The Respiratory Function of 
the Human Larynx. From 
Experimental Studies in 
the Physiological Lab- 
oratory of Harvard 
University. 
BY 
FRANKLIN H. HOOPER, M. D., 
BOSTON. 
REPRINTED PROM 
&l)e "Wrto York fttetucal .Hourual 
for July If, 1885. Reprinted from the New Yorlc Medical Journal 
for July 4, 1885. 
THE RESPIRATORY FUNCTION OF THE 
HUMAN LARYNX.* 
FROM EXPERIMENTAL STUDIES IN THE PHYSIOLOGICAL 
LABORATORY OF HARVARD UNIVERSITY. 
By FRANKLIN H. HOOPER, M. D., 
BOSTON. 
The human larynx has two principal functions: (a) The 
respiratory, (b) the phonatory. They are mentioned in the 
order of their importance, for, while the muscles concerned 
in phonation, supplemented by other constrictors, are 
charged with the additional duty of closing the laryngeal 
aperture to protect the air-passages from the entrance of 
foreign bodies, yet it must be conceded that, whether em- 
ployed in phonation — marvelous as this function is—or 
brought into action to exclude some foreign substance, the 
part performed by these constrictors is entirely subordinate 
to that of the respiratory muscle of the larynx, whose office 
is to hold the glottis open in order to insure an uninter- 
rupted passage of air to and from the lungs, f Nevertheless, 
* Read before the American Laryngological Association, June 24, 
1885. 
\ The intrinsic laryngeal muscles are in pairs except one, the trans- 
verse arytenoid. The posterior crico-arytenoids are the respiratory 
muscles. The phonatory muscles, which, like the respiratory muscles, 
are attached to the arytenoid cartilages, are the internal thyro-aryte- 
noids, the lateral crico-arytenoids, and the transverse arytenoid. These 2 
THE RESPIRATORY FUNCTION OF 
it is this important muscle which is not only the chief 
among the intrinsic muscles of the larynx, but also one of 
the most essential of the whole body—a muscle, be it re- 
membered, of organic life *—that many writers would have 
us believe has a special tendency to succumb to disease. 
Gerhardt, in his well-known paper,f was perhaps the first to 
speak of unilateral paralysis of this muscle (the posterior 
crico-arytenoid) as the most innocent of all forms of laryn- 
geal paralyses. He points out that neither the voice nor 
the respiration is impaired in such lesions. SchechJ writes 
in the same strain, and believes that, as the voice and quiet 
respiration are not affected in these instances, this circum- 
stance accounts for their having escaped more frequent men- 
tion. Two prominent exponents of this theory (Rosenbach # 
and Semon ||) have stated that in central or peripheral affec- 
phonatory muscles are, when it is necessary, brought into action solely 
to close the glottis and not for the purpose of phonation. Under these 
circumstances they are supplemented by the muscles which compose 
the aryteno-epiglottidean folds, and which, together with certain other 
muscular fasciculi, may be classed as the sphincter group—the con- 
strictor vestibuli laryngis. The thyro-cricoids are also phonatory mus- 
cles ; but with these, on account of their anatomical situation, we have 
nothing to do in this paper. 
* By this expression we refer to the normal automatic character of 
the muscular action, and not to the microscopic structure of the muscle 
itself. 
f “ Studien u. Beobachtungen iiber Kehlkopflahmung,” Virchow’s 
“Archiv,” vol. xxvii, p. 88, 1863. 
% “ Experimentelle Untersuchungen iiber die Funktionen der Ner- 
ven und Muskeln des Kehlkopfes,” “Zeitsch. f. Biologie,” Band ix, p. 
268, 1873. 
* “Bresl. arztl. Zeitschr.,” Nos. 2-3, 1880; “Berlin, klin. Wochen- 
schr.,” No. 17, 1884; Virchow’s “Archiv,” Band 99, 1886. 
|| Mackenzie, “ Diseases of the Throat and Nose,” German edition, 
1880; “Arch, of Laryngology,” vol. ii, No. 3, 1881; “ Berlin, klin. 
Wochenschr.,” Nos. 46-49, 1883; Ibid., No. 22, 1884. THE HUMAN LARYNX. 
3 
tions where the filaments of the recurrent laryngeal nerve are 
compressed, the fibers innervating the respiratory muscle are 
earlier affected than those going to the phonatory muscles; 
that this is in accordance with the well-ascertained fact that, 
in central or peripheral nerve lesions, the extensor muscles * 
are more readily paralyzed than the flexors; that there is a 
“ proclivity of the adductor fibers of the recurrent laryngeal 
nerve to become affected sooner than the adductor fibers, or 
even exclusively, in cases of undoubted central or peripheral 
injury, or disease of the roots or trunks of the pneumogas- 
tric, spinal accessory, or recurrent nerves.” Another au- 
thor f has recently gone so far as to say that the vul- 
nerability of these adductor fibers is a fact upon which all 
observers are now agreed. 
We hazard the opinion, notwithstanding, that if we 
investigate this complicated subject from a somewhat differ- 
ent point of view—one not strictly clinical—we may dis- 
cover certain reasons why one should not subscribe uncon- 
ditionally to this conception of the pathology of laryngeal 
neuroses. We propose, therefore, to inquire into the truth 
of this problem purely from an anatomical, physiological, 
and experimental standpoint. This being, then, in no sense, 
a clinical paper, clinical evidence will not be offered, al- 
though the writer’s experience is far from being in accord 
with the dictum that the nerve filaments which preside over 
the most useful and important function of the larynx should 
be especially prone to have that function arrested. The 
superior laryngeal nerve, and the median laryngeal, recently 
described by Exner,J need not in this study concern us. 
The only other nerve, as far as we know to-day, going to 
* To this assumption that the posterior crico-arytenoid muscles are 
extensors we shall recur. 
f Gottstein, “ Die Krankheiten des Kehlkopfes,” p. 192, Wien, 1884. 
+ “ Die Innervation des Kehlkopfes,” “ Sitzungsb. d. k. Akademie 
d. Wissenschaften,” Band 89, Abth. iii, 1 u. 2 Heft, 1884. 4 
THE RESPIRATORY FUNCTION OF 
the intrinsic muscles of the larynx is the inferior or re- 
current laryngeal. This nerve, according to our present 
knowledge, is purely motor, * and supplies all the intrinsic 
laryngeal muscles except the longitudinal tensors, the thyro- 
cricoids. It is an anatomical fact that it does not send off 
any branches to these muscles until it has reached the 
border of the cricoid cartilage. In its trunk, therefore, are 
contained two sets of nerve fibers—the respiratory and the 
phonatory—which must necessarily be strictly differentiated, 
since they are destined for muscles which carry on two 
separate and distinct functions. Now, where do these two 
sets of nerve filaments come from ; is their origin as dis- 
tinct as their function; whence do they derive their sepa- 
rate individualities; which are relatively or numerically the 
stronger ? 
The sources from which nervous impulses for the larynx 
may be received are the brain, the medulla oblongata, and 
the spinal cord. The channels through which they may be 
transmitted are the several motor nerves which join the 
pneumogastric before the recurrent is given off, for we are 
aware that from this point the recurrent proceeds to the 
larynx without any branch or junction which is in any way 
connected with the functions of that organ. 
The experimental researches of Krause,f and the clinical 
observations of Delavan,J justify the belief that there is a 
* We are aware that some have stated, but without giving experi- 
mental data to substantiate the assertion, that the recurrent contains 
sensory as well as motor fibers. We have not the space here to dwell 
upon our own experiments to determine this point, but they justify our 
remark that the recurrent is “purely motor.” 
f “Ueber die Beziehungen der Grosshirnrinde zu Kehlkopf und 
Rachen,” “ Sitzungsberichte der kgl. preuss. Akad. der Wissensch. zu 
Berlin,” November, 1883. 
X “ On the Localization of the Cortical Motor Center of the Larynx,” 
New York “ Med. Record,” February 14, 1885. THE HUMAN LARYNX. 
5 
center of motion for the larynx in the cortical substance of 
the brain. It is also probable, as advanced by many, that the 
several nerve filaments of the recurrent laryngeal may have 
independent ganglionic centers somewhere in the brain or 
medulla. Let us now follow down the real motor nerve tract 
of the larynx from the medulla oblongata to the point of exit 
of the recurrent laryngeal from the pneumogastric, and enu- 
merate the different nerves which, from what we know posi- 
tively or imagine hypothetically, may in any way influence 
either of the functions of the larynx. In so doing we shall 
adopt Longet’s classification,* who divided them into the 
direct and the indirect. Starting, then, at the medulla, we 
name as the direct communications to the pneumogastric the 
internal branch of the spinal accessory, the facial, the hypo- 
glossal, and the anterior branches of the first and second cer- 
vical. The sympathetic may also furnish some direct fibers. 
Under the head of indirect nerves—namely, those which join 
the pneumogastric after having previously passed through 
the sympathetic ganglia—we have all the branches of the 
cervical below the second, and those of the dorsal nerves 
situated, of course, above the point where the inferior 
laryngeal shoots off from the pneumogastric to run its back- 
ward course to the laryngeal muscles. 
Our knowledge of -the part played by these different 
nerves in the performance of the functions of the larynx is 
now, and, from the inherent difficulties of the problem, 
must for a long time to come remain, unsatisfactory. The 
mass of contradictory statements which one encounters 
in working up a subject in any way connected with the 
respiration, and consequently with the pneumogastric nerve, 
is a sufficient admonition against too positive and dog- 
matic assertions. We approach this question, therefore, 
with reserve, admitting, as we must, that a great part of 
* “ Traite de physiologie,” vol. iii, p. 512, Paris, 1869. 6 
THE RESPIRATORY FUNCTION OF 
the subject is yet hardly beyond the confines of plausible 
conjecture. 
It is pretty certain, however, as determined by the relia- 
ble experiments of Bischoff,* Longet,f Cl. Bernard,]; and 
Schech (loc. cit.), that the spinal accessory is a purely motor 
nerve presiding over phonation, and having nothing to do 
with the respiratory function of the larynx.* That there 
may be other phonatory fibers in the pneumogastric we can 
not gainsay. Now, how is the respiratory function inner- 
vated ? Probably in many different and complex ways, in 
accordance with the truth of the physiological law enunciated 
* “Nervii accessorii Willisii anat. et physiol.,” Heidelberg, 1832. 
f “ Rech. experimen. sur les fonctions des mus. et des nerfs du lar- 
ynx,” etc., “ Gaz. med. de Paris,” 1841. 
\ “ Fonctions du nerf spinal,” etc., “ sur la physiologie et la 
pathologie du systeme nerveux,” tome ii, Paris, 1858. 
# Experimental physiology teaches us that if we cut the recurrent 
nerves of a kitten or a puppy a few days old it immediately dies of 
suffocation, which is not the case in old animals. The reason of this, 
as originally explained by Legallois (“ Experiences sur le principe de la 
vie,” Paris, 1812), is because in very young animals the cartilaginous 
portion of the glottis is but slightly developed, and, the soft and yield- 
ing parts not being held in position by the muscles, the laryngeal walls 
are sucked together by the inspiratory effort, and the laryngeal aperture 
is accordingly completely closed. Cl. Bernard showed that section of 
the spinal accessory in a kitten five weeks old was followed by aphonia, 
but glottic respiration remained free. Two days afterward, the kitten 
having remained well but voiceless, its recurrents were cut, when it in- 
stantly died asphyxiated. He concludes from this that the pneumogas- 
tric has a motor power independent of the spinal accessory which per- 
mits the animal to breathe after the latter has been cut; or, in other 
words, the larynx is a vocal organ when excited by the spinal accessory, 
and a respiratory organ when under the influence of the pneumogastric, 
or more probably of other motor nerves associated with it. In certain 
animals, as the chimpanzee, the internal branch of the spinal accessory 
does not blend with the pneumogastric, but goes direct as a separate 
nerve to the larynx. THE HUMAN LARYNX. 
7 
by Longet.* “ Les moyens d’innervation propres a entretenir 
le jeu d’un organe se multiplient en raison de son importance 
physiologique.” The posterior crico-arytenoids—the respi- 
ratory muscles of the larynx—are paramount to all the rest 
in physiological importance. From many sources they re- 
ceive an abundant nerve supply, which is to protect them 
from disease, not to open up new channels by which harm 
might come to them. With others we assume that there 
are independent ganglia in the central nervous system which 
are essentially their own. Being respiratory muscles, it is 
more than probable that they may receive nerve force from 
such respiratory nerves as the facial, the hypoglossal, and 
the others already mentioned which run into the pneumo- 
gastric. But in this connection we must quote Longet’s 
own words: f “Si la phonation, fonction secondaire et 
accessoire, depend d’un nerf unique et disparait avec lui, la 
dilatation respiratoire de la glotte, si essentielle, si indispen- 
sable a la conservation de la vie, est sous la dependance ou 
plutot sous la protection de nerfs multiples qui, dans cer- 
tains limites, peuvent se suppleer les uns les autres. Aussi, 
comrne je l’ai deja, fait remarquer, precisement avant de 
donner origine aux recurrents qui animent les muscles crico- 
arytenoidiens posterieurs, voit-on les pneumogastriques em- 
prunter des fibres motrices a des nerfs qui tons intervien- 
nent dans la respiration.” 
Summing up what has preceded, we can say that it all 
points to the conclusion that the respiratory nerve filaments 
contained in the recurrent laryngeal are derived from a 
greater variety of sources than the phonatory. 
We pass now to the experimental evidence bearing on 
this point. It is a fact, familiar to all, that if anything 
* “Trait6 de phys.,” vol. iii, p. 517, Paris, 1869. 
f Loc. cit., p. 518. 8 
THE RESPIRATORY FUNCTION OF 
other than air finds its way into the larynx it produces, by 
reflex action, a sudden closure of the glottis. It is equally 
certain that, under normal conditions, the same contraction 
of the laryngeal muscles may be instantly called forth by 
direct stimulation of one or both of the recurrent nerves. 
Now, it may with reason be asked, How is it that this con- 
stricting action of the phonatory muscles is brought about 
if it be true that the nerve fibers animating the dilators of 
the glottis are the stronger and the more numerous ? Why 
should we not get adduction of the vocal bands instead of 
adduction on irritating the recurrent nerves ? The phona- 
tory muscles are to the respiratory muscles as five to two, 
and the closure of the glottis has always been ascribed to 
the superior numerical strength of these constrictors. Yet 
if we compare, bulk for bulk, the muscular fibers which 
compose the five muscles of phonation with those of the two 
respiratory muscles, we do not find that they are much, if 
any, in excess of the latter, and we venture to think that 
there is some other factor concerned in this phenomenon 
apart from mere muscular force. It may be sought, per- 
haps, in this important difference between the respiratory 
and the phonatory function of the glottis—namely, that, 
while the respiratory muscles are ever on the alert, holding 
the glottis open during the entire healthy life of an indi- 
vidual, in his waking as well as in his sleeping hours, the 
phonatory muscles, on the other hand, are more dependent 
upon the consciousness of the individual in order to respond 
to any irritation. To explain : The phonatory function of 
the phonatory muscles could, as far as life is concerned, be 
dispensed with. Not so their constricting action with the 
view of excluding the passage of foreign bodies to the lungs. 
The constrictor muscles of the larynx are the sentinels who 
guard the approach to these vital organs. But they cease 
to act if the animal is in profound narcosis ; they are asleep, THE HUMAN LARYNX. 
9 
so to speak, on their watch. A man in the condition known 
as “ dead drunk,” lying, let us suppose, on his back with his 
mouth open, would offer no obstacle to prevent any living 
insect that chanced his way from crawling in and out of his 
mouth, or meandering round in his larynx a volonte, without 
exciting reflex contraction of its muscles. The power of 
ether, chloroform, and other anaesthetics to impair the action 
of these constrictors is too well known to need mention. 
To carry this line of thought a little further, should we not 
expect that, provided we could preserve the organic life of 
an animal while its volition was at the same time completely 
abolished—should we not expect, we ask, under these cir- 
cumstances, to get a dilatation of the glottis on irritating the 
recurrent nerves instead of a closure, for the posterior crico- 
arytenoid muscles are muscles of organic life ? Indeed we 
believe we should, and we submit the following experiments 
in support of that belief. In performing the experiments 
the writer has had the advantage of the collaboration of 
Professor Henry P. Bowditch, to whom he would express 
his thanks. With one exception, when a horse was the sub- 
ject of an experiment, the animals used were dogs, the 
proper selection of which for studies in experimental laryn- 
gology is highly important. If a dog is either very old or 
very large he is most unsatisfactory, if not absolutely worth- 
less. He should be small and young ; the breed is of no 
consequence. By arranging him in the following manner a 
perfect view of the glottis can be obtained : After being 
thoroughly etherized, he is secured on his back to a dog- 
holder. A longitudinal incision is made in the skin cover- 
ing the larynx, the fascia is divided, and the muscles are 
drawn aside. The larynx and trachea are thereby brought 
into view. One or both of the recurrent laryngeal nerves 
may now be exposed. The mouth is held open by the up- 
per jaw being firmly attached to the cross-bar of the dog- 10 
THE RESPIRATORY FUNCTION OF 
holder, while a cord, tied round the lower jaw and secured 
to any fixed point, keeps the jaws separated to the extent 
desired. If the animal is placed before a window, the light 
is transmitted through the wall of the trachea, illuminating 
the glottis below, while the ordinary head reflector throws 
the light in through the open mouth from above. The 
tongue may be stretched up over the lower jaw and secured 
to the skin by a thread. The epiglottis may be either tied 
up by a string passed through its tip, or held up by an in- 
strument suitably curved, having a long handle. The ac- 
companying picture, taken from a photograph of a dog in 
readiness for experimentation, may serve to make our de- 
scription somewhat clearer. The animal is here shown 
under conditions by which both recurrents could be stimu- 
lated simultaneously.* 
* For the sake of completeness of the figure, the primary coil is 
represented as connected with a small bichromate cell, but in practice 
it was connected with a Grove cell in a battery-closet. The induction 
apparatus is the one described and figured in the “ Proceedings of the 
American Academy of Arts and Sciences,” October 12, 18Y5. THE HUMAN LARYNX. 
11 
The phenomenon of an irritation applied to the recur- 
rent laryngeal nerve producing an adduction of the corre- 
sponding vocal band was first observed by accident. A 
small dog, of no particular breed, of an age estimated at 
about ten months, as it still had some of its puppy teeth, 
was being prepared for a different order of research. On 
looking for the left recurrent nerve, it was not found in its 
proper anatomical situation, but two small nerves were dis- 
covered near by. As it was doubtful what these two 
branches were, or whether they went to the larynx at all, a 
shielded electrode was placed on the outer and larger nerve, 
and, while the vocal bands were watched through the mouth, 
it was irritated. The very unexpected result of the stimu- 
lation was a forcible adduction of the left vocal band. Dr. 
J. W. Warren, assistant in physiology, was requested to 
come and witness this unusual sight. The ether sponge had 
been removed from the dog since the beginning of the ex- 
periment, and by the time Dr. Warren was ready to look at 
the larynx the animal was somewhat out of its influence.* 
At all events, on stimulating the nerve a second time, the 
familiar closure of the glottis wras manifested instead of the 
dilatation so evident a few moments before. On the assump- 
tion that the degree to which the animal was narcotized 
might have something to do with these phenomena, a large 
quantity of ether was again administered. After the dog 
was profoundly under its influence, the nerve was irritated 
a second time, when both Professor Bowditch and Dr. War- 
ren observed the adduction of the vocal hand, which wras 
more marked in proportion as the stimulation was more in- 
tense. On removing the anaesthetic the dilatation became 
less and less as the animal regained its consciousness, when 
finally a contraction of the glottis supervened. The dif- 
ferent stages in this experiment were readily followed by 
* Not in any of these experiments sufficiently to feel pain. 12 
THE RESPIRATORY FUNCTION OF 
watching the dog’s vocal hands while, at the same time, the 
recurrent nerve was irritated at intervals of a few moments. 
Between extreme dilatation and forcible contraction, under 
these circumstances, there seemed to he a neutral point, so 
to speak, when the stimulation produced merely a vibratory 
movement of the vocal band ; but this was soon succeeded 
by an attempt at contraction, and this in turn passed into a 
frank and decided closure of the glottis as the animal, as 
before mentioned, came out of the effects of the ether. 
Similar results followed stimulation of one or the other of 
the divisions of the left recurrent nerve. These branches, 
as was shown by subsequent dissection, and as you will see 
on the specimen, united into one nerve fifteen millimetres 
below the cricoid cartilage, and from this point to the larynx 
it is a single nerve. The effects of irritation applied to the 
right recurrent (which was single) agreed with those on the 
left. Stimulation was effected by means of an ordinary 
induction apparatus,* the intensity varying from 1 to 40. 
In general, however, in this and in subsequent investiga- 
tions on other dogs, the intensity used was from 1 to 8, 
never over 10, and generally about 3. The experiment 
many times observed on this animal was repeated, with 
confirmatory results, on eight different dogs. But the ex- 
tent and the force, it must be mentioned, with which the 
vocal bands were abducted differed in different dogs. In 
five instances the arytenoid cartilage was rotated outward 
so forcibly that the vocal band lay flat against the wall of 
the larynx. Moreover, in one case there was a marked 
adduction of the vocal hand on the opposite side. In 
* The electrical apparatus was the same as that used by the writer 
in former experiments, to which the reader is referred for an explana- 
tion of the terms employed. (See “ Experimental Researches on the 
Tension of the Vocal Bands,” “Trans, of the Amer. Laryngological As- 
sociation,” 1883, p. 121.) THE HUMAN LARYNX. 
13 
other dogs a mixed movement was observed—that is, 
the band approached the median line anteriorly, while 
a simultaneous contraction of the posterior crico-aryte- 
noid muscle took place posteriorly, which left, in the 
respiratory portion of the glottis, a large triangular open- 
ing, the glottic picture resembling an exaggerated form of 
paralysis of the arytaenoidaeus transversus muscle. These 
phenomena were observed after the recurrent nerve had 
been cut and its peripheral end stimulated as well as 
when the nerve was intact. Usually when a young dog 
is under ether the vocal bands are seen moving rhythmic- 
ally and regularly with respiration. Occasionally, in this 
condition of profound narcosis, we noticed that, although 
the animal was breathing, the respiratory excursions of the 
vocal bands had entirely ceased, the glottis remaining wide- 
ly dilated. As soon as the respiratory movements had re- 
commenced, irritation of the recurrent nerve was followed 
by the usual adduction of the vocal band, an action we have 
become accustomed to regard as the normal one, provided 
the consciousness of an animal is completely abolished by 
sulphuric ether. The most striking demonstration, how- 
ever, of this dilatation of the glottis is obtained by placing 
an electrode on each of the recurrent nerves and irritating 
the two nerves at the same time. Both arytenoid cartilages 
are now rotated simultaneously outward, the glottis is held 
widely open during the stimulation, and the effect is one 
not soon to be forgotten. Krause * has noticed the differ- 
ence in the mobility of the vocal bands according as the 
animal was more or less narcotized. Just in proportion as 
consciousness was deadened, the adductors became sluggish. 
We have repeatedly observed the same effect when the dog 
was under morphine, chloral, or chloroform, but we failed 
* “ Experimentelle Untersuchungen und Studien viber Contracturen 
der Stimmbandmuskeln,” Virchow’s “ Archiv,” Band 98, 1884. 14 
THE RESPIRATORY FUNCTION OF 
with all these agents to obtain the total abolition of the ac- 
tion of the constrictors, on irritating the recurrent nerves, 
which is so marked when large quantities of ether, which 
can be given with safety, are administered. 
From the enormous development of the respiratory 
laryngeal muscles of the horse we conjectured that their 
contraction might be even more easily called forth than 
that of a dog’s. In this we were disappointed in the single 
experiment we have performed on this animal. Chloroform 
was the anajsthetic used. An incision was made in the 
hyro-cricoid membrane, through which the finger was in- 
serted and directed between the vocal bands. On irritating 
the recurrent nerve the finger was tightly squeezed by the 
contracting glottis. It is probable, however, that if ether 
had been employed instead of chloroform, and the horse 
thoroughly saturated with it, we should have felt the glottis 
dilate and not contract. We were indebted to the Harvard 
Veterinary College for this observation, and chloroform, for 
reasons of convenience, is the only anaesthetic used in that 
institution. 
With a view to ascertaining whether certain fibers in 
the recurrent were more vulnerable than others, we under- 
took a series of observations of which the following may be 
taken as the type: The nerve was exposed and a small 
crystal of chromic acid was laid upon it. The electrode 
being placed below this point, the nerve was irritated at in- 
tervals while the chromic acid was working its slow destruc- 
tion. In order to watch the effect upon the vocal band, the 
dog was arranged as in the previous experiments. When 
the animal was thoroughly etherized, the results did not dif- 
fer materially from those already described. Stimulation 
produced adduction of the vocal band. As the destructive 
process of the acid progressed, the vocal band gradually be- 
came completely paralyzed. But, even after the respiratory THE HUMAN LARYNX. 
15 
movements of the vocal band had entirely ceased, irritation 
was followed by an outward rotation of the arytenoid carti- 
lage. This was only occasionally seen, and lasted but a mo- 
ment, for, as soon as the conductivity of the nerve was 
completely destroyed, stimulation naturally produced no 
effect. We can only say that under these circumstances we 
were able to produce an adduction of the vocal band as long 
as any action at all was produced. How early or how late 
in the destructive process the adductor or phonatory fila- 
ments were attacked we know not. Being few in number 
(probably) as compared with the respiratory filaments, and 
as ether, as we have shown, arrests so effectually their ac- 
tion, we can not say here whether there was a “ proclivity ” 
of either the one set or the other to become affected. We 
simply demonstrated that the adductors held on to the last 
moment, for, as long as a single nerve-fiber of any kind was left 
intact, we got a contraction of the posterior crico-arytenoid 
muscle. When the destruction of the nerve was complete, 
the vocal band stood motionless in the cadaveric position. 
In proceeding now to a new order of experiment, we 
are able to record the endurance of the respiratory filaments 
contained in the recurrent laryngeal nerve, while those des- 
tined to supply the phonatory apparatus were altogether 
unable to respond to stimulation. We took a small, young 
dog, exposed the left recurrent nerve, and carefully passed 
a thread through the middle of it. The two ends of the 
thread were tied together in order to prevent its slipping 
out, but no pressure was exerted on the nerve itself. The 
object of the thread was simply to act as a foreign body. It 
was hoped that inflammation might thereby be excited, and, 
as the respiratory or phonatory fibers were the more readily 
attacked, the effect of an irritation applied to the nerve be- 
low the thread would be followed by certain derangements 
of motion of the vocal band. After the thread had been 16 
THE RESPIRATORY FUNCTION OF 
secured in the nerve, the parts were restored as nearly as 
possible to their normal situations, and the incision in the 
neck was sewed up. Inspection of the glottis showed that 
both vocal bands were moving normally with respiration. 
The following day the dog was again etherized and the 
glottis examined. No apparent change had taken place 
in either the appearance or natural mobility of the parts. 
The nerve was not disturbed. Since the thread had been 
introduced in it the nature of the dog had undergone a-* 
change. From having been a confirmed howler he had be- 
come a model of propriety. This happy improvement in 
his disposition lasted until he was destroyed. The quieting 
effect of a thread in the recurrent nerve has been noticed in 
many dogs subsequently. At the end of a week, the dog 
having been etherized and the glottis inspected on four dif- 
ferent occasions, he was again placed under the anajsthetic. 
As soon as a cannula could be placed in the external jugu- 
lar vein chloral was injected into it and the ether re- 
moved. It is important to remember that in the following 
experiments the animal was chloralized and not under 
the influence of ether. A slight but evident change was 
now observable in the vocal band corresponding to the 
nerve operated upon. Although the arytenoid cartilage of 
this side appeared to move with respiration as naturally as 
did the right cartilage, the anterior portion of the left vocal 
band seemed to have lost its “ tone ”; it did not come up 
with the same “snap” on expiration as its fellow. On 
opening the incision in the neck, the nerve was found im- 
bedded in a considerable mass of inflammatory tissue, from 
which it was impossible to separate it. After exposing the 
nerve below this point, it was placed in a shielded electrode. 
Irritation with an intensity varying from 1 to 10 produced 
adduction of the left vocal band, and cessation of its respi- 
ratory movements, the band remaining in the position of THE HUMAN LARYNX. 
17 
deep inspiration as long as the stimulation was kept up. 
On ceasing the irritation the respiratory movements went 
on as before. The right vocal band was in no way influ- 
enced when the left recurrent was stimulated with an inten- 
sity not exceeding 10. When, however, a more powerful 
stimulation (15) was employed, the right vocal band was 
brought to the median line (phonatory position), while at 
the same time the left band was pulled outward. We have, 
then, here a double effect: adduction of the vocal band on 
the healthy side, and adduction on the side where some 
alteration had taken place in the nerve fibers; or, in other 
words, the normal action of constriction of the right side 
was manifested while the left band was abducted, owing to 
the degeneration of the phonatory fibers, the respiratory 
filaments remaining unharmed ; and, consequently, the respi- 
ratory muscle alone responded to the stimulation. The 
right vocal band was now paralyzed by section of the right 
pneumogastric, the band coming to a standstill in the cadav- 
eric position, or the position we are accustomed to see in 
cases of “ recurrent paralysis.” Stimulation applied to the 
right recurrent resulted in a smart closure of the glottis, 
effected by the right vocal band being brought forcibly 
against its fellow, as well as by the contraction of the ary- 
tmnoidyeus transversus, which approximated the two aryte- 
noid cartilages. It could not be accurately determined 
whether the anterior portion of the left band contracted or 
not, as even a feeble irritation produced such a rapid and 
complete closure of the laryngeal aperture. If the closure 
of the left vocal band was brought into action, it was very 
slight; it was evident that the closure of the glottis was 
chiefly effected by the contraction of the constrictors on 
the right side, and by the arytsenoidaeus transversus muscle. 
The electrode was again changed to the left recurrent below 
the insertion of the thread. Stimulation was followed by 18 
THE RESPIRATORY FUNCTION OF 
the same outward rotation of the left arytenoid cartilage as 
was observed in the first experiment. There was also a 
marked movement of the right arytenoid cartilage toward 
its fellow, as if by the contraction of the arytaenoidfeus trans- 
versus muscle. The action of this muscle was prominently 
brought into play in the next experiment, when the periph- 
eral end of the left recurrent was stimulated, after section of 
the nerve below the thread. Both vocal bands were now 
paralyzed and standing in the cadaveric position. All 
avenues to the brain were thereby cut off except through 
the anastomoses of the terminal branches of the recurrent 
with those of the superior laryngeal, and, perhaps, also with 
those from the pharyngeal plexus. Irritation of the periph- 
eral end of the left recurrent produced both a contraction 
of the left posterior crico-arytenoid and transverse arytenoid 
muscles. That is, there was a distinct outward rotation of 
the vocal process of the left arytenoid cartilage, and an ap- 
proximation of both arytenoid cartilages at the same time. 
Positive as were the results of this series of experiments, 
we lay no stress upon them. If they are of any worth, it 
will be by suggesting to others some better method than 
was here employed, for all our attempts to verify the ob- 
servations have failed. Even when the thread had been 
previously soaked in a one-per-cent, solution of chromic 
acid it did not cause any material disturbance when intro- 
duced through the nerve and retained there for many days. 
The only change noticed was that, in some of the dogs, a 
more powerful stimulation was required to produce a con- 
traction of the vocal muscles through the nerve operated 
upon than in the opposite healthy side. 
CONCLUSIONS. 
The principal fact herein demonstrated is, to our mind- 
the power and the endurance of the posterior crico-arytenoid THE HUMAN LARYNX. 
19 
muscles and of the nerves which supply them. We have 
spoken of the theoretical reasons: (1) The physiological 
importance of these muscles; (2) their belonging to organic 
life; (3) their extensive nerve-supply, all of which would 
tend to preserve their functional integrity. Moreover, if it 
he true that there is a “proclivity” of the adductor fibers 
to become diseased, and that unilateral paralysis of the ab- 
ductor muscle is such a common and harmless lesion, should 
we not expect, theoretically, that bilateral paralysis of this 
muscle would occur more frequently ? Yet there can be no 
dispute whatever that bilateral paralysis of the posterior 
crico-arytenoids is a disease as rare as it is grave. 
Now, with regard to these muscles being extensors, and, 
like the extensors in other parts of the body—the forearm, 
for instance—more liable to succumb to disease than the 
fiexors, we would ask this simple question: AVhy should the 
terms “ extension ” and “ flexion ” be applied to the rota- 
tion of the arytenoid cartilages ? The principal office of 
the posterior crico-arytenoids is to maintain the respiratory 
patency of the glottis. From the beginning to the end of 
life they are in a state of semi-contraction—holding the 
glottis open. They come, therefore, just as near being- 
flexors as extensors ; but, as a matter of fact, they are neither 
the one nor the other in the ordinary acceptation of these 
terms as applied to muscles of the general system. They 
are respiratory muscles carrying on a special function. One 
might as w ell speak of the movements of the pupil as exten- 
sion and flexion, or compare the diastole of the heart to the 
extension of the forearm, or its systole to the bending of 
the little toes. Muscles are analogous as they discharge 
analogous functions. We recognize no more analogy be- 
tween the posterior crico-arytenoid muscles of the larynx 
and the extensor communis digitorum of the forearm than 
there is between “respiration” and “prehension.” If we 20 
RESPIRATORY FUNCTION OF THE HUMAN LAR\NX. 
wish to seek muscles that are analogous, let us turn to other 
respiratory muscles and ask how they are affected by dis- 
ease. In diffused, progressive diseases of the nervo-muscu- 
lar system we know that of all muscles, except the heart 
itself, those belonging to the respiratory system are al- 
ways the last to he attacked, and there is no valid reason 
why the respiratory muscles of the larynx—either one or 
both—should offer an exception to the rule, especially as 
they are the most important of all. 
We propose to investigate this subject from a clinical 
aspect at some future date, when, perhaps, the positions 
which immobile vocal bands assume may he sufficiently ex- 
plained without attributing to a wise and conservative na- 
ture a “ proclivity ” to attack one of the most vital muscles 
of the human system.