ON Tilt TENTH PAIR OP NERVES. 
297 
Expending itself on the Larynx. —Having reached the upper 
part of the trachea, the recurrent nerve terminates in ramifications 
on the dilator muscles of the larynx, and also on the membrane 
of the glottis. This is a very important branch ; the dilators are 
the muscles most concerned in the adaptation of the larynx to the 
inspiration and expiration of air in common or in hurried respira¬ 
tion, and also in the production and management of the voice. 
They are numerous and powerful, while the closing of the laryn¬ 
geal aperture is effected by the elasticity of the cartilages, assist¬ 
ed by one small muscle alone. 
The Explanation of the Retrograde Course of this Nerve .— 
We can see, then, some reason why the branch which is to 
accomplish, or to aid in the accomplishment of, the most im¬ 
portant division of these processes, should take this singular 
course. Being given off from the very base of the trachea, 
climbing up on each side of it, yielding filaments to it at almost 
every assignable point from its bronchial divarication to its laryn¬ 
geal termination, and its ultimate fibres diffused over the larynx, 
there results a sympathy, a co-operation between every part of 
the respiratory tube, best adapted to produce, and which alone 
can secure, the perfection of this portion of the respiratory func¬ 
tion. 
The Effect of the Division of the Laryngeal and Recurrent 
Branches. —When speaking of the respiratory system, and the 
mechanism of the voice, I described the effects produced by the 
division of the laryngeal and recurrent branches. When the la¬ 
ryngeal branch is divided, the voice is changed and rendered 
hoarse, for the dilators continue to act, but the power of the con¬ 
strictors is lost. When, on the other hand, the recurrent branch 
is cut, the dilators have lost their power, and the constrictors alone 
act; the glottis is closed, the voice lost, and the animal threatened 
with suffocation. The power of deglutition likewise is materially 
affected by the division of these nerves : when the recurrent nerve 
is divided, and the constrictors alone act, the glottis is closed, 
and the food passes over without danger; when the laryngeal is 
divided, the constrictors cease to act, the dilators expand the 
glottis, a portion of the food often enters the windpipe, and dis¬ 
tressing cough, if not suffocation, ensues. 
The Pulmonary Plexuses. —These are very remarkable ramifi¬ 
cations of the cerebro-visceral nerve. They are given off on each 
side, both from the main trunk of the nerve and the recurrent 
branch, and are divided into two portions; the superior one is 
partly given to the pericardium, and entwines around the pulmo¬ 
nic arteries and veins, and accompanies them into the substance 
of the lungs ; the inferior plexus is more attached to the bronchi 
and the bronchial vessels, and can be satisfactorily traced along 
