THE VERTEBRATE ANIMALS 



287 



the frog more in detail when we discuss the structure and uses of 

 the parts of the body in man, we may now learn something of the 

 position and use of some of the structures found within the body 

 cavity. 



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- 



Backbone Oviduct Spinal cord 



rain 



--Tongue 



Glottis 



Liver 

 ^Pancreas 



Diagram of the internal anatomy of a frog. 



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

 the large intestine. This in turn leads into the cloaca (Latin, 

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

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

 function 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 salivary 

 glands, which pour their juices into the mouth, the gastric glands 

 in the walls of the stomach, and the liver and pancreas, which 

 open into the intestine. (See Digestion, pages 352-365.) 



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- 



