The Frog: A Representative Vertebrate 61 



spherical spleen. This latter organ is dark red in color due to the 

 amount of blood stored in it. 



Dorsal to the ventral visceral organs are the sex organs. In the 

 female there are two ovaries. At times these are very large and filled 

 with dark spherical eggs. When this condition occurs, the ovaries may 

 fill all the spaces of the coelom and even displace the other organs. The 

 female also has two twisted oviducts that are located along the dorsal 

 wall of the coelom. 



The male has two small dorsal testes. Each one has jat bodies 

 connected to it. These are conspicuous yellow structures that are 

 very much branched. 



Dorsal to the sex organs and lying back of the peritoneum is a 

 pair of dark, elongate bodies, the kidneys. The urinary ducts from 

 the kidneys, the ducts that carry the sex products, and the large in- 

 testine all open into a posterior chamber, the cloaca. The cloaca in 

 turn opens to the outside through the anus. Opening from the cloaca 

 is a small ventral, thin-walled sac, the urinary bladder. 



THE DIGESTIVE SYSTEM 



The digestive system (Fig. 15) of the frog is essentially a tube 

 modified in different regions for particular functions. The tract be- 

 gins in the frog's mouth where food is first taken in. The tongue and 

 teeth play an important role in capturing and securing the food. Swal- 

 lowing of the food is made possible by the raising of the floor of the 

 mouth. During swallowing the eye balls are depressed and help to 

 push the food back into the pharynx. From the pharynx, the food 

 passes through the short esophagus into the stomach. 



The anterior end of the stomach is known as the cardiac region 

 due to its proximity to the heart. The posterior end is the pyloric 

 region, and is separated from the small intestine by the muscular pyloric 

 valve. When food is sufficiently digested, it passes through this valve 

 into the small intestine. The anterior part of the small intestine ex- 

 tending from the stomach to the first backward curve is known as 

 the duodenum. The remainder of the small intestine is much coiled 

 and is called the ileum. Within the small intestine, digestion is com- 

 pleted and the food is absorbed. Posterior to the small intestine is 

 the large intestine or rectum which opens into the cloaca. Undigested 

 remains of food pass into the cloaca from where they are expelled 

 as jeces. 



