THE RESPIRATORY SYSTEM. 173 



8 1 and 82). The walls of these air sacs are very thin, 

 somewhat like the peritoneum. Over them course numer- 

 ous thin- walled capillaries, so that the carbon dioxid of 

 the blood passes out into the air as the oxygen passes 

 into the blood. Expiration is the process of forcing the 

 air out of the lungs which have been filled by an inspira- 

 tion chiefly effected by depressing the diaphragm and 

 elevating the ribs. The two processes together are 

 spoken of as a respiration. 



PRACTICAL QUESTIONS AND SUGGESTIONS. 



1. Of what four elements are the soft parts of the body largely com- 

 posed ? 



2. What waste* gas is formed in every part of the body exercised? 



3. Through what three channels do waste materials pass from the 

 -blood? 



4. Describe the manner in which the oxygen of the air reaches the 

 blood. 



5. Write a description of the pharynx. 



6. Bisect the larynx in the sagittal plane, make a drawing of the cut 

 aspect, and label all features. 



7. How many cartilaginous rings in the trachea and what is their 

 use? 



8. Describe as much of the pleura as can be seen in your specimen. 



9. Do the right and left bronchi have the same number of main 

 branches? 



10. Why do the air cells seldom become clogged? 



11. What muscles are largely used in respiration? 



12. Describe the hyoid bone as seen from your dissection. 



13. What part of this bone can you feel beneath your mandible? 



14. How does the carbon dioxid given off by the cells in the foot reach 

 the lungs? 



15. What causes the air to enter the lungs? 



16. Innate the lungs of a freshly killed animal by forcing air from 

 your lungs into a glass tube tied into its trachea. 



17. After retaining a full inspiration of air as long as possible, expire 

 it through a glass tube into the bottom of a two-liter bottle and insert 

 into the bottle a lighted splinter. 



18. Describe the pulmonary circulation. 



