CHAPTER V 

 THE RESPIRATORY SYSTEM 



THE ORGANS OF RESPIRATION 



The respiratory apparatus comprises the nasal cavity, the 

 pharynx, the larynx, the trachea, the bronchi, and the lungs. 

 The lungs are the essential organs of respiration; all the other 

 parts simply act as passages for air to and from them. Two 

 accessory structures, the pleura and diaphragm, will also be briefly 

 described in this chapter. 



The nasal cavity is a cylindric passage divided by the cartil- 

 aginous nasal septum into symmetric halves. Its walls are made 

 up of portions of all the facial bones except the mandible and 

 hyoid. In the living animal it is lined by mucous membrane, 

 which is continuous at the nostrils with the skin and posteriorly 

 with the lining of the pharynx. The nostrils are supported and 

 kept dilated by two comma-shaped alar cartilages attached to the 

 nasal septum. A blind, pouch-like diverticulum of the skin, 

 called the false nostril, lies above each nostril. The external 

 opening of the nasolacrimal duct may be seen on the floor of the 

 nasal cavity about 2 inches from the nostril when the latter is 

 dilated. The two turbinated bones divide each half of the nasal 

 cavity into three passages or meatuses — the superior, middle, and 

 inferior. Of these, the inferior meatus is the largest, and is the 

 direct communication between the nostrils and the pharynx. 

 It runs along the upper surface of the palatine process of the 

 maxilla. 



The pharynx has been described with the organs of the digestive 

 system, as it is common to both the digestive and the respiratory 

 tracts. 



The larynx is a short, tube-like apparatus placed between the 

 pharynx and the anterior end of the trachea. It regulates the 

 amount of air passing to and from the lungs and prevents the 

 aspiration of foreign bodies. It is made up of five pieces of car- 

 tilage — the cricoid, the thyroid, and the epiglottis, which are 



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