96 Roaring in Horses. 



after division of both dilator muscles, the vocal cords pass 

 beyond the ordinary position inwards, towards the middle 

 line, and lose the power of separating on inspiration. But 

 the full median position and continuous dyspnoea do not 

 immediately appear, and the power of narrowing the glottis, 

 as well as the vibratory function of the vocal cords, is undis- 

 turbed ; so that "the voice or bark remains intact. As a 

 rule, the operation was immediately followed by consider- 

 able dyspnoea, but this soon subsided; and Schech was of 

 opinion that it was the result of the constriction of the 

 glottis, which takes place at once after the operation, and 

 which, again, necessitates deeper and more frequent respira- 

 tions. In this •wa.y there arises a difference of tension in the 

 columns of air above and below the glottis, the vocal cords 

 approach each other still closer, and thus the entrance of 

 air is yet more impeded. The abatement of the dyspnoea 

 soon after the operation on animals is due, on the one hand, 

 to the fact that the respiration gradually becomes quieter, 

 and, on the other, because the creature soon becomes accus- 

 tomed to the hindrance in breathing ; though it is assumed 

 that the constrictors of the glottis never exert their power 

 suddenly, but only after a certain period. The dyspnoea 

 and stridulous inspiration make their appearance, however, 

 immediately the animal attempts any sudden and violent 

 exertion. 



Such is the function of respiration and its mechanism, so far 

 as the larynx is concerned ; and it is necessary to bear these 

 details in memory while studying the pathology of Roaring, 

 and especially the part the recurrent nerve assumes in rela- 

 tion to its muscles. It is also necessary to remember that 

 conclusions arrived at from experiments on creatures other 

 than the horse cannot always be made applicable to that 

 animal with certainty. Exner,i Jlandelstamm,^ and others, 

 for instance, have maintained that in the distribution of the 

 recurrent nerve there are frequent individual variations. 



1 " Centralblatt fiir Laryngologie," February, 1885. 

 ' " Monatschft. fiir Ohrenheilkunde," December, 1884. 



