FBOGS AND THEIR RELATIVES 103 



b. If the nostrils are now open will the air move into 



the mouth cavity or out? Why? 

 2. When the floor of the mouth is raised — 



a. Will the size of the mouth cavity be increased or 



decreased ? 

 h. Will the pressure of the air in the mouth cavity 



be increased or decreased ? 



c. If .both the nostrils and the glottis are now open, 



in what directions will air be forced ? 



d. What causes the slight outward movements of 



the sides of the trunk in the region of the 

 lungs ? 



F. How the lungs are fitted for breathing organs. (Suggested 



as home work.) 



When the lungs are inflated (see B, 4 above) 

 they look like bags (Fig. 80). The lungs are 

 hollow, and their walls are composed of thin 

 material. In these membranous walls are thin- 

 walled blood vessels known as capillaries. The 

 heart forces blood that has come from the 

 body into these capillaries of the lungs, and 

 then back to the heart. Bearing in mind that 

 respiration in animals is essentially the same 

 as in plants (P. B., 82) — 



1. State what waste substance the blood brings to the 



lungs to be given off from the capillaries. 



2. What gas will the blood in the capillaries take up 



from the air in the lungs ? 



3. How are the walls of the lungs and of the capillaries 



of the lungs fitted by structure to make this 

 interchange of gases possible ? 



G. Food-getting. 



To the Teacher. — Select a number of as large pre- 

 served or freshly killed frogs as you can get. Open 

 the jaws as far as possible and keep them in this 

 position by means of small pieces of wood. 



