90 THE HOESE IN HEALTH AND DISEASE 



single, and the arytenoids, which are paired. These cartilages 

 articulate by true joints, and are moved by means of two systems 

 of muscles — (1) the extrinsic group, which find one attachment to 

 the larynx and the other to some point outside the organ; (2) the 

 intrinsic group, which pass between the different cartilages. 

 The interior of the larynx shows two vocal cords stretched from 

 the lateral walls; the opening between these cords is called the 

 glottis. When the vocal cords vibrate, sounds are produced. 

 On each side of the larynx is a pocket-like depression of mucous 

 membrane, known as the ventricle. 



The trachea connects the larynx with the lungs. It is formed 

 of fifty to fifty-five rings of cartilage, attached to each other by a 

 fibro-elastic membrane. The rings are not complete circles, for 

 their two ends overlap superiorly. Through these rings the organ 

 is kept permanently open and is made flexible. The average 

 caliber is about 2| inches. At the entrance to the lungs the trachea 

 divides to form the bronchi. 



The bronchi are two in number, the right being the larger. 

 Together with the pulmonary vessels they form the "root of the 

 lung." They are continued posteriorly by the smaller bronchial 

 tubes, which ramify throughout the lungs. 



The lungs are designated right and left. They practically fill 

 the thoradc cavity. Three systems of tubes embedded in con- 

 nective tissue are found in the lungs: (1) the ramifications of the 

 bronchi; (2) the pulmonary arteries; (3) the pulmonary veins. 

 For description, each lung may be considered as having a base, an 

 apex, and two surfaces. The base is situated against the dia- 

 phragm, which conforms to its shape. The apex lies opposite the 

 first and second ribs. The external surface is convex and adapted 

 to the ribs and the intercostal muscles. The internal surface is 

 irregular and less extensive. In the living animal the lung is of a 

 pinkish color, due to the blood in its tissues. It becomes pale gray 

 in the bled subject, while the unbled lung is dark red. The lung is 

 soft, spongy, and very elastic. It floats in water. 



Minute Structure of Trachea, Bronchi, and Lungs. — A histo- 

 logic examination of the trachea shows it to be lined with a mucous 

 membrane composed of ciliated epithelium, interspersed with 

 mucous cells. The former actively wave backward and forward 

 during life and work the dust-ladened mucus toward the mouth. 

 The bronchi and bronchial tubes have flakes of cartilage rather 



