I 82 VERTEBRATES 



amine the contents of the crop. What do you find? What 

 does it show concerning the food of the pigeon? 



(3) Observe the base of the tongue. Do you find 

 a bone there? What is its shape? Through an opening in 

 this, find the trachea. Is it open or closed ? In life is it 

 open? When the bird swallows its food, does it go di- 

 rectly into the esophagus or does it pass first over the 

 trachea? Do you see anr apparatus there to prevent the 

 food from passing into the trachea? Insert a tube into 

 the trachea and inflate the lungs. Do the entire lungs 

 come up at once, or do they expand part at a time? What 

 part first? Observe the trachea from the throat down to 

 the lungs. Is it the same size all the way down? Where 

 is it largest? The enlargement at the top is called the 

 larynx, and the one just above the lungs is called the 

 syrinx. The latter is the place where the organ of voice 

 in birds is located. The divisions of the trachea are called 

 bronchi. Are they the same size? 



(4) Study the pear-shaped organ, the heart. Carefully 

 lift up the lobes of the lungs and see if there is any con- 

 nection between the lungs and the heart. Do you find 

 blood vessels running to and from the heart? How can 

 you tell which vessels run to the heart and which ones 

 run from the heart ? Find the pulmonary artery and pulmo- 

 nary vein. Do you find the great aorta? Follow it as far 

 as you can, noting the branches that go out from it. Find 

 the venae cavae — the large veins that gather the blood from 

 all parts of the body, and bring it back to the heart. On 

 which side of the body is it? Why? 



(5) With a small stout cord tie in two places each of 

 the vessels carrying blood to or from the heart, as far from 



