22 



THE RESPIRATORY SYSTEM. 



The organs of respiration are the nostrils, nasal chambers, 

 jjharijnx, larynx, trachea, bronchii, bronchial tubes, and air 

 cells, which are all lined, except the air cells, with mucous mem- 

 brane. The nostrils are two, right and left, oblong openings 

 situated in the anterior part of the face, at the commencement 

 of the nasal chambers. The nasal chambers extend from the 

 nostrils to the pharynx and are separated from each other by the 

 cartilaginous septum nasi; each chamber is divided by the tur- 

 binated bone into three passages, and all are lined with a deli- 

 cats, pale rose-colored membrane, the Schneiderian membrane, 

 which is continuous with the skin of the nostrils. 



The i^harynx is a muscular, membranous cavity, common to 

 the digestive and respiratory canals, somewhat cylindrical in 

 form, and extending backward to the larynx and the esophagus. 



The larynx is a complex musculo-cartilaginous valve, situated 

 at the anterior part of the trachea or windpipe. It gives passage 

 to air and at the same time is the organ of voice. The anterior 

 extremity opens into the pharynx and the posterior into the 

 trachea; it lies in the posterior part of the maxillary space and 

 is commonly known as "Adam's apple." 



The trachea, or windpipe, is a cylindrical, flexible tube consist- 

 ing of a series of incomplete cartilaginous rings, numbering from 

 forty to fifty, according to the length of the neck. It succeeds 

 the larynx, runs down the neck, enters the thorax or chest, and 

 terminates at the base of the heart where it branches into the 

 right and left bronchii, which enter the limgs and subdivide into 

 branches termed bronchial tubes. These, becoming gradually 

 smaller as they divide, finally terminate in air cells. The entire 

 ramification, when isolated, has the appearance of a tree, the 

 trachea being the trimk, the hronchii and bronchial tubes the 

 branches, and the air cells the leaves. These structures are 

 accompanied throughout by arteries, veins, and nerves. 



The thorax, or chest, is formed by the ribs, sternum, and bodies 

 of the dorsal vertebrae, the intercostal muscles, and the dia- 

 phragm. It contains the lungs, heart, large blood vessels, the 

 trachea, esophagus, and a number of nerves. The thorax is 

 lined by two serous membranes, the right and left plenra, each 

 pleura lining one-half the thorax and enveloping the structures 

 contained therein. 



