804 
and also some of those distributed upon the 
pharynx and back of the tongue, so that it 
1s chiefly composed of sensiferous and incident 
filaments. e inferior laryngeal furnishes 
incident and sensiferous filaments to the greater 
part of the trachea, to the cervical portion of 
the cesophagus, a few to the mucous surface of 
the pharynx, and still fewer to the larynx ; it 
supplies the motor filaments of the cervical 
portion of the esophagus and of all the muscles 
which are attached to and move the arytenoid 
cartilages, and is chiefly composed of motor 
filaments.* When any excitation is applied to 
the mucous membrane of the larynx in ‘the 
healthy state, this does not excite the contraction 
of the muscles which move the arytenoid carti- 
lages by acting directly upon these through the 
mucous membrane, but is the result, as Dr. M. 
Hall+ had maintained, of a reflex or excito- 
motory action, in the performance of which the 
superior laryngeal is the incident, and the infe- 
rior laryngeal the motor nerve. In each re- 
current nerve two sets of motor filaments are 
included, one set transmitting the nervous in- 
fluence which stimulates the opening muscles 
of the larynx to act synchronously with the other 
muscles of inspiration, the other set transmit- 
ting the nervous influence which calls the 
closing muscles into synchronous action with 
the muscles of expiration.{ 
Upon these views we can readily explain how, 
when the inferior laryngeal nerves are cut, all 
the movements of the muscles of the arytenoid 
cartilages are arrested, and the superior aper- 
ture of the larynx, as was first pointed out by 
Legallois, can no longer be dilated during in- 
Spiration. In fact, the sides of the larynx are 
not only no longer separated by an active in- 
fluence, but are rendered quite passive, and 
yield readily within the limits of their natural 
movements to any external force applied to 
them. When the recurrent nerves are cut in 
an adult animal, where the cavity of the larynx 
is large, a quantity of air may still find its way 
through the diminished aperture, adequate, in 
many Cases, to carry on the respiratory process 
in a sufficient manner, particularly if the mus- 
cles of inspiration are not acting violently. If, 
on the other hand, the capacity of the larynx be 
proportionally smaller as in young animals, the 
air rushes through the diminished superior aper- 
ture of the larynx in a narrower stream and with 
increased force, more especially when the in- 
Spiratory movements are powerful—or in other 
words, when the capacity of the thorax is sud- 
denly and greatly enlarged,—and an insufficient 
quantity of air reaches the lungs. This quan- 
tity is still further reduced a} the circumstance 
that the now passive sides of the superior aper- 
ture of the larynx are carried inwards by the 
* We also suggested that some of these filaments 
distributed in the trachea pe a be motor, though 
we had not succeeded in obtaining experimental 
evidence of it. 
t Lectures ‘on the Nervous System and its Dis- 
eases, Lecture 1, 1836. 
¢ Each of these two sets may again be subdivided 
into other two—one composed of the excito-motory 
filaments of Dr. M. Hall, the other of sensifero- 
volitional filaments. 
PAR VAGUM. ‘ 
current of air, and at each inspiration the ary- 
tenoid cartilages may be so closely Re a 
imated as to prevent the ingress of air and suf- 
focate the animal. It is the ina 3 
of the animal which is difficult, for the expira~ 
tion is easy. The occurrence or non-occurrence 
of dypsneea, or suffocation, after section of the 
inferior laryngeals, is to be explained by the — 
greater or less capacity of the larynx in the indi- — 
vidual animal, and the activity and extent of 
its respiratory movements at the time. Th 
crowing sound which frequently attends — 
condition of the larynx is a mere 
effect, and depends upon the current of air — 
rushing rapidly through the diminished aper- — 
ture of the larynx, and may be imitated in the — 
dead larynx. Severe dyspnea amounting to- 
suffocation may arise both from the opposite — 
conditions of irritation and compression of the 
inferior laryngeal nerves or the trunks of the 
penereapiette above the origin of this branch. 
e have stated above that on irritating one 
recurrent nerve we observed that the arytenoid 
cartilages were approximated so as in 
cases to shut completely the superior apertu 
of the larynx, and we have already explained 
how paralysis of this nerve by com i 
any other cause should produce this effect by 
arresting the movements of all the muse 
attached to the arytenoid cartilages.* We 
found that after the mae rabbits they “i0r 
laryngeal nerves in dogs an i 
load solids and fluids readily, and wi 
exciting cough or difficulty of breathing. 
Mr. Hilton has arrived at the conclusion, from 
the anatomical distribution of ev ce e 
that the superior laryngeal is chi ensitive 
and that honals motor filaments which it con 
tains are distributed in the crico-thyroid musel 
while the inferior laryngeal supplies all | 
muscles attached to the arytenoid -cartilags 
with motor filaments,—a view in exact a 
cordance with that which we have given abov 
Volkmann in his experiments found that 
movements of the glottis were not affected 
dividing the superior laryngealnerves.4 Longe 
* Professor Henderson (Cormack’s Journal 
Medical Science, p. 10, for 1841) adduces casi 
shew that in the human species the narrowin 
the superior aperture of the larynx, termed la 
gismus stridulus, may be induced both by irrit 
and paralysis of the recurrents. 4 
+ An account of the above experiments and 
ferences was read at the meeting of the Bi 
Scientific Association in 1837; a short epitom 
them was given in the Atheneum for Sept 
1837, and they were published in full in the I 
—— Medical and Surgical Journal for Jan 
¢ Guy’s Hospital Reports for October, 
forming part of the 2nd volume. — 
§ Opus cit. Volkmann states that on irr 
the external branch of the superior 
dogs and calves, not only the crico-thyroid 1 
was thrown into contraction, but also the con: 
penyecene superior and the thyro-hyoid. 
e confirmed, these two last muscles mu 
their motor nervous filaments from two 
the constrictor receives a supply from the pha 
geal branch of the vagus, and the th yoid f 
the hypoglossal. io 
\| Hocbetchat Expérimentales sur les Fa 
des Nerfs, des Muscles du Larynx, &c, Paris, 10 
y 
ee 
