278 



RESPIKATION. 



respiration is going on, there is a regular movement of the vocal chords, 

 synchronous with the inspiratory and expiratory movements of the 

 chest, by which the size of the glottis is alternately enlarged and dimin- 

 ished. At inspiration, the glottis opens and allows the air to pass freely 



Fig. 96. 



HUMAN LARVNX, viewed from above 

 in its ordinary post-mortem condition. a. 

 Vocal chords, b. Thyroid cartilage, c, c. 

 Arytenoid cartilages. o. Opening of the 

 glottis. 



The same, with the glottis opened by sepa- 

 ration of the vocal chords. a. Vocal chords. 

 b. Thyroid cartilage, c, c. Arytenoid carti- 

 lages, o. Opening of the glottis. 



Fig. 98. 



into the trachea ; at expiration it collapses, and the air is driven out 

 from below. These movements are 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 move- 

 ments of respiration are hurried, those of the glottis become accelerated 



at the same time ; and when the movements 

 of the chest are slower or fainter than 

 usual, those of the glottis are diminished 

 in the same proportion. 



In the respiratory motions of the glottis, 

 as in those of the chest, the movement of 

 inspiration is an active one, and that of ex- 

 piration passive. In inspiration, the glottis 

 is opened by contraction of the posterior 

 crico-arytenoid muscles. These muscles 

 originate from the posterior surface of the 

 cricoid cartilage, near the median line ; and 

 their fibres, running upward and outward, 

 are inserted into the external angles of the 

 arytenoid cartilages. By the contraction 

 of these muscles, during the movement of 

 HUMAN LARYNX, POSTERIOR inspiration, the arytenoid cartilages are 



VIEW. a. Thyroid cartilage, b. ,. . * .. . ,. 



Epiglottis, c, c. Arytenoid carti- rotated upon their articulations, so that 

 lages. d. Cricoid cartilage, e, e. their anterior extremities are carried out- 

 Posterior crico-arytenoid muscles. , . , . t , i 



/. Trachea, ward, and the vocal chords stretched and 



