212 



STUDIES IN PHYSIOLOGY 



cous secretion collects most of the dust and germs that have 

 passed the hairs in the nostrils. Beneath this thin lining 

 are countless branches of blood vessels, which act like 

 small hot-water pipes to warm the air before it reaches the 

 throat cavity. 



FIG. 99. The Windpipe and the Lungs. 



The Throat and Larynx. The action of the epiglottis has 

 been already described in connection with the digestive ap- 

 paratus (see p. 85). Except when something is being swal- 

 lowed, the glottis is always open, thus allowing a free passage 

 for the air from the throat, through the larynx, into the wind- 

 pipe. All the varied sounds of articulate speech which, more 

 than anything else, distinguishes man from other animals, 

 are made in the larynx. The structure and action of this 

 wonderful mechanism will be discussed in a later chapter 

 (see chapter XIV). 



The Windpipe and its Branches. The windpipe and its 

 branches are kept open by the incomplete rings of cartilage 



