Sense of SightSense 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 Organ of Sight The bulb of the eye (bulbus oculi; eyeball), or organ of sight ~ contained in the cavity of the orbit, where it is protected from injury and moved by the ocular muscles. ~ imbedded in the fat of the orbit, but is separated from it by a thin membranous sac, the fascia bulbi ~ composed of 2 segments: 1) anterior segment: transparent, and forms about 1/6 of the bulb : more prominent than the posterior segment 2) posterior segment: larger sphere, and is opaque : forms about five-sixths of the bulb.

• 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

The Tunics of the Eye

(1) A fibrous tunic: a) sclera : opaque : constitutes the posterior 5/6 of the tunic b) cornea : transparent : forms the anterior 1/6

(2) a vascular pigmented tunic: comprising the choroid, ciliary body, and iris;

(3) a nervous tunic, the retina.

diagram of the eye & orbit muscles diagram of the eye & orbit muscles

The Sclera - has received its name from its extreme density and hardness - a firm, unyielding membrane, serving to maintain the form of the bulb, much thicker behind than in front - external surface is of white color, and is in contact with the inner surface of the fascia of the bulb - the Recti and Oblique muscles are inserted into it - anterior part is covered by the conjunctival membrane - inner surface is brown in color and marked by grooves, in which the ciliary nerves and vessels are lodged.

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

 The Eyebrows (supercilia) are two arched eminences of integument, which surmount the upper circumference of the orbits, and support numerous short, thick hairs, directed obliquely on the surface. The eyebrows consist of thickened integument, connected beneath with the Orbicularis oculi, Corrugator, and Frontalis muscles.

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 Eyelids (palpebræ) are two thin, movable folds, placed in front of the eye, protecting it from injury by their closure. The upper eyelid is the larger, and the more movable of the two, and is furnished with an elevator muscle, the Levator palpebræ superioris. When the eyelids are open, an elliptical space, the palpebral fissure (rima palpebrarum), is left between their margins, the angles of which correspond to the junctions of the upper and lower eyelids, and are called the palpebral commissures or canthi.

• 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 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 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 glandstarsal 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 punctum lacrimale

The Lacrimal Apparatus ~ consists of: (a) the lacrimal gland, which secretes the tears, and its excretory ducts, which convey the fluid to the surface of the eye; (b) the lacrimal ducts, the lacrimal sac, and the nasolacrimal duct, by which the fluid is conveyed into the cavity of the nose.

lacrimal gland: lodged in the lacrimal fossa, on the medial side of the zygomatic process of the frontal bone : oval form, about the size and shape of an almond, and consists of two portions, described as the superior and inferior lacrimal glands : in structure and general appearance the lacrimal resembles the serous salivary glands

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

The Lacrimal Sac (saccus lacrimalis) ~ the upper dilated end of the nasolacrimal duct, lodged in a deep groove formed by the lacrimal bone and frontal process of the maxilla ~ oval in form. The Nasolacrimal Duct ( nasal duct) ~ a membranous canal, which extends from the lower part of the lacrimal sac to the inferior meatus of the nose,, ~ provided with an imperfect valve, the plica lacrimalis (Hasneri), formed by a fold of the mucous membrane ~ contained in an osseous canal, formed by the maxilla, the lacrimal bone, and the inferior nasal concha

lacrimal apparatus lacrimal apparatus

The Bony OrbitThe Bony Orbit Roof of orbit Roof of orbit

1.Orbital plate of frontal bone1.Orbital plate of frontal bone

2.Lesser wing of sphenoid2.Lesser wing of sphenoid

Floor of orbitFloor of orbit

1.Orbital plate of maxilla1.Orbital plate of maxilla

2.Orbital surface of zygomatic bone2.Orbital surface of zygomatic bone

3.Orbital process of palatine bone3.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 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 -- End -

Sense of HearingSense of Hearing

The Organ 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 muscles of external ear

The intrinsic muscles are the:

• Helicis major.

• Antitragicus.

• Helicis minor.

• Transversus auriculæ.

• Tragicus.

• Obliquus auriculæ.

The Helicis major is a narrow vertical band situated upon the anterior margin of the helix. It arises below, from the spina helicis, and is inserted into the anterior border of the helix, just where it is about to curve backward. The Helicis minor is an oblique fasciculus, covering the crus helicis. The Tragicus is a short, flattened vertical band on the lateral surface of the tragus. The Antitragicus arises from the outer part of the antitragus, and is inserted into the cauda helicis and antihelix. The Transversus auriculæ is placed on the cranial surface of the pinna. It consists of scattered fibers, partly tendinous and partly muscular, extending from the eminentia conchæ to the prominence corresponding with the scapha. The Obliquus auriculæ, also on the cranial surface, consists of a few fibers extending from the upper and back part of the concha to the convexity immediately above it. The Obliquus auriculæe: consists of a few fibers extending from the upper and back part of the concha to the convexity immediately above it.

Nerves.—The Auriculares anterior and superior and the intrinsic muscles on the lateral surface are supplied by the temporal branch of the facial nerve, the Auricularis posterior and the intrinsic muscles on the cranial surface by the posterior auricular branch of the same nerve.

The arteries of the auricula are the posterior auricular from the external carotid, the anterior auricular from the superficial temporal, and a branch from the occipital artery. The veins accompany the corresponding arteries.

  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

The Middle Ear or Tympanic Cavity

~ an irregular, laterally compressed space within the temporal bone ~ filled with air, which is conveyed to it from the nasal part of the pharynx through

the auditory tube ~ contains a chain of movable bones, which connect its lateral to its medial wall, and serve to convey the vibrations communicated to the tympanic membrane across the cavity to the internal ear.

~ 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.

malleusmalleus

incusincus

stapesstapes

The Muscles of the Tympanic Cavity: Tensor tympani and Stapedius Tensor tympani - larger - contained in the bony canal above the osseous portion of the auditory tube,

- O: cartilaginous portion of the auditory tube and the adjoining part of the great wing of the sphenoid osseous canal in which it is contained I: manubrium of the malleus N.S.: a branch of the mandibular nerve through the otic ganglion. A: draws the tympanic membrane medialward, and thus increases its tension

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.

The Inner Ear or Labyrinth

~ the essential part of the organ of hearing, receiving the ultimate distribution of the auditory nerve~ called the labyrinth, from the complexity of its shape)

~ 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 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. Right osseous labyrinth. Lateral view.

Interior of right osseous labyrinth 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. The osseous spiral lamina: a bony shelf or ledge which projects from the modiolus into the interior of the canal, and, like the canal, takes two-and three-quarter turns around the modiolus.

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

: reaches about half-way toward the outer wall of the tube, partially dividing its cavity into two passages or scalæ:

scala vestibuli= the upper passage scala tympani = the lower one The osseous labyrinth's free surface is smooth and pale, covered with a layer of epithelium, and secretes a thin, limpid fluid, the perilymph. A delicate tubular process of this membrane is prolonged along the aqueduct of the cochlea to the inner surface of the dura mater. b) the membranous labyrinth - a series of communicating membranous sacs

and ducts, contained within the bony cavities. 1 - partly separated from the bony walls by the perilymph - contains fluid, the endolymph - the ramifications of the acoustic nerve are distributed on its walls - consists of two membranous sacs, the utricle, and the saccule. Utricle = the larger of the two = oblong form = occupies the upper and back part of the vestibule = the thickened floor and anterior wall receives the utricular

filaments of the acoustic nerve Saccule = the smaller of the two vestibular sacs = globular in form = lies in the recessus sphæricus near the opening of the scala vestibuli of the cochlea = its anterior part exhibits an oval thickening to which are distributed the saccular filaments of the acoustic nerve.

membranous labyrinth membranous labyrinth

Semicircular Ducts (membranous semicircular canals) = about one-fourth of the diameter of the osseous canals, but precisely similar in number, shape, and general form and each presents at one end an ampulla.

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

• 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 SmellSense of Smell

Lateral wall of nasal cavityLateral wall of nasal cavity

Sense of TasteSense of Taste

• The Tongue (The Tongue (lingualingua).—The ).—The tongue is the principal organ tongue is the principal organ of the sense of taste, and an of the sense of taste, and an important organ of speech; it also important organ of speech; it also assists in the mastication and assists in the mastication and deglutition of the food. It deglutition of the food. It is situated in the floor of the is situated in the floor of the mouth, within the curve of the mouth, within the curve of the body of the mandiblebody of the mandible

• Its Root is directed backward, Its Root is directed backward, and connected with the hyoid and connected with the hyoid bone by the Hyoglossi and bone by the Hyoglossi and Genioglossi muscles and the Genioglossi muscles and the hyoglossal membrane; with the hyoglossal membrane; with the epiglottis by three folds epiglottis by three folds ((glossoepiglotticglossoepiglottic) of mucous ) of mucous membrane; with the soft palate by membrane; with the soft palate by the glossopalatine arches; and the glossopalatine arches; and with the pharynx by the with the pharynx by the Constrictores pharyngis Constrictores pharyngis superiores and the mucous superiores and the mucous membrane.membrane.

• Its Apex , thin Its Apex , thin and narrow, is directed and narrow, is directed forward against the lingual forward against the lingual surfaces of the lower incisor surfaces of the lower incisor teeth.teeth.

• Its Inferior Surface is Its Inferior Surface is connected with the mandible connected with the mandible by the Genioglossi; in the by the Genioglossi; in the middle line, it is elevated into middle line, it is elevated into a distinct vertical fold, the a distinct vertical fold, the frenulum linguæ. frenulum linguæ. On either side lateral to the On either side lateral to the frenulum is a slight fold of the frenulum is a slight fold of the mucous membrane, the plica mucous membrane, the plica fimbriata, the free edge of fimbriata, the free edge of which occasionally exhibits a which occasionally exhibits a series of fringe-like processesseries of fringe-like processes

-The Dorsum of the -The Dorsum of the Tongue is convex and Tongue is convex and marked by amarked by a

-median sulcus, which -median sulcus, which divides it into divides it into symmetrical halves; this symmetrical halves; this sulcus ends behind, about sulcus ends behind, about 2.5 cm. from the root of 2.5 cm. from the root of the organ, in a depression, the organ, in a depression, the foramen cecum, from the foramen cecum, from which a shallow groove, which a shallow groove, the sulcus terminalis, runs the sulcus terminalis, runs lateralward and forward lateralward and forward on either side to the on either side to the margin of the tongue. 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 tongueIntrinsic muscles of the tongue1. Sup. Longitudinal muscle 2. Inf. Longitudinal muscle

3. Transverse muscle 4. Vertical muscle

N.S. Hypoglossal n.