ROARING IN HORSES. 13 



crico-arytenoidean, the thyro-arytenoldean and 

 arytenoldean muscles degenerate, and are 

 incapable of accomplishing their physiological 

 work. The transverse dimensions of the 

 superior opening of the larynx are already 

 lessened and are incapable of being extended, 

 and the opening is more reduced during 

 inspiration, especially when the respiratory 

 movements are quickened. As long as 

 the respiration is calm, the air passes the 

 laryngeal passage in silence ; but as soon 

 as it is quickened by exercise the left 

 arytenoid, instead of being taken upwards 

 and outwards by the action of the corre- 

 sponding muscles, is displaced in an inverse 

 direction. Pressed by the air inspired — 

 being carried below and inwards towards the 

 glottis and against the opposite arytenoid 

 cartilage, taking with it the vocal cord, the 



