136 Veterinary Medicine. 



from the frequency with which the author has met with them in 

 his dissection he is convinced that they deserve greater attention 

 than has been awarded them. 15th, Percivall records a case of 

 inveterate roaring in which, even tracheotomy having failed to 

 cure, the patient was destroyed and the kings found to be exten- 

 sively consolidated, many of the air tubes having been so com- 

 pressed as to be almost impervious. I have known a case of 

 roaring from the presence of a pedunculated tumor in the lower 

 end of the windpipe where it divides to enter the lungs, and the 

 same result may ensue from the partial obstruction of the bron- 

 chial tubes by masses of tenacious mucus in chronic bronchitis. 



1 6th. The immediate cause of roarijig in the immense majority 

 of cases is the paralysis and fatty degeneration of certain 

 muscles on the left side of the larynx. The muscles supplied 

 with motive power by the left recurrent laryngeal nerve 

 (Crico-arytenoideus posticus, Crico-arytenoideus lateralis, thyro- 

 arytenoideus, and the left half of the arytenoideus) are those 

 constantly and exclusively affected, while those supplied by the 

 siiperior laryngeal nerve (Crico-thyroideus, hyo-thyroideus and 

 hyo-epiglottideus) remain unchanged. The left recurrent nerve 

 is also wasted and considerably attenuated as compared with that 

 on the opposite side. The modus operandi of this paralj^sis and 

 wasting in the production of roaring is beautifully seen when the 

 upper part of the windpipe is laid open so as to expose the in- 

 terior of the larynx in laryngectom\^ The triangular opening of 

 the glottis is seen fairly dilated while the muscles are relaxed in 

 the act of expiration. As soon, however, as inspiration com- 

 mences the left arytenoid cartilage slides completely into the 

 passage, its lower border projecting so much to the right that it 

 forms a prominent crest extending beyond the median line and in 

 some cases closely approaching the right wall of the larynx, the 

 superior elastic and free border of the same cartilage meanwhile 

 gets drawn inward by the suction power of the air so as to block 

 up the passage still more. The closure of the glottis being thus 

 seen to be largely controlled by the current of inspired air, it be- 

 comes evident that any increase in the force of the current will 

 aggravate it and a decrease will lessen the extent of the closing 

 and alleviate the distress of breathing. This fact furnishes 

 a means of palliating the symptoms. (See treatment.) It ex- 



