CHAP. V 



RESPIRATION 



finally, thousands of little air pouches, or sacs of the 

 lungs. 



These tubes are made of a firm substance like gristle, 

 called cartilage, which gives them their shape and holds 

 them open so that we can 

 breathe easily day and 

 night. The cartilage is 

 covered with muscles and 

 connective tissue. The 

 tubes are all lined with 

 a moist, delicate, velvety 

 lining called a mucotis 

 membrane. The differ- 

 ent organs of the air 

 passages are alike in 

 their general structure, 

 but they differ much in 

 size and shape. 



45. The Nose. This 

 diagram shows how large 

 and irregular is the space 

 in the nose through 

 which air passes. That 

 is for the purpose of 



FIG. 13. Showing the nose and mouth. 

 (From Huxley's " Elementary Physi- 

 ology ") : a, spinal column ; b, food 

 passage or gullet ; c, windpipe ; d, voice 

 box; e, epiglottis; / soft palate; 

 g, Eustachian tube ; h, opening of the 

 tear duct; i, hyoid bone; k, tongue; 

 /, hard palate ; m, n, bones of the skull ; 

 o, p, q, turbinate bones of the nose. 



spreading the air out 



over a large area, so that 



it may be changed to the 



temperature of the body 



before going into the delicate little air sacs of the lungs. 



The moist mucous membrane of the nose picks out dust 



