RESPIRATION AND ENERGY IN MAN 



125 



shown in Fig. 39), and then through the two nasal passages 

 it enters the throat cavity. In the lower region of the throat 

 is the slit-like glottis opening, 

 through which the air enters 

 the larynx or voice box. The 

 latter, commonly known as 

 "Adam's apple," projects some- 

 what on the front of the neck. 

 Below the larynx is the contin- 

 uation of the windpipe, which, 

 just above the level of the heart, 

 divides into two main branches 

 (Fig. 40), one of which supplies 

 air to the right lung, the other 

 to the left limg. Within the 

 lungs these tubes branch off 

 into a vast number of very 

 small pipes, called bronchial 

 tubes. The finest divisions of 

 these tubes open into extremely 

 thin-walled air sacs (Fig. 41). 



177. The nose cavity. — The 

 openings into the nasal passages 

 are guarded by a mass of pro- 

 jecting hairs, by means of which 

 a considerable amount of dust 

 is kept from entering the lungs. 

 The nose itself is lined by mu- 

 cous membrane which covers 

 the whole interior of the nasal 

 chambers. Its mucous secretion collects most of the dirt 

 and germs that hs,ve passed the hairs in the nostrils. 



Fig. 39, — Longitudinal section of 

 head and neck showing food and 

 air passages. 



a = vertebral column. 



b = gullet. 



c = windpipe. 



d = larynx. 



'e = epiglottis. 



/ = uvula. 



g = opening of left Eustachian tube. 



h = opening to tear duct. 



k = tongue. 



I = hard palate. 



