SECTION III. THE VISCERAL CAVITY 



1. The Viscera Undisturbed 



Place the frog on the dissecting board, ventral side up, and 

 with the head away from you. Holding the skin away from 

 the underlying body wall with forceps, make an incision 

 through the skin only from the pelvic girdle to the lower 

 jaw. Carefully lift the skin with forceps and note the 

 following. 



25. Subcutaneous lymph spaces are separated by the 

 points of attachment between the body wall and the 

 skin. In life they are filled with a colorless fluid, the 

 lymph. 



26. On the inner surface of the skin are the cutaneous 

 arteries and veins, by means of which cutaneous 

 respiration is performed. Make out the points at 

 which these enter the underlying tissues. 



27. There is an abdominal vein, showing through the 

 muscles of the body wall on the mid-line. 



Cut through the body wall slightly to one side of the ab- 

 dominal vein. Lift the body wall away from the under- 

 lying organs with your forceps and take care not to cut 

 across any blood vessels. Use heavy scissors to cut across 

 the pectoral girdle. Complete this incision to the same 

 limits attaified in the skin incision. Note the following 

 structures without disturbing their position. 



28. At the cephalic end is the heart, underneath the 

 pectoral girdle. 



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