THE RESPIRATORY SYSTEM 14$ 



The trachea is a membranous tube with cartilaginous 

 rings, which, upon its entrance into the chest, divides into 

 right and left bronchi. It is about 5 inches in length and 

 f inch in diameter. 



The lungs are so constructed as to receive a very large 

 amount of atmospheric air by the most extraordinary 

 mechanism. The entire extent of the respiratory surface 

 in the lungs has been estimated at 100 times that of the 

 cutaneous surface of the body; the blood in the pul- 

 monary capillaries, distributed in this large surface, and 

 being in immediate proximity to the air in the cavity of the 

 vesicles, is placed under the most favorable conditions for 

 its rapid and complete oxygenation. 



Bach pulmonary vesicle is covered upon its exterior 

 with a close network of capillary blood-vessels, which 

 penetrate into the septa between it and the adjacent 

 cavities, and which are thus exposed on both sides to the 

 influence of the atmospheric air. The walls of the 

 vesicles, as well as the interspaces between the lobules, are 

 supplied with an abundance of elastic tissue, which gives 

 to the pulmonary structure its property of resiliancy. 



Thus the oxygen of the air combines with the blood, 

 while a portion of the deleterious material also takes on 

 new combinations and passes off with the carbon dioxid. 



THE LUNGS 



The lungs are situated in the uppermost portion of the 

 chest, and, when inflated, completely fill that cavity. 

 They are of irregular shape and two in number one right 

 and the other left. Bach is enclosed in a sac formed by 

 the pleural membrane; that portion of the thoracic cavity 

 between the right and left pleural sac is known as the 

 mediastinum. The right lung is the larger of the two, and 

 is divided by two fissures into three lobes, whereas the 

 left lung is divided by one fissure into two lobes. 

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