Notes on the Ear 
BY 
HORACE J. WHITACRE, M. D. 
NEW YORK 
1894 THE EAR. 
The ear, the organ of hearing, is subject to three general 
divisions: the external ear, the middle ear or tympanum, and 
the labyrinth or internal ear. 
The external ear includes the pinna, that portion which 
projects from the head, and the external auditory canal which 
leads from this to the membrana tympani at the bottom. The 
general form of the pinna is concave, with a surface thrown into 
various hollows and elevations calculated to collect the sound- 
waves for transmission to the membrana tympani. The detail 
of the irregularities of its form is familiar and the designation 
of the various elevations and depressions can be sufficiently given 
in diagram. The structure is of a yellow fibro-cartilaginous 
plate covered by a thin skin, and certain ligaments intrinsic and 
extrinsic. In addition there are a number of small muscles of 
little significance. 
The meatus auditorius externus is the canal, about one 
inch in length, extending from the concha to the membrana 
tympani. Its course is forward, slightly upward, and inward, 
then forward, inward, and downward. It has a cartilaginous and 
osseous portion. The former occupies less than one half the en- 
tire length of the canal, and is formed by an inflection of the 
cartilage of the pinna. The latter or osseous portion is narrower 
in calibre, and presents at its inner end a narrow groove, the 
sulcus tympanicus, which extends around the sides and floor 
of the meatus, but is deficient above. The membrana tympani is 
inserted into this sulcus. The skin of the canal is continuous 
with that of the pinna and is continued over the outer surface of 
1 2 
the membrana tympani as its outer layer. The osseous portion 
is free from hairs and glands, but the portion exterior to this is 
supplied by fine hairs and glands (glandulaa ceruminosae) which 
secrete the ear-wax. 
The Middle Ear or Tympanum. 
The middle ear is an irregular chamber, situated in the 
petrous portion of the temporal bone, at the bottom of the ex- 
ternal auditory meatus. It is empty except for a chain of minute 
bones across the cavity. The cavity is made quite irregular by 
various prolongations or depressions (tympanic recesses), which 
are formed when a ligament or nerve stretching across the cavity 
is covered by a fold of mucous membrane from the wall. Six 
boundaries are usually described : 
The roof is formed by a thin plate of bone, the tegmen 
tympani, situated upon the anterior surface of the petrous bone 
near the angle of union with the squamous portion. The tegmen 
also roofs in the canal of the Eustachian tube and tensor tym- 
pani muscle. The floor is narrow, and passes imperceptibly into 
the anterior and posterior boundaries. It is formed by a thin 
plate of bone which separates the cavity from the jugular fossa, 
and presents a small aperture through which Jacobson's nerve 
passes. The outer wall is formed mainly by the membrana 
tympani, but to a small extent by bone. Directly in front of the 
tympanic ring is the inner extremity of the Glaserian fissure, and 
very near to this is found the iter chordae anterius, a small 
opening for the exit of the chorda tympani nerve. The mar- 
gin of the tympanic ring is incomplete above where the promi- 
nent anterior and posterior tympanic spines mark off the in- 
cisura Rivini, a notch at this point. 
The membrana tympani is an elliptical membranous disk, 
about nine by ten millimetres, inserted into the sulcus tympanicus 3 
at the inner end of the external auditory canal. Its long axis is 
directed downward and forward, and its plane, a very oblique 
one, inclined downward, forward, and toward the median line. 
This oblique placing makes the anterior wall and floor of the 
auditory canal much the longer. The handle of the malleus 
descends in contact with the membrane, between its middle and 
outer layers, and owing to its firm connection at the center and 
the inward direction of the bone the membrane is given a conical 
shape, depressed on the outer side. The membrane is about OT 
millimetres thick, but becomes much thicker, as the annulus 
fibrosus, at its insertion into the sulcus tympanicus. From the 
anterior and posterior tympanic spines this thickened portion is 
prolonged as two ligamentous bands to the short process of the 
malleus, as the anterior and posterior tympano-malleolar liga- 
ments, and form the low'er boundary of the membrana flac- 
cida. The membrane is made up of three elements: the middle 
fibrous layer or tunica propria ; the outer covering, a prolonga- 
tion from the skin of the external auditory meatus; and an inner 
covering, a portion of the lining membrane of the tympanum. 
The fibres of the tunica propria are in the main radial with a 
few circular. The integumental layer is thickened at the umbo, 
the most depressed part, and to some extent along the malleolar 
line. At the upper and anterior part of the membrane the 
stronger fibres stretch across the notch of Rivinus, which is occu- 
pied by the membrana flaccida, of much the same structure 
as the main membrane. 
The inner wall of the tympanum is very uneven, and pre- 
sents many important points. It separates the middle from the 
internal ear, and through it the communication is established be- 
tween the two. Near the upper part is an oval opening into the 
vestibule, the fenestra ovalis, which in the recent state is 
closed in by the base of the stapes and membrana obtura- 
toria, an annular ligamentous membrane. Its long axis is antero- 4 
posterior, and about three mm. in length. Above this opening, 
and separating it from the roof is a tubular ridge indicating the 
course of the Fallopian aqueduct; while below is a more de- 
cided rounded prominence, the promontory, which represents 
the first turn of the cochlea, and is marked by numerous grooves 
for the tympanic plexus. Below and behind the promontory, 
situated at the bottom of a funnel-shaped depression, is another 
opening, the fenestra rotunda, which in the recent state is 
closed in by the secondary membrane of the tympanum. 
This membrane separates the tympanum from the scala tym- 
pani, and, like the membrana tympani, is made up of three ele- 
ments-a tunica propria, and the lining membranes of the two 
cavities. A third fossa, the sinus tympani, is seen posterior 
to the promontory and between the two fenestrae. 
The posterior boundary of the tympanum is mainly formed 
by the opening into the antrum mastoideum, a space of vari- 
able dimensions above and behind the tympanum proper. From 
this the mastoid cells branch off to form the mastoid portion of 
the temporal bone. The antrum and cells are lined by a mucous 
membrane directly continuous with that of the tympanum. Just 
below this orifice into the antrum is a depression for the attach- 
ment of the lower ligament of the incus. There is also a conical 
prominence, the pyramid, at this point, just below the antrum 
and behind the fenestra ovalis and sinus tympani. The apex of 
the pyramid gives exit to the stapedius muscle, which has its origin 
on the internal surface and its insertion into the neck of the 
stapes. In the angle of junction of the outer and posterior walls, 
on a level with the middle of the membrana tympani, is the iter 
chordae posterius, the point of entrance of the chorda tympani 
nerve. 
The tympanum gradually narrows anteriorly into two ori- 
fices, the Eustachian tube, and that for the tensor tympani 
muscle. The canal which lodges the tensor tympani is about 5 
one half inch long, is placed above the Eustachian tube, and sepa- 
rated from it by a thin lamina of bone, the processus cochleari- 
formis. The inner orifice of the canal is located just anterior to 
the fenestra ovalis, and is surrounded by an expansion of the bony 
lamina. The Eustachian tube is a bony and cartilaginous canal 
about one and a half inches long, extending from the tympanum 
to a point on the lateral pharyngeal wall just posterior to the in- 
ferior turbinated bone and above the hard palate. Its direction 
from the ostium tympanicum is downward, forward, and inward 
at a decided angle (about 45°). The osseous portion is one half 
an inch in length, has a funnel shape, with its expanded portion at 
the tympanic end, and is placed along the line of junction of the 
squamous aud petrous portions of the temporal bone. The car- 
tilaginous portion, one inch long, is funnel-shaped in the op- 
posite direction, and is formed by an incomplete fibro-cartilagi- 
nous plate. The ostium pharyngeum is rather expanded, and is sur- 
rounded by the projection of the cartilaginous plate. The ridge 
posterior separates it from the fossa of Rosenmuller, a blind 
pouch. Through the Eustachian tube the mucosa of the pharynx 
becomes continuous with that of the tympanum. 
The lining membrane of the tympanum forms folds over 
the various structures in such a way that small pouches are par- 
tially or wholly shut off. These are known as the pouches of 
the tympanum, and have received special names. 
The Small Bones of the ear, the malleus, incus, and stapes, 
form an angular-jointed rod, extending from the membrana 
tympani to the fenestra ovalis, which transmits sound vibrations 
as received by the membrana to the internal ear. 
, The malleus (hammer) is placed in contact with the mem- 
brana tympani, and consists of a head, neck, handle, and two 
processes. The head is the rounded upper extremity, present- 
ing on its posterior surface an elliptical articular facet with prom- 
inent margins for articulation with the incus. The lower edge 6 
of the facet is prominent as the spur of the malleus. The ma- 
nubrium, or handle, separated from the head by the constricted 
neck, is the tapering, slightly twisted point of the malleus which 
runs downward and inward along the inner surface of the mem- 
brana tympani. Its attachment to this membrane is periosteal 
and cartilaginous throughout its whole length. A small tubercle 
on its inner side marks the point of attachment of the tensor 
tympani muscle. The processus gracilis is a very slender pro- 
cess of bone extending at right angles from the neck of the mal- 
leus downward and forward to the Glaserian fissure, where it is 
connected by bony and ligamentous fibres. The processus 
brevis is a short, conical projection from the neck, which lies 
in contact with and is attached to the membrana tympani. f 
The incus (anvil) is shaped much-like a tooth with two roots 
differing in size and widely separated. The body presents a 
saddle-shaped articular area on its anterior surface for articula- 
tion with the malleus. The shorter process, conical in shape, 
projects horizontally backward, and is movably articulated by 
ligaments with the posterior and outer walls of the tympanum 
near the entrance to the mastoid cells. The longer process 
tapers more gradually, and passes downward and inward parallel 
to the handle of the malleus, mesial to and behind it. At the 
extremity it is sharply turned inward, and presents a tubercle, 
the lenticular process, marked off by a narrow' neck. The 
lenticular process articulates with the head of the stapes. 
The innermost bone of the chain, the stapes, is horizontally 
placed, and bears a close resemblance to a stirrup. The head 
articulates with the long process of the incus. The base is an 
oval plate of bone which fills the fenestra ovalis, together with 
the annular ring of elastic fibrous tissue which allows of motion 
of the base. The crura diverge from the neck in a curved 
course to the ends of the base. The anterior crus is the shorter 
and straighter of the two. 7 
The articulations of the small bones together are by regular 
joints with annular ligaments. Their connection with the tym- 
panic wall is by several distinct ligaments. The anterior liga- 
ment of the malleus, formerly believed to be muscular, is a 
strong, broad band of fibres connecting the base of the processus 
gracilis and the part of the malleus just above this to the ante- 
rior wall of the tympanum, just external to the fissure of Glaser. 
Many of its fibres form the thickened anterior margin of the 
membrana flaccida. The external ligament of the malleus is 
fan-shaped, has its origin from the margin of the notch of Rivi- 
nus, and converges to the short process of the malleus. The 
superior ligament is a delicate, round bundle, passing down- 
ward and outward from the roof of the tympanum to the head 
of the malleus. It serves to check outward movement of the 
malleus and membrana tympani. The ligament of the incus 
is a short, stout band connecting the short process of the incus 
with the posterior wall of the tympanum, just below the orifice 
of the antrum mastoideum. 
The muscles connected with these bones are the tensor tym- 
pani and the stapedius. The tensor tympani takes origin from 
the cartilaginous end of the Eustachian tube, the under surface 
of the petrous bone, and from the canal in which it is contained. 
Its tendon bends outward at nearly a right angle over the pro- 
cessus cochleariformis, and is inserted into the handle of the mal- 
leus near its base. Its action is to draw the whole malleus and 
membrana tympani inward, tightening the latter. It exerts very 
little rotating action on the malleus. The stapedius muscle is 
a distinct small muscle lodged in the interior of the pyramid. 
Its tendon emerges from the apex, passes forward in a fibrous 
sheath, and is inserted into the back part of the neck of the 
stapes. The muscle draws the head of the stapes backward, and 
in so doing presses the posterior part of the base inward, while 
the anterior part is drawn outward. 8 
The Internal Ear or Labyrinth. 
The osseous labyrinth is another cavity in the petrous por- 
tion of the temporal bone, for the reception of the most important 
organs of hearing. It does not consist of a single chamber, but 
of a series of regular spaces and passages which communicate 
with each other, and is constructed in conformity with the mem- 
branous labyrinth which is contained within it. The true osseous 
cavity consists of the vestibule, the cochlea, and the semicircular 
canals. 
The vestibule forms a central chamber of the labyrinth, to 
some extent the place of reunion of the other parts, with the 
cochlea in front, semicircular canals posterior, and tympanum ex- 
ternally. It is an elliptical shell of bone with six walls. In the 
outer wall is seen the fenestra ovalis opening into the tym- 
panum. Its inner wall is in contact with the outer end of the 
internal auditory meatus, and exhibits, running from above 
downward, a ridge of bone-the crista vestibuli. This is 
prominent above as the pyramid of the vestibule, while 
inferiorly it bifurcates to inclose the recessus cochlearis. 
The crest separates two fossae, the anterior (fovea hemispher- 
ica) and the posterior (fovea hemielliptica). Behind the 
lower part of the crest is a small canal, the aqueduct of the 
vestibule. On the anterior wall is seen a large opening, 
communicating with the scala vestibuli, while on the pos- 
terior wall are the five openings into the semicircular canals. 
The semicircular canals are three tubes, each forming 
about two thirds of an ellipse, placed in planes perpendicular to 
each other, behind and above the vestibule ; one extremity of each 
is dilated (the ampulla) at its point of origin from the vestibule. 
The contiguous ends of two of the canals are joined, and enter by 
a common orifice. The superior canal is nearly vertical, lies 9 
transversely to the axis of the petrous bone, and forms a bulging 
(the jugum pyramidale) on its upper surface. The posterior 
canal, the largest, is also nearly vertical. Its ampulla is at the 
lower and back part of the vestibule, and its opposite end ter- 
minates in common with the superior. The external canal 
arches horizontally outward and backward, and opens by two dis- 
tinct orifices into the vestibule. 
The cochlea is a tapering osseous tube spirally wound about 
a central bony axis (the modiolus), to form a low cone, the base 
at the bottom of the internal auditory meatus, and its apex point- 
ing downward, forward, and outward. The tube makes two 
and a half turns about the modiolus, and ends by a closed ex- 
tremity, the cupola. This tube is partly divided along its whole 
extent by a thin osseous plate, the spiral lamina, which pro- 
jects horizontally from the modiolus. The division is made com- 
plete in the recent state by membranous structures, into the 
scala tympani below and scala vestibuli above, which com- 
municate only by a small opening at the apex of the cochlea 
known as the helicotrema. The upper end of the lamina, the 
hamulus, is hooklike, and bounds the helicotrema. The scala 
tympani begins at the fenestra rotunda, where it is separated 
from the tympanum by the secondary membrane of the tym- 
panum. The scala vestibuli begins in the vestibule. The 
modiolus, a central bony axis for the cochlea, is traversed by 
many small canals for vessels and nerves and a larger central 
canal of the modiolus. Its base at the bottom of the internal 
auditory meatus presents the foramen centrale, which trans- 
mits nerves to pass through the central canal for the last turn of 
the cochlea, and the tractus foraminulentus, which transmits 
many small nerves for the remaining coil and a half. 10 
The Membranous Labyrinth. 
Within the osseous labyrinth, and separated from it by peri- 
lymph, is the membranous labyrinth which bears a general resem- 
blance to the osseous cavity, and serves for the ultimate ramifica- 
tions of the auditory nerve. 
Within the vestibule are two membranous sacs-the utricle 
and saccule. The utricle, the larger, is lodged in the fovea 
hemielliptica, at the upper and back part of the vestibule, and 
has opening into it the ends of all the semicircular canals. 
Within the sac are found calcareous particles or otoliths. The 
saccule, of smaller size, is situated in the lower and fore part of 
the vestibule, and occupies the fovea hemispherica. It narrows 
below into a funnel-shaped duct, the canalis reuniens, which 
opens directly into the canal of the cochlea (scala media). 
The semicircular canals are but one third to one fifth the 
diameter of the osseous tubes, and are made up of three layers- 
a fibrous outer layer, a tunica propria, and a flattened lining epi- 
thelium. The ampullae more nearly fit their osseous cavities, and 
each presents on its inner surface a transverse projection, the 
septum transversum, which partly divides the cavity. The 
most prominent part of this septum is covered by columnar 
auditory epithelium surmounted by long conical filaments (audi- 
tory hairs), and is termed the crista acoustica. 
The membranous cochlea is separated into three distinct 
parts, throughout its whole length, by two membranes. First, 
the lamina spiralis is directly prolonged by the strong basilar 
membrane, which stretches straight across to the outer wall of 
the cochlea and meets an inward prolongation of the periosteum 
known as the spiral ligament. In this way an upper boundary 
for the scala tympani is formed, but not a lower boundary for 
the scala vestibuli, because from the upper surface of the lamina 11 
spiralis, near its edge, a second delicate membrane, known as 
Reissner's membrane, stretches obliquely upward and out- 
ward to the outer wall of the cochlea. In this way a third trian- 
gular canal is formed throughout the entire length of the cochlea, 
known as the canal of the cochlea, or ductus cochlearis, or scala 
media. This canal is lined by variously modified epithelium, 
and claims greatest attention as the part of the cochlea most con- 
cerned in the function of hearing. It terminates in blind ex- 
tremities at the apex (lagena) and base, but near the latter the 
small canalis reunions establishes a communication between the 
saccule and this canal. The structures on the floor of this canal 
are of especial importance as making up the highly specialized 
organ of Corti. A detailed description of this region would 
be almost wholly one of the relations of the various parts of the 
organ to each other ; and the histological detail being unnecessary 
in an elementary treatise, it seems that accurate diagrams will 
serve to give a sufficient idea of the structure of the part.