150 Veterinary Medicine. 



vical (Crico-thyroideus, hyo-thyroideus and hyo-epiglottideus) 

 remain unchanged. The left recurrent nerve is also wasted and 

 considerably attenuated as compared with that on the opposite 

 side. The modus operandi of this paralysis and wasting in the 

 production of roaring is beautifully seen when the upper part of 

 the windpipe is laid open so as to expose the interior of the 

 larynx in laryngectomy. The triangular opening of the glottis 

 is seen fairly dilated while the muscles are relaxed in the act of 

 expiration. As soon, however, as inspiration commences the left 

 arytenoid cartilage slides completely into the passage, its lower 

 border projecting so much to the right that it forms a prominent 

 crest extending beyond the median line and in some cases closely 

 approaching the right wall of the larynx, the superior elastic and 

 free border of the same cartilage meanwhile gets drawn inward 

 by the suction power of the air so as to block up the passage still 

 more. The closure of the glottis being thus seen to be largely 

 controlled by the current of inspired air, it becomes evident that 

 any increase in the force of the current will aggravate it and a 

 decrease will lessen the extent of the closing and alleviate the 

 distress of breathing. This fact furnishes a means of palliating 

 the symptoms. (See treatment.) It explains moreover why 

 roaring should not be heard in quiet breathing and why it should 

 increase in force and in pitch as the respiration becomes more 

 and more hurried. It further accounts for the noise being heard 

 only during the act of inspiration, the outward rush of the air in 

 the expiratory act being of itself sufficient to carry this valvular 

 cartilage out of the passage and secure a free and unimpeded 

 current. 



The paralysis and wasting of the left recurrent nerve and 

 muscles are in their turn due to very varied morbid states. 



It may commence in the larynx from distortion of its cartilages 

 and inflammation of the mucosa, in which case the wasting of the 

 nerve is probably a result of its prolonged inactivity. This mode 

 of origin is strongly insisted on by Percivall, and no doubt occa- 

 sionally arises. Under this explanation, however, it is difficult 

 satisfactorily to account for its almost invariable occurrence on the 

 left side. The mere fact that the horse is habitually approached 

 on this side and more commonly turned toward it is a most in- 

 sufficient reason. 



