CHAPTER IX. 

 THE LUNGS AND RESPIRATION. 



Besides the heart and the great vessels the chest 

 contains the lungs, the chief organ of respiration, which, 

 with the rest of the respiratory system, will now be 

 treated. The nose and mouth, through which the air 

 first enters the body, have already been spoken of. 

 From them the air passes through the larynx to the 

 trachea, thence to the bronchi, and so to the lungs, 

 where the supply of oxygen for the tissues is taken from 

 the air by the hemoglobin, of the blood. 



The Larynx. The larynx lies in front of the pharynx 

 at the upper and fore part of the neck, where it causes 

 a considerable projection, k'lown as Adam's apple. 

 It is a triangular box, base up, flattened at the back, 

 in front, and at the sides, but becoming cylindrical be- 

 low. Above it opens into the bottom of the pharynx 

 and below into the trachea. It is lined with mucous 

 membrane. Its opening at the base of the tongue is 

 closed during swallowing by a little door-like valve of 

 fibre-cartilage, the epiglottis, to pre , ent the" entrance 

 of food. 



Nine cartilages go to make up the larynx, of which 

 the most important are the thyroid and cricoid car- 

 tilages and the epiglottis already mentioned. The 

 thyroid is the largest and is open behind, its two alae 

 or wings meeting in an acute angle in front and forming 

 the Adam's apple, always more prominent in the male 

 than in the female. It is attached above to the hyoid 

 bone and has cornua or horns on either side, top and 

 bottom. The cricoid or ring-like cartilage resembles 

 a seal ring with the stone placed posteriorly. It is 

 stronger than the thyroid and forms the lower part of 



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