74 HUMAN PHYSIOLOGY CHAP. 



the pharynx, the gullet or oesophagus, the stomach, and 

 the small and large intestines. 



There are no bones and cartilages in this tube as are 

 found in the air passages, but its walls are made up of 

 several coats that extend through its entire length. 



(1) On the outside we find a thin, serous covering whose 

 function is quite like that of the pleura of the lungs. 

 It serves to keep the surfaces that move upon each 

 other well oiled and in that way prevents friction. 



(2) The next is a heavy, muscular coat consisting of two 

 separate layers all along the canal, except in the stomach 

 where there are three. The outer layer has muscle fibers 

 that run lengthwise, while in the inner they are all 

 circular or extend around the canal, and in the stomach 

 the fibers of the third layer run obliquely. (3) The 

 third is a very thick mucous membrane that lines the 

 entire digestive tract. This canal extends from the mouth 

 to the lower end of the spine, but it is so coiled up that 

 it is really about thirty feet long. 



Ask your butcher to get a pig's stomach for you. In size, shape, 

 and general structure it is quite like man's. Study the various coats 

 as carefully as you can. Notice the velvety mucous membrane on 

 the inside. 



66. Glands. A number of very important organs 

 called glands are found along the alimentary canal. 

 These glands pour certain fluids into the canal, which 

 aid in changing solid foods into blood. Such organs are 

 the salivary glands of the mouth, the gastric glands of 

 the stomach, the intestinal glands, the pancreas, and the 

 liver. 



