114 



STUDIES IN PHYSIOLOGY 



beneath which is a green gall bladder. A pancreas is like- 

 wise present, which, as in man, pours its secretions through 

 the common bile duct into the small intestine. The alimen- 

 tary canal of the frog is several times the length of the 

 body, and hence it is more or less coiled. This increased 

 length provides a greater surface for digestion and ab- 

 sorption. 



The Alimentary Canal of the Pigeon. Striking modifica- 



Cer*6ra/ 

 ' fiem/spfteres 



---Gutter 

 ---Crop 

 " "- <5yr/'nx 

 "-/tight avr/'c/e 



FIG. 40. Longitudinal Section of a Bird. 



tions, due to the absence of teeth in the mouth, are seen in the 

 digestive apparatus of birds. In the first place, the gullet 

 is relatively large to allow the passage of the more or less 

 solid food. Two thirds of the way down the gullet on its 

 ventral surface is a saclike enlargement of considerable size 



