THE PIGEON. 113 



called the muscular stomach. Note also its tough 

 lining ; examine the contents of the gizzard ; why 

 does the gizzard have such a thick coat of muscle ? 

 do all birds have this kind of gizzard ? 



17. In front of the liver is the heart, in a thin sac, the 

 pericardium. Cut through its posterior wall, and 

 turn the heart forward, to see the dark vein, the 

 inferior vena cava, running to it from the liver ; pull 

 the heart backward, to see the whitish arteries run- 

 ning forward from it. The main artery runs forward, 

 and turns to the right before going backward, while in 

 man the corresponding artery turns to the left. Prick 

 a hole in one of the large veins near the heart; insert 

 the point of a blowpipe, and inflate the heart ; its red, 

 conical part is composed of the ventricles; the dark 

 base is made up of the two auricles. Tie a thread 

 around the veins at the anterior and posterior borders 

 of the liver, and cut this organ away. 



18. On each side are the pink lungs. Pick away the thin 

 membranes bordering the outer hinder borders of the 

 lungs ; look for holes through which the lungs com- 

 municate with the abdominal air-sacs ; look for the 

 trachea. Remove the lungs, not failing to see how 

 closely they are attached to the back, being indented 

 by the ribs. 



19. In the hinder part of the body-cavity are the dark- 

 colored, irregular kidneys. Tear them away, observ- 

 ing how they are composed of several lobes, which fit 

 into the hollows of the pelvis. After removing the 

 kidneys, observe the white nerves extending outward 

 from the sides of the spinal column to pass to the 

 thighs. 



