134 MANUAL OF EQUINE MEDICINE. 



ROARING is a loud unnatural sound made during 

 inspiration. It is in some cases symptomatic of acute 

 laryngitis, and then only indicates temporary unsound- 

 ness. 



Roaring is generally due to atrophy and fatty degenera- 

 tion of certain muscles of the larynx, especially those which 

 pass between and attach the arytenoid cartilages to the 

 cricoid posteriorly. The origin of the degenerative changes 

 in the muscles leading to the paralysis is not certainly 

 known. The disease is generally confined to the left 

 laryngeal muscles, and many have supposed that this is due 

 to the fact that the recurrent laryngeal nerve passes from 

 the pneumogastric at a more distant spot than does the 

 corresponding nerve of the right side, and that, moreover, 

 the nerve on the left side winds round the posterior aorta. 

 According to this view, the left recurrent nerve is thus 

 more likely to be involved in any disease of the chest than 

 on the right side, where it is given off opposite the first rib, 

 and winds round the dorsal artery. 



Such an explanation, however, is open to many objec- 

 tions ; firstly, roaring is not a common sequel of pulmonary 

 disease ; secondly, many roarers have never had any chest 

 affection ; thirdly, mares and ponies are less liable to 

 become roarers than large geldings and stallions, but are 

 equally prone to chest affections ; fourthly, the nerve itself 

 shows no pathological change, as far as we know; and 

 finally, the atrophic change in the muscles, though usually 

 seen on the left side of the larynx only, is not uncommon 

 on the right side also, though to a less extent. 



The disease of the muscles is, however, of an essentially 

 nervous origin, and ought to be classed as a form of wasting 

 palsy — paralysis atrophicans. 



Koaring is in most instances gradually developed. At 

 first the sound may be intermittent, and even weeks may 



