70 ELEMENTARY PHYSIOLOGY. 



produces vocal sounds of different pitch. Their 

 loudness depends upon the degree of force with which 

 the breath is forced through the glottis. But this is 

 not speech. To produce the articulate sounds of 

 language, the sounds which are made by the vocal 

 cords are very much modified and variously shaped 

 by the changing position of tongue and mouth, which 

 are produced in speaking. This is illustrated in 

 every word we speak, and you will find it to be an 

 interesting experiment to utter slowly the sounds 

 which compose some word, while noticing the changes 

 which you make in the position of your mouth and 

 tongue. 



OTTTLINE. 



THE HESPIRATORY SYSTEM. 



Lungs, very light and spongy, chiefly composed of 



air-cells. 



Trachea commonly called wind-pipe. 

 Larnyx upper part of trachea, and organ of the 

 WHAT ' voice. 



Air-passages through mouth and nose. 



Chief respiratory muscles the diaphragm and 



inter-costal muscles. 



f Lungs in middle of the chest. 

 J Trachea between throat and lungs. 

 ERE . < Diaphragm between chest and abdomen. 

 [^ Inter-costal muscles between the ribs. 



f To furnish oxygen to the blood. 



WHY / j rji Q 6X p 6 i impurities which come from venous 

 blood. 



