AIST ESSAY 
ON 
THE MECHAISTISM OE THE 
OSSICLES OF THE EAR 
alekrt n. buck, m.d., 
BY 
Asbisxant Aubad Sdbgkgn to tttk New York Eye and Ear Infirmary. 
NEWYORK: 
WILLIAM WOOD AND COMPANY. 
MDCCCLXX. Reprinted from the Archives of Ophthalmology and Otology, 
Vol. 1., No. 2. ON THE MECHANISM OF THE OSSICLES OF THE EAR. 
ALBERT H. BUCK, M.D., op New York* 
In 1851 Edward Weber f put forth the doctrine that 
in the transmission of sound from the external ear to 
the acoustic nerve the ossicles play the part of a solid 
angular lever, whose office is to transmit to the fluid of 
the labyrinth the movements imparted to the memhrana 
tym/pani by waves of sound. According to this doctrine 
the fluid of the labyrinth is moved only as a whole, and 
the function of the memhrana tymjpani secundaria is 
simply that of affording a point where the ' fluid can 
yield to the pressure made upon it by the base of the 
Stirrup. 
On the other hand, the prevailing doctrine was that 
the ossicles form a connecting medium through which 
waves of rarefaction and condensation are transmitted 
from the memhrana tymypani to the fluid of the labyrinth, 
and that some waves of sound also reach the labyrinth 
by way of fenestra rotunda. 
* An essay to which a prize was awarded by the Alumni Association of the Col- 
lege of Physicians and Surgeons of New York. 
f Berichte fiber die Yerhandlungen der K. Sachs, Gesellschaft der Wissenschaften 
zu Leipzig. Math. Phys. Classe, 1851. 
1 Between these two views physiologists have been di- 
vided in opinion even up to the present time, although 
the majority perhaps favor the former doctrine. 
In the following experiments an attempt has been 
made to determine by direct observation which view is 
the correct one. The method employed in the investi- 
gation is very simple, and free from the objections to 
which Politzer’s method is liable.* This experimenter 
attached hne glass rods to different parts of the ossicles 
and studied their action whilst concentrated waves of 
sound were being conducted into the external auditory 
canal. As will be seen farther on, these rods constitute 
an important disturbing element, both by their weight 
and elasticity. 
I am indebted to Prof. Helmholtz as well for the sug- 
gestion of this method, as for his constant assistance 
throughout the course of the experiments. 
Material used, mode of preparing it for observation, 
and means employed for conducting waves of sound in- 
to the external auditory canal. 
Specimen. 
Age. 
Sex. 
Nos. 1 and 2. 
30. 
Male. 
No. 3. 
20. 
Female. 
Nos. 4 and 5. 
50. 
Male. 
No. G. 
40. 
Male. 
No. 7. 
20. 
Male. 
Nos. 8 and 9. 
29. 
Male. 
Nos. 10 and 11. 
29. 
Male. 
In the following experiments eleven human adult tem- 
poral bones were used. They were removed from the 
* Archiv fur Ohrenheilkunde, 1864. 3 
bodies as soon as possible after death, and preserved in a 
very weak solution of spiritus vini. 
A portion of the cartilaginous external auditory canal 
was left attached to each temporal bone, sufficient to ad- 
mit of the introduction of a suitable sound-conducting 
tube. The roof of the drum was then carefully chiselled 
away until a good view could be obtained of the greater 
part of the hammer and anvil, and of the head of the 
stirrup. The labyrinth and all the connections of the 
membrane of the drum and ossicles, with the exception 
of the ligamentum mallei sujperius, were left undisturbed. 
As a sound-producing medium, organ-pipes were found 
to answer the purpose best. To connect these with the 
ear in such a way that the vibrations within the pipe 
might be conveyed with the least possible loss to the air 
contained in the external auditory canal, the open end of 
the pipe was closed with a thin board cover, and a glass 
tube 17 cm. long, and with a lumen of 14 mm., was firm- 
ly inserted into an opening in the centre of the board. 
The free end of the glass tube had been previously 
drawn out so as to present a lumen of 5 mm. This 
was made to fit tightly in the external ear by surround- 
ing the end with sealing-wax. For light an ordinary 
kerosene lamp was used, the rays from which were con- 
centrated by means of a convex lens on the spot to be 
observed. This had been previously dried with the end 
of a heated wire, and then sprinkled with powdered 
starch. These fine masses of starch, when examined 
with a low power of the microscope (24 diam.), appear- 4 
Ed as sliarply defined luminous points, or, when set in 
rapid motion, as luminous lines. In the course of the 
experiments, however, it was ascertained that starch 
could be dispensed with, as the simple irregularity and 
moisture of the parts offered a sufficient number of 
luminous points for all purposes of observation. 
Lengths of excursions on different parts of the os- 
sicles. 
The following measurements were made by means of 
an ocular micrometer. By turning the eye-piece round 
until the luminous lines ran exactly at right angles to 
the subdivisions of the micrometer, their lengths could 
then be readily measured. As far as possible they were 
taken from the same positions, namely, from above, as 
seen in Fig. 1, and from the side, as seen in Fig. 2. 
With an organ-pipe of 110 vibrations. 
Number Head of Body of 
of Hammer Anvil 
Specimen, from above, from above. 
Head of Head of 
Stirrup Stirrup 
1 0.07 mm. 0.04 mm. 
from above. from side. 
0.03 mm. Not observed. 
2 0.09 mm. 0.04 mm. Scarcely visible. “ “ 
3 0.08 mm. 0.03 mm. 0.03 mm. “ “ 
5 0.04 mm. 0.03 mm. Scarcely visible. Scarcely visible. 
6 0.04 mm. 0.03 mm. 
Average = 0.05 mm. 0.03 mm. 0.01 mm. 
With an organpipe of 220 vibrations. 
Number Head of Body of 
of Hammer Anvil 
Specimen, from above, from above. 
Head of Head of 
1 0.38 mm. 0.14 mm. 
2 0.28 mm. 0.16 mm. 
Stirrup Stirrup 
from above. from side. 
0.03 mm. Not observed. 
0.06 mm. 0.06 mm. 5 
3 0.12 mm. 0.07 mm. 
4 0.13 mm. 0.06 mm. 
5 0.06 mm. 0.03 mm. 
6 0.09 mm. 0.05 mm. 
7 0.24 mm. 0.12 mm. 
0.03 mm. 0.04 mm. 
0.03 mm. 0.08 mm. 
Scarcely visible. Scarcely visible. 
“ “ 0.03 mm. 
0.03 mm. Not observed. 
Average = 0.17 mm. 0.09 mm. 0.035 mm. 0.03 mm. 
With an organ-pipe of 400 vibrations. 
Number Head of Body of 
of Hammer Anvil 
Head of Head of 
Stirrup Stirrup 
from above. from side. 
Specimen, from above, from above. 
1 0.38 mm. 0.13 mm. 
3 0.21 mm. 0.13 mm. 
3 0.21 mm. 0.12 mm. 
4 0.19 mm. 0.09 mm. 
6 0.31 mm. 0.09 mm. 
7 0.21 mm. 0.12 mm. 
8 0.09 mm. 0.06 mm. 
9 0.31 mm. 0.34 mm. 
10 0.31 mm. 0.16 mm. 
11 0.31 mm. 0.16 mm. 
0.06 mm. Not observed. 
0.06 mm. “ “ 
0.06 mm. 0.07 mm. 
0.03 mm. 0.04 mm. 
0.03 mm. 0.03 mm. 
0.04 mm. 0.04 mm. 
0.04 mm. Not observed. 
0.12 mm. 0.31 mm. 
0.08 mm. Not observed. 
0.01 mm. “ “ 
Average = 0.23 mm. 0.128 mm. 
*0.048 mm. 0.09 mm. 
With an organ-pipe of 600 vibrations. 
Number 
Head of 
Body of 
Head of 
Head of 
of 
Hammer 
Anvil 
Stirrup 
Stirrup 
Specimen. 
from above. 
from above. 
from above. 
from side. 
1 
0.09 mm. 
0.04 mm. 
0.01 mm. 
Not observed. 
2 
0.07 mm. 
0.04 mm. 
0.01 mm. 
U U 
3 
0.07 mm. 
0.04 mm. 
0.03 mm. 
u u 
4 
0.06 mm. 
0.03 mm. 
Scarcely visible. 
u u 
Average = 
0.07 mm. 
0.037 mm. 
0.012 mm. 
* By compressing the air in the external auditory canal and measuring the 
displacement in a column of mercury connected with the superior semi-circular 
canal, Helmholtz estimated the length of an excursion of the base of the stir 
rup at 0.05 + mm.—Mech. der OehdrkndcJielchen, etc.. 1869.) 6 
Direction of luminous lines on different parts of the 
os sijC les . 
As observed from above, the luminous lines on the 
beads of tbe hammer and anvil appeared slightly diver- 
gent outwards (see Fig. 1). This divergence was found 
to be the same on all the specimens. As observed from 
the side, in a direction at right angles to the long axis of 
the hammer, they presented the following appearance: 
-—On the hammer the luminous lines 
appeared to be arcs of circles whose com- 
mon centre lay in the immediate neigh- 
borhood of the Processus Folianus (see 
Fig. 2). On two of the specimens it was 
noticed that the luminous lines, measured 
at the very end of the handle of the ham- 
mer, were 0.43 mm. and 0.38 mm., whilst 
those measured at the head were 0.31 
mm,; in other words, that in these in- 
stances, at least, the axis of rotation did 
not pass through the middle of the ossicle, but somewhat 
above it. On the anvil the luminous lines followed the 
direction marked in Fig. 2. On the lower part of the 
long process they seemed to be nearly or quite vertical, 
but on approaching the body of the bone they became 
more oblique. Owing to the enclosed position of the 
anvil, it was not found practicable to obtain an obser- 
vation from the side higher up than the one marked in 
Fig. 2. On four specimens the relative measurements 
Fig. 1. 7 
on the body (seen from above) and the long process (seen 
from the side) of the anvil were as follows:— 
Number of Long 
Specimen. Body. ' Process. 
8 *2 li 
9 8 10 
10 5 2 
11 5 3 
They are of interest, as helping to indicate the position 
of the axis of rotation of this 
ossicle. In specimens No. 8, No. 
10, and No. 11, the hammer and 
anvil were joined together in the 
ordinary manner as represented 
in Fig. 3, whilst in specimen No. 
9 the anvil was more inclined 
inwards (see Fig, 4). In Fig. 3 
(drawn from specimen No. 10) 
the luminous lines are arcs of 
circles whose common centre is 
at A. The top of the body of 
the anvil being twice as far from 
this centre as the end of its long 
process, its excursion is twice as 
great In Fig, 4 (drawn from 
specimen No. 9) the different 
lengths of excursion can only be 
explained by supposing the axis 
of rotation to be placed nearer 
the body of the ossicle (as at A'). As observed from 
Fig 2. 
* Number of micrometer subdivisions. 8 
above, the luminous lines on tlie stirrup appeared in 
the majority of cases to be directed nearly, though not 
quite, at right angles to its base. In only 
two cases was it found possible to obtain a 
view of both arms of the stirrup at once. In 
one of these cases the luminous lines were 
directed at right angles to the base (see Fig. 
5), while in the other they ran somewhat 
obliquely toward it. The inclination in all 
cases was toward the anterior extremity of the base 
(see Fig. 6). 
Viewed from the side, the luminous lines on the stir- 
rup were in all instances directed oblique- 
ly upwards and inwards across the head 
and anterior arm (see Fig. 2). 
In spec. No. 6 the upper and inner wall 
of the vestibule wTas carefully chiselled 
away, so as to present an inner view of 
the base of the stirrup. When it was 
put in vibration the luminous lines on the upper border 
of the base measured 0.03 mm., and were vertical, but 
on the lower border there was not sufficient motion to 
admit of measurement. 
Fig. 3. 
Fig. 4. 
Fenestra Rotunda. 
Enough of the lower wall of the drum was removed 
in specimen No. 1 to admit of a good view of the mem- 
hrana tympani secundaria. The moment the organ-pipe 
was sounded the bright spot in the centre of the mem- 9 
brane lengthened out into a distinct luminous line of 
0.04 mm. On the head of the stirrup, as seen from 
above, the luminous lines mea- 
sured only 0.03 mm. The su- 
perficial area of the fenestra 
rotunda being smaller than that 
of the base of the stirrup, a 
greater excursion might rightly 
be expected from the membrane 
of the former. In the present 
case the membrane was observed 
obliquely from the side and not directly in profile, so to 
speak; hence the measurement would represent only 
a portion of the true length of the excursion. The 
measurements on different parts of the ossicles, before 
and after breaking up the membrane, were the same. 
Fig. 5. 
The influence of the different ligaments. 
Tendons of the tensor tympani and stapedius. The 
measurements immediately before 
and after the division of these 
tendons (considered as ligaments) 
were precisely the same, and no 
difference could be observed in 
the direction of the luminous 
lines on the stirrup after the di- 
vision of the tendon of the stape- 
dius. 
Pig. 6. 10 
The modifications produced by attaching fine glass 
rods to the hammer and anvil. 
A fine glass rod, of about tbe thickness of a fine bristle, 
and 5 cm. long, was glued in an upright position to the 
head of the hammer. Before doing this the measure- 
ments with an organ-pipe of 400 vibrations were : 
Head of hammer = 0.31 mm. 
Body of anvil = 0.16 mm. 
Afterwards they were found to be : 
Head of hammer = 0.12 mm. 
Body of anvil = 0.06 mm. 
Cutting off 1 cm. from the end of the rod, the measure- 
ments were: 
Head of hammer = 0.16 mm. 
Body of anvil = 0.09 mm. 
Cutting off 2 cm. they were: 
Head of hammer = 0.16 mm. 
Body of anvil = 0.09 mm. 
Cutting off 3 cm. they were: 
Head of hammer = 0.18 mm. 
Body of anvil = 0.10 mm. 
Cutting off 4 cm. the measurements remained the same. 
Leaving nothing but the small drop of glue, the measure- 
ments were: 
Head of hammer = 0.24 mm, 
Body of anvil = 0.12 mm 
After removing the glue from the head of the ham- 
mer and fastening a glass rod 5 cm. long and of the 
same thickness as the preceding to the body of the anvil, 11 
the measurements with an organ-pipe of 400 vibrations 
were ; 
Head of hammer = 0.31 mm. 
Body of anvil = 0.12 mm. 
Cutting oft 1 cm. they were; 
Head of hammer = 0.31 mm. 
Body of anvil = 0.13 mm. 
Cutting off 2 cm, the measurements remained the same. 
Cutting off 3 cm. they were : 
Head of hammer = 0.31 mm. 
Body of anvil = 0.16 mm. 
These experiments would show that the method of 
using glass rods to determine the character of the vibra- 
tions of the ossicles is not trustworthy. Even a drop 
of glue, the size of a pin’s head, attached to the head of 
the hammer was sufficient to reduce its excursion 0.07 
mm. On the anvil the disturbing influence of a weight 
or rod was much less than on the hammer. 
Anatomical study of the manner of attachment of the 
Stirrup to the Fenestra Ovalis. 
After having determined the direction in which the 
stirrup vibrates, the question presented itself, whether 
its base were not attached to the fenestra ovalis in a 
manner specially adapted to this mode of vibration. 
Works on anatomy give such meagre and conflicting in- 
formation on this point that it was thought necessary to 
investigate it more thoroughly. The method employed 12 
was suggested by Prof. Julius Arnold, under whose kind 
supervision the investigation was made. 
The stirrup, together with the mass of bone immedi- 
ately surrounding it, was first removed from the tempo- 
ral bones of new-born children and adults as soon as pos- 
sible after death, and in such a manner as to obtain this 
ossicle with all its attachments to the fenestra oralis 
uninjured. These specimens were placed in three ounces 
of a 1% solution of chromic acid, the solution being re- 
newed every fourth day after. At the end of a month 
a 2°/° solution was used. Two weeks later, two of the 
specimens were soft enough to be cut with the razor. 
The others remained a week longer in a 2°/« solution, to 
which three drops of concentrated hydrochloric acid had 
been added. From these solutions of chromic acid the 
specimens were transferred to alcohol, and, when suf- 
ficiently hardened, they were imbedded in paraffine. Fine 
sections were now made with the razor in both horizontal 
and vertical directions. In order to make the sections 
exactly parallel with the two axes of the base (the long 
or nearly horizontal, and the short or nearly vertical) the 
paraffine was carefully removed from the vestibular side 
of the stirrup, so as to expose only its base to view, 
whilst all the rest of the bone remained firmly imbedded 
in it. As some of the horizontal sections included the 
musculus stapedius, the anterior and posterior parts 
were easily determined. In the vertical sections the 
presence of the tensor tympani afforded the same assis- 
tance in locating the upper and lower parts. 13 
In the study of these horizontal and vertical sections 
the base of the stirrup is found to be attached to the 
fenestra ovalis by a circular band of uniform strength 
throughout. Its fibres run in a convergent direction from 
the margin of the fenestra to the opposite margin of the 
base of the stirrup. In their course they cross each other 
at very acute angles. They are rich in oval nuclei, and 
are separated only by a slight quantity of an homogene- 
ous, but dense intercellular substance. The periosteal 
covering of the bone in the immediate neighborhood of 
the fenestra ovalis is continuous with this circular band, 
or, in other words, the tympanic and vestibular layers of 
periosteum unite at the margin of the fenestra, then run 
together as one band as far as to the margin of the base 
of the stirrup, where they subdivide to take the base 
between their folds, and serve it in the capacity of peri- 
osteal covering. 
On the outer side the band is covered everywhere with 
the mucous membrane of the drum, which was found 
here to be rich in blood-vessels of various sizes. In many 
of the horizontal and vertical sections, cross-sections were 
found of large arteries at the very edge of the fenestra, 
or even directly in front of the band. These sent off 
smaller branches that pierced the band in various direc- 
tions. 
On the inner side the band is also covered with an 
epithelial layer, which is, however, much thinner than the 
outer one. 
In adults the bone forming the fenestra ovalis differs 14 
in nowise from ordinary bony tissue, except that at the 
periphery, immediately beneath the periosteum, there is 
always found a thin layer of cartilage-like tissue, con- 
sisting of ovoidal and spindle-shaped cells and an homo- 
geneous intercellular substance (periosteal cartilage). 
The same tissue is also found at the periphery of the 
bone in children, and moreover, in the very substance of 
the bone small cartilaginous islands are often seen. 
The base of the stirrup is likewise formed of true bone, 
at the periphery of which there is found a thin layer of 
periosteal cartilage immediately beneath the periosteum, 
and intimately united with it. In adults the base was 
found to be thicker at the two ends than in the centre ; 
the two ends were, however, very nearly alike in thickness. 
In children the posterior end was found to be thick and 
quadrangular, whilst the anterior was narrow and round- 
ed (see accompanying plate). The layer of cartilage 
beneath the vestibular periosteum was found, moreover, 
to be much thicker than in the adult. 
It is necessary to state here that unless the sections are 
either parallel or at right angles to the long axis of the 
base, they will totally misrepresent the true relations of 
the parts. For instance, among a number of vertical 
sections cut from the same specimen, I obtained three 
entirely different views : one where the lower border ap- 
peared somewhat flattened, whilst the upper was smaller 
and more pointed; a second, where the reverse was 
found to be the case; and a third, where both ends 
appeared alike. The breadth of the circular band varied 15 
also, according to the direction in which the section was 
made. 
To state briefly the results of this anatomical study: 
(1) The stirrup is attached to the fenestra ovalis by 
means of a circular band composed of elastic tissue; 
(2) The fibres of this band run from the margin of the 
fenestra to the base of the stirrup in a convergent direc- 
tion ; (3) The band is formed of the layers of periosteum 
covering the bone in the immediate neighborhood of the 
fenestra, and on reaching the base of the stirrup it 
again resumes its function of periosteum; (4) The band 
is everywhere of equal breadth. 
From the preceding experiments two conclusions are 
arrived at: (1) That the bones of the ear vibrate as a 
whole ; and (2) That with each vibration there is a cor- 
responding displacement of the fluid of the labyrinth.* 
This is precisely the doctrine held by Weber twenty 
years ago. It also appeared that with each wave of 
sound the membrane of the drum is driven inwards a 
certain distance and then returns to its original position, 
so that the end of the handle of the hammer, which is 
imbedded in the substance of the membrane of the 
* Politzer first proved experimentally that the ossicles vibrate as a whole 
(Archiv fur Ohrenheilkunde, 1864). The chief question of dispute had been 
concerning the movement of the fluid of the labyrinth as a whole. Politzer 
and Helmholtz sided with Weber, whilst Henke and Schmiedekam held the con- 
trary view. 16 
drum, makes an excursion to and fro of equal length, 
and the length of such an excursion may amount to 0.43 
mm. without any appreciable injury to the parts. But 
if one places the glass tube of the organ-pipe in his own 
ear the shock produced on the membrane of the drum is 
felt to be too painful to be borne for any length of time, 
so that the ordinary excursion of the membrane of the 
drum during; life would seem to be much less than this 
measurement. The axis of rotation of the hammer lies 
nearly midway between its two extremities, so that 
when the end of the handle is driven inwards the head 
makes an equal excursion outwards. The particles form- 
ing the upper part of the head of the hammer move 
very nearly horizontally outwards, whilst those near the 
lower margin of the malleo-iiicudal joint move upwards 
as much as outwards. Helmholtz has shown that the 
hammer and anvil are united by a joint which in princi- 
ple resembles that used in watch-keys, where the head of 
the key can be made to rotate in one direction without 
carrying the body with it, whilst in the opposite direc- 
tion the body must necessarily follow. The lower tooth 
of the incudal half of the joint fits into a depression on 
the inner side of the hammer, just where the particles 
forming that part vibrate in an upward and outward di- 
rection. From an observation of the luminous lines on 
different parts of the anvil it was found that in fact 
such an upward and outward motion is communicated to 
this ossicle. 
But in addition to this motion the body of the anvil 17 
is thrown slightly backwards, or, in other words, the end 
of its long process is thrown forwards, as if the axis of 
rotation ran from the end of the shorter process of the 
anvil forwards, downwards, and outwards through the 
processus brevis of the hammer. 
The head of the stirrup being joined to the end of the 
long process of the anvil by a fully formed capsular 
joint, it is obliged to follow to a great extent the direc- 
tion taken by the end of the long process of the anvil, 
namely, upwards, slightly inwards, and forwards. As a 
result of this, the upper and anterior border of the base 
of the stirrup is driven farther into the vestibule than 
the lower and posterior border; * in other words, its 
axis of rotation runs either through the lower border of 
the margin of the fenestra avails, or a little below and 
parallel to it. Hence a displacement of the entire mass 
of the fluid of the labyrinth takes place, and in no other 
manner can the vibrations observed on the memhrana 
tympani secundaria be explained. 
The average measurements show that an impulse given 
to the centre of the drum is communicated from ossicle 
to ossicle with a loss in the following ratio;— 
Hammer == 4 
Anvil = 2 
Stirrup = 1 
In two cases (see first table of measurements) where the 
* By a somewhat different method of investigation Helmholtz determined 
the axis of rotation of the stirrup. The above result confirms his description 
in its essential points. 18 
membrane of the drum was caused to vibrate feebly, 
scarcely any loss took place in the transmission of the 
impulse from the hammer to the stirrup. Taking into 
consideration, moreover, that all these measurements may 
be looked upon as representing rather the maximal than 
the ordinary excursions of the ossicles, it may well be 
doubted whether during life the loss in transmission be 
not much smaller than that given above Tab 1 
GailsTuke._CkFr.MulleT’schelith.iiLstalt. 
JGiapp ScMoos Archiv, 1.2. 
F.Feith ad.nat.del. TabJ. 
C arlsruie J3trJr.MullflT'sdlie lith.Anstalt 
Knapp ic Moos Archio, I 2. 
I. Veitti ad nat.del.