238 ANATOMY FOR NURSES [Chap. XIII 



which we call the voice. The pharynx, mouth, and nasal cavities 

 above the glottis act as resonating cavities, and by alterations in 

 their shape and size, they are ai)le to pick out and emphasize cer- 

 tain j)arts of the tones produced in the larynx. 



Differences between male and female voice. — At puberty in 

 the male, the larynx enlarges, giving rise to what is commonly 

 called Adam's apple. The increase in the size of the larynx causes 

 an increase in the length of the vocal cords. To this is due the 

 lower pitch of the voice in the male. 



THE TRACHEA 



The trachea, or windpipe, is a fibrous and muscular tube. 

 It measures about four and a half inches (112 mm.) in length, 

 and three-quarters of an inch (19 mm.) from side to side. It 

 extends down into the tliorax from the lower part of the larynx 

 to opposite the third thoracic vertebra, where it divides into 

 two tubes, — the two bronchi, — one for eacli lung. 



The walls are strengthened and rendered more rigid by hoops 

 of cartilage embedded in the fibrous tissue. These hoops are 

 C-shaped and incomplete behind, the cartilaginous rings being 

 completed by bands of plain muscular tissue where the trachea 

 comes in contact with the oesophagus. Like the larynx, it is 

 lined by mucous membrane, and has a ciliated epithelium upon 

 its inner surface. The mucous membrane, which also extends 

 into the bronchial tubes, keeps the internal surface of the air- 

 passages free from impurities ; the sticky mucus entangles par- 

 ticles of dust and other matters breathed in with the air, and the 

 incessant movements of the cilia continually sweep this dirt- 

 laden mucus upward and outward. 



THE BRONCHI 



The two bronchi, into which the trachea divides, differ slightly; 

 the right bronchus is shorter, wider, and more nearly horizontal, 

 the left bronchus is longer, narrower, and more nearly vertical. 

 They enter the right and left lung, respectively, and then break up 

 into a great number of smaller branches which are called the bron- 

 chial tubes, or bronchioles. The two bronchi resemble the trachea 

 in structure ; but as the bronchial tubes divide and subdivide 



