CHAPTER YIL 



PATHOLOGY AND COURSE OF CHRONIC ROARING. 



After Avhat has been described of the anatomy and 

 physiology of the horse's larynx in the last chapter, there 

 will be less difficulty in understanding the nature of the 

 morbid alterations which occasion those disturbances in 

 breathing that chiefly manifest themselves by Roaring. 



It is now nearly three-quarters of a century since the 

 characteristic changes that are observed in the larynges of 

 horses which had been affected with chronic Roaring during 

 life were first alluded to. But, then, as we have seen when 

 reviewing the history of the infirmity, the notices of these 

 changes were only casual and rare ; and, though the appear- 

 ances are extremely striking, and should have received 

 serious attention,yet but little importance seems to have been 

 assigned to them, and their significance was lost amid the 

 many conjectures indulged in as to what was really the 

 cause of the noisy, and oftentimes distressed, respiration. 



Percivall, in 1824, saw some of the more marked of these 

 changes exactly as we now see them. "Another, and a not 

 very uncommon cause of Roaring," he says, " is a wasting, 

 or, in some instances, a total absorption of one or more of 

 the small muscles of the larynx. I have lately examined a 



horse of Mr. J y'S — a remarkable instance of it. In his 



larynx, upon the near side, the crico-arytsenoideus posticus 

 was very pale, and shrunk to half its original size ; the 

 crico-arytsenoideus lateralis, the thyro-aryt?enoideus, and 

 the arytffinoideus, were altogether colourless, and scarcely 



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