ALIMENTARY CANAL 



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the same condition exists in animals. In order that food may be 

 of use to man, it must be changed into a state that will allow its 

 passage in a soluble form through the walls of the alimentary canal, 

 or food tube. This is done by the enzymes which cause digestion. 



Alimentary Canal. — In nearly all vertebrate animals, food is 

 taken in the mouth and passed through a food tube in which it is 

 digested. In vertebrate animals, including man, this tube is com- 

 posed of different portions, named, respectively, as we pass from 

 the mouth downward, pharynx 

 (far'ir)ks), gullet, stomach, small 

 intestine, and large intestine. 



Comparison of Food Tubes 

 of Frog and Man. — At this 

 time it will be wise for each 

 member of the class to dissect 

 a frog, with a view to compar- 

 ing the organs of digestion with 

 those in our own bodies. On 

 making this comparison, we 

 find that part for part they are 

 much the same. But we notice 

 that the intestines of man, 

 both small and large parts, are 

 relatively longer than those of 

 the frog. We also notice that 

 in man the body cavity or space in which the internal organs rest 

 is divided into two parts by a wall of muscle, the diaphragm, which 

 separates the heart and lungs from the other internal organs. In 

 the frog no muscular diaphragm exists. We can also see plainly 

 the silvery transparent mes'entery or double fold of the lining of 

 the body cavity in which the organs of digestion are suspended. 

 Numerous blood vessels can be found especially in the walls of 

 the food tube, which carry the digested nutrients to other parts 

 of the body. 



Glands and their Work. — In addition to the alimentary canal 

 proper, and connected with it, we find a number of digestive glands, 

 varying in size and position. In man there are the saFivary glands 

 of the mouth, the gastric glands of the stomach, the pancreas 



Digestive tract of a frog and of a man : 

 Gul, gullet ; S, stomach ; L, liver ; G, gall 

 bladder ; Sp, spleen ; P, pancreas ; SI, 

 small intestine ; LI, large intestine ; V, 

 vermiform appendix; A, anus. 



