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V1
C2
V2
V3
C3
Fig. 5.6 Dermatomes of the head and neck. V1, oph-
thalmic division of trigeminal nerve; V2, maxillary
division of trigeminal nerve; V3, mandibular division
of trigeminal nerve.
Muscles of facial expression
• Supercial muscles that can move the skin and supercial fascia in various directions, thus altering facial
expression.
• Orbicularis oculi surrounds the eye. e palpebral part
is in the eyelid and closes the eye as in sleep; the orbital
part surrounds the orbit and forcibly closes the eye, e.g.
when dust blows in the face.
• Orbicularis oris surrounds the mouth. In gentle contraction it closes the lips, in powerful contraction it protrudes the lips, as in whistling and kissing.
• Buccinator is the main muscle of the cheek. It keeps the
cheek in contact with the gums so that food does not
accumulate in the vestibule.
• Occipitofrontalis elevates the eyebrows as in a look of
surprise.
Clinical Points
• To test the integrity of the facial nerve one can ask the
patient to screw up the eyes, to smile or to whistle.
• Loss of muscle tone causes the normal skin folds to disappear on the side of the lesion.
• Paralysis of the palpebral part of orbicularis oculi causes
the lower eyelid to fall away from the eye, with tears
draining over the cheek.
CHAPTER 5 The Head, Neck and Spine
111
• Loss of orbicularis oris can cause dribbling of saliva.
• Paralysis of buccinator may lead to food accumulating
in the vestibule of the mouth.
Blood Vessels of the Face
Arteries
• Main arterial supply to face is facial artery (branch of
the external carotid).
• Enters face by passing over lower border of mandible
with anterior border of masseter, in close relation to the
submandibular gland.
• Has a tortuous course.
• Anastomoses between facial artery and other small
arteries on the same side and on the other side of the
face are common.
• e face is therefore very vascular and cuts bleed considerably but heal quickly.
• Supercial temporal artery (branch of the external
carotid artery) can oen be seen over the temporal area.
• Pulsation can be felt just in front of tragus of ear.
• Becomes more noticeable in age when it becomes
tortuous.
• Wide anastomosis between supercial temporal artery
and facial artery.
Veins
• e main vein draining the face is the facial vein.
• Communicates freely with deeper veins such as those of
the pterygoid venous plexus.
• Communicates with veins of orbit and then with the
cavernous sinus.
• Central area of the face is sometimes known as the ‘dangerous area’, as infection can spread via the veins to the
cavernous sinus.
The Scalp
e scalp consists of ve layers:
• S: skin
• C: connective tissue
• A: aponeurosis
• L: loose areolar tissue
• P: periosteum.
• Skin:
• rich in sebaceous glands
• scalp common site for sebaceous cysts.
• Subcutaneous connective tissue:
• lobules of fat between tough brous septae
• has richest cutaneous blood supply of body
• haemorrhage from scalp laceration is therefore profuse
• blood vessels of the scalp lie in this layer
• divided vessels retract between brous septae and
cannot be picked up individually by artery forceps in
the usual way.
112
Lambdoid suture
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SECTION I Anatomy
• Aponeurotic layer:
• part of occipitofrontalis, which is brous over the
vertex of the skull but muscular in the occipital and
frontal areas.
• Loose connective tissue:
• skin of scalp very mobile under underlying tissue
• ‘scalping’ occurs through this layer
• wounds gape when aponeurosis is torn owing to the
‘pull’ of occipitalis and frontalis.
• Periosteum:
• adherent to suture lines of skull
• collections of blood beneath this layer are therefore
limited by suture lines, e.g. cephalohaematoma.
CRANIAL CAVITY
e cranium consists of the cranial cavity and the facial skeleton. Most bones of the cranial cavity are at bones and have:
• two plates of compact bone separated by a thin layer of
trabecular bone or diploë
• inner and outer surfaces are lined by periosteum
• inner periosteum is the endosteal layer of the dura
mater.
e bones of the cranial cavity are:
• frontal
• occipital
• sphenoid
• ethmoid
• paired temporal bones
• parietal bones.
e cranial cavity consists of:
• cranial vault
• base of cranium containing three cranial fossae.
Cranial Vault (Fig. 5.7)
• Roof of the cranial cavity.
• Formed by:
• frontal bone anteriorly
• paired parietal bones laterally
• occipital bone posteriorly.
• A midline sagittal groove marks the position of the
superior sagittal sinus.
• Falx cerebri is attached along the lips of the groove.
• Irregular depressions along the groove lodge the arachnoid granulations.
• Sagittal suture separates two parietal bones in midline.
• Coronal suture divides the frontal from parietal bones.
• e lambdoid suture divides the two parietal bones
from the occipital bone and the temporal bones.
• Posterior to the coronal suture, the middle meningeal
vein accompanied by the middle meningeal artery
groove the vault of the skull.
Coronal suture
Sagittal
suture
Fig. 5.7 The vault of the skull from below.
• e lambda is the junction between the lambdoid suture
and the sagittal suture (it is the area of the posterior
fontanelle in the infant).
• e bregma is the junction between the coronal and
sagittal suture (it is the area of the anterior fontanelle in
infants).
• e glabella is the prominence above the nasion, which
is the depression between the two supraorbital margins.
• e pterion is the thin part of the skull at the junction of
the parietal, frontal and temporal bones, and the greater
wing of the sphenoid in the temporal region of the skull.
• e anterior branch of the middle meningeal artery traverses the pterion.
Cranial Fossae (Fig. 5.8)
ere are three cranial fossae:
• anterior
• middle
• posterior.
Anterior Cranial Fossa
• Overlies the orbit and nasal cavities.
• Formed by the orbital plate of the frontal bones supplemented posteriorly by the lesser wing of the sphenoid.
• e ethmoid bone with its cribriform plate and the
crista galli occupies the gap between the two orbital
plates.
• Orbital plates separate anterior cranial fossa from orbit.
Anterior cranial fossa
Lesser wing of sphenoid
Petrous part of temporal bone
Squamous part of temporal bone
Greater wing of sphenoid
Foramen rotundum
Hypophyseal fossa
Foramen ovale
Middle cranial fossa
CHAPTER 5 The Head, Neck and Spine
Crista galli
Cribriform plate
Orbital plate of frontal bone
Optic canal
Anterior clinoid process
Posterior clinoid process
Foramen spinosum
Tegmen tympani
113
Fig. 5.8 The floor of the cranial cavity.
• e frontal lobe of the brain lies in the anterior cranial
fossa.
• e cribriform plate roofs the nasal cavities.
• e following structures pass between the anterior cranial fossa and the nasal cavity:
• olfactory nerves: pass through cribriform plate and
enter olfactory bulb, which lies in cribriform plate
• emissary veins: connecting cerebral veins in nasal
cavity also pass through cribriform plate
• anterior ethmoidal nerves and arteries accompanied
by veins: pass through the anterior part of the cribriform plate into the nasal cavities.
• Fracture of anterior cranial fossa may cause bleeding into
the nose and/or orbit and CSF rhinorrhoea. Bleeding into
the orbit may manifest as subconjunctival haemorrhage.
Fractures involving the cribriform plate will aect the
sense of smell (see Ch. 6 section on Olfactory Nerve).
Middle Cranial Fossa
• Body of sphenoid forms oor of pituitary fossa.
• Laterally are the greater wings of the sphenoid and the
squamous parts of the temporal bones.
• Petrous part of the temporal bone contains the middle
and inner ear.
• Pituitary fossa is bounded in front and behind by the
anterior and posterior clinoid processes.
• e middle cranial fossa contains the following foramina:
• optic canal
• superior orbital ssure
Foramen lacerum
Posterior cranial fossa
Internal occipital protuberance
• foramen rotundum
• foramen ovale
• foramen spinosum
• foramen lacerum.
Structures passing through the various foramina are
detailed in Table 5.2.
• Fractures of the middle cranial fossa are common as the
bone is weakened by the foramina and canals:
• fracture involving the tegmen tympani results in
bleeding into the middle ear
• excessive bleeding into the middle ear can rupture
the tympanic membrane, resulting in bleeding from
the ear
• CSF otorrhoea may occur
• cranial nerves VII and VIII may also be involved, as
they run in the petrous temporal bone.
Posterior Cranial Fossa
• Anterior wall formed by petrous temporal bone laterally
and body of sphenoid and basilar part of occipital bone
medially.
• Latter two form the clivus, which extends from the fora-
men magnum to the dorsum sellae.
• Occipital bone forms most of the oor and lateral walls
of the fossa.
• Internal occipital protuberance is in the midline on the
posterior wall.
• Above the internal occipital protuberance the skull is
grooved by the superior sagittal sinus.
Arcuate eminence
Internal auditory meatus
Foramen magnum
114
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SECTION I Anatomy
TABLE 5.2 Skull Foramina and Contents
Fossa Foramina Contents
Anterior cranial fossa Cribriform plate (multiple small
foramina)
Middle cranial fossa Optic canal optic nerve
Superior orbital fissure oculomotor nerve
Foramen rotundum maxillary division of trigeminal nerve
Foramen ovale mandibular division of trigeminal nerve
Foramen spinosum middle meningeal artery
Foramen lacerum internal carotid artery
Posterior cranial fossa Foramen magnum medulla oblongata, continuing into spinal cord
Jugular foramen internal jugular vein (continuation of sigmoid sinus)
Hypoglossal canal hypoglossal nerve
Internal auditory meatus facial nerve
olfactory nerve
emissary veins
arteries and veins
ophthalmic artery
trochlear nerves
abducens nerve
ophthalmic division of trigeminal nerve
ophthalmic veins
sympathetic nerves
accessory meningeal artery
meningeal branch of mandibular nerve
accessory nerves
vertebral arteries
glossopharyngeal, vagus and accessory nerves
inferior petrosal sinus
meningeal branch of ascending pharyngeal artery
vestibulocochlear nerve
labyrinthine artery
(Facial nerve exits the base of the skull via the
stylomastoid foramen)
• Transverse sinuses run anterolaterally on either side of
the internal occipital protuberance, continuing down
beneath the petrous temporal bone as the sigmoid sinus.
Base of the Skull
e bones of the base of the skull and the various foramina
are shown in Fig. 5.9.
• e posterior cranial fossa contains the following foramina:
• jugular foramen
ORBIT AND EYEBALL
• hypoglossal canal
• foramen magnum
• internal acoustic meatus.
• Fractures of the posterior cranial fossa may involve the
basilar part of the occipital bone, which separates the
pharynx from the posterior cranial fossa. Bleeding may
occur into the pharynx. More lateral fractures can bleed
into the back of the neck.
The Bony Orbit (Fig. 5.10)
e function of the orbit is to:
• protect the eye against external blows
• maintain the constant distance between the pupils necessary for binocular vision.
Contraction of the external ocular muscles must rotate
the eye and not displace it. e margins of the orbit are
Alveolar process
Greater palatine foramen
Stylomastoid foramen
Lesser wing of sphenoid
Greater wing of sphenoid
Superior orbital fissure
Orbital plate of frontal bone
Supraorbital notch
Zygomatic arch
Carotid canal
Pharyngeal tubercle
Jugular foramen
Groove for
digastric muscle
Fig. 5.9 The base of the skull from below.
CHAPTER 5 The Head, Neck and Spine
Incisor foramen
Palatal process of maxilla
Horizontal plate
of palatine bone
Medial pterygoid plate
Lateral pterygoid plate
Foramen ovale
Foramen spinosum
Styloid process
Occipital condyle
Mastoid process
Foramen magnum
Inferior nuchal line
115
Fig. 5.10 The bony orbit.
formed by the frontal, maxillary and zygomatic bones. e
more precise boundaries are as follows.
• Roof:
• frontal bone anteriorly
• lesser wing of sphenoid posteriorly.
• Lateral wall:
• frontal process of zygomatic bone
Inferior orbital fissure
Zygomatic process
of frontal bone
Zygomatic bone
Maxillary process
of zygomatic bone
Optic foramen
Orbital plate of ethmoid
Lacrimal fossa
Orbital surface of maxilla
• zygomatic process of frontal bone.
• Floor:
• maxillary process of zygomatic bone laterally
• maxilla medially.
• Medial wall:
• frontal process of maxilla
• frontal bone
116
Cornea
centralis
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SECTION I Anatomy
• lacrimal bone
• orbital plate of ethmoid bone
• body of the sphenoid.
Structures Entering and Leaving the Orbit
Passing through the optic foramen are:
• the optic nerve
• the ophthalmic artery.
Passing through the superior orbital ssure are:
• the three cranial nerves supplying the external ocular
muscles:
• oculomotor nerve
• trochlear nerve
• abducens nerve
• the ophthalmic division of the trigeminal nerve
• the ophthalmic veins draining back into the cavernous
sinus.
Passing through the inferior orbital ssure are:
• the infraorbital nerve, the major branch of the maxillary
division of the trigeminal nerve
• veins draining orbital structures into the veins of the
pterygopalatine ssure and infratemporal fossa.
Passing through the nasolacrimal canal is:
• nasolacrimal duct.
• Passing through the anterior and posterior ethmoidal
foramina are:
• anterior and posterior ethmoidal vessels.
Choroid
Iris
Lens
Fig. 5.11 Horizontal section of the eyeball, showing
the optic and visual axes.
Visual axis
Optic axis
Optic disc
Fovea
Optic
nerve
• Cornea is continuous with the sclera at the sclerocorneal junction.
• Sclera is tough brous membrane which maintains the
shape of the eyeball and receives insertion of the extraocular muscles.
• Sclera is continuous posteriorly with the dural sheath of
the optic nerve.
• Posteriorly the sclera is pierced by the optic nerve 3 mm
to the medial side of the optical axis (posterior pole).
THE CONTENTS OF THE ORBIT
e contents of the orbit are:
• eyeball
• extraocular muscles.
The Eyeball (Fig. 5.11)
e eyeball is spherical and contained within the orbit. It is
formed by segments of two spheres with the segment of the
smaller sphere, corresponding to the cornea, superimposed
anteriorly. It consists of three coats enclosing three refractive media. e coats are:
• brous: sclera, cornea
• vascular: choroid, ciliary body, iris
• neural: retina.
e refractive media are:
• aqueous humour
• vitreous body
• lens.
Fibrous Coat
• Transparent anterior part: cornea.
• Opaque posterior part: sclera.
Vascular Coat
is is composed of:
• choroid
• ciliary body
• iris.
Choroid
• in, highly vascular membrane lying in a surface of
sclera.
• Pierced posteriorly by optic nerve.
• Connected anteriorly to iris by ciliary body.
Ciliary body
e ciliary body includes:
• ciliary ring: a brous ring continuous with the choroid
• ciliary processes: approximately 70 folds arranged
radially between the ciliary ring and the iris, and
connected posteriorly to the suspensory ligament of
the lens
• ciliary muscles: outer radial and inner circular layer of
smooth muscle responsible for changes in the convexity
of the lens in accommodation.
Iris
• Coloured membrane suspended in the aqueous humour
behind the cornea and in front of the lens.
Lateral
Medial
Macula lutea
central fovea
Anterior
sclera
r
• In its centre is a circular aperture, the pupil.
• Connected to the circumference of the ciliary body.
• Consists of four layers:
• anterior mesothelial layer
• connective tissue stroma containing pigment cells
• smooth muscle: radial (dilator pupillae), circular
(sphincter pupillae)
• posterior layer of pigmented cells.
Neural
• Retina is the expanded termination of the optic
nerve.
• Consists of an outer pigmented and an inner nervous
laye r.
• Lies between the choroid and hyaloid membrane of the
vitreous body.
• Anteriorly is an irregular edge, the ora serrata.
• Posteriorly, the surface nerve bres join to form the
optic nerve.
• e inner surface contains (Fig. 5.12):
• macula lutea (yellow spot) situated at the posterior
pole on the optical axis
• fovea centralis: a depression in the macula
• optic disc (medial to the macula), where the optic
nerve enters
• central vessels of the retina coursing over the optic
disc
• central artery of the retina emerging from the optic
disc and dividing into upper and lower branches, e.g.
dividing into a nasal and temporal branch.
• e retina consists of:
• rods and cones: inner receptor cell layer
• intermediate bipolar neurons
• layer of ganglion cells whose axons form the super-
cial layer of optic nerve bres.
Contents of the Eyeball (Fig. 5.13)
Lens
• Biconvex.
• Enclosed in lens capsule.
• Lies between vitreous and aqueous humour just behind
iris.
• Surrounded by suspensory ligament connecting it to
ciliary processes.
Aqueous humour
• Filtrate of plasma secreted by vessels of iris and ciliary
body into space between lens and iris (posterior chamber of eye).
• Passes through pupillary aperture into area between
cornea and iris (anterior chamber of the eye).
• Reabsorbed into ciliary veins via canal of Schlemm
(sinus venosus sclerae).
CHAPTER 5 The Head, Neck and Spine
with
117
Artery
Vein
Optic
disc
Fig. 5.12 The right fundus as seen by ophthalmoscopy.
Iris Lens
Posterio
chamber
Suspensory
ligament
Ciliary body
Ciliary muscle
Conjunctiva
Sclera
Cornea
Tarsal
glands
Eyelid
Orbicularis oculi
chamber
Sinus venosus
Fig. 5.13 The sclerocorneal junction.
Vitreous body
• Occupies posterior four-hs of eyeball.
• So gelatinous substance contained within the hyaloid
membrane.
• Hyaloid membrane passes forwards in front where it is
thickened, receiving the attachments from the ciliary
processes and giving rise to the suspensory ligament of
the lens.
• e hyaloid canal (containing lymph) passes forwards
through the vitreous from the optic disc as far as the
capsule of the lens.
ORBITAL MUSCLES
e orbital muscles are:
• levator palpebrae superioris which elevates the upper
eyelid
118
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SECTION I Anatomy
• medial, lateral, superior, inferior recti
• superior and inferior oblique.
Four Recti
• Originate from tendinous ring around optic nerve and
medial part of superior orbital ssure.
• Insert into sclera anterior to equator of eyeball.
Superior Oblique
• Originates just above tendinous ring.
• Inserts via a tendon which loops around a brous pulley on the medial part of the roof of the orbit, into the
sclera, just lateral to the insertion of superior rectus
behind the equator of the eyeball.
Inferior Oblique
• Originates from the medial part of the oor of the front
of the orbit.
• Inserts by passing on the undersurface of the eye, into
the sclera between superior and lateral recti behind the
equator of the eyeball.
Nerve Supply
• Lateral rectus: abducens (VI).
• Superior oblique: trochlear (IV).
• All others: oculomotor (III).
• tarsal glands
• conjunctiva.
• Eyelashes arise at mucocutaneous junction (infection of
hair follicle here results in a stye).
Meibomian glands (large sebaceous glands) open behind
eyelashes and, if blocked, produce Meibomian cysts.
Conjunctiva
• Mucous membrane lining the inner surface of the lids.
• Reected over anterior part of sclera to cornea.
• ick and highly vascular over eyelids, thin over sclera,
and single layer of cells only over cornea.
• Lines of reection from lid to sclera are called the
fornices.
Lacrimal Apparatus
• Lacrimal gland lies in depression at superolateral angle
of orbit.
• Twelve to fourteen ducts open into the superior conjunctival fornix.
• Tears are drained away by lacrimal canaliculi, which
pass medially to open into the lacrimal sac.
• Lacrimal sac lies in a small depression on the medial
surface of the orbit.
• Lacrimal sac drains via nasolacrimal duct into the anterior part of the inferior meatus of the nose.
Movements of the Eyeball
• Elevation.
• Depression.
• Adduction.
• Abduction.
• Rotation.
• Medial recti: adduction—move eyeball in one axis only.
• Lateral recti: abduction—move eyeball in one axis only.
• Superior rectus: elevation, adduction, medial rotation.
• Inferior rectus: depression, adduction, lateral rotation.
• Superior oblique: depression, abduction, medial rotation.
• Inferior oblique: elevation, abduction, lateral rotation.
• Superior rectus and inferior oblique acting together:
pure elevation.
• Inferior rectus and superior oblique acting together:
pure depression.
Eyelids
• Upper is larger and more mobile.
• Upper contains levator palpebrae superioris.
• Each eyelid consists of following layers from without in:
• skin
• connective tissue
• orbicularis oculi
• tarsal plates (brous tissue)
THE EAR
e ear is composed of three parts:
• external
• middle
• internal.
External Ear
is is composed of:
• auricle
• external auditory meatus.
Auricle (Fig. 5.14)
• Plate of elastic cartilage covered with skin.
• It has numerous ridges and depressions.
External Auditory Meatus
• Extends inwards to tympanic membrane.
• Approximately 3.5 cm long.
• Formed partly by cartilage and partly bone.
• Passes medially upwards and forwards, then medially and backwards, and nally medially forwards and
downwards.
• Lined by skin with hairs and ceruminous glands, which
secrete wax.
Helix
Antihelix
Concha
Long process
the malleus
Anterior
Posterior
CHAPTER 5 The Head, Neck and Spine
Handle of
119
Pars flaccida
of the incus
Tragus
Antitragus
Lobule
Fig. 5.14 The auricle.
Middle Ear
• Narrow slit-like cavity contained in the petrous temporal bone (tympanic cavity).
• Contains a chain of bones (ossicles) which transmit
sound vibrations from tympanic membrane to internal
ea r.
• Communicates with pharynx via auditory or pharyngotympanic (Eustachian) tube.
Tympanic Cavity
e tympanic cavity has four walls, a roof and a oor.
Lateral Wall
• Tympanic membrane separating it from the external
auditory meatus.
Medial Wall
• Separates the cavity from the inner ear.
• Presents the following features:
• fenestra vestibuli (oval window): occupied by the
base of the stapes
• promontory below the fenestra vestibuli: formed by
the projection of the rst turn of the cochlea
• fenestra cochleae (round window): lies at the bottom
of a funnel-shaped depression behind the promontory; closed by the secondary tympanic membrane
• prominence caused by the underlying canal for the
facial nerve.
Posterior Wall
• Carries a small pyramidal projection at the level of the
fenestra vestibuli, which houses stapedius muscle.
• Posterior wall continues into mastoid process and mastoid air cells.
Pars tensa
Umbo
Fig. 5.15 The tympanic membrane as seen through
an auroscope.
Anterior Wall
• Contains openings of canal for tensor tympani and of
the auditory canal.
• Below these, a thin plate of bone separates the cavity
from the canal for the internal carotid artery.
Floor
• in plate of bone separating the cavity from the bulb of
the jugular vein.
Roof
• in sheet of bone: the tegmen tympani.
• Tegmen tympani separates the epitympanic recess
(which extends laterally superior to the tympanic membrane) from the oor of the middle cranial fossa and the
temporal lobe of the brain.
Tympanic Membrane (Eardrum) (Fig. 5.15)
• Separates middle ear from external auditory meatus.
• Consists of three layers:
• outer stratied squamous epithelium
• middle layer of brous tissue
• inner mucous layer facing the tympanic cavity and
continuous with the mucoperiosteum of the cavity.
• Faces laterally downwards and forwards.
• Bulges into middle ear, making lateral surface concave.
• Upper part is thin and loose: pars accida; the remainder is taut: pars tensa.
• Translucent except at its margins: it is possible to see the
underlying malleus and part of the incus through it.
• e point of greatest concavity is the umbo, marking the
attachment of the handle of the malleus to the membrane.
The Ossicles
ese are:
• malleus
120
Posterior semicircular canal
Saccule
r
•
semicircular ducts
•
•
•
duct of the cochlea (within the cochlea).
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SECTION I Anatomy
• incus
• stapes.
ey form an interconnecting chain of bones conducting
sound through the middle ear.
• Malleus is the largest and has:
• a handle attached to tympanic membrane
• a head articulating with the incus
• a lateral process from which the malleolar folds radiate.
• Incus has:
• a body which articulates with the malleus
• a short process attached to the posterior wall of the
middle ear
• a long process articulating with the stapes.
• Stapes has:
• a head for articulation with the incus
• a base xed to the membrane closing the fenestra
vestibuli (oval window)
• two muscles which serve to dampen high-frequency
vibrations are associated with the ossicles:
• stapedius: attached to the neck of the stapes and
supplied by the facial nerve
• tensor tympani: inserted into the handle of the
malleus and supplied by the mandibular division
of the trigeminal nerve.
Auditory Tube (Eustachian Tube)
• Passes downwards, forwards and medially from the
anterior part of the tympanic cavity to the lateral wall of
the nasopharynx.
• It is 35 mm long, the rst part being bony and the rest
cartilaginous.
• Lined by columnar ciliated epithelium.
• Its nasopharyngeal opening is surrounded by lymphoid tissue, the tubal tonsil, which may swell with infection, blocking the tube and predisposing to middle ear infection.
Inner Ear (Fig. 5.16)
e inner ear or labyrinth is divided into two parts:
• bony labyrinth
• membranous labyrinth.
e membranous labyrinth lies within the bony labyrinth.
e bony labyrinth comprises:
• vestibule
• semicircular canals
• cochlea.
e membranous labyrinth comprises:
utricle within the
saccule vestibule
Features of the inner ear
• e membranous labyrinth contains a uid: endolymph.
• e bony labyrinth contains perilymph surrounding the
membranous labyrinth.
• e vestibulocochlear nerve divides into:
• a vestibular division supplying utricle, saccule and
• a cochlear division running up the central canal of
}
semicircular ducts
the cochlea and supplying the organ of Corti in the
cochlear duct.
Posterior semicircular duct
Ampulla of anterior
Fig. 5.16 The membranous labyrinth superimposed on the osseous labyrinth.
semicircular duct
Helicotrema
Cochlear duct
Utricle
Lateral semicircula
duct
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