240 



RESPIRATION. 



noticed that the opening of the glottis is very much smaller than 

 the cavity of the trachea below. The glottis itself presents the 

 appearance of a narrow chink, while the passage for the inspired 

 air widens in the lower part of the larynx, and in the trachea 

 constitutes a spacious tube, nearly cylindrical in shape, and over 

 half an inch in diameter. We have found, for instance, that in 

 the human subject the space included between the vocal chords 

 has an area of only 0.15 to 0.17 square inch ; while the calibre 

 of the trachea in the middle of its length is 0.45 square inch. 

 This disproportion, however, which is so evident after death, does 

 not exist during life. While respiration is going on, there is a 

 constant and regular movement of the vocal chords, synchronous 

 with the inspiratory and expiratory movements of the chest, by 



Fig. 73. 



Fie. 74. 



HUMANLAKYNX, viewed from above 

 in its ordinary post-mortern condition. a, 

 Vocal chords, b. Thyroid cartilage, cc. Ary- 

 tenoid cartilages, o. Opening of theglottis. 



The *amc, with the glottis opened by 

 separation of the vocal chords. a. Vocal 

 chords. 6. Thyroid cartilage, cc. Aryte- 

 noid cartilages, o. Opening of the glottis. 



which the -size of the glottis is alternately enlarged and diminished. 

 At every inspiration, the glottis opens and allows the air to pass 

 freely into the trachea ; at every expiration it collapses, and the 

 air is driven out through it from below. These movements are 

 called the " respiratory movements of the glottis." They correspond 

 in every respect with those of the chest, and are excited or retarded 

 by similar causes. Whenever the general movements of respiration 

 are hurried and labored, those of the glottis become accelerated and 

 increased in intensity at the same time ; and when the movements 

 of the chest are slower or fainter than usual, owing to debility, 

 coma, or the like, those of the glottis are diminished in the same 

 proportion. 



