578 MUSCLES OF EXPIRATION. [BOOK n. 



larynx (the details of which we shall have to deal with at a later 

 part of this work) is examined with the laryngoscope, it is frequently 

 seen that, while during inspiration the glottis is widely open, with 

 each expiration the arytenoid cartilages approach each other so as 

 to narrow the glottis, the cartilages of Santorini projecting inwards 

 at the same time. Thus, synchronous with the respiratory expan- 

 sion and contraction of the chest, and the respiratory elevation 

 and depression of the alae nasi, there is a rhythmic widening and 

 narrowing of the glottis. Like the movements of the nostril, this 

 respiratory action of the glottis is much more evident in laboured 

 than in tranquil breathing. Indeed in the latter case it is 

 frequently absent. The manner in which this rhythmic opening 

 and narrowing is effected will be described when we come to study 

 the production of the voice. Whether there exists a rhythmic 

 contraction and expansion of the trachea and bronchial passages, 

 especially the smaller and more exclusively muscular ones, effected 

 by means of the plain muscular tissue of those organs and 

 synchronous with the respiratory movements of the chest, is 

 uncertain. 



