118 



RESPIRATION. 



entire epiglottis, which was observed in the Bellevue Hospital, the patient experienced 

 slight difficulty in swallowing, from the passage of little particles into the larynx, which 

 produced cough. This case seemed to show that the presence of the epiglottis, in the 

 human subject at least, is necessary to the complete protection of the air-passages in 

 deglutition. 



Passing down the neck from the larynx toward the lungs, is a tube, from four to four 

 and a half inches in length and about three-quarters of an inch in diameter, which is 

 called the trachea. It is provided with cartilaginous rings, from sixteen to twenty in 

 number, which partially surround the tube, leaving about one-third of its posterior por- 

 tion occupied by fibrous tissue mixed with a certain number of non-striated muscular 

 fibres. Passing into the chest, the trachea divides into the two primitive bronchi, the 

 right being shorter, larger, and more horizontal than the left. These tubes, provided, like 

 the trachea, with imperfect cartilaginous rings, enter the lungs, divide and subdivide, until 

 the minute ramifications of the bronchial tree open directly into the air-cells. After 

 penetrating the lungs, the cartilages become irregular and are in the form of oblong, 

 angular plates, which are so disposed as to completely encircle the tubes. In tubes of 

 very small size, these plates are less numerous than in the larger bronchi, until, in tubes 

 of a less diameter than T V of an inch, they are lost altogether. 



FIG. 30. Lungs, anterior view. (Sappey.) 



1, upper lobe of the left lung ; 2, lower lobe ; 3, fissure ; 4. notch corresponding to the, apex of the heart ; 5. 

 pericardium; 6, upper lobe of the right lung; 7, middle lobe; 8, lower lobe; $, fissure ; 10, fissure; 11, 

 diaphragm ; 12, anterior mediastinum ; '13, thyroid gland ; 14. middle cervical aponeurosis ; 15, process of attach- 

 ment of the mediastinum to the pericardium; 16, 16, seventh ribs; 17, 17, transversales muscles; 18, linea alba. 



