THE FROG, A TYPICAL VERTEBRATE 



247 



Food passes from the mouth through the tubelike (esophagus 

 into the stomach (Fig. 142, M). The walls of the stomach are 

 thick and muscular and contain a great many glands for the 

 secretion of gastric juice. These glands are stimulated by the 

 presence of food, and the gastric juice they secrete acts upon the 



FIG. 142. Internal anatomy of the frog. 



B, bladder ; D, intestine ; E, ovaries ; H, heart ; L, liver ; Lg, lungs ; M, stomach. 



(From Ecker.) 



food particles in such a way as to dissolve them. This solution 

 of food material in preparation for absorption is the object of 

 digestion. 



The food next passes into the intestine where the pancreatic 

 juice from the pancreas, and the bile, which is stored up by the 



