CH. V] 



THE RESPIRATORY ORGANS 



67 



entering the lungs. The narrow slit -like opening from the 

 pharynx into the larynx is called the glottis. The larj^ix is the 

 enlarged first portion of the trachea. The latter organ which is 

 commonh' called the wind-pipe is kept open for the free passage 

 of air by a number of rings of cartilage Avhich are not quite 

 complete. After reaching the thorax the trachea divides into 

 the two bronchi which are pro\ided with similar cartilaginous 

 rings, and these bronchi after entering the hnigs divide into 

 smaller air tubes each of which in turn divides further into a 



i ^ 









0n 



Fig. 37. Longitudinal section of trachea (after Klein, from 

 Schafer). d ciliated epithelium, h basement membrane, 

 c and (/ mucous membrane, the superficial part with 

 vessels and lymphoid tissue, the deeper part with elastic 

 tissue, e submucous areolar tissue containing glands, fat 

 etc., /fibrous tissue, .'/ adipose tissue, // cartilage. 



number of bronchioles. In addition to the cartilaginous rings 

 the walls of the trachea and bronchi contain some muscular and 

 connective tissue and are lined internally by a ciliated epithelium. 

 The bronchioles \\iden out into the air sacs of the lungs, which 

 are arranged around the ends of the bronchioles like bunches of 

 grapes. The walls of the air sacs are very thin, and are in 



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