ANATOMY AND PHYSIOLOGY 5 



a pipette or handle of a needle into the anus. Then, with a scalpel, 

 cut through the skin and thin sheet of muscle in the mid-line between 

 the bases of the hind legs. A somewhat translucent region will then 

 be seen separating the muscles of the legs in the mid-line. Carefully 

 controlling your scalpel, cut directly down through this region, without 

 injuring the urinary bladder or the posterior end of the digestive 

 tract. Now separate the legs widely and pin them down. Find where 

 the urinary bladder is attached at its anterior end and free it from 

 its membranes. Turn the bladder to one side and observe that the large 

 intestine narrows posteriorly and is continuous with a slender tube, 

 the cloaca, which communicates with the outside by way of the anus. 

 The neck of the bladder is attached to the ventral surface of the 

 cloaca and should not be injured. 



C. The Digestive System 

 Exercise 5. — The Mouth Cavity. 



(a) The digestive system consists of the digestive tract and the 

 attached digestive glands. The mouth cavity is the most anterior 

 region of the digestive tract and, in addition, is a part of the respira- 

 tory system. Only the structures which are directly related to the 

 digestive system of the frog will be described now. Open the mouth 

 wide, cutting a little at the angles of the jaws if necessary. Locate 

 the teeth by rubbing with a finger. Are they found on both jaws? 

 Examine with a handlens. Which way do the teeth slant? How can 

 the frog use its teeth? Observe two patches of teeth on the roof of 

 the mouth; these are the vomerine teeth, so called because they are 

 attached to a bone known as the vomer. Posteriorly, the mouth 

 cavity narrows and is continuous with the esophagus, which leads to 

 the stomach. How does the place of attachment of the tongue differ 

 from that in man? How does the frog use its tongue? 



Exercise 6. — The Ccelomic Organs of the Digestive System. 



(b) Identify again the remaining parts of the digestive tract, 

 namely, the esophagus, stomach, small intestine, large intestine, and 

 cloaca (Fig. 9). Notice the transparent, sheetlike mesentery which 

 is attached to the stomach and intestine. Understand from charts or 

 diagrams the relation between the mesentery and the parietal peri- 

 toneum, which is the innermost layer of the body wall and lines the 

 ccelom, and the visceral peritoneum, which covers all organs that are 

 suspended in the ccelom (Fig. 10). Observe the blood vessels in the 

 mesentery. What are the functions of the mesentery? The visible 



