54 DISEASES OF THE AIR-PASSAGES. 



lished, in the ' Recueil de Medecine Veterinaire/ an account 

 of some extremely interesting experiments on this subject. 

 He found that either compression or division of the eighth 

 pair of nerves had the effect of producing roaring ; and the 

 rational explanation he gave of the phenomenon was, that as 

 the inferior laryngeal nerves, which supply the dilator muscles 

 of the glottis, are branches of the par vagum, of course those 

 muscles would become paralyzed; while the superior laryn- 

 geal, going to the constrictors of the larynx, preserving their 

 power, would contract and cause the glottis to be nearly 

 closed, and thus occasion the animal to roar. Here is a 

 new field opened for observation. We are rarely 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, Uttle gan- 

 glions upon the nerve, compressing it. Youatt fancied the 

 pressure of the collar or lower jaw might 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 I augur any great deal of practical utility from 

 this new light. 



Spasm of the muscles of the glottis. — Vatel places 

 roaring among " nervous disorders,^^ though he admits there 

 are but few cases in which it is referable to spasm. My 

 lamented friend, Mr. John Field, whose opinion on every point 

 of veterinary pathology was valuable^ very sagaciously ob- 

 served, that the frequent cause of roaring, in cases of ulcera- 

 tion 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 the 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 

 roaring which supervenes during the development of glanders 

 is precisely of this description." To prove the influence of 



' See Proceedings of Veterinary Association, in the Veterinarian for 1837. 



