM. 



THE alimentary tract is an apparatus in which food, the 

 crude material of which the organism is built up, is received 

 and digested by the action of various secretions, the elab- 

 orated products absorbed into the circulation, and the 

 detritus discharged. It is a complex mechanism with many 

 varied parts and functions, all working harmoniously to- 

 gether. It consists essentially of a long coiled muscular 

 tube, the alimentary canal, opening at each end on the surface 

 of the body, the walls of which contain glandular structures 

 which secrete fluids and pour them into the canal to act on the 

 raw food-materials, so as to fit them for absorption and nutri- 

 tion. They also contain absorbent vessels by which the 

 digested and elaborated food is introduced into the circulation. 



The different parts and organs of this system are the mouth ; 

 teeth ; tongue ; salivary glands ; tonsils ; pharynx ; oesophagus ; 

 stomach ; small intestine ; large intestine ; rectum and anus ; 

 peritoneum ; liver and gall-bladder, and pancreas. 



The Mouth. 



The lining of the mouth consists of mucous membrane, 

 which over the lips, floor of the mouth, cheeks, and soft 

 palate rests upon the voluntary muscles in those situations ; 

 and over the bony parts, the maxillary and palate bones, rests 

 upon the periosteum. 



The mucous membrane of the mouth is continuous with that 

 of the pharynx and tongue and with the skin, and in structure 

 is similar to the latter. It consists of an epithelial lining, a 

 tunica propria, and submucosa. 



The epithelial layer is the representative of the epidermis 

 of the skin, and consists of stratified squamous epithelium. 



ill 



