RESPIRATION AND THE VOICE. 127 



7, A tree is another illustration of a lung. The trunk 

 represents the bronchus, or great air-tube, which enters 

 the lung. The branches represent the small (bronchial) 

 tubes. The leaves represent the air-cells. If we suppose 

 tubes to be laid along the trunk and branches, constantly 

 dividing, until finally each leaf is covered with a net- 

 work from which other tubes come off, and run back 

 toward the trunk, uniting as they go, we shall have 

 again something like a lung, with the fibrous tissue, 

 the nerves, and lymphatic vessels and glands, still to be 

 added. 



8, Do not suppose, however, that, on examining a lung, 

 you would see all these tubes and cells. On the contrary, 

 you would see only a light-gray or pinkish substance, 

 mottled with black spots, very smooth on the outside. If 

 you were to cut into it, it would look a little like fat. 

 The cells, and many of the tubes, are so small, that only 

 very careful study with the microscope has given us our 

 knowledge of them. 



THE AIR-PASSAGES. 



SECTION III. 1, The passages by which the air gets 

 to the lungs, are, 



The nose, The larynx, ) 



The mouth, The trachea, j (*WH*PI*)- 



The throat, The bronchi. 



2, The nose is the true breathing passage. It consists 

 of two parts: 



i. The triangular projection from the face. This is 

 partly cartilage, which is flexible, and partly bone. 



$. The cavities behind, called the nasal fossse. There 

 are two of these, corresponding to the two nostrils, sepa- 



