Special Senses

Sense of Sight


Orbital Fascia
forms the periosteum of the orbit.
It is loosely connected to the bones and can readily be separated from them.



The Fascia Bulbi (capsule of Ténon) is a thin membrane which envelops the bulb of the eye from the optic nerve to the ciliary region, separating it from the orbital fat and forming a socket in which it plays

diagram of the eye & orbit muscles



- pierced behind by the optic nerve, and is
continuous through the fibrous sheath of this nerve with the dura mater.

lamina cribrosa scleræ:
a thin cribriform lamina formed by the sclera at the point where the optic nerve passes thru the minute orifices in this lamina
serves for the transmission of the nervous filaments
One of these openings occupying the center of the lamina transmits the central artery and vein of the retina.

- in front, the sclera is directly continuous with
the cornea, the line of union being termed the
sclero-corneal junction.

- in the inner part of the sclera close to this junction is a circular canal, the sinus venosus scleræ (canal of Schlemm). The sinus is lined by endothelium and communicates externally with the anterior ciliary veins.
- The aqueous humor drains into the scleral sinuses by passage through the “pectinate villi” which are analogous in structure and function to the arachnoid villi of the cerebral meninges.

The Cornea
— the projecting transparent part of the external tunic
- convex anteriorly and projects like a dome in front of the sclera
- degree of curvature varies in different individuals, and in the same individual at
different periods of life, being more pronounced in youth than in advanced life
- dense and of uniform thickness throughout
- Immediately in front of the sclero-corneal junction the cornea bulges inward as a thickened rim, and behind this there is a distinct furrow between the attachment of the iris and the sclero-corneal junction, the sulcus circularis corneæ.


filtration angle of the eye:
-an angular recess between the trabecular tissue that forms the inner wall of the sinus venosus sclerae and the anterior surface of the attached margin of the iris.
scleral spur:
-a projecting rim of scleral tissue immediately outside of the filtration
non-vascular structure; the capillary vessels ending in loops at its circumference
are derived from the anterior ciliary arteries
nerves are numerous and are derived from the ciliary nerves

The Vascular Tunic
~ formed from behind forward by:
the choroid- invests the posterior 5/6 of
the eyeball
- extends as far forward as the ora
serrata of the retina.
the ciliary body - connects the choroid to the
circumference of the iris.
the iris- a circular diaphragm behind the
cornea, and presents near its center a
rounded aperture, the pupil.



Choroid: a thin, highly vascular membrane, consisting
mainly of a dense capillary plexus, and of
small arteries and veins carrying blood to
and from this plexus
: dark brown or chocolate color, investing
the posterior five-sixths of the globe
: pierced behind by the optic nerve
: outer surface is loosely connected with the
sclera;
: its inner surface is attached to the pigmented
layer of the retina.
: One of the functions is to provide nutrition for
the retina, and to convey vessels and
nerves to the ciliary body and iris.



Ciliary Body: comprises the orbiculus ciliaris,
the ciliary processes,
the Ciliaris muscle.

orbiculus ciliaris: a zone of about 4 mm. in width, directly
continuous with the anterior part of the
choroid;
: it presents numerous ridges arranged in
a radial manner
ciliary processes : formed by the inward folding of the various
layers of the choroid i.e., the choroid proper
and the lamina basalis,
: received between corresponding foldings of
the suspensory ligament of the lens
: arranged in a circle, and form a sort of
frill behind the iris, around the margin
of the lens


Ciliary Body
The ciliary body lies just behind the iris.  Attached to the ciliary body are tiny fiber "guy wires" called zonules.  The crystalline lens is suspended inside the eye by the zonular fibers.  Nourishment for the ciliary body comes from blood vessels which also supply the iris.  
One function of the ciliary body is the production of aqueous humor, the clear
fluid that fills the front of the eye.  It also controls accommodation by changing
the shape of the crystalline lens.  When the ciliary body contracts, the zonules relax.  This allows the lens to thicken, increasing the eye's ability to focus up close.  When looking at a distant object, the ciliary body relaxes, causing the zonules to contract.  The lens becomes thinner, adjusting the eye's focus for distance vision.
Angle Structures
The area in the anterior chamber where the cornea and iris join is known as the angle.  This is comprised of several structures that make up the eye's drainage system.  The angle structures include:  the outermost part of the iris, the front of the ciliary body, the trabecular meshwork, and the Canal of Schlemm.

Ciliaris muscle (Bowman’s muscle)
: consists of unstriped fibers forming a
grayish, semitransparent, circular band,
on the outer surface of the fore-part of the
choroid
: the chief agent in accommodation, i. e., in
adjusting the eye to the vision of near
objects. When it contracts it draws forward
the ciliary processes, relaxes the
suspensory ligament of the lens, and thus
allows the lens to become more convex

Iris: received its name from its various colors in
different individuals
: a thin, circular, contractile disk, suspended
in the aqueous humor between the cornea
& lens, and perforated a little to the nasal
side of its center by a circular aperture, the
pupil
: by its periphery it is continuous with the
ciliary body, & is also connected with the
posterior elastic lamina of the cornea by
means of the pectinate ligament
: divides the space between the lens and
the cornea into an anterior and a posterior
chamber


anterior chamber
: bounded in front by the posterior surface of
the cornea behind by the front of the iris and
the central part of the lens.

posterior chamber
: a narrow chink behind the peripheral part of
the iris, and in front of the suspensory
ligament of the lens and the ciliary processes

.


The Retina
~ a delicate nervous membrane, upon which the
images of external objects are received
~ outer surface is in contact with the choroid
its inner with the hyaloid membrane of the vitreous
body;
behind, it is continuous with the optic nerve.
~ extends nearly as far as the ciliary body, where it
appears to end in a jagged margin, the ora serrata

The arteria centralis retinæ and its accompanying vein pierce the optic nerve.



The Refracting Media: Aqueous humor.
Vitreous body.
Crystalline lens.

Aqueous Humor: fills the anterior and posterior chambers
of the eyeball
: small in quantity, has an alkaline reaction,
: consists mainly of water,
: less than 1/5 of its weight being solid
matter, chiefly chloride of sodium.
Vitreous Body: forms about four-fifths of the bulb of the eye
: fills the concavity of the retina,
: hollowed in front, forming a deep concavity,
the hyaloid fossa, for the reception of the lens
: transparent, of the consistency of thin jelly,
composed of an albuminous fluid enclosed in
a delicate transparent membrane, the hyaloid
membrane.


in the center, running from the entrance of the optic nerve to the posterior surface of the lens, is a canal, the hyaloid canal, filled with lymph and lined by prolongation of the hyaloid membrane.
the fluid from the vitreous body is nearly pure water; it contains, however, some salts, and a little albumin.


The hyaloid membrane envelopes the vitreous body. The portion in front of the ora serrata is thickened by the accession of radial fibers and is termed the zonula ciliaris (zonule of Zinn).

: splits into two layers, one of which is thin and lines the hyaloid fossa; the other is named the suspensory ligament of the lens


Crystalline lens: enclosed in its capsule which is a
transparent & a structureles membrane
: immediately behind the iris,
in front of the vitreous body
encircled by the ciliary processes,
: transparent, biconvex body
: in the fetus, the lens is nearly spherical,
has a slightly reddish tint; is soft and
breaks down readily on the slightest
pressure.
: In the adult, the lens is colorless,
transparent, firm in texture, and devoid
of vessels.
: In old age it becomes flattened on both
surfaces, slightly opaque, of an amber
tint, & increased in density

Vessels and Nerves.
The arteries of the bulb of the eye are the
long, short, and anterior ciliary arteries, and
the arteria centralis retinæ.
The ciliary veins are seen on the outer surface of the choroid, and are named, from their arrangement, the venæ vorticosæ;
Another set of veins accompanies the anterior ciliary arteries. All of these veins open into the ophthalmic veins.
The ciliary nerves are derived from the nasociliary nerve and from the ciliary ganglion.


The Accessory Organs of the Eye
~ include:
the ocular muscles,
the fasciæ,
the eyebrows,
the eyelids,
the conjunctiva,
and the lacrimal apparatus.



The Ocular Muscles:

Levator palpebræ superioris
Superior oblique
Inferior oblique
Medial rectus
Superior rectus
Lateral rectus.
Inferior rectus


Levator palpebræ superioris
: thin, flat, and triangular in shape
: arises from the under surface of the
small wing of the sphenoid, above and in
front of the optic foramen, from which it
is separated by the origin of the Rectus
superior.
: inserted into the upper margin of the superior tarsus

Levator palpebrae superior - raises the upper eyelid, and is the direct antagonist of the Orbicularis oculi.

L orbicularis oculi

The four Recti
= arise from a fibrous ring which surrounds
the upper medial, and lower margins of the
optic foramen and encircles the optic nerve.
Two specialized parts of this fibrous ring may be made out:
1) a lower, the ligament or tendon of Zinn
- gives origin to the Rectus inferior,
part of the Rectus internus, and the
lower head of origin of the Rectus
lateralis;


2) an upper, which gives origin to the
Rectus superior,
the rest of the Rectus medialis,
the upper head of the Rectus
lateralis.

This upper band is sometimes
termed the superior tendon of
Lockwood..
.



Although these muscles present a
common origin and are inserted in a
similar manner into the sclera, there are
certain differences to be observed in them
as regards their length and breadth. The
Medial Rectus is the broadest, the Lateral
Rectus is the longest, and the Superior
Rectus the thinnest and narrowest.




muscle movements

A given extraocular muscle moves an eye in a specific manner, as follows:

medial rectus (MR)—moves the eye toward the nose

lateral rectus (LR)—moves the eye away from the nose

superior rectus (SR)—primarily moves the eye upward and secondarily rotates the top of the eye toward the nose

inferior rectus (IR)—primarily moves the eye downward and secondarily rotates the top of the eye away from the nose

superior oblique (SO)—primarily rotates the top of the eye toward the nose and secondarily moves the eye downward

inferior oblique (IO)—primarily rotates the top of the eye away from the nose and secondarily moves the eye upward



Muscle innervations
Each extraocular muscle is innervated by a specific cranial nerve (C.N.):
medial rectus (MR)—cranial nerve III
lateral rectus (LR)—cranial nerve VI
superior rectus (SR)—cranial nerve III
inferior rectus (IR)—cranial nerve III
superior oblique (SO)—cranial nerve IV
inferior oblique (IO)—cranial nerve III

The following can be used to remember the cranial nerve innervations of the six extraocular muscles:
LR6(SO4)3.
That is, the lateral rectus (LR) is innervated by C.N. 6, the superior oblique (SO) is innervated by C.N. 4, and the four remaining muscles (MR, SR, IR, and IO) are innervated by C.N. 3.




eyelashes (cilia): attached to the free edges of the eyelids
: short, thick, curved hairs, arranged in a double or triple row
: near their attachment are the openings of a number of glands, the ciliary glands, arranged in several rows close to the free margin of the lid regarded as enlarged and modified sudoriferous glands.



The lateral palpebral commissure ( external canthus) is more acute than the medial, and the eyelids here lie in close contact with the bulb of the eye: but the medial palpebral commissure ( internal canthus) is prolonged for a short distance toward the nose, and the two eyelids are separated by a triangular space, the lacus lacrimalis At the basal angles of the lacus lacrimalis, on the margin of each eyelid, is a small conical elevation, the lacrimal papilla, the apex of which is pierced by a small orifice, the punctum lacrimale, the commencement of the lacrimal duct.
punctum lacrimale

Structure of the Eyelids (palpebrae)
~ composed of the following structures taken in their order from without inward: integument, areolar tissue, fibers of the Orbicularis oculi, tarsus, orbital septum, tarsal glands and conjunctiva.
The upper eyelid has the aponeurosis of the Levator palpebræ superioris.
integument - extremely thin, and continuous at the margins of the eyelids with the conjunctiva.
subcutaneous areolar tissue - very lax and delicate, and seldom contains any fat.
palpebral fibers of the Orbicularis oculi: thin, pale in color, and possess an involuntary action


tarsi (tarsal plates)
- two thin, elongated plates of dense connective
tissue
- one is placed in each eyelid, and contributes to its form and support
a) superior tarsus (superior tarsal plate)
= larger, a semilunar form
= to the anterior surface of this plate
the aponeurosis of the Levator palpebræ superioris is attached
b) inferior tarsus (inferior tarsal plate)
= smaller, is thin, elliptical in form

tarsi and ligaments

Tarsal Glands (Meibomian glands)
~ situated upon the inner surfaces of the
eyelids, between the tarsi and conjunctiva,
and may be distinctly seen through the latter on
everting the eyelids, presenting an
appearance like parallel strings of pearls.
~ there are about thirty in the upper eyelid, fewer in
the lower
~ imbedded in grooves in the inner surfaces of the tarsi,
and correspond in length with the breadth of these
plates
~ longer in the upper than in the lower eyelid. Their ducts
open on the free magins of the lids by minute foramina.


tarsal glands

orbital septum (septum orbitale; palpebral ligament)
- a membranous sheet, attached to the edge of the orbit, where it is continuous with the periosteum.
- perforated by the vessels and nerves which pass from the orbital cavity to the face and scalp.
The eyelids are richly supplied with blood


Conjunctiva
~ the mucous membrane of the eye
~ lines the inner surfaces of the eyelids
~ reflected over the forepart of the sclera and cornea.

1) Palpebral Portion (tunica conjunctiva palpebrarum)
- thick, opaque, highly vascular, and covered with numerous
papillæ,
- at the lateral angle of the upper eyelid the ducts of the
lacrimal gland open on its free surface
- at the medial angle it forms a semilunar fold, the plica
semilunaris


The line of reflection of the conjunctiva from the upper eyelid on to the bulb of the eye is named the superior fornix, and that from the lower lid the inferior fornix.

2) Bulbar Portion (tunica conjunctiva bulbi)
- upon the sclera the conjunctiva is
loosely connected to the bulb of the
eye;
- thin, transparent, destitute of papillæ,
and only slightly vascular


Lymphatics arise in the conjunctiva in a delicate zone around the cornea, and run to the ocular conjunctiva.

Conjunctiva
The conjunctiva is the thin, transparent tissue that covers the outer surface of the eye.  It begins at the outer edge of the cornea, covering the visible part of the sclera, and lining the inside of the eyelids.  It is nourished by tiny blood vessels that are nearly invisible to the naked eye.  
The conjunctiva also secretes oils and mucous that moisten and lubricate the eye.
 

Caruncula lacrimalis
~ a small, reddish, conical-shaped body, situated at the medial palpebral commissure, and filling up the lacus lacrimalis
~ consists of a small island of skin containing sebaceous and sudoriferous glands, and is the source of the whitish secretion which constantly collects in this region.
~ lateral to the caruncula is a slight semilunar fold of conjunctiva, the concavity of which is directed toward the cornea & is called the plica semilunaris.
The nerves in the conjunctiva are numerous and form rich plexuses. According to Krause they terminate in a peculiar form of tactile corpuscle, which he terms “terminal bulb.”

punctum lacrimale


The Lacrimal Ducts (lacrimal canals)
~ one in each eyelid, commence at minute orifices, termed puncta lacrimalia, on the summits of the papillæ lacrimales
~ seen on the margins of the lids at the lateral extremity of the lacus lacrimalis.
superior duct
inferior duct


lacrimal apparatus
The Bony Orbit
Roof of orbit
1.Orbital plate of frontal bone
2.Lesser wing of sphenoid








Floor of orbit
1.Orbital plate of maxilla
2.Orbital surface of zygomatic bone
3.Orbital process of palatine bone


Medial wall of orbit
1.Frontal process of maxilla
2.Lacrimal bone
3.Orbital plate of ethmoid
4.Body of sphenoid

Lateral wall of orbit
1.Zygomatic bone
2.Greater wing of sphenoid

Foramina of the Orbit
Supraorbital notch/foramen
Infraorbital foramen
Superior orbital fissure
Inferior orbital fissure
Optic canal
Ethmoidal foramina

Supraorbital foramen – supraorbital vessels & nerves

Infraorbital foramen – infraorbital vessels & nerves


Supraorbital fissure
Lacrimal n. Frontal n.
Trochlear n. Oculomotor n.
Nasociliary n. Abducens n.
Sup. Ophthalmic v.

Infraorbital fissure
Maxillary n.
Zygomatic n.
Branchesof pterygopalatine ganglion
Inf. ophthalmic v.


Optic canal: optic n.
ophthalmic artery

Ethmoidal foramina:
Ant. ethmoidal foramen :ant. ethmoidal n. & a.
Post. ethmoidal foramen: post. ethmoidal n. & a.
- End -
Sense of Hearing




External Ear

1. Auricle:
Single elastic cartilage.
Covered by skin.
Continuous medially with external auditory meatus.
Innervation:
auriculotemporal nerve,
great auricular nerve.

The External Ear
~ consists of:
1) auricula/pinna: the expanded portion
: projects from the side of the
head
: serves to collect the vibration
of the air by w/c sound is
produced
2) external acoustic meatus
:leads inward from the bottom
of the auricula
:conducts the vibrations to the
tympanic cavity


The Auricula or Pinna
= ovoid form, with its larger end directed
upward.
= the prominent rim of the auricula is
called the helix
Where the helix turns downward behind, a small tubercle, the auricular tubercle of Darwin, is frequently seen; this tubercle is very evident about the sixth month of fetal life.
Another curved prominence, parallel with and in front of the helix, is called the antihelix
The narrow-curved depression between the helix and the antihelix is called the scapha;

In front of the concha, and projecting backward over the meatus, is a small pointed eminence, the tragus, so called from its being generally covered on its under surface with a tuft of hair, resembling a goat’s beard.

The muscles of the auricula
- consist of two sets:
(1) the extrinsic: connect it with the skull and scalp and move the auricula as a whole
(2) the intrinsic: extend from one part of the auricle to another


- The Auricularis anterior, the smallest of the three, is thin, fan-shaped, and its fibers are pale and indistinct. It arises from the lateral edge of the galea aponeurotica, and its fibers converge to be inserted into a projection on the front of the helix.
  - The Auricularis superior , the largest of the three, is thin and fan-shaped. Its fibers arise from the galea aponeurotica, and converge to be inserted by a thin, flattened tendon into the upper part of the cranial surface of the auricula.
 - The Auricularis posterior consists of two or three fleshy fasciculi, which arise from the mastoid portion of the temporal bone by short aponeurotic fibers. They are inserted into the lower part of the cranial surface of the concha.
Actions.—In man, these muscles possess very little action: the Auricularis anterior draws the auricula forward and upward; the Auricularis superior slightly raises it; and the Auricularis posterior draws it backward.
muscles of external ear
The intrinsic muscles are the:
Helicis major.
Antitragicus.
Helicis minor.
Transversus auriculæ.
Tragicus.
Obliquus auriculæ.



  External auditory meatus:
Outer 1/3:
S-shaped,
cartilaginous,
skin contains hairs, sebaceous and ceruminous glands.
Inner 2/3:
bony,
narrower (isthmus).
Inferior wall about 5 mm longer than superior wall due to obliquity of tympanic membrane.
Innervation:
auriculotemporal nerve,
auricular branch of vagus.



The External Acoustic Meatus
= extends from the bottom of the concha to the tympanic membrane
tympanic membrane: closes the inner end of the meatus
= formed partly by cartilage and membrane, and partly by bone, and is lined by skin


~ consists of two parts:
1) the tympanic cavity proper: opposite the tympanic membrane
2) attic or epitympanic recess: above the level of the membrane;
: contains the upper half of the malleus and the greater part of the incus.
~ bounded laterally by the tympanic membrane
medially by the lateral wall of the
internal ear
communicates behind, with the tympanic antrum and through it with the mastoid air
cells, in front with the auditory tube

The Tegmental Wall or Roof (paries tegmentalis):
~ formed by a thin plate of bone, the tegmen tympani, which separates the cranial and tympanic cavities
~ situated on the anterior surface of the petrous portion of the temporal bone close to its angle of junction with the squama temporalis


The Jugular Wall or Floor (paries jugularis)
~ narrow, and consists of a thin plate of bone (fundus tympani) which separates the tympanic cavity from the jugular fossa
~ presents, near the labyrinthic wall, a small aperture for the passage of the tympanic branch of the glossopharyngeal nerve.

The Membranous or Lateral Wall (paries membranacea; outer wall)
~ formed mainly by the tympanic membrane, partly by the ring of bone into which this membrane is inserted. This ring of bone is incomplete at its upper part, forming a notch (notch of Rivinus), close to which are three small apertures: the iter chordæ posterius,
the petrotympanic fissure, and
the iter chordæ anterius


Tympanic Membrane
= separates the tympanic cavity from the bottom of the external acoustic meatus
= a thin, semitransparent membrane
= directed very obliquely downward and inward
= pars flaccida: the small, somewhat triangular part of the membrane above the anterior & posterior folds w/c is lax and thin
= the manubrium of the malleus is firmly attached to the medial surface of the membrane
= the most depressed part of the concavity is named the umbo.



         Tympanic Membrane (Ear Drum)
Semi-transparent oval membrane.
Separates external and middle ears.
Is obliquely placed.
Handle of malleus attached to its inner side, resulting in concavity towards the external auditory meatus.
Moves in response to air vibrations which are transmitted via middle ear bones to the inner ear.
External surface is innervated mainly by the auriculotemporal nerve.



Labyrinthic or Medial Wall (inner wall)
~ vertical in direction, and presents for examination
the fenestræ vestibuli
cochleæ,
the promontory, and
the prominence of the facial canal


fenestra vestibuli (fenestra ovalis)
= a reniform opening leading from the tympanic cavity into the vestibule of the internal ear
= in the recent state it is occupied by the base of the stapes
fenestra cochleæ
= below and a little behind the fenestra vestibuli, from which it is separated by a rounded elevation, the promontory


The mastoid or posterior wall (paries mastoidea)
~ wider above than below, and presents for examination the entrance to the tympanic antrum, the pyramidal eminence, and the fossa or mastoid antrum which communicates behind and below with the mastoid air cells

pyramidal eminence (pyramid)
= immediately behind the fenestra vestibuli,
and in front of the vertical portion of the
facial canal
= hollow, and contains the Stapedius muscle


The Carotid or Anterior Wall

~ corresponds with the carotid canal, from which it is separated by a thin plate of bone perforated by the tympanic branch of the internal carotid artery, and by the deep petrosal nerve
~ at the upper part of the anterior wall are the orifice of the semicanal for the Tensor tympani muscle and the tympanic orifice of the auditory tube, separated from each other by a thin horizontal plate of bone, the septum canalis musculotubarii


The tympanic cavity contains a chain of three movable ossicles:
malleus, incus, stapes
malleus - attached to the tympanic membrane
- so named from its fancied resemblance
to a hammer
- consists of a head, neck, and three
processes, viz., the manubrium, the
anterior and lateral processes
head (capitulum mallei): the large upper
extremity of the bone
: oval in shape
: articulates posteriorly
with the incus


manubrium mallei (handle): connected by its lateral margin with the
tympanic membrane.
: on its medial side, near its upper end, is a
slight projection, into which the tendon of
the Tensor tympani is inserted.


incus - connected to both by delicate articulations
- received its name from its supposed resemblance to an
anvil, but it is more like a premolar tooth

stapes - attached to the circumference of the fenestra vestibul
- so called from its resemblance to a stirrup
- consists of a head, neck, two crura, and a base.

malleus
incus
stapes


Stapedius - O: wall of a conical cavity, hollowed out of the interior of the pyramida eminence
I: posterior surface of the neck of the
stapes
N.S.: a branch of the facial nerve.
A: pulls the head of the stapes
backward
By the action of the muscle the tension of the fluid within the internal ear is probably increased.



~ consists of two parts:
a) the osseous labyrinth - a series of cavities within the petrous part of the temporal bone
- consists of three parts: the vestibule, semicircular canals, and cochlea (cavities hollowed out of the substance of the bone, and lined by periosteum; they contain a clear fluid, the perilymph, in which the membranous labyrinth is situated)
bony labyrinth

The Vestibule = the central part of the osseous labyrinth
= medial to the tympanic cavity, behind the cochlea, and in front of the semicircular canals
= its lateral or tympanic wall is the fenestra vestibuli on its medial wall, at the forepart, is a small circular depression, the recessus sphæricus, which is perforated by several minute holes (macula
cribrosa media) for the passage of filaments of the acoustic nerve to the saccule behind this depression is an oblique ridge, the crista vestibuli, which bifurcates below to enclose a small depression, thefossa cochlearis perforated by a number of holes for the passage of
filaments of the acoustic nerve which supply the vestibular end of the ductus cochlearis

The Bony Semicircular Canals = three in number, superior, posterior, and lateral, = situated above and behind the vestibule
= unequal in length, compressed from side to side, and each describes the greater part of a circle.
= presents a dilatation at one end, called the ampulla, = open into the vestibule by five orifices, one of the apertures being common to two of the canals.

Right osseous labyrinth. Lateral view.
Interior of right osseous labyrinth


The Cochlea = bears some resemblance to a common snail-shell
= forms the anterior part of the labyrinth
= conical in form, and placed almost horizontally in front of the vestibule
= its base corresponds with the bottom of the internal acoustic meatus, perforated by numerous apertures for the passage of the cochlear division of the acoustic nerve

= consists of: a conical shaped central axis, the modiolus;
A canal, the inner wall of which is formed by the central axis, wound spirally around it for two turns and three-quarters, from the base to the apex the osseous spiral lamina, a delicate lamina which projects from the modiolus, and, following the windings of the canal, partially subdivides it into two.
helicotrema: a small opening at the apex of the modiolus connecting the 2 passages of the canal ( the scalae )
modiolus: the conical central axis or pillar of the cochlea.
: perforated by numerous orifices, which transmit filaments of the cochlear division of the acoustic nerve
cupula: where the bony canal terminates and forms the apex of the cochlea

membranous labyrinth


The acoustic nerve (auditory nerve or nerve of hearing)
- divides near the bottom of the internal acoustic meatus into:
a) anterior or cochlear branch: divides into numerous filaments at the base of the modiolus
b) posterior or vestibular branch: supplies the utricle, the saccule, and the ampullæ of the semicircular ducts.

The arteries of the labyrinth:
- the internal auditory, from the basilar: divides at the bottom of the internal acoustic meatus into two branches: cochlear and vestibular.
cochlear branch- subdivides into twelve or fourteen
twigs and are distributed in the
lamina spiralis and basilar
membrane.
vestibular branches - distributed to the utricle, saccule,
and semicircular ducts
- the stylomastoid, from the posterior
auricular

Sense of Smell
Lateral wall of nasal cavity
Sense of Taste

The Tongue (lingua).—The tongue is the principal organ
of the sense of taste, and an important organ of speech; it also assists in the mastication and deglutition of the food. It
is situated in the floor of the mouth, within the curve of the body of the mandible
Its Root is directed backward, and connected with the hyoid bone by the Hyoglossi and Genioglossi muscles and the hyoglossal membrane; with the epiglottis by three folds (glossoepiglottic) of mucous membrane; with the soft palate by the glossopalatine arches; and with the pharynx by the Constrictores pharyngis superiores and the mucous membrane.

Its Apex , thin
and narrow, is directed forward against the lingual surfaces of the lower incisor teeth.
Its Inferior Surface is connected with the mandible by the Genioglossi; in the middle line, it is elevated into a distinct vertical fold, the frenulum linguæ.
On either side lateral to the frenulum is a slight fold of the mucous membrane, the plica fimbriata, the free edge of which occasionally exhibits a series of fringe-like processes

-The Dorsum of the Tongue is convex and marked by a
-median sulcus, which divides it into symmetrical halves; this sulcus ends behind, about 2.5 cm. from the root of the organ, in a depression, the foramen cecum, from which a shallow groove, the sulcus terminalis, runs lateralward and forward on either side to the margin of the tongue.

Extrinsic muscles of
the tongue:
1. Genioglossus
2. Hyoglossus
3. Chondroglossus
4. Styloglossus
5. Palatoglossus
N.S. Hypoglossal n. except the Palatoglossus w/c is innervated by the cranial accessory/
vagal component of the pharyngeal plexus.
Intrinsic muscles of the tongue
Sup. Longitudinal muscle 2. Inf. Longitudinal muscle
Transverse muscle 4. Vertical muscle
N.S. Hypoglossal n.

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