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ANIMAL PATHOLOGY. 
tor muscles; and thus by means of all this seemingly complicated 
but really simple machinery, a co-operation between every part 
of the respiratory apparatus is procured, adapted to produce and 
to secure the perfect working of the whole. 
The Division of the Laryngeal and, Recurrent Branches . — 
Many experiments have been tried with regard to the division 
of the superior laryngeal, and the recurrent nerves. If the 
superior laryngeals are divided, the action of the constrictor 
muscles is lost; but the dilators continue to act without any 
antagonist power. The consequence of this is, that the voice 
is rendered hoarse, the glottis is permanently expanded, and 
portions of food enter into the trachea, producing distressing 
cough, and sometimes threatening suffocation. If the recurrent 
nerve is divided, the antagonists of the constrictors are removed. 
The glottis is closed — no air can enter or escape, and not only 
the voice but life itself is lost. In all experiments, therefore, in 
which the division either of the recurrent branch or the main 
trunk of the great spinal organic is required, an opening is pre- 
viously made into the trachea, below the larynx, in order that 
respiration may not be suspended, and the animal destroyed. 
Roaring, as connected with the Larynx . — Among the various 
causes of roaring, we look to the larynx, as furnishing us, if not 
with the most frequent yet the most decisive. In some cases 
there is ulceration on the rimee glottidis, or within the cavity of 
the larynx ; and the glottis sympathising with every part by 
means of the numerous connexions that have been stated, and 
more particularly with the membrane in its immediate neigh- 
bourhood, is spasmodically contracted, in order to preserve the 
denuded and irritable surface beneath from too violent a current 
of air falling upon it and inflicting pain. The passage of the air 
through the contracted orifice is accompanied by this peculiar 
sound. 
Among the other mischiefs produced by tight reining, and the 
brutal system of breaking that is occasionally adopted, are com- 
pression and distortion of the larynx. It is sometimes so much 
deformed, so much bent and twisted on one side, that the muscles 
on that or on the contrary side lose all power of contracting or di- 
lating the larynx ; and then they follow the law by which mus- 
cular action in every part of the frame is regulated ; they waste 
away for want of use. The muscles on the other side increase 
in size in proportion to the additional labour imposed upon them. 
The consequence of this distortion and unequal action of the 
muscles is, that neither the dilatation nor the closure of the 
glottis can be perfectly accomplished, and the air rushes through 
the partial opening, and the sound of roaring is produced. 
