20-00
The Ear(Vestibulo-acoustic
Organs)
20-00 The Ear(Vestibulo-acoustic Organs)

20 The Ear (Vestibulo-acoustic Organs)Menu
20-00.

The Ear(Vestibulo-acoustic Organs)

20-002. Vestibular Organs

20-01.

Location of vestibulo-acoustic organs in the temporal bone ( Scheme )20-17.

Vestivulum 1. Sacculus and ampulla posterior. Monkey， H-E stain， x 5.0.

20-02.

Scheme showing the structure of membranous labyrinth.

20-18.

Vestibulum 2. Stapes and utriculus 1. Monkey， H-E stain， x 5.0.

20-19.

Vestibulum 3. Stapes and utriculus 2. Monkey， H-E stain， x 5.0.

20-001. Cochlea，and External and Middle Ear
20-03.

Cochlea， vertical section， 1. Monkey， Held’ s hematoxylin stain， x 4.

20-20.

Vestibulum 4. Macula utriculi and crista ampullaris posterior. Monkey， H-E stain， x 5.0.

20-04.

Cochlea， vertical section， 2. Monkey， Held’ s hematoxylin stain， x 10.

20-21.

20-05.

Cochlear canal， vertical section， 3. Monkey. Held’s hematoxylin stain， x 25.

Vestibulum 5. Crista ampullaris anterior and crista amp. lateralis. Monkey，H-E stain， x
5.0.

20-06.

Cochlear duct and organ of Corti 1. Monkey， Held’s hematoxylin stain， x 64.

20-22.

Crista ampullaris 1. Monkey， H-E stain， x 13.2.

20-07.

Cochlear duct and organ of Corti 2. Monkey， H-E stain， x 50.

20-23.

Crista ampullaris 2. Monkey， H-E stain， x 50.

20-08.

Cochlear duct and organ of Corti 3. Monkey， H-E stain， x 64.

20-24.

Macula utriculi 1. Monkey， H-E stain， x 33.

20-09.

Organ of Corti. Monkey， H-E stain， x 100.

20-25.

Macula utriculi 2. Monkey， H-E stain， x 100.

20-10.

Scheme showing the structure of organ of Corti

20-003. Horizontal Sections of Human Temporal Bone

20-11.

Reticular membrane ( Scheme )20-26.

Horizontal section of human temporal bone 1. H-E stain， x 1.0.

20-12.

Spiral ganglion. Monkey， Held’s hematoxylin stain， x 160.

20-27.

Horizontal section of human temporal bone 2. H-E stain， x 1.0.

20-13.

Stria vascularis. Monkey， H-E stain， x 100.

20-28.

Horizontal section of human temporal bone 3. H-E stain， x 1.0.

20-14.

Tympanic membrane 1. Monkey， H-E stain， x 64.

20-29.

Horizontal section of human temporal bone 4. H-E stain， x 1.8.

20-15.

Tympanic membrane 2. Monkey， H-E stain， x 160.

20-16.

External acoustic meatus. Monkey， H-E stain， x 2.5.

Tuba auditiva

Median line
Sella turcica

Cavum tympani

A. carotis int.

Membrana
tympaniSuperior borderof petrous part

Meatusacusticus ext.

Cochlea

N. facialis

Sinus
sigmoudeus

Ductussemicircularisanterior
Antrummastoideum

ForamenmagnumDuctussemicirc. lat.

Meatus acusticus
internus

Saccus endolymphaticus

Utriculus

20-01 Location of vestibulo-acoustic organs in the temporal bone ( Scheme )Ductussemicirc.
post.

Ampulla ductus semicircularis anterior

Ductus semicircularis anterior
Utriculus and macula utriculi
Sacculus and macula sacculi

Ampulla ductus semicircularis
lateralis

Spiral organ

Ductus semicircularis lateralis

Ductus semicircularis
posterior

Ductus reuniens
Ductus cochlearis
Ampulla ductus
semicircularis posterior

20-02 Scheme showing the structure of membranous labyrinth.

Saccusendolymphaticus
Ductus endolymphaticus

20-001
Cochlea,andExternaland Middle Ear
20-001 Cochlea，and External and Middle Ear

Helicotrema

N. tympanicus
Promontrium

Bone

Bone
Internal acustic meatus

Cochlear nerve
20-03 Cochlea， vertical section， 1. Monkey， Held’ s
hematoxylin stain， x 4.

N. tympanicus

svdc

Promontrium

sv

st

st

Bone

sv
dc

dc
sv

st
st
Ggl. spirale

20-04 Cochlea， vertical section， 2. Monkey， Held’ s
hematoxylin stain， x 10.

Cochlear nerve

stSpiral ganglion

Bone

Stria vascularis
Vestibular membranesv
Spiral limbus

dc
Organ of Corti
ssi

ssl

Osseous spiral lamina

Lamina basilaris

Spiral ligament

Bone

Cochlear nervest
Spiral ganglion

20-05 Cochlear canal， vertical section， 3. Monkey.
Held’s hematoxylin stain， x 25.

Vestibular membrane

Stria vascularissvdc
Spiral limbus
Spiral prominence

Tectorial membrane

Cells of Hensen

sse

ssi

N
T

Lig. spirale
Cells of
Claudius

Outer pillar

Lamina basilaris

Inner pillar

st20-06 Cochlear duct and organ of Corti 1. Monkey，
Held’s hematoxylin stain， x 64.

N. cochlearis
Osseousspiral lamina

BoneVestibular membrane

sv
Stria vascularisdc

Spiral limbus

Spiral prominence
Tectorial membrane
Organ of Corti

ssi

sse
Spiral ligament

Osseous spirallaminaCochlear nerve

Tunnelst

Lamina basilaris

20-07 Cochlear duct and organ of Corti 2. Monkey，
H-E stain， x 50.

Stria vascularis

Vestibular membranesv
Spiralprominencedc

Spiral limbus
Tectorial membrane

Cells of Hensen
Cells of
Claudius

ssi

N

sse

T

Inner pillar cell
Osseus spirallaminaCochlear nerve

Outer pillar cell

Lamina basilarisst

20-08 Cochlear duct and organ of Corti 3. Monkey，
H-E stain， x 64.

Spiral ligament
Cells of
Deiterssv

Inner hair celldc

Tectorial membrane

Outer hair cells

Spirl limbus
Cells of Hensen

N

ssi

sse

T

Cells of Deiters

Inner pillar cell

Cochlear nervest

Inner pillar

Outer pillar cell
Outer pillar

Cells of Claudius

Lamina basilaris
T: Tunnel
N: Space of Nuel

20-09 Organ of Corti. Monkey， H-E stain， x 100.

Head plate of inner pillar andphalangeal process of outer pillar

Inner hair cell
Epithelium of limbus

Membrana
tectoria

Blood
vessels

Outer hair cell of the 3rd row

Ve
Sulcusspiralis
internus

Periosteum

Stria vascularis

External tunnel
Cells of Hensen

Border cell

Limbuslaminaespiralis

Outer hair cell of the
1st row
Phalangeal processof Deiters cell

Prominentia
spilaris

Sulcusspiralis
externusTy

Lig.
spilareLaminaspiralis
ossea

Inner
pillarEndothelium ofacala tympani Cochleal nerv
(myelinated)

Innerphalangeal
cell
SpiralvesselOuter
Cells ofpillarDeiters Lamina
Fiber ofbasilaris
RetziusOuter pillar cell
Unmyelinated nerve fibers

Innerpillarcell

20-10 Scheme showing the structure of organ of Corti

Cells of
Claudius

T: Tunnel
Nu: Space of Nuel
Ve: Labium vestibuli
Ty: Labium tympaniIH:
inner hair cell

H1,H2,H3:
outer hair cell
D1,D2,D3:
Deiters’ cell

Head plate ofOuter hair cell
inner pillar cell
Inner phalangeal cell
Phalangeal process ofouter pillar cell

Inner hair cell
Border cell

20-11 Reticular membrane ( Scheme )Cell of Hensen
Phalangeal process of
Deiters’ cell①②20-12 Spiral ganglion. Monkey， Held’s hematoxylin
stain， x 160.

Bone
Vestibular membrane

Spiralligament

Stria vascularis

Spiralligament
Spiral prominence

20-13 Stria vascularis. Monkey， H-E stain， x 100.

Skin

Mucous membraneBone
20-14 Tympanic membrane 1. Monkey， H-E stain， x 64.

Skin

Radial fibers

Mucous membrane

Circular fibers

20-15 Tympanic membrane 2. Monkey， H-E stain， x 160.

Elastic cartilage
Gl. cerminosa

Lumen

Dermis20-16 External acoustic meatus. Monkey， H-E stain， x 2.5.

20-002
Vestibular
Organs
20-002 Vestibular Organs

Secondary tympanic membrane
Macula sacculi

Crista amp. posterior

Round window

Bone

Bone
Bone

Sacculus
Vestibulum
Vestibular ganglion

20-17 Vestivulum 1. Sacculus and ampulla posterior.
Monkey， H-E stain， x 5.0.

Ampulla posterior

Utriculus

Canalis semicircularis
StapesMacula utriculi

Bone

Bone

Vestibulum
Vestibular nerve

20-18 Vestibulum 2. Stapes and utriculus 1. Monkey，
H-E stain， x 5.0.

Stapes
Vestibulum

N. facialis
Utriculus

Bone

Base of crista ampullaris posterior

Bone

Macula utriculi

20-19 Vestibulum 3. Stapes and utriculus 2. Monkey，
H-E stain， x 5.0.

N. facialis
Vestibulum

Ampulla et crista amp. posterior

Base of crista ampullaris ant. et lat.
Utriculus

20-20 Vestibulum 4. Macula utriculi and crista
ampullaris posterior. Monkey， H-E stain， x 5.0.

Vestibulum

N. facialis

Ampulla et crista amp. anterioris

Bone

Bone

Ampulla posterior

Ampulla et crista amp. lateralis

20-21 Vestibulum 5. Crista ampullaris anterior andcrista amp. lateralis. Monkey，H-E stain， x 5.0.

Bone20-22 Crista ampullaris 1. Monkey， H-E stain， x 13.2.

CupulaNeuroepitelium

Supporting cells

NervesBone
20-23 Crista ampullaris 2. Monkey， H-E stain， x 50.

Utriculus

Otolithic membrane
Sensory epithelium

VestivulumBone

20-24 Macula utriculi 1. Monkey， H-E stain， x 33.

Otolithic membrane
Otoliths

Neuroepithelium
Supporting cells
Basement membrane
Nerves20-25 Macula utriculi 2. Monkey， H-E stain， x 100.

20-003
Horizontal Sectionsof
Human TemporalBone
20-003 Horizontal Sections of Human Temporal Bone

②
③
①
④

⑤

⑥

Bone

⑪

⑩

⑨

⑧

20-26 Horizontal section of human temporal bone 1.
H-E stain， x 1.0.

⑦

②

③

④

①

⑤

⑮

⑥

⑦
⑧

Bone

⑬

⑭

⑫

⑪

⑩

20-27 Horizontal section of human temporal bone 2.
H-E stain， x 1.0.

⑨

②

①

③

④

⑤
⑪

⑥

⑦

⑩

⑨

20-28 Horizontal section of human temporal bone 3.
H-E stain， x 1.0.

⑧

③
①

④

⑤
⑥
②
⑦
⑪

⑫

⑧

⑯

⑩
⑨
⑬
⑭
⑮

20-29 Horizontal section of human temporal bone 4.
H-E stain， x 1.8.

Bone

20-00 The Ear(Vestibulo-acoustic Organs)•••

The ear ( vestibulo-acoustic organs ) consists of vestibular organs and acoustic organs; theformer concern the sense of equilibrium and motion of the body and reflex control of the skeletal
muscles， and the latter， the perceiving the vibration of the air， the sound， which developed
phylogenetically later than the former.
These organs originate embryologically from a common anlage， namely from the otic vesicle. In
the early half of the fourth gestational week， in the area adjacent to the dorsal end of thesecond branchial groove the surface ectoderm invaginates into the mesenchyme and forms aspherical vesicle， the otic vesicle. This vesicle， enclosed by the ectodermal epithelium，undergoes afterwards complicated morphological changes and finally establishes a complex ofvesicles and connecting ducts， called the labyrinth， consisting of ductus cochlearis， sacculus，
utriculus， three semicircular ducts， and ductus and saccus endolymphaticus ( see 20-02 ).
Among these， the cochlear duct concerns the hearing of the sound， and all others， the senseof equilibrium. These are called， as a whole， the membranous labyrinth， because they are allcomposed of the ectodermal epithelium and supporting connective tissue. Around them develops
a bony capsule of about the same form but of somewhat larger size， called osseous labyrinth，
Except for the definite places， where the membranous adheres to the osseous， there is aninterspace between the membranous and osseous labyrinths， that is filled by fluid， called
perilymph. The membranous labyrinth is a closed system， also filled by fluid， called endolymph.
There is no communication between the endolymph and perilymph.
The membranous ductus cochlearis corresponds in form with the osseous canalis cochlearis，
but the sacculus， utriculus， and three ampullae of ductus semicirculares are accommodated in
one cavity in the petrous part of the temporal bone， called the vestibulum， because of thatthey are called the vestibular organs.

20-01 Location of vestibulo-acoustic organs in the temporal bone
( Scheme )
•

•
•

•

The vestibulo-acoustic organs are embedded in the petrous part of the temporal bone; the cochlear duct at the antero-medial
position， indicated by the internal acoustic meatus， and the sacculus， utriculus and three semicircular ducts at the posterolateral position. The longitudinal axis of the vestibulo-acoustic organs is parallel to the upper margin of the petrous part of thetemporal bone.
The external ear consists of the auricle， external acoustic meatus， and tympanic membrane. They collect the sound wave andconduct it to the middle ear.
The middle ear is composed of the tympanic membrane， three otic ( auditory ) ossicles， the eustachian tube and tympanic
cavity. The tympanic membrane and three otic ossicles transmit the sound wave to the internal ear as the mechanical vibrations， that are converted to the movement of the fluid， perilymph， of the internal ear.
The red line indicates the axis of the cochlear duct， which is horizontal， and perpendicular to the longitudinal axis of thesuperior border of the petrous part.

20-02 Scheme showing the structure of membranous labyrinth.

•This is a schematic drawing of the right side membranous labyrinth， seen from inside. The locations of the sensory epithelium
are indicated by light blue color.

20-001 Cochlea，and External and Middle Ear

•

•

•

The cochlea consists of the membranous ductus cochlearis and the osseous canalis cochlearis. The ductus cochlearis is a spiralduct with blind end at each extremity. The number of spiral turns are two and three fourths in human and three and half inmonkey. The basal turn is the largest and it becomes smaller as going to the top.
The ductus cochlearis and the surrounding osseous canalis cochlearis are structurally and functionally not dividable and should
be described as a whole. Their structures are composed symmetrically around a conical pillar of spongy bone， called themodiolus.
For the convenience of description， words of directions are set here as follows: direction nearing modiolus is medial-ward ( inner)， leaving it， lateral-ward ( outer ); direction to the base of the spiral is downward， and to the top， upward.

20-03 Cochlea， vertical section， 1. Monkey， Held’ s hematoxylin stain， x
4.
•

•

•

This is a general view of a monkey cochlea， exactly vertically sectioned through the plane
containing the modiolus. This section was stained with Held’s hematoxylin， which stains bonedark blue and others light bluish-violet.
The upper left contour of this figure is the inner wall of the tympanic cavity， where thepromontrium and tympanic nerve are seen. The lower contour is the inner surface of thepetrous part of the temporal bone and the internal acoustic meatus containing the cochlear
nerve is evident.
As in monkey the cochlear turns are three and half， sections of cochlear canal ( ducts )appear six and at the top the hericotrema is clearly recognized ( indicated with a bilateralarrow ).

20-04 Cochlea， vertical section， 2. Monkey， Held’ s hematoxylin stain， x
10.
•Higher magnification of the upper left quadrant of the figure 20-03， and the first， the second， and the third turns of thecochlear canal are seen. Along the right edge of the figure stands the modiolus containing the cochlear nerve and at its top thehelicotrema is seen， indicated with a bilateral arrow. Each turn of the cochlear canal is divided by a horizontal plate into two，
upper and lower， cavities; the lower is called scala tympani ( st ). The upper is further divided by a thin oblique membrane intolarger medial cavity， scala vestibuli ( sv )， and smaller lateral cavity， ductus cochlearis ( dc ). At the helico- trema， scala
tympani is continuous with scala vestibuli. The interior of the modiolus is filled by cochlear nerve fibers， stained blueish violet.
The bone is stained dark blue and conspicuous to the soft tissue， stained blueish violet.

20-05 Cochlear canal， vertical section， 3. Monkey. Held’s hematoxylin
stain， x 25.
•••

A thin spiral osseous plate projects from the modiolus into the cochleal canal， called
osseous spiral lamina， and from its lateral edge a sheet of connective tissue extends
across the canal to its opposite wall to join the spiral ligament， which is a special
thickening of the periosteum. On the lateral half of the osseous spiral lamina， the cells of
the periosteum proliferate and form a spiral limbus. Between its upper medial edge and theupper portion of the opposite wall a thin membrane is spread; this is the vestibular
membrane. The lumen of the cochlear canal is， thus， partitioned into three spiralchambers: the scala vestibule ( sv )， above， scala tympani( st )， bolow， and scala media，that is ductus cochlearis ( dc ).
On the lateral half of the osseous spiral lamina and on its lateral continuation， lamina
basilaris， locates the organ of Corti， the organ of hearing.
In the modiolus， at the lower medial portion to the osseous spiral lamina there is a group of
bipolar nerve cells; this is called the spiral ganglion of the cochlear nerve. The distal axons
starting from this ganglion run upper-laterally， then through the space between the upperand lower osseous laminae laterally and attain the organ of Corti. The proximal axons enter
into the interior of the modiolus and form all together the cochlear nerve.

20-06 Cochlear duct and organ of Corti 1. Monkey， Held’s hematoxylin
stain， x 64. (1/4)•••

The ductus cochlearis is triangular in cross section with its apex at the limbus. Its roof is thevestibular membrane and its floor is formed by the spiral lamina and basilar membrane. Its lateralwall consists of stria vascularis and prominentia spiralis， both underlaid by the connective tissueof spiral ligament. The cochlear duct is filled by fluid， named endolymph， and its inner surface iscovered throughout by the ectodermal epithelial cells， that show， however， marvelous local
specialisations.
The cells covering the inner surface of the vestibular membrane are simple squamous in shape，
containing a nucleus protruding into the lumen. They continue at lower medial corner of thecochlear duct to the cells covering the spiral limbus， that are simple columnar in shape and theirbases are firmly embedded in the connective tissue of the thickened periosteum of the osseous
spiral lamina. These cells secrete from the apical surface tectorial membrane， which extends
laterally and covers the organ of Corti. The tapering upper and lower edges of the spiral limbus
project laterally as vestibular and tympanic lips; the latter is continuous with the basilar
membrane. The space surrounded by these two lips is named the internal spiral sulcus ( ssi )，whose surface is covered by flat simple squamous epithelial cells.
At the upper lateral corner of the cochlear duct the epithelial cells of the vestibular membrane
are continuous with the cells of the stria vascularis， that constitutes the lateral wall of thecochlear duct. The stria vascularis consists of a stratified columnar epithelium containing an
intraepithelial plexus of capillaries. Its lower end protrudes into the lumen of the cochlear duct as
spiral prominence， covered by a simple squamous epithelium. At the lower end of the spiralprominence begins the simple cuboidal epithelial cells， which cover the lowermost portion of thelateral wall of the cochlear duct and then medially the upper surface of the most lateral portionof the basilar membrane. These cells are called the cells of Claudius. The space below the spiralprominence and lined by the cells of Claudius is called the external spiral sulcus ( sse ).

20-06 Cochlear duct and organ of Corti 1. Monkey， Held’s hematoxylin
stain， x 64. (2/4)•••

The organ of Corti locates on the medial half of the basilar lamina and is composed of thehighly specialized cells. It consists of the sensory cells ( hair cells ) and the supporting cells (about the details see 20-12 to 20-16 ).
The supporting cells have certain characteristics in common. They are tall slender cells
extending from the basilar membrane to the free surface of the organ of Corti and they
contain conspicuous bundles of microtubules and filaments. Although the bodies of some ofthese cells are separated by wide intercellular spaces， their apical portions are in contact
with each other， and with the hair cells， to form a highly ordered continuous free surface ofthe organ of Corti， referred to the reticular membrane ( 20-16 ). The several types of
supporting cells include inner and outer pillar cells， inner and outer phalangeal cells， border
cells， and the cells of Hensen.
The inner pillar cells have a broad base resting on the basilar lamina and a slender conicalbody extending upward. The segment of cell body containing the nucleus is situated basally，
at the inner angle of a wide triangular intercellular space， called the inner tunnel ( T ). This
space is continuous throughout the length of the cochlea and is bounded below by thin lateralextensions of the base of the pillar cells that rest on the basilar lamina. It is bounded above by
the converging cylindrical bodies of the inner and outer pillar cells. The most distinctive
feature of the inner pillar cells， viewed with the light microscope， is a large， dark-staining
bundle of filaments that courses from the base， upward through the slender cell body to end
at the apex， where the cell widens into a thin horizontal plate that contacts neighboring pillar
cells and the inner hair cells.

20-06 Cochlear duct and organ of Corti 1. Monkey， Held’s hematoxylin
stain， x 64. (3/4)••

The outer pillar cells are longer and more oblique in their orientation， leaning toward the inner
pillars. They have a broad thin base adjoining that of the inner pillar cells. The cell body issimilar， but its expanded upper end has a somewhat different shape. It abuts the under side of
the flat head of the inner pillar cells. From lower down on the cell body， it also sends out aphalangeal process with a flat head that forms junctions， in the reticular lamina， with the haircells and the expanded head of the phalangeal processes of the outer phalangeal cells， locatedbetween the rows of hair cells. The inner pillar cells number about 5600 and the outer pillars
3800. On average， the heads of three inner pillars abut the heads of two outer pillars. The
area of contact between them is quite large， ensuring that they form a sound support for thehair cells.
The outer phalangeal cells ( cells of Deiters ) are the supporting cells for the three or four rowsof outer hair cells. Their base is columnar with a cup-shaped upper end occupied by theinferior one third of a hair cell. Thus， they surround the base of the hair cell and also thebundles of afferent and efferent nerves traveling to the hair cells. The apex of these cells does
not reach the free surface of the organ of Corti， but a slender phalangeal process projectingfrom the side of the cell does reach the reticular lamina. This process is internally reinforced
by a bundle of microtubules and filaments and its expanded distal end forms a flat plate joined，
at its edges， to the hair cell it is supporting， and to the hair cell in the next row. The upper
two-thirds of the hair cells is not immediately surrounded by other cells but is exposed within a
fluid-filled space of Nuel ( N )， which communicates with the inner tunnel through clefts
between the pillar cells.

20-06 Cochlear duct and organ of Corti 1. Monkey， Held’s hematoxylin
stain， x 64. (4/4)
•

•
•

•

The inner phalangeal cells are arranged in a row on the inner side of the inner pillar cells. In
contrast to the outer phalangeal cells， there are no large intercellular spaces between these
supporting cells and the inner hair cells; indeed， they completely surround them. The inner
phalangeal cells are contiguous with a row of slender cells， termed border cells， which markthe inner boundary of the organ of Corti.
The outer border of the organ of Corti is delimited by the tall cells of Hensen adjacent to thelast row of outer phalangeal cells. These are arranged in several rows decreasing rapidly inheight to become continuous laterally with the cells of Claudius.
There are two types of hair cells in the cochlea. The inner hair cells are arranged in a single
row along the entire length of the organ of Corti. The outer hair cells form three rows and arelodged between the outer pillar cells and outer phalangeal cells. In human， a fourth row may befound near the apex of the cochlea.
The cochlear nerve fibers starting from the spiral ganglion run laterally， as the myelinatednerve fibers， through the space between two laminae of osseous spiral lamina and at its lateralend they loose the myelin sheath and penetrate， as naked nerve fibers， the basilar lamina at
the base of the inner phalangeal cells， and here divide into two groups: the one attains thebase of the inner hair cells and forms the synapses with them; the other travels through theintercellular spaces between the inner pillar cells， tunnel， intercellular spaces of the outerpillar cells， space of Nuel， and attains the base of the outer hair cells， and forms thesynapses with them.

20-07 Cochlear duct and organ of Corti 2. Monkey， H-E stain， x 50.

••

These three pictures are made from the specimen， in which preservation of the fine structures was very well so that the detailsof the organ of Corti are clearly seen. The above descriptions in 20-06 about the organ of Corti are all recognized in thesepictures. The stria vascularis， shown in 20-13， was also microphotographed from this specimen.
20-07 shows the general view of the cochlear duct. The inner surface of the cochlear duct ( dc ) is covered throughout by theectodermal epithelial cells， that show the marvelous local specialization. The inner surfaces of scala tympani ( st ) and scalavestibuli ( sv ) are lined by very flat mesenchymal squamous cells.

20-08 Cochlear duct and organ of Corti 3. Monkey， H-E stain， x 64.

••

These three pictures are made from the specimen， in which preservation of the fine structures was very well so that the detailsof the organ of Corti are clearly seen. The above descriptions in 20-06 about the organ of Corti are all recognized in thesepictures. The stria vascularis， shown in 20-13， was also microphotographed from this specimen.
In 20-08 the arrangement of various types of cells constituting the lower surface of the cochlear duct is evidently seen. The
innermost portion， the spiral limbus， is lined by simple and / or pseudostratified columnar epithelium， then the surface of theinner spiral sulcus， by the flat squamous epithelium， next， border cell， inner phalangeal cell and inner hair cell， inner andouter pillar cells， then outer phalangeal cells and outer hair cells， followed by the cells of Hensen and cells of Claudius. The
lower surface of the basilar membrane is covered by mesenchymal cells， which continue laterally with the spiral ligament. A thin
naked nerve fiber traveling the tunnel is clearly seen.

20-09 Organ of Corti. Monkey， H-E stain， x 100.

••

These three pictures are made from the specimen， in which preservation of the fine structures was very well so that the detailsof the organ of Corti are clearly seen. The above descriptions in 20-06 about the organ of Corti are all recognized in thesepictures. The stria vascularis， shown in 20-13， was also microphotographed from this specimen.
20-09 shows the detail of the organ of Corti. The inner pillar and inner pillar cell， and the outer pillar and outer pillar cell areevident. The myelinated cochlear nerve fibers loose the myelin sheath at the base of the inner pillar and the naked nerve fibers
penetrate the basilar lamina and attain the base of the inner hair cell. The inner hair cell leaning on the inner pillar and the threerows of the outer hair cells supported by the outer phalangeal cells， cells of Deiters， are evident. The cells of Hensen and cellsof Claudius are also conspicuous. The lining cells of the spiral limbus and the tectorial membrane are well recognized. The naked
nerve fiber traveling the tunnel is faintly suggested.

20-10 Scheme showing the structure of organ of Corti•

This is to show the structural details of the organ of Corti. Compare with 20-05 ~ 20-09.

20-11 Reticular membrane ( Scheme )••This scheme shows the surface view of the reticular membrane. As is seen here the position of the apical surface of the innerand outer hair cells is quite firmly kept by the border cells， inner phalangeal cells， head plate of the inner pillar cells，
phalangeal process of outer pillar cells， phalangeal process of cells of Deiters of the first， second and third row， and cells ofHensen.
The arrangement of the hairs of the inner hair cells and that of the outer hair cells differs from each other and both arecharacteristic， respectively.

20-12 Spiral ganglion. Monkey， Held’s hematoxylin stain， x 160.

•

The spiral ganglion consists of bipolar nerve cells and locates in the medial wall of the cochlear duct， lower medial to thestarting place of the osseous spiral lamina In this figure， a nerve cell is seen with the distal ( ① ) and the proximal ( ② ) axons.
In this ganglion the Schwann cells enclose not only the nerve fibers but also the cell body of the nerve cells; they are indicatedby short arrows. The myelin sheath is blackened by the pretreatment with the osmic acid.

20-13 Stria vascularis. Monkey， H-E stain， x 100.

•

The stria vascularis composes the most of the lateral wall of the cochlear duct and consists of a thick stratified columnar
epithelium， which contains an intraepithelial plexus of blood capillaries. In this epithelium three layers of cells are distinguished.
The superficial layer consists of cylindrical cells arranged perpendicular to the free surface of the stria vascularis. They are
believed to produce the endolymph. The cells of basal and intermediate layers are polyhedral in shape and contain a round oroval nucleus. The intraepithelial capillaries are closely enveloped by protoplasmic processes of the epithelial cells. The basal cells
are underlain by the connective tissue of the spiral ligament. The epithelial cells of the stria vascularis are continuous with thecells that cover the lower surface of the vestibular membrane， superiorly， and inferiorly， with a thin layer of the squamous
epithelial cells over the spiral prominence， which is a highly vascular thickening of the connective tissue of the spiral ligament. .

20-14 Tympanic membrane 1. Monkey， H-E stain， x 64.

••

The tympanic membrane is a roughly round strong membrane of about 10 mm in diameter andabout 0.1 mm in thickness， which bounds the tympanic cavity from the external acoustic
meatus， It is covered by the skin， exteriorly， and by the mucous membrane of the tympanic
cavity， interiorly. Its substance consists of two layers of collagenous fibers and fibroblasts. In
the outer layer the collagenous fibers are oriented radially， whereas those of the inner layer
have a circular disposition. The skin is very thin and consists of a stratified squamous
epithelium supported by very little connective tissue. The moucous membrane of the tympanic
cavity is also very thin and consists of a squamous epithelium and a thin lamina propria
containing sparse collagen fibers and capillaries.
In 20-14， it is clearly seen that at the periphery of the tympanic membrane the radiating
collagen fibers disperse and adhere to the bone.

20-15 Tympanic membrane 2. Monkey， H-E stain， x 160.

••

The tympanic membrane is a roughly round strong membrane of about 10 mm in diameter and about 0.1 mm in thickness， whichbounds the tympanic cavity from the external acoustic meatus， It is covered by the skin， exteriorly， and by the mucous
membrane of the tympanic cavity， interiorly. Its substance consists of two layers of collagenous fibers and fibroblasts. In theouter layer the collagenous fibers are oriented radially， whereas those of the inner layer have a circular disposition. The skin isvery thin and consists of a stratified squamous epithelium supported by very little connective tissue. The moucous membrane of
the tympanic cavity is also very thin and consists of a squamous epithelium and a thin lamina propria containing sparse collagenfibers and capillaries.
In 20-14， it is clearly seen that at the periphery of the tympanic membrane the radiating collagen fibers disperse and adhere to
the bone.

20-16 External acoustic meatus. Monkey， H-E stain， x 2.5.

•

This is a general view of transverse section of the external acoustic meatus. Its wall is composed of concentrically arranged
layers; around the lumen encircles the skin consisting of a thin epidermis and very thick dense dermis， and very loose
subcutaneous connective tissue， containing the cerminosa glands. The outermost layer is the thick elastic cartilage.

20-002 Vestibular Organs (1/3)

•
•
•

•

The vestibular organs consist of sacculus， utriculus and three semicircular ducts opening into the utriculus. During suddenchanges in orientation， sensory receptors in the semicircular ducts and the sacculus as well as utriculus respond toacceleration of the head to generate nerve impulses to the brain that initiate reflexes which tend to restore normal body position.
The semicircular ducts ( 20-17， 20-20 ~ 20-23 ).
Three semicircular ducts are named according to their position， namely ductus semicircularis anrerior ( D.s.ant.)， ductus
semicircularis posterior ( D.s.post.)， and ductus semicircularis lateralis ( D.s.lat. ). D.s.ant. turns vertically upward and perpendicular to the long axis of the petrous part ( of the temporal bone ). D.s.post. turns vertically postero-lateral-ward and parallel tothe long axis of the petrous part. D.s.lat. turns horizontally lateral-ward and parallel to the long axis of the petrous part. Eachduct opens into the utriculus with two openings; one with a small dilatation ( ampulla ) and another without ampulla ( simple limb).
In the floor of each ampulla， there is a transverse ridge， called the crista ampullaris. The orientation of the ridge ensures that it
is affected by any movement of the ridge with respect to the endolymph within the semicircular duct. The sensory epithelium
over the top of the crista consists of two cell types， namely hair cells and supporting cells. The hair cells do not extend down tothe basal lamina but occupy rounded recesses between the apices of the surrounding supporting cells. On their free surface，
they have a single kinocilium and a cluster of specialized stereocilia ( “hairs” ) that extend upward into the base of gelatinous
structure， called the cupula， which projects into the lumen of the ampulla.

20-002 Vestibular Organs (2/3)

•

•

•

•

•

Two types of hair cells are recognized. Type I hair cells are plump， flask-shaped cells with a round base and narrower neckregion. The nucleus locates basally and surrounded by mitochondria. The Golgi complex locates in the supranuclear region. The
50 to 100 stereocilia on the free surface vary in length in a stepwise fashion， so that the bundle， as a whole， has a beveled
appearance， with the tallest hairs ( 10μｍ ) near the kinocilium and the shortest ( 1μｍ ) on the opposite side.
The type II hair cells are more columnar in form and their kinocilium， stereocilia， and cytoplasmic organelles are similar to thoseof the type I cells. The distinction between the two types of hair cells depends more on the configuration of their innervation
than on the cytological differences.
In the case of the type-I hair cells， nerves penetrate between the supporting cells and form a chalice-like ending completely
investing their rounded base. At one or more sites in the peripheral cytoplasm of the rounded base of the hair cell， there is adense band oriented perpendicular to the plasmalemma and surrounded by a halo of small vesicles， These structures resemble
the so-called synaptic ribbons.
The nerves to the type-II hair cells do not form a calyx but end in a number of relatively small terminal boutons. Synaptic ribbons
are also found in the peripheral cytoplasm of the type-II hair cells opposite the thickened plasmalemma of certain of terminal
boutons.
The sacculus and the utriculus ( 20-17 ~ 20-20， 20-24 and 20-25 ).

20-002 Vestibular Organs (3/3)•••

The vestibulum is a roughly rectangular cavity in the petrous part of the temporal bone，
locating medio-anterior to the tympanic cavity， in which the sacculus， the utriculus and threeampullae of the semicircular canals are accommodated.
The sacculus is a flattened cone， setting the round base on the medio-anterior wall of thevestibulum and projecting the top into the vestivular cavity. The utriculus is an oblong vesicle
protruding horizontally from the medio-anterior wall into the vestibular cavity， upper andposterior to the sacculus. The lining cells of the sacculus and the utriculus are simple squmous
epithelial cells， except for the specialized sensory regions that are called macula sacculi andmacula utriculi， respectively. In the sacculus the macula covers most of the basal wall，
whereas in the utriculus it covers the wall from the medio-anterior portion to the lateroanterior portion， that protrudes into the vestibular cavity.
Both the macula sacculi and the macula utriculi consist of two kinds of tall columnar epithelial
cells， namely， hair cells and supporting cells. They are essentially identical to that of thecrista ampullaris， except for that the stereocilia are even in length. The kinocilium andstereocilia of the hair cells project into the underside of the covering membrane， otolithic
membrane， that is a moderately thick layer of the gelatinous material. The otilithic membrane
contains a multitude of minute crystalline bodies ( 3 to 5μｍ in largeness ). These are called
the otoliths or otoconia and are partially embedded in the upper surface of this membrane.
These consist of protein and calcium carbonate. They are thought to provide additional inertiathat resists displacement of the membrane by external force. Thus， when a linear acceleration
is applied to the head， the otolithic membrane tends to remain stationary while the hair cells
beneath it slide slightly， bending the hairs backward. Bending of the hairs triggers changes in
the frequency of the nerve impulses reaching the brain.

20-17 Vestivulum 1. Sacculus and ampulla posterior. Monkey， H-E stain， x
5.0.
•This is a roughly vertical section of a monkey vestibulum. In this section， the round window ( fenestra cochleae ) closed by thesecondary tympanic membrane， the sacculus with the macula， and ampulla and crista posterior are encountered. Outside of thevestibulum， inferior to the macula sacculi， the vestibular nerve and its ganglion are recognized.

20-18 Vestibulum 2. Stapes and utriculus 1. Monkey， H-E stain， x 5.0.

•This is a parallel section to the 20-17. The whole figure of the stapes， whose base is fitted in the oval window ( fenestra
vestibuli )， and macula utriculi are shown.

20-19 Vestibulum 3. Stapes and utriculus 2. Monkey， H-E stain， x 5.0.

••

20-19 ~ 20-25 are photomicrographs of another series of specimens， sectioned in the different plane than 20-17 and 20-18.
In 20-19， the stapes with the base fitting in the oval window， the utriculus with macula utriculi， and the base of the crista
ampullaris posterior are seen. Facial nerve in the canalis facialis is also shown.

20-20 Vestibulum 4. Macula utriculi and crista ampullaris posterior. Monkey，
H-E stain， x 5.0.
•

In this figure macula utriculi， ampulla and cista ampularis posterior and the basal portions of the anterior and lateral cristae
ampullares are seen. The facial nerve in the canalis facialis is also seen.

20-21 Vestibulum 5. Crista ampullaris anterior and crista amp. lateralis.
Monkey，H-E stain， x 5.0.
•

In this figure， crista ampullaris anterior and crista ampullaris lateralis are shown. The ampulla posterior is now empty. The facial
nerve is still recognized.

20-22 Crista ampullaris 1. Monkey， H-E stain， x 13.2.

•

This is the higher magnification of 20-20. As the cupula towers so highly that in some sections the cupula appears to tie together
the both side of the wall of the crista. The left side of the ampulla goes into the crus simplex of the semicircular duct and theright side it continues with the utriculus. Between the bone and membranous ampulla is filled by very loose connective tissue.
The substance of the crista consists of proliferated connective tissue and nerve fibers.

20-23 Crista ampullaris 2. Monkey， H-E stain， x 50.

•

The higher magnification of 20-22. The surface of the crista ampullaris is covered by two kinds of epithelial cells， namely，
neuroepithelium ( sensory cells ) and supporting cells. The nuclei of the supporting cells align densely above the basement
membrane and their apical cytoplasm supports the basal portion of the neuroepithelial cells ( hair cells ). The nuclei of the haircells locate at about the middle height of the epithelium. A number of the cinocilia are tied up in a bundle and form the cupula.
Beneath the basement membrane among the proliferated connective tissue a number of sections of the vestivular nerve fibers
are seen.

20-24 Macula utriculi 1. Monkey， H-E stain， x 33.

••

The utriculus is an oblong vesicle protruding horizontally from the medio-anterior wall into the vestibular cavity. The macula
utriculi， consisting of the tall sensory epithelium， extends from the medio-antderior portion to the latero-anterior portion of theutricular wall， that protrudes into the vestibular cavity. The macula utriculi is covered by a relatively thick gelatinous membrane， called otolithic membrane， which contains a multitude of minute ( 3 to 5μｍ ) crystalline bodies， called otoliths or otoconia.
In this figure， the macula utriculi covers the utricular wall protruding into the vestibulum. Beneath the macula underlies the loose
connective tissue， in which numerous sections of vestibular nerve fibers are seen.

20-25 Macula utriculi 2. Monkey， H-E stain， x 100.

•••Higher magnification of 20-24.
The supporting cells are tall slender cells standing on the conspicuous basement membrane and extending to the free surface ofthe macula. Their nuclei are densely aligned above the basement membrane. Among the hair cells two types are dis- tinguished;
the one are plump， flask-shaped cells with a round base and narrower neck region， the other are more slender and columnar inform. The basal portion of both types of hair cells does not extend down to the basement membrane but occupies roundedrecesses between the apices of the surrounding supporting cells. The hair cells have one long kinocilium and numerous
stereocilia of even length that project into the under side of the covering gelatinous membrane， called otolithic membrane， that
contains a multitude of minute crystalline bodies ( otoliths or otoconia ). They are partially embedded in its upper surface.
Beneath the basement membrane among the very loose connective tissue numerous sections of vestibular nerve fibers are seen.

20-003 Horizontal Sections of Human Temporal Bone•This specimen was donated by a patient died of cancer of the middle ear. The temporal bone of the sound side was carefully
treated and prepared for the specimen and sectioned horizontally.

20-26 Horizontal section of human temporal bone 1.
H-E stain， x 1.0.
•

This is the uppermost section passing through the upper pert of the tympanic cavity.
①：Tendon of M. tensor tympani.
②：Malleus.
③：Incus.
④：Tympanic cavity.
⑤：Ampulla and crista ampullaris.
⑥：Antrum mastoideum.
⑦：Ductus semicircularis.
⑧：Vestibular nerve.
⑨：Cochlear nerve.
⑩：Cochlear canal， the first turn.
⑪：Internal acoustic meatus.

20-27 Horizontal section of human temporal bone 2.
H-E stain， x 1.0.
•

The section is passing through the modiolus.
①：The space where the M. tensor tympani locates in.
②：Tympanic cavity.
③：Manubrium mallei with tendon of M. tensor tympani.
④：Tympanic membrane.
⑤：Chorda tympani.
⑥：Crus longum of incus.
⑦：Basis of stapes⑧：Sacculus and macula sacculi.
⑨：Vestibulum.
⑩：Modiolus.
⑪：Vestibular nerve.
⑫：Cochlear nerve.
⑬：Cochlear canal， the first turn.
⑭：Internal acoustic meatus.
⑮：External acoustic meatus.

20-28 Horizontal section of human temporal bone 3.
H-E stain， x 1.0.
•

Section of lower portion of cochlea passing through the tendon of M. stapedius.
①：Eustachian tube.
②：Tympanic cavity.
③：Manubrium mallei.
④：Tympanic membrane.
⑤：Crus longum of incus.
⑥：Head of stapes⑦：Tendon of M. stapedius.
⑧：Vestibulum.
⑨：Cochlear canal.
⑩：Internal acoustic meatus.
⑪：External acoustic meatus.

20-29 Horizontal section of human temporal bone 4.
H-E stain， x 1.8.
•

Higher magnification of the central portion of 20-18; section passing through the modiolus.
①：The space where M. tensor tympani locates is.
②：Tympanic cavity.
③：External acoustic meatus.
④：Tympanic membrane.
⑤：Manubrium mallei with tendon of M. tensor tympani.
⑥：Chorda tympani.
⑦：Crus longum of incus.
⑧：Basis of stapes.
⑨：Vestibulum.
⑩：Sacculus and macula sacculi.
⑪：Modiolus.
⑫：Cochlear canal， the first turn.
⑬：Cochlear nerve.
⑭：Vestibular nerve.
⑮：Internal acoustic meatus.
⑯：Canal through which facial nerve passes through.