THE RESPIRATORY APPARATUS 



279 



living tissues are the seat of those combustion processes which consume 

 oxygen and produce carbon dioxide. These processes occur in all parts of 

 the body in the substance of the living active tissues, and are the true respira- 

 tory processes, sometimes called internal or tissue respiration. 



THE RESPIRATORY APPARATUS. 



The object of the respiratory movements being the interchange of gases 

 in the lungs, it is necessary that the atmospheric air shall pass into them 

 and that the changed air shall be ex- 

 pelled from them. The lungs are 

 contained in the chest or thorax, which 

 is a closed cavity having no communi- 

 cation with the outside except by 

 means of the respiratory passages. 

 The air enters these passages through 

 the nostrils or through the mouth, 

 thence it passes through the larynx 

 into the trachea or windpipe, which 

 about the middle of the chest divides 

 into two tubes, the bronchi, one to 

 each lung. 



The Larynx. The upper part of 

 the passage which leads exclusively 

 to the lung is formed by the thyroid, 

 cricoid, and arytenoid cartilages, 

 figure 218, and contains the vocal cords, 

 by the vibration of which the voice is 

 chiefly produced. These vocal cords 

 are ligamentous bands covered with 

 mucous membrane and attached to 

 certain cartilages which are capable of 

 movement by muscles. By their ap- 

 proximation the cords can entirely 

 close the entrance into the larynx; but 

 under ordinary conditions the entrance 

 of the larynx is formed by a more or 

 less triangular opening between them, 

 called the rima glottidis. Projecting 

 at an acute angle between the base of 

 the tongue and the larynx to which it 



is attached, is a leaf- shaped cartilage the trachea, showing sixteen cartilaginous 

 . - ^. . rings; b, the right, and b', the left bronchus. 



FIG. 218. Outline Showing the General 

 Form of the Larynx, Trachea, and Bronchi, 

 as seen from Before, h, The great cornu 

 of the hyoid bone; e, epiglottis; /, superior, 

 and t r , inferior cornu of the thyroid carti- 

 lage; c, middle of the cricoid cartilage; tr, 



.,,._,, . - ^. . 



with its larger extremity free. This 



(Allen Thomson.) 



