. 
. 
THE CAUSE AND THE RELIEF OF THE DYSPNCEA 
RESULTING FROM LARYNGEAL HEMIPLEGIA 
IN THE HORSE (ROARING).* 
By Louis P. Cook, D.V.S., Cincinnati Veterinary College. 
External to each vocal cord there is in the larynx a lateral 
ventricle. In the horse this air sack, when distended, is large 
enough to accommodate the egg of a bantam hen. It is lined b y 
a very thin mucous membrane. Functionally, the sack is related 
to the production and regulation of the voice. It is dilated by 
certain laryngeal muscles and contracted by others, all of which 
are attached to and move the arytenoid cartilage. In the normal 
larynx, with all the muscles performing their functions, the ven¬ 
tricle does not remain dilated during the respiratory movements. 
Now in the “ roarer” there is a paralysis of certain of the 
laryngeal muscles, which, under normal conditions, force the air 
out of the ventricle of the left side of the larynx, this paralysis 
resulting from some pathological condition of the motor nerve of 
such muscles, namely, the left recurrent laryngeal. Whenever an 
animal so affected is put to any exertion and caused to breathe 
deeply, the ventricle of the affected side fills with air and bal¬ 
loons, and remains so for a time, in consequence of the paralyzed 
muscles being unable to force the air out. This ballooning of the 
lateral ventricle closes, or almost closes, the narrow glottis, 
dyspnoea or even asphyxiation resulting. If an animal in such 
respiratory distress is allowed to rest, the dyspnoea soon subsides. 
The dyspnoea in the “roarer ” then , is due solely to the disten¬ 
sion of the left lateral ventricle, a condition that is possible only 
* Read before the Ohio State Veterinary Medical Association January 18, 1912. 
Following the reading of the paper the operation described was performed by the writer. 
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