With the writer's Compliments. 
EXPERIMENTAL RESEARCHES ON THE 
TENSION OF THE VOCAL BANDS. 
0)—THE ACTION OF THE TilYRO-CRICOID MUSCLE. 
(b)—THE ACTION OF THE EXPIRATORY BLAST OF AIR. 
BY 
F. H. HOOFER, M.D. H 
BOSTON 
ASSISTANT THYSICIAN TO THE CLINIC FOR DISEASES OF THE THROAT, MAS- 
SACHUSETTS GENERAL HOSPITAL ; FELLOW OF THE AMERICAN 
LARYNGOLOGICAL ASSOCIATION, ETC. EXPERIMENTAL RESEARCHES ON THE TEN- 
SION OF THE VOCAL BANDS. 
(a). THE ACTION OF THE THYRO-CRICOID MUSCLE/ 
(£). THE ACTION OF THE EXPIRATORY BLAST OF AIR.V 
By F. H. HOOPER, M.D., Boston, 
ASSISTANT PHYSICIAN TO THE CLINIC FOR DISEASES OF THE THROAT, MASSACHUSETTS GENERAL 
HOSPITAL ; FELLOW OF THE AMERICAN LARYNGOLOGICAL ASSOCIATION, ETC. 
THE experiments recorded in this paper were per- 
formed in the physiological laboratory of the Har- 
vard Medical School, in conjunction with Professor Henry 
P. Bowditch. 
The diagrams and figures contained in the text were re- 
produced from the original tracings and drawings by the 
photo-electrotype engraving process. 
(a).—THE ACTION OF THE THYRO-CRICOID MUSCLE. 
Although the literature pertaining to the function of this 
important tensor—commonly but incorrectly called the 
crico-thyroid muscle—is not extensive, it furnishes us with 
every possible variety, of opinion. The muscle is usually- 
described as arising from the front and lateral part of 
cricoid cartilage ; its fibres pass upward and outward, diverg- 
ing slightly, and are inserted into the inferior and inner 
border of the thyroid cartilage from near the median line 
in front, and as far back as the anterior border of its lower 
cornu. Its nervous supply comes principally from the ex- 
ternal branch of the superior laryngeal nerve. 
The observers who have directed their attention to its 
action may be divided into six classes:— 2 
F. H. HOOPER. 
I. Those who hold that it tilts the thyroid cartilage 
downward and forward on to the cricoid. (This is the gen- 
erally received theory in regard to it, and is the view ex- 
pressed in such standard works of anatomy and physiology 
—with the exception of the ninth edition of Quain, which 
has only recently appeared—as Galen, Casserius, Gray, Hyrtl, 
Henle, Meyer, Meckel, Hartmann, Cruveilhier, Sappey, 
Morel et Duval, Carpenter, Huxley, Todd and Bowman, 
Foster, Hermann, and others; and among laryngologists, 
Turck, Stoerk, Mackenzie, Schrotter, and Seiler.) 
II. Those who affirm that it draws the cricoid up on to 
the thyroid. (Cowper, 1724; Magendie, 1813; Lauth, 1835; 
Bishop, 1839; Longet, 1841 ; Cuvier, 1846; Harless, 1853 ; 
Battaille, 1861; Fourni£, 1866; Jelenffy, 1873; Schech, 
1873; Schmidt, 1873; Milne Edwards, 1876; Cohen, 1880; 
Elsberg, 1882 ; Quain’s Anat., 9th ed.) 
III. Those who maintain that it draws both cartilages 
together by its contraction, the predominance of movement 
being in the thyroid. (Vesalius, Merkel, Theile, B£clard, 
Harrison.) 
IV. Those who assert that its action is according to the 
fixation of the cartilages ; that when the cricoid is the point 
fixed, the thyroid is the one moved, and vice versa. (Budge, 
Riegel, Mandl.) 
V. Those who insist that instead of drawing the car- 
tilages together, its function is to retain them in a fixed 
position when separated. (Vierordt, Luschka.) 
VI. The sixth class is purely of historical interest. 
Brown (1683) stated that “when the muscle is contracted, 
it extends the cartilage cricois, or annularis, and so openeth 
its cleft for a more deep and greater voice or sound.’' 
Dionis (1695) considered that its action was to dilate the 
sides of the thyroid, thereby enlarging the glottis. Haller 
(1766) agreed with this view, but thought also that it ap- 
proximated the two cartilages. 
But one explanation can be offered to account for these 
conflicting theories. Except in the case of four observers 
(Magendie, Longet, Schech, Schmidt), the above hy- 
potheses were not founded upon experimentation. They TENSION OF THE VOCAL BANDS. 
3 
are mere speculations unsupported by reliable experimental 
proof. And it is a significant fact that the four observers 
named—the only ones who substantiated their opinions by 
experiments upon animals—all agree concerning the action 
of the muscle. 
Magendie in 1813 not only gave a very clear description of 
the distribution of the laryngeal nerves, but he was the first, 
by experimentation, to observe and record the true action 
of the thyro-cricoid muscle. He fails to tell us upon what 
animal he made his observation, and contents himself with 
saying: “ Quand on la peau du col, de maniere h 
apercevoir 1’ intervalle crico-thyroidien, on a lieu de se con- 
vaincre que dans la production des son aigus, et surtout & 
I’ instant de la deglutition, le cartilage cricoide s’ £l£ve au 
point que son bord sup£rieur s’ engage sous le bord inf£rieur 
du cartilage thyroide.” 
We find mentioned, however, in Cowper (1724), that the 
function of the muscle “ is to pull up the annularis rather 
than to bring down the scutiformis.” 
Our own experiments, performed in a different manner 
from any hitherto recorded, result, we think, in definitely 
determining the chief effect produced upon the cartilages by 
the contraction of the muscle. They prove the accuracy 
of Magendie’s early observation, and force us to reject the 
theory, so generally accepted, that the thyroid cartilage is 
drawn down by its influence. The dogs used in the investi- 
gations were prepared as follows: 
The animal being thoroughly etherized and secured to a 
dog-holder on a table, both superior laryngeal nerves were 
exposed and placed on shielded electrodes. The nerves 
were tied just above the electrodes, in order to prevent 
reflex stoppage of the respiration on irritation. The thy- 
roid and cricoid cartilages were next exposed without 
disturbing any muscular attachment. Two levers, twenty- 
eight centimetres in length, composed of ordinary straw, 
and terminating at one end in a strong pin, were stuck into 
the centre of each cartilage. The farther end of each lever, 
being tipped with a delicate metallic point, was so arranged 
as to record graphically on a smoked paper of a revolving 4 
F. H. HOOPER. 
cylinder the movements of the cartilages produced by irri- 
tating the superior laryngeal nerves. 
Stimulation was produced by a rapid succession of induc- 
tion shocks from an apparatus graduated empirically by 
Fick’s method. The graduation was such that an intensity 
of 1,000 corresponded to the stimulation produced when a 
secondary coil of 10,260 turns of fine wire was pushed 
wholly over the primary coil. After repeated trials, it was 
determined that an intensity of fifteen was the most appli- 
cable to the purpose, and this intensity was, therefore, 
employed in all the experiments. 
The tracings are to be read from left to right. The 
asterisk denotes the beginning of the stimulation, the 
dagger the end. 
Fig 1 
Thyroid. 
Cricoid. 
DOG ETHERIZED ; SUP. LARYNGEAL NERVES TIED. 
The undulations of the above tracing in fig. i represent 
the respiratory movements of the larynx. At the point of 
stimulation, it will be noticed that the cricoid cartilage was 
drawn up toward the thyroid, as indicated by the marked 
rise of the cricoid curve. As soon as the irritation ceased, 
the lever immediately fell to its previous level. No up- TENSION OF THE VOCAL BANDS. 
5 
ward or downward movement of the thyroid, however, can 
be observed. The respirations are somewhat shortened 
during the stimulation, but the recording pen attached to 
the thyroid cartilage remains on the same level throughout 
the experiment. The next experiment, performed after the 
dog had been killed by section of the medulla oblongata, 
yields the same result. 
Fig 2 
Thyroid 
Cricoid. 
DOG ; MEDULLA DESTROYED. 
In this figure (2) it will be noted that, respiration having 
ceased, the pens trace a straight line. As in the previous 
experiment (fig. 1), stimulation of the nerves caused the 
same rise of the cricoid, while no appreciable effect was pro- 
duced on the thyroid. The minute elevations in the thyroid 
line, at the points of irritation, were probably accidental, as 
will be explained hereafter. The following experiment was 
performed on a different animal, but under similar condi- 
tions as the preceding. 
Here (fig. 3) the same effects as in the foregoing experi- 
ments are evident, only more pronounced, the rise of the 
cricoid being very powerful. The undulations in the thyroid 
line will be readily understood when we consider what an in- 
finitely small amount of movement of the cartilage would be 6 
F. H. HOOPER. 
sufficient to produce a change in a flexible pen at the end 
of a lever of the length used in these researches. Indeed, 
it is surprising that there is not more oscillation, for, the 
thyroid not being absolutely fixed, the contraction of the 
muscle would necessarily cause enough motion to account 
for the slight unevenness of the thyroid lines. But that 
there is no positive movement imparted to the thyroid by 
the action of the muscle seems beyond doubt. 
Thyroid 
Fiy 3. 
Cricoid 
DOG ; MEDULLA DESTROYED. 
These experiments were repeated many times, on the 
same and different dogs, always with confirmatory results. 
A dissection was made subsequently in every instance, in 
order to be sure that the electrodes had been on the su- 
perior laryngeal nerves,—a necessary precaution in such in- 
vestigations. 
We by no means submit these researches as establishing 
the entire function of the thyro-cricoid muscle; inasmuch as 
this, like all the intrinsic muscles of the larynx, has the impor- 
tant characteristic of being arranged or divided into bundles TENSION OF THE VOCAL BANES. 
7 
of fibres. Under what conditions these bundles act, how 
they act, whether they can act separately or only jointly, is 
as yet undetermined. Nevertheless, the salient point clear- 
ly demonstrated by our experiments is, that the principal 
effect of the contraction of the muscle is to draw the ante- 
rior portion of the cricoid cartilage up on to the thyroid, 
the latter remaining practically fixed. The posterior plate 
of the cricoid, with every thing attached to it, being, there- 
fore, rotated downward and backward, the bands are neces- 
sarily stretched. It would be beyond the scope of this paper, 
besides leading us into the field of speculation, to discuss the 
probable working of the different bundles of the muscle. 
But it is not improbable that the vocal bands, being 
stretched in the first place in the manner described, the 
oblique bundles may then, in their turn, come into play, 
and increase the tension by pulling the cricoid cartilage di- 
rectly backward. When we bear in mind that (with the 
exception of a small part of the inferior constrictor) not a 
single extrinsic muscle is attached to the cricoid cartilage, 
and reflect upon the mechanical construction of the larynx, 
it is difficult to comprehend by what mechanism it can pos- 
sibly be fixed in a sense that would permit the thyroid to 
be pulled down upon it. Nature, doubtless, never intended 
that it should be. On the contrary, its extreme mobility is 
one of its most striking and distinguishing characteristics. 
In vocalization the thyroid cartilage, steadied by the pow- 
erful extrinsic muscles inserted into it, may be regarded (as 
compared to the cricoid) as the passive agent, while the lat- 
ter, owing to the manner in which it swings upon the short 
processes of the thyroid behind, and to the elasticity of the 
parts in front, and to a certain extent on the sides, is per- 
mitted to play upon it with every delicacy of adjustment 
through he agency of the intrinsic muscles of the larynx 
attached to it, and of another force presently to be alluded 
to. Indeed, were it not for this free and unrestrained move- 
ment of the cricoid cartilage on to the thyroid, the marvel- 
lous capabilities possessed by certain phenomenal voices 
would be impossible. For to it the stretching of the vocal 
bands is, in a great measure, directly due. When we are 8 
F. II. HOOPER. 
told,1 by J. Solis-Cohen, that a certain singer, with a compass 
of three octaves, was capable of effecting as many as two. 
thousand one hundred changes of pitch, and “that the va- 
riation of tension between the tones that she could produce 
would represent a successive lengthening and shortening of 
the vibrating edges of the vocal bands in successive propor. 
tions of one seventeen-thousandth of an inch,” we are simply 
lost in astonishment. It is therefore interesting to inquire 
whether muscular action is the only agent concerned in 
effecting such extensive as well as delicate adjustment as 
this. 
Passing now to our second series of experiments we shall 
attempt to point out another, and not an unimportant, 
factor concerned in tightening the vocal bands, which, act- 
ing independently of all muscular innervation, exerts its in- 
fluence upon the cricoid cartilage, causing a movement of it 
identical with that produced by the action of the tensor just 
considered. 
(&) THE ACTION OF THE EXPIRATORY BLAST OF AIR. 
Hitherto the action of the air-blast as a tensor of the 
vocal bands has been recognized as producing its effect (as 
any current of air might stretch an elastic membrane) 
merely by its force in coming in contact with them. But it 
is the purpose of the subjoined experiments to establish the 
fact, that in addition to the general rise of the whole larynx, 
as in singing high notes, the pressure of air causes an 
excessive and independent upward movement of the 
cricoid cartilage on to the thyroid, of which no mention, to 
our knowledge, has heretofore been made. 
The method adopted in arranging the dogs was as 
follows : 
Having been thoroughly etherized during the early part 
of the operation, the animal was subsequently killed by 
bleeding and section of the medulla oblongata. The thyroid 
and cricoid cartilages were first exposed by a careful dissec- 
tion in order that the normal position of the external 
muscles of the larynx might be disturbed as little as pos- 
1 “ The Throat and the Voice,” p. 105. TENSION OF THE VOCAL BANDS. 
9 
sible. The sternum being removed, a T-shaped canula was 
firmly tied into the trachea very near the base of the lung. 
One arm of the canula communicated with a Fick’s man- 
ometer which registered the pressure of the air blown into the 
trachea through the other arm by the experimenter. The 
larynx being nearly closed during life by the approximation 
of the vocal bands in phonation or in singing it was neces- 
sary in some way to imitate, as satisfactorily as possible, the 
natural condition of the parts by closing up the larynx. 
This was effected by a pad of cotton-wool, extending 
down to the vocal bands, upon which a small quantity of 
plaster of Paris was poured, which on hardening rendered 
the larynx sufficiently tight for the performance of the 
experiments. The same levers used in the foregoing ex- 
periments were stuck into the thyroid and cricoid cartilages 
respectively at points represented in the drawing by black 
dots. Advantage was also taken of the same graphic 
method, the pens tracing, on a horizontal revolving cylinder 
bearing a smoked paper, the curves made by the moving 
cartilages under the pressure of the column of air coming 
from the trachea below. The vertical line bearing the num- 
bers 20, 40, 50 represents the pressures in millimetres of 
mercury, the Fick’s manometer having been experimentally 
graduated. The dotted lines show the positions of the 
ascending levers attached to the cartilages at corresponding 
pressures. 
The arrow indicates the direction in which the curves are 
to be read. 
The tracings in this figure (1) were obtained by inflation 
of the trachea when the extrinsic muscles of the larynx were 
intact. A glance at the diagram shows that at equal 
pressures the rise of the cricoid curve above its zero line 
exceeds that of the thyroid. By measurement we have at 
a pressure of 20 mm. Hg., an ascent of the cricoid lever of 
8 millimetres, while that of the thyroid at the same 
pressure is 7. As the force of the blast of air is in- 
creased, the difference is more marked. At a pressure 
of 40 mm. Hg., the cricoid moves up 16 mm., the 
thyroid 10.5 mm. At a pressure of 50 mm. Hg., the 10 
F. H. HOOPER. 
increase is still greater. Under this pressure the cricoid 
goes up 19.5 mm. to 12 mm. of the thyroid. At all pres- 
sures, therefore, in this experiment, we have an excess of 
movement of the cricoid cartilage over that of the thyroid. 
F,g r. 
?V7"a.v\ owietev, 
Tty ocol i 
Cvi c o ccf. 
MUSCLES INTACT. 
The difference in the height of the curves at the several 
pressures being i, 5.5, 7.5, represents in millimetres the 
approximation of the cricoid pen to that of the thyroid, 
and a consequent stretching of the vocal bands. The 
amount of stretching may be computed by dividing this 
difference by the ratio of the length of the lever (28 cm) to 
the distance from the vocal process to the crico-thyroid 
articulation (16 mm.). This ratio being 17.5 to 1 we obtain 
a lengthening of the vocal bands of about .06 mm., at 
a pressure of 20 mm. Hg., .31 mm. at 40 mm. Hg., 
and .43 mm. at 50 mm. Hg. TENSION OF THE VOCAL BANDS. 
In order to determine what influence, if any, the extrinsic 
muscles of the larynx coming from the sternum and attach- 
ed in front of the axis of rotation of these cartilages, would 
exert upon their movements, experiments were made of 
blowing up the trachea after section of the sterno-hyoid and 
sterno-thyroid muscles on each side. The accompanying 
diagrams (reduced about one third) of a dissected larynx of 
one of the dogs used, show the relation of the parts very 
clearly. 
LARYNX OF DOG. FRONT VIEW. 
In the above dissection the sterno-hyoidei have been drawn 
slightly apart with the intention of exposing the anterior 
surface of the thyroid cartilage, in order to show the point 
of insertion of the lever. In the following 12 
F. H. HOOPER 
SIDE VIEW 
the asterisk marks the point of articulation of the two carti- 
lages. The supposition that the powerful muscles attached 
anteriorly to this pivot might effect the movements of the 
cartilages, was sustained by the following experiments. 
F,g.Z. 
Ma.no meter 
'Thy*' oid. 
CrcCoi£. 
STERNO-HYOIDEI CUT. TENSION OF TIIE VOCAL BANDS. 
13 
F;,.3. 
\Ta.Hom*t*r- 
1~k yrotaC 
Cri,toid. 
Inspection of these curves (figs. 2 and 3) suffices to show 
the increase in their height on inflation, after the depressor 
muscles had been divided, as compared with fig. 1 when 
those muscles were intact. Their relative distances in num- 
bers at the different pressures may be best appreciated by 
the following table. 
SI'ERNO-HYOIDEI AND STERNO-THYROIDEI CUT. 
Am’t. of pressure 
Movem’t 
Movem’t 
Difference, representing 
Amt. of stretch- 
in mm. Ilg. 
of cri- 
of thy- 
approximation of the 
ing of the vocal 
coidpen. 
roidpen. 
cricoid cartilage to the 
bands in mm. 
thyroid. 
(about) 
20 
8. 
7- 
1. 
.06 
40 
16. 
10.5 
5-5 
•3r 
50 
19-5 
12. 
7-5 
•43 
FIG. 2.—STERNO-HYOIDF.I CUT. 
20 
4- 
7- 
—3- 
—.17 
40 
16. 
12.5 
3-5 
.20 
50 
22. 
15- 
7- 
.40 
FIG. 3. 
—STF.RNO-HYOIDEI AND STERNO-THYROIDEI CUT. 
20 
4-5 
4. 
• 5 
.03 
40 
17. 
15- 
2. 
.11 
50 
27. 
21. 
6. 
• 34 
FIG. I.—MUSCLES INTACT. F. //. HOOPER. 
Ninety-two experiments of this character were recorded, 
which were performed on nine different dogs, and although 
the general results corresponded with the above figures, it 
must be admitted they were not invariably uniform in regard 
to the effect of section of the muscles. The discrepancies 
were, however, more probably owing to the many and ob- 
vious difficulties which beset the complicated nature of the 
experiments, than to any error in the principles involved. 
Not presenting them, therefore, as being scientifically accu- 
rate, the point we wish especially to emphasize, namely, 
the greater excursion of the cricoid cartilage over that of 
the thyroid, was evident, and we think the following facts 
may be said to have been established : 
I. At high pressures the cricoid cartilage invariably moved 
more than the thyroid. It may safely be asserted that at 
all pressures such ought to be the result, for in only six out 
of the ninety-two experiments was the thyroid found to 
have made a larger excursion than the cricoid. This, in 
each instance, happened at the lowest pressure; due, 
perchance, to some minute obstacle on the revolving cylin- 
der which impeded the immediate rise of the pen, or to 
some such accidental cause. In fig. 2, at the low pressure, 
it will be observed that this anomalous movement took 
place. 
II. At high pressures, after section of the muscles, both 
cartilages move up more freely. But inasmuch as the thy- 
roid rises more, in proportion to the cricoid, than when the 
muscles are intact, the difference between the curves, it will 
be noted, is less, and consequently also the stretching of the 
bands. That the uncut muscles, therefore, which are 
attached anteriorly to the axis of rotation of these cartilages 
should restrain their motions, to some degree, especially 
that of the thyroid, seems probable. 
It is evident, then, from these researches, that the air 
escaping from the lungs produces a decided upward move- 
ment of the cricoid cartilage, in addition to the general 
rise of the larynx, which movement increases in propor- 
tion to the force with which the air is expelled from the 
chest. TENSION OF THE VOCAL BANDS. 
15 
This movement may be readily observed by taking an 
excised human larynx or that of one of the lower animals, 
dog or cat, and arranging it in this manner. Suspend the 
larynx to an ordinary iron holder by a clamp attached to the 
hyoid bone. Plug the glottis with cotton-wool and plaster. 
Inflation of the trachea causes the front part of the cricoid 
cartilage to rise on to the thyroid. Easy as it is to demon- 
strate this phenomenon, we meet with a difficult problem in 
proceeding to explain the cause of it. It seems fair to infer 
that from the anatomical construction of the larynx the 
ascent of the cricoid must be an active, and the descent a 
passive movement. For when the parts are at rest physio- 
logically, the attachment of the cricoid to the trachea 
and the strength of the thyro-cricoid ligament would 
prevent any downward movement of the cricoid cartilage 
per sc ; if any such movement did take place, it would have 
to be shared also by the thyroid cartilage and the trachea. 
It was at first thought that the trachea itself, stretched and 
expanded by inflation, would push the cricoid upward, and 
thus approximate it to the thyroid. But we were compelled 
to abandon this view, as it was found that, after cutting the 
trachea off close to the cricoid, leaving only enough (two 
rings) to attach the canula, the phenomenon took place as 
before. 
It was then suggested that the force arising from the 
communication of motion of the current of air passing from 
the trachea into the laryngeal cavity might communicate its 
onward motion to the cricoid, and thus raise it on to the 
thyroid. The non-resisting and elastic crico-thyroid mem- 
brane offering no obstacle to such a movement of the cricoid 
cartilage, while the ascent of the thyroid would be checked 
by the resistance arising from the approximation of the 
bands inside, and the influence of the extrinsic muscles out- 
side. Not being thoroughly satisfied, however, that this 
explanation solved the problem, we surmised that the ex- 
pansion of the larynx itself, when inflated, might play an 
important part in producing the phenomenon. 
The construction of the larynx is so complicated, it is 
not at first sight clear why such a movement as we have 16 
F. //. HOOPER. 
described should be caused by inflation, for when the cricoid 
cartilage is pulled up on to the thyroid (as by the action of 
the thyro-cricoid muscle) the vertical dimensions of the 
larynx are diminished, while the antero-posterior dimen- 
sions are increased. Whether the capacity of the larynx is 
increased or diminished by this movement cannot well be 
determined a priori. Therefore the following experiment 
was made in order to ascertain whether an upward move- 
ment of the cricoid cartilage was necessarily associated 
with an increased capacity of the larynx. 
EXPERIMENT. 
Small dog. Curarized. Artificial respiration. Pharynx 
plugged with cotton-wool; a cord strongly tied around the 
head and jaw in front of the ears, to compress the cotton 
and the passages leading upward. Trachea divided between 
second and third rings. A tubulated cork secured in the 
upper end, connected by a rubber tube with a delicate 
Marey’s drum, whose lever indicates for every millimetre of 
excursion a certain fraction of a cubic centimetre of change 
of volume (i mm. of curve = o.oi cc. of volume). Irritation 
of the thyro-cricoid muscle on one side caused a descent of 
the lever of io mm., indicating an increase of the capacity 
of the larynx of one tenth of a cubic centimetre. When 
both thyro-cricoid muscles were simultaneously stimulated 
the lever went down 15 mm., showing, as might be ex- 
pected, a still greater increase of the capacity of the larynx, 
as both of the muscles working together would naturally 
produce a more forcible rise of the cricoid than one alone. 
It may be questioned, certainly, how far an experiment 
of this nature can be applied to the living human larynx, or 
with what logical justice we can draw conclusions from it. 
We believe, nevertheless, and we shall append additional 
proof to sustain our opinion, that the lumen of the larynx 
is enlarged by an upward movement of the cricoid cartilage, 
and therefore in violent phonic efforts the cricoid, owing to 
the expansion of the larynx, must move upon the thyroid 
in such a way as to stretch the bands, since by so doing it 
increases the capacity of the larynx. TENSION OF THE VOCAL BANDS. 
17 
Inspection of the dissected human larynx enables us to 
see that the distance from the vocal process of the aryte- 
noid cartilage to the crico-thyroid articulation is greater 
than the distance from this point to the anterior edge of 
the cricoid cartilage. The pivot then being at the articula- 
tion, the long arm of the lever is above, the short arm in 
front of the fulcrum. The diagram herewith presented, 
drawn from exact measurements, and representing the 
inside of the right lateral half of a human larynx from which 
the soft parts have been removed, shows us at a glance the 
relative proportions of the unequal arms of the lever. The 
fulcrum, denoted by the black dot, is directly opposite the 
crico-thyroid articulation. 
Now here are two artificial larynges roughly constructed 
to illustrate the points of the present inquiry. The models 
are composed of a skeleton of wood, enclosed in a piece of 
thin rubber tubing, which renders them air-tight, with the 
exception of a small opening in the top, into which a glass 
tube is inserted. For convenience of description they may 
be designated as Nos. I and 2. No. I is articulated on the 
principle of the human larynx, namely, with the short arm 18 
F. H. HOOPER. 
of the lever in front of the fulcrum. Connecting this by 
means of the rubber tube with the Marey’s drum, and imi- 
tating the action of the thyro-cricoid muscle, by pushing 
the cricoid upward, we notice a fall of the lever denoting 
an increase in the capacity of the model. No. 2, on the 
other hand, is articulated in such a manner that the long 
arm of the lever is in front of the pivot. It will be seen in 
this case that, in making the same movement, the lever at- 
tached to the drum will ascend. Now, if the human larynx 
were constructed on this principle, it is evident that a blast 
of air would, by increasing the capacity of the larynx, relax 
the vocal bands. The relaxation being due in such a case 
to the fact that, as the horizontal arm of the lever is longer, 
and offers a larger area than the vertical arm, the pressure 
of the air inside the larynx would tend to force the former 
downward rather than the latter backward. The dotted 
lines in the following two cuts, indicating the manner the 
lever would move in the two instances, make our reasoning 
clear. No. 1 is according to the leverage of the human 
larynx ; No. 2, not. The line a b represents the vocal 
band. 
/o.l 
/To. 2 
These researches may, perhaps, offer a suggestive clue in 
elucidating certain pathological conditions.1 For instance, 
the fact that the singing voice can be relied upon, while, in 
the same individual, conversation is impossible, may, per- 
chance, in a measure, be explained by this action of the air- 
blast as a tensor at high pressures. We know that the 
1 See case reported by Solis-Cohen: “ Diseases of Throat,” p. 642. Ed., 1880. TENSION OF THE VOCAL BANDS. 
famous singer, Malibran, was always at constant war with 
her rebellious voice. She would never admit that it could 
resist her ; it was something to be conquered. And it is 
only necessary to refer to the interesting pages by M. Le- 
gouve upon this remarkable woman to learn the power of a 
strong will and powerful lungs to overcome vocal difficulties, 
and how she, with her characteristic saying, “ I will force it 
to obey me,” was able, in spite of severe pharyngeal inflam- 
mation, to electrify an audience solely by the violence of 
her efforts. It is insufficient to ascribe such vocal feats to 
“inspiration” so-called. There can be no vocal effects 
produced without definite physical causes. There may be 
many which are not demonstrable, for the working of the 
intrinsic muscles of the larynx is so complex that it is 
doubtful if we can devise any means of investigation suffi- 
ciently delicate to determine accurately all the laws which 
regulate their marvellous adjustments. Experimentation 
on one’s self, after the fashion of certain writers, by push- 
ing the cartilages with the fingers this way and that, pre- 
sumably imitating the action of some muscle, is too gross a 
method to apply to such a delicate apparatus as the larynx ; 
and theories founded on such manipulations, however inter- 
esting, cannot be accepted as reliable. To insure accuracy, 
the nerve supplying the muscle, or muscular bundles, ought 
to be exposed and irritated, and the working of the fibres 
graphically registered in some such manner as we have 
attempted. We think the facts demonstrated by these 
researches justify the following conclusions: 
I. The cricoid cartilage is the most movable part of the 
laryngo-tracheal tract. 
II. The thyro-cricoid muscle, according to its physiologi- 
cal action, should be described as arising from the thyroid 
cartilage, and inserted into, and giving motion to, the cri- 
coid. 
III. The air-blast, in virtue of the mechanism herein set 
forth, is a direct- and important longitudinal tensor of the 
vocal bands. 20 
F. H. HOOPER. 
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