CHAP, ii.] RESPIRATION. 549 



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. 



