228 CHAPTER 23. 



obstruction in some part or other of the respiratory passages, and usually 

 in the larynx. 



455. Causes. 



Eoaring is veiy frequently, indeed almost always caused by paralysis 

 of the muscle of the arytenoid cartilage of the Larynx. 



This paralysis is due to atrophy of the left recurrent nerve -which, if 

 in health, would supply the motor force to the muscle. This force being 

 absent, the muscle loses its power and wastes away. Hence the left half 

 of the arytenoid muscle drops down, and bars the ingress of the air at 

 each inspiration, which therefore strikes violently against the helpless 

 cartilage. Hence the noise we hear. 



On the other hand, as the cartilage has been flattened down, the expira- 

 tion is easily effected. Therefore the roarer makes no noise in expiration. 



456. Treatment. 



Every kind of treatment from firing down the outside of the throat 

 to excision of the muscle has been tried without success. 



As, however, in broken wind and chronic cough, hard and regular 

 work with high condition exercise a favorable influence, and may for a 

 length of time render a roarer useful for many purposes ; but with all 

 our care the disease, when arising from the above cause, generally in- 

 creases until the animal becomes useless. 



457-8. Other Causes. Tight reining U2i. 



Occasionally the derangement of the Larynx is due to other causes. 

 Among the most common of these is the system of tight reining up. In 

 our endeavour to give an arched appearance to the neck, we sometimes 

 in horses not naturally so formed produce distortion of the laiynx, and 

 consequently obstruction to the free ingress of the air. Horses, in which 

 the branches of the lower jaw are not set sufficiently wide apart to allow 

 of the head being freely and easily bent, often make a roaring noise, if 

 the head is reined in, when they are ridden; and a continuance of this 

 forced position may induce thickening of the membrane and ultimately 

 roaring. If taken in time, the remedy is obvious. 



459. Tumour in the Nose. 



A sound somewhat similar to roaring may arise from a tumour in the 

 nose. It may be possible to remove it. Or it may arise from a 

 thickened state of the membrane of the bronchial tubes as sometimes 

 found after catarrh, laryngitis, etc. The usual treatment is blistering. 



460. Class of horse predi>< posed to Roaring. 



Large horses, especially those which are long in the wind-pipe, are 

 more predisposed to roaring than smaller animals. Ponies ai"e seldom 

 if ever affected. 



