THE FROG 



243 



M 



The Food Tube and its Glands. The mouth leads like a funnel 

 into a short tube, the gullet. On the lower floor of the mouth can 

 be seen the slitlike glottis leading to the lungs. The gullet widens 

 almost at once into a long stomach, which in turn leads into a much 

 coiled intestine. This widens abruptly at the lower end to form 

 the large intestine. The latter leads into the cloaca (Latin, 

 sewer), into which open the kidneys, urinary bladder, and repro- 

 ductive organs (ovaries or spermaries) . Several glands, the func- 

 tion of Which is to produce digestive fluids, open into the food 

 tube. These digestive fluids, by means of the ferments or enzymes 

 contained in them, change insoluble food 

 materials into a soluble form. This allows 

 of the absorption of food material through 

 the walls of the food tube into the blood. 

 The glands (having the same names and 

 uses as those in man) are the sali- 

 vary glands, which pour their juices 

 into the mouth, the gastric glands 

 in the walls of the stom- 

 ach, and the liver and 

 pancreas, which open 

 into the intestine. 



Circulation. The frog 

 has a well-developed heart,, 

 composed of a thick-walled 

 muscular ventricle and two 

 thin-walled auricles. The 

 heart pumps the blood 

 through a system of closed 

 tubes to all parts of the 

 body. Blood enters the 

 right auricle from all parts 

 of the body ; it then con- 

 tains considerable carbon 

 dioxide; the blood enter- 

 ing the left auricle comes 



from the lungs, hence it contains a considerable amount of oxygen. Blood 

 leaves the heart through the ventricle, which thus pumps some blood 



Internal organs of a frog: M, mouth; T, tongue; Lu, 

 lungs; H, heart; St, stomach; I, small intes- 

 tine; L, liver; G. gallbladder; P, pancreas; C, 

 cloaca; B, urinary bladder ; S, spleen; K, kidney, 

 Od, oviduct; O, ovary; Br, brain; Sc ; spinal 

 cord; Ba, back bone. 



