116 Roaring in Horses. 



tlie left side of the larynx should be in, it may be said, 

 every case alone involved ; and what occasions the muscle- 

 wasting ? 



Here, again, we find much mystery and obscurity pre- 

 vailing. " Why the change is greater on the left than the 

 right side, is," says Williams, "one of those things for 

 which no more satisfactory explanation can be given than 

 why the ulcers of Glanders are oftener seen in the left than 

 in the right nostril."i I am not aware that the ulcers of 

 Glanders are more frequently noticed on one side of the head 

 than the other — all my experience leading me to believe 

 that neither is particularly favoured in this respect. But 

 why the left side of the larynx should be that which is 

 alone involved in chronic Roaring, there should be now no 

 difficulty whatever in comprehending. It is due entirely to 

 the difference in the course and relations of the left 

 recurrent nerve, and which I have been at some pains to 

 indicate in describing the innervation of the larynx. The 

 anatomical distinction between the right and left nerves was 

 shown to be remarkably great ; and it is upon the special 

 features observed in the detachment, situation, connections, 

 and environment of the latter nerve, that we can account 

 for the side of the larynx it supplies with stimulus being 

 the one to suffer from the characteristic pathological 

 changes which occasion Roaring. 



It has been shown that the right nerve is comparatively 

 short, being given off from the right vagus nerve imme- 

 diately after the latter enters the chest, in which it has 

 scarcely any relations or connections : whereas the left one 

 is detached from the left vagus nerve deep in the cavity, at 

 the base of the heart, and is connected and related with the 

 sac (pericardium) in which that organ is enveloped, with 

 the great arterial trunk springing from the heart, with the 

 pleural membrane and its dependencies, with lymphatic 

 glands — intra- and extra-thoracic— and with ganglia of the 

 ' Op. cit., p. 510. 



