BREATHING 
445 
vessels are adapted to the passage of oxygen into the 
blood. 
The lungs of man, then, consist of two large bronchial 
air tubes, many branches of the bronchi, air cells, blood 
vessels, and a few nerves, all bound up into two definite 
bodies (Figure 392). 
The voice box or larynx (lar'inks) is found just below the 
opening into the windpipe and is called “ Adam’s apple.” 
The larynx is formed by several large pieces of cartilage 
Figure 394 . — Voice Box or Larynx. 
lined with a mucous membrane. On the inside of the larynx 
project two folds of elastic tissue which are called the vocal 
cords. 
354. Breathing. — The lungs are elastic and can be 
squeezed like a sponge. Inspiration is the term applied 
to the taking of air into the lungs, and expiration to the 
forcing out of air. When air is drawn into the lungs, the 
chest expands, and the diaphragm (Figure 395), the horizontal 
muscle which divides the lung cavity from the abdomen, is 
drawn down. Thus the chest cavity is enlarged and air is 
sucked into the lungs. In expiration the air passes out gently. 
When we breathe naturally, only a small part of the air 
in the lungs is exchanged at each inspiration and expiration, 
