14 THE FROG 



Lift the liver and observe: 



58. The lungs are brown, more or less shriveled struc- 

 tures at the cephalic end of the abdominal cavity. 

 In the fresh specimen they may be demonstrated by 

 inserting the blow pipe into the glottis (21) and in- 

 flating them. The blood vessels then apparent are 



59. the pulmonary arteries and veins. 



60. The tube leading from the glottis to the lungs is the 

 larynx. Probe it. 



Add the lungs to Drawing 4, and show the larynx by 

 dotted lines, 



5. The Visceral Arteries 



The digestive system must be removed in order to see the 

 underlying structures more clearly. But before doing this 

 it is advisable to identify the, arteries and veins associated 

 with these structures. In an uninjected specimen the arter- 

 ies, carrying blood away from the heart, are usually empty 

 and colorless, while the veins, which carry blood toward 

 the heart, are congested and therefore reddish brown in 

 color. In singly injected specimens the arteries are filled 

 with a colored starch mass, while the veins are filled with 

 blood. In doubly injected specimens, the portal systems 

 (76-80) are injected with a contrasting color mass. Triply 

 injected frogs have a mass of a third color injected into 

 the remaining veins. 

 Identify the following arteries without cutting anything. 



61. Tip the liver to one side and lift the stomach, turn- 

 ing it to your left, and in the mesentery proper (51) 

 in front of the spleen (57) observe the coeliaco- 

 mesenteric artery. It arises from the dorsal aorta 

 (139) and soon divides into two branches (62 and 

 69). 



