V. THE SPECIAL ANATOMY OF THE FROG 



We have seen that organisms are composed of cells, that cells are combined 

 to form tissues, and tissues to make up organs. The organs are united in groups 

 called systems. We have already studied these systems in a general way, and 

 they are now to be studied in detail. 



A. THE DIGESTIVE SYSTEM 



1. Esophagus. Use your preserved frog. Cut through the tissues bound- 

 ing the anterior wall of the coelome to the left of the left lung, and turn the lung 

 and heart to the right. This exposes the esophagus. It extends from the end 

 of the mouth cavity, called the pharynx, to the stomach. A slight enlargement 

 usually marks the beginning of the stomach (Holmes, pp. 138-42). 



2. Stomach The end of the stomach continuous with the esophagus is 

 called the cardiac end; the opposite end is the pyloric end, and is marked by a 

 constriction, the pylorus. Slit open the stomach by a longitudinal slit from 

 cardiac to pyloric end. Note the longitudinal ridges, or rugae, in the lining of 

 the stomach, and compare with the lining of the esophagus and small intestine. 

 Examine the cut surface, and note that the layers of the stomach wall, which 

 have already been seen in microscopic section, can be distinguished with the 

 naked eye. The mucosa and submucosa appear as a single layer, which can be 

 separated from the underlying thick circular muscle layer; the longitudinal 

 muscle layer forms a thin white outer coat. 



3. The small intestine. The first part of the small intestine is called 

 duodenum, and it receives the common bile duct which carries the secretions of the 

 liver and pancreas. The remaining coiled part of the small intestine is the 

 ileum (Holmes, p. 148). 



4. The liver. The liver consists of the following parts: The left lobe is the 

 largest, and is divided by a deep fissure into an anterior part, which lies to the 

 left, and a posterior part which occupies the middle. The right lobe is not sub- 

 divided, but lies to the right of the median line extending somewhat dorsally. 

 The middle lobe of the liver is not visible ventrally unless the other lobes are 

 pushed apart. It then appears as a small squarish lobe extending far dorsally 

 and continuous with the posterior part of the left lobe. Between the right lobe 

 and the posterior part of the left lobe on the dorsal side is the green round gall 

 bladder (Holmes, p. 152). 



5. The pancreas. Turn the lobes of the liver forward and study the pancreas. 

 It is an irregular, branched, yellowish gland lying in the gastro-hepato-duodenal 



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