THE EBSMEATOEY SYSTEM. 



213 



each bronchus, are the special agents of song. They sound as 

 does an oboe or any other reed instrument. Their action is 

 modified by special muscles which act on adjacent parts. These 

 are called extrinsic muscles if they pass between the respiratory 

 tube and parts external to it. They are called intrinsic muscles 

 if they only pass from one part of the respiratory tube (trachea 

 and bronchi) to another. Generally there are two paii-s of 

 " extrinsic " muscles, passing from the clavicles, or the sternum. 



Kg. 164. 



MtrscLEs OP Syhinx of Raven. 



A. Front view of Byrinx. B. Side view. 



a&f, Inferior bifurcations of the lateral tracheal muecle (fracheo-laferalis) 

 going to the third bronchial half-ring; b, shorter muecle (broncho- 

 trachealis brevis) inserted into posterior end fef second bronchial half- 

 ring ; e, posterior common laryngeal muecle — bronchialis posticus, going 

 from last tracheal ring to hinder end of second bronchial half-ring ; 

 e, anterior ditto — bronchialis antic^is, from last tracheal ring to fore 

 ends of first and second bronchial half-rings ; d, relaxor of tympani- 

 form membrane (sterno-trachealis) going from the side of the trachea 

 to the sternum ; g, membranous inner walls of the bronchi. 



to the trachea. In addition to these there is commonly one 

 pair or there may be five or six pairs of " intrinsic " muscles, 

 passing down from the trachea to the bronchial rings,. These 



