LARYNX OR WINDPIPE. 
47 
supply the dilator muscles of the glottis are branches of the par 
vagum, of course those muscles would become paralyzed; while 
the superior laryngeal, going to the constrictors of the larynx, pre¬ 
serving their power, would cause the glottis to be nearly closed, 
and thus occasion the animal to roar. Here is a new field opened 
for observation. We are not to expect division or destruction of 
continuity; but there are changes and accidents that may occasion 
compression, either of the par vagum or recurrent nerve, on one 
or both sides. Some French veterinarians have discovered, they 
say, little ganglions upon the nerve, compressing it. Mr. Youatt 
fancies the pressure of the collar or lower jaw may have the same 
effect. The formation of a tumour, any where in the course of the 
nerve, might, perhaps, do it. After all, however, I cannot say 
that I augur any great deal of elucidation from this new light. 
Spasm of the Muscles of the Glottis. —Vatel places roar¬ 
ing among nervous disorders,” though he admits there are but 
few cases in which it is referrible to spasm. My lamented friend 
Mr. John Field, whose opinion on every point of veterinary patho¬ 
logy was valuable*, very sagaciously observed, that the frequent 
cause of roaring, in cases of ulceration of the rima glottidis, is 
“ spasm of the glottis. While the horse,” says Mr. Field, “ is 
suffering great pain from the passage of the air over these denuded 
surfaces, the instinctive action of the muscles, more powerful than 
th^ will of the animal itself, partially closes- the air-tube, and thus 
lessens the irritation. I have seen many cases of this kind, and 
by opening the trachea have obtained immediate relief. The roar¬ 
ing which supervenes during the development of glanders is pre¬ 
cisely of this description.” To prove the influence of the recurrent 
nerve Mr. Field made the following experiment:— 
“ Having ascertained that the organs of respiration of a horse used for farm¬ 
ing purposes were sound, I cast him, and laid bare the recurrent nerve of the 
off-side, and passed a ligature loosely around it: he was then allowed to get 
up, and, after a few minutes, gaUopped severely without evincing the slightest 
defect in his breathing. The nerve was then drawn out by the ligature, and 
one inch and a half of it excised; and immediately, on only trotting the horse a 
short distance, such a degree of roaring was occasioned, that, had the exertion 
been continued, he would soon have fallen. I kept this horse four years ; 
and, though his breathing became much better, he continued a sad roarer: at 
the end of that time]I destroyed him for the larynx, which exhibited the usual 
condition of wasted muscles on the side deprived of the influence of the recur¬ 
rent nerve.” 
Roaring, hereditary. —That roarers have both bred and got 
roarers, I believe, there are instances enough on record to prove ; 
but whether this be referrible to some peculiar or faulty conform- 
aiion, or can be regarded as the transmission of the disease itself, is 
* See Proceedings of Veterinary Association, in The Veterinarian for 1S‘17. 
