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External Ear


External ear consists of following structures:-

Auricle (Pinna)

This is out most visible part of the ear and is made up of single piece of yellow elastic cartilage except for lobule which does not contain cartilage. Elastic cartilage is covered with skin which is closely adherent to perichondrium on its lateral surface and slightly loose on medial surface.


External auditory canal (External acoustic meatus)

External auditory canal is a 'S' shaped canal with length of 24-25 mm and it is divided into two parts:-

  1. Cartilaginous part
    It forms outerlateral 1/3 (8mm) of the external auditory canal. It has two fissures / deficiencies in the anterior part called fissure of santorini through which parotid or superficial mastoid infection can appear in the canal and vice versa. Skin covering it is thick and has ceruminous glands (modified apocrine sweat glands), pilosebaceous glands and hair. Since hair is confined to cartilaginous part, furuncles are seen only in the outer third of the canal.
  2. Bony part
    It forms inner/medial 2/3 (16 mm) of external auditory canal. Skin lining the bony part is thin and is devoid of hair and ceruminous glands. Isthmus is the narrowest portion of bony canal and is 5 mm lateral to tympanic membrane. Foreign bodies get lodged in isthmus are difficult to remove as it is the narrowest part. 'Foramen of Huschke' is a deficiency present in antero-inferior part of bony canal in children upto 4 years of age, permitting infection to and from parotid.

Nerve supply of pinna (auricle) and external auditory canal

  1. Pinna (auricle)
    1. Lateral surface: - Great auricular nerve (C2, C3, auricular branch of vagus (Arnold's nerve), facial nerve, and auriculotemporal nerve.
    2. Medial surface: - Great auricular nerve, auricular branch of vagus (Arnold's nerve), facial nerve, lesser occipital nerve.
  2. External auditory canal
    1. Anterior wall and roof: - auriculotemporal nerve.
    2. Posterior wall and floor: - auricular branch of vagus. Posterior wall (not floor) also receives sensory fibres from facial nerve through auricular branch of vagus; therefore hypoesthesia of posterior meatal wall is seen in facial nerve injury 'Hitzelberger's sign '.

Tympanic membrane (Ear drum)

Tympanic membrane separates the external ear from middle ear and transmits sound to the ossicles inside the middle year. It is 9-10 mm tall, 8-9 mm wide and 0.1 mm thick. In a healthy ear it is shiny and pearly grey / pale grey in colour. Normal tympanic membrane is mobile with maximum mobility at peripheral. It is divided into two parts:-   

  1. Pars tensa    
  2. Pars flaccida

Nerve supply of tympanic membrane

  1. Lateral surface
    1. Anterior half     Auriculotemporal
    2. Posterior half   Auricular branch of vagus
  2. Medial surface Tympanic branch of glossopharyngeal (Jacobson's nerve)


The Middle Ear (Tympanic Cavity)


The middle ear lies between the tympanic membrane laterally and the cochlea medially. The middle ear (tympanic cavity) is divided into:-

  1. Mesotympanum (tympanic cavity proper)
    It is the narrowest part of tympanic cavity (transverse dimension is 2 mm. It lies opposite to pars tensa.
  2. Epitympanum (attic)
    It is the part of tympanic cavity which extends above the tympanic membrane (pars tensa) and lies opposite (medial) to shrapnel's membrane (pars flacida) and bony lateral attic wall. It is the widest part of tympanic cavity (transverse dimension is 6 mm). Epitympanum (attic) communicates with mastoid air cell system, through a small opening called aditus. Prussak's space communicates with epitympanum through a posterior gap. Attic area (epitympanum) is a crowded place and only a thin plat of bone (tegmen) separates this region from middle cranial fossa. Any infection in this area is prone to affect the temporal lobe of brain through erosion of this plate. Infections and inflammations in this area are considered to be unsafe due to impending intracranial complications.
  3. Hypotympanum
    It is the part of the tympanic cavity which extends below the pars tensa. Its transverse dimension is 4 mm. Sometimes the portion of middle ear around the tympanic orifice of the eustachian tube is called as protympanum.


Mesotympanum:- Handle of malleus, long process of incus, stapes, oval window, round window.

Epitympanus :- Head & neck of malleus, Body & short process of incus.

Boundaries of middle ear cavity:-

The middle ear cavity may be described as a six-sided box with a roof, a floor, a medial wall, a lateral wall, an anterior wall and a posterior wall.


Roof or Tegmental wall (Pariestegmentalis)

It is formed by a thin plate of bone called the tegmen tympani. It separates the tympanic cavity from middle cranial fossa. It is situated on the anterior surface of the petrous portion of temporal bone.


Floor or Jugular wall (Pariesjugularis)

It consists of a thin plate of bone called the fundus tympani. It separates the tympanic cavity from the jugular bulb. It presents, near medial (Labyrinthic) wall, a small aperture for the passage of the tympanic branch of the glossopharyngeal nerve.

Anterior or Carotid wall (pariescarotica)

It is formed by thin plate of bone which separates the tympanic cavity from internal carotid artery. Through the opening of carotid canal (Glaserian fissure) passes superior and inferior caroticotympanic nerves and tympanic branch of internal carotid artery. Middle third has opening for Eustachian tube. Just above it is a canal containing tensor tympani muscle which extends to the medial wall to form a pulley called as processus cochleariformis.


Posterior wall

It lies close to the mastoid air cells and has following features:-

  1. A bony projection called the pyramid which contains stapedius muscle.
  2. There is an opening for exit of chorda tympani nerve.
  3. Aditus is an opening through which attic communicates with the mastoid antrum.
  4. Facial nerve runs in the posterior wall just behind the pyramid.
  5. Facial recess, also known as posterior sinus or suprapyramidal recess is a depression in the posterior wall lateral to the pyramid. It is bounded medially by the vertical part of VII nerve, laterally by chorda tympani and above by the fossa incudis.

Lateral or outer or membranous wall (pariesmembranacea)

It is mainly formed by tympanic membrane and also partly by the ring of bone into which this membrane is inserted, i.e. scutum. The ring of bone is incomplete at its upper part, forming a notch (notch of Rivinus).


Medial or inner or labyrinthic wall (parieslabyrinthica)

  1. It is formed by labyrinth and separates the middle ear cavity from internal ear. It has following features:-
  2. A bulge called as promontory formed by basal turn of cochlear.
  3. Fenestra vestibuli (oval window) lies posterosuperior (behind and above) to the promontory and opens into scala vestibuli. It is occupied by foot plate of stapes fixed by annular ligament. Its, size on average is 3.25mm long & 1.75 mm wide.
  4. Fenestra cochleae (round window) lies posteroinferior to the promontory and opens into scala tympani of cochlea. It is closed by secondary tympanic membrane. The round window is closest to ampulla of posterior semicircular canal. Round window is a triangular opening. Its diameter is between 1.8 to 2.3 mm.
  5. The round window opening is separated from oval window opening by a posterior extension of the promontory known as subiculum.
  6. Occasionally, another ridge of bone, the ponticulus, leaves the promontory above the subiculum and runs to the pyramid on the posterior wall of the cavity.
  7. Prominence of facial nerve canal (known as fallopian canal) lies above the fenestra vestibuli curving downwards into posterior wall of middle ear.
  8. Anterior to oval window lies a hook-like projection called the processus cochleariformis for tendon of tensor tympani. The cochleariform process marks the level of the Genu of the facial nerve which is an important landmark for surgery of the facial nerve.
  9. Medial to the pyramid is a deep recess called sinus tympani which is bounded by the subiculum below and the ponticulus above. It is the most inaccessible site in the middle ear & mastoid.

Contents of tympanic cavity

Contents of middle ear (tympanic cavity) are:-

  1. Ear ossicles Malleus, incus, stapes
  2. Muscles Tensor tympani, stapedius
  3. Chorda tympani
  4. Tympanic plexus

Ossicles of middle ear

Middle ear contains three ear ossicles (from lateral to medial):- Malleus, incus and stapes. The ossicles transmit sound vibrations from the large tympanic membrane into the small oval window, at a huge mechanical advantage.

The malleus articulates with incus, which in turn articulates with the stapes. Types of joint are;-

  1. The incudomalleolar joint Saddle type of synovial.
  2. The incudo-stapedial joint Ball & socket type of synovial. 

Stapes foot plate is held in the oval window by annular ligament.

Tympanic cavity has two muscles:


Nerve supply of middle ear

The nerve supply of middle ear is derived from tympanic plexus which lies over the promontory. The inferior ganglion of the glossopharyngeal nerve gives off the tympanic nerve which enters the middle ear through the tympanic canaliculus and takes part in formation of the tympanic plexus on the medial wall of middle ear. This distributes its fibres to the middle ear, and also to the auditory tube, mastoid antrum and air cells.


Mastoid antrum

  1. It is an air sinus in the petrous temporal bone. Its upper anterior wall has the opening of aditus, while medial wall is related to posterior semi-circular canal (SCC). Posteriorly lies the sigmoid sinus. The posterior belly of digastric muscle forms a groove in the base of mastoid bone. The corresponding ridge inside the mastoid lies lateral not only to sigmoid sinus but also to facial nerve and is a useful landmark. The roof is formed by tegmenantri separating it from middle cranial fossa and temporal lobe of brain. Anteroinferior is the descending part of facial nerve canal (or fallopian canal). Lateral wall is formed by squamous temporal bone and is easily palpable behind the pinna.
  2. MacEwen's triangle or suprameatal triangle overlies the lateral wall of mastoid antrum. It is bounded above by supramastoid crest, anteroinferiorly by posterosuperior margin of external auditory canal and posteriorly by a tangent drawn from zygomatic arch.
  3. Mastoid develops from squamous and petrous bone. It is an important surgical landmark for locating mastoid antrum. Körner’s septum is persistence of petrosquamous suture in the form of a bony plate.

Important facts

  1. Stapedius is the smallest muscle of body
  2. Tensor tympani is also called 'Toynbee's muscle

Eustachian tube

  1. It is a channel connecting the tympanic cavity with the nasopharynx. It is also called pharyngotympanic tube. It helps to equalize pressure on both sides of tympanic membrane. Length of Eustachian tube is 36 mm (reached by the age of7 years), Lateral third (i.e. 12 mm) is bony. Medial 2/3 (i.e. 24 mm) is fibrocartilaginous. Bony and cartilaginous part meets at isthmus which is the narrowest part of tube. In adults it is placed at an angle of 45° with saggital plane while in infants it is short, wide and placed horizontally. So in infants infections of middle ear are more common. Muscles of eustachian tube are tensor palati (dilator tube is a part of it) supplied by branch of mandibular nerve and levator palati supplied by pharyngeal plexus through XIth cranial nerve.
  2. Arterial supply is through branches from ascending pharyngeal, middle meningeal and-artery of pterygoid canal (both branches of maxillary artery). Venous drainages is to the pterygoid venous plexus. Nerve supply is by tympanic plexus. The fibres of origin of tensor palati muscles are attached to lateral wall of the tube. Contraction of this muscle during swallowing, yawning and sneezing opens the tube and this helps in maintaining equality of air pressure on both sides of tympanic membrane. Contraction of levator palati muscles which runs below the floor of cartilaginous part also helps in opening the tube. It is lined by pseudostratified columnar ciliated epithelium (cartilaginous part contains numerous mucous glands):

Opening and closing of Eustachian tube

  1. Opening and closing functions of the eustachian tube are physiologically and pathologically important.
  2. Normal opening of the eustachian tube equalizes atmospheric pressure in the middle ear; closing of the eustachian tube protects the middle ear from unwanted pressure fluctuations and loud sounds.
  3. The muscles of the eustachian tube system help to open and close the tube, thus allowing it to perform its function.
  4. The muscles are :-
    1. Tensor veli palatini (tensor palatini):- Contraction of this muscle during swallowing, yawning and sneezing opens the tube. Defective function of this muscle in cleft palate results in eustachian tube dysfunction.
    2. Tensor tympani: -Tensonises the tympanic membrane.
    3. Levator veli palatini: - Sometimes, it also helps to open the tube, however it is usually considered as a velopharyngeal valve muscle only.
    4. Salpingopharyngeus: - Its functional significance is questionable.
  5. Eustachian tube is innervated by tympanic plexus (formed by tympanic branch of glossopharyngeal and caroticotympanic nerve of sympathetic origin) and from pharyngeal branch of pterygopalatine ganglion.

Cartilaginous part of auditory tube lies inferior to sphenopetrosalsynchondrosis.


Inner Ear

The inner ear within the petro us part of temporal bone consists of a membranous labyrinth enclosed in a bony (osseous) labyrinth. So, inner ear has two parts: -

  1. Bony labyrinth: - Cochlea, Vestibule, Semicircular canals.
  2. Membranous labyrinth: - Cochlear duct, utricle, Saccule, three semicircular ducts, and endolymphatic duct & sac.


  1. Bony Labyrinth
    It is a layer of laminar bone that surrounds the membranous labyrinth, separating it from the cancellous bone of skull. It consists of three parts: the vestibule, the semicircular canals and the cochlea.


It is the central part of bony labyrinth (between cochlea and semicircular canals). In its lateral wall lies the oval window (fenestra vestibuli) which is closed by the footplate of the stapes and annular ligament. The medial or inner wall presents two recesses: -

  1. Spherical recess: - For saccule
  2. Elliptical recess: - For utricle. 

Below the elliptical recess there is small opening of aqueduct of vestibule through which passes the endolymphatic duct. The posterior, superior and inferior walls contain five openings of the semicircular canals.


Cochlea (bony cochlea)

It is a spiral tube anterior to the vestibule and has two and a half turns about its central axis called modiolus.

Around the modiolus and winding spirally like the thread of a screw, is a thin plate of bone called osseous spiral lamina which divides the cochlea incompletely and gives attachment to the basilar membrane. The bony cochlea contain three compartments: -

  1. Scala vestibuli (upper part)
  2. Scala tympani (lower part)
  3. Membranous cochlea or scala media (between the above two).

Semicircular canals

They are three in number, the lateral (Horizontal), posterior and superior, and lie in planes at right angle to each other. Semicircular canals have two ends :-

  1. Ampullated end - Each canal has an ampullated end which opens independently into the vestibule.
  2. Non-ampullated end - The lateral (horizontal) semicircular canal has separate non-ampullated end which opens into the vestibule, while the non-ampullated ends of posterior and superior canals unit to form a common channel called the crus commune.

Thus, three canals open into the vestibule by five opening: - Three for independent ampullated end of the three canals, one for non-ampullated end oflateral canal and one for crus-commune (united non-ampullated part of post & sup. canal).


The bony cochlea contains three compartments: -

  1. Scala vestibuli - Upper part and is in contact with oval window.
  2. Scala tympani - Lower part and is in contact with round window.
  3. Scala media or membranous cochlea.
  1. The scala vestibuli and scala tympani are filled with perilymph and communicate with each other at the apex of cochlea through an opening called helicotrema. The scala media is filled with endolymph. The scala vestibuli is closed by the footplate of stapes which separates it from the air filled middle ear. The scala tympani is closed by secondary tympanic membrane; it is also connected with subarachnoid space through the aqueduct of cochlea (Cochlear aqueduct). Therefore, infection can spread to the inner ear from the infected CSF via cochlear aqueduct.
  2. It is worth noting here that though bony cochlea contains three compartments (Scala vestibuli, Scala tympani, Scala media), only first two (scala vestibuli, and scala tympani) are the part of bony cochlea. Scala media (also called cochlear duct or membranous cochlea) is a part of membranous labyrinth.
  1. Membranous Labyrinth
    Membranous labyrinth is enclosed in the bony labyrinth like an inner tube (membranous labyrinth) in a tyre (bony labyrinth). It contains vestibular and auditory components. It is separated from bony labyrinth by perilymph.
    Membranous labyrinth, itself, is filled with endolymph. Membranous labyrinth consists: -

Cochlear duct (Scala media or membranous cochlea)

  1. It is a blind coiled tube, coiled round a central bony pillar called the modiolus. It appears triangular on cross-section and has three walls formed by : -
    1. The basilar membrane which supports the organ of corti.
    2. The Reissner's membrane which separates it from the scala vestibuli.
    3. The stria vascularis, which contains vascular epithelium and is concerned with secretion of endolymph.
  2. Cochlear duct is connected to the saccule by ductus reuniens. The length of basilar membrane increases as we proceed from the basal coil to the apical coil. So higher frequencies of sound are heard at the basal coil while lower ones are heard at the apical coil.

Components of organ of corti

  1. Organ of corti is the sense organ of hearing & situated on basilar membrane.
  2. Tunnel of Corti: Formed by inner & outer rods.
  3. Hair cells: They are important receptor cells of hearing & transducer sound energy into the electrical energy
  4. Inner hair cells: Form a single row & more important in the transmission of auditory impulse
  5. Outer hair cells: Arranged into three or four rows
  6. Supporting cell: Deiter cell &Hensen Cell.
  7. Tectorial membrane: Consists of gelatinous matrix with delicate fibres.

Utricle and Saccule

The utricle lies in the posterior part of bony vestibule. It receives the five openings of the three semicircular ducts. It is connected to the saccule through utriculosaccular ducts. The sensory epithelium of the utricle is called the macula and is concerned with linear acceleration and deceleration. The saccule also lies in the bony vestibule. Its sensory epithelium is also called the macula. Its exact function is not known. It probably also responds to linear acceleration and deceleration.


Semicircular canals

They are three in number and correspond exactly to the three bony canals. They open in the utricle. The ampullated end of each duct contains a thickened ridge of neuroepithelium called crista ampullaris which responds to angular acceleration. 


Endolymphatic Sac and duct

  1. Endolymphatic duct is formed by the union of two ducts, one each from the saccule and the utricle. It passes through the vestibular aqueducts. Its terminal part is dilated to form endolymphatic sac which lies under the dura on the posterior surface of the petrous bone. Endolymphatic duct connects scala media to epidural (extradural) space.
  2. Arcuate eminence in petrous part of temporal bone is caused by superior semicircular canal.
  3. Internal ear derives its blood supply from labyrinthine (internal auditory) artery which is usually a branch of anterior inferior cerebellar artery or sometimes of basilar artery.



Nose is divided into :- i) External nose, ii) Internal nose.

External nose

External nose has an osteocartilaginous framework of which upper one - third is bony and lower two-third is cartilaginous.

  1. Bony part: - Consists of two nasal bones.
  2. Cartilaginous part: - Consists of two upper lateral cartilages, two lower lateral cartilages, two or more lesser alar (or sesmoid) cartilages and a septal cartilage. So, there are 3 paired and 1 unpaired cartilages.

Internal nose

  1. Internal nose has following parts
    1. Nasal cavity proper: - Internal nose is divided into right and left nasal cavities by nasal septum. Each nasal cavity communicates with the exterior through naris or nostrils and with nasopharynx through posterior nasal aperture or posterior nares or Choanae.
    2. Vestibule of nose: - Anterior and inferior part of the nasal cavity is lined by skin and is called vestibule of nose. It contains sebaceous glands, hair follicles and the hair called vibrissae.
  2. Each nasal cavity has a lateral wall, a medial wall (nasal septum), a roof, and a floor.
  3. The olfactory mucosa lines upper 1/3 of nasal cavity including the roof formed by cribriform plate, and medial and lateral wall up to the level of superior concha. 

Lateral wall (lateral nasal wall)

It has 3 bony projections called as turbinates or conchae. From below upwards they are inferior, middle and superior turbinates. The inferior turbinate is a separate bone, while rest of the turbinates are a part of ethmoidal bone. Below and lateral to each turbinate is the corresponding meatus. Inferior turbinate is largest one.


  1. Inferior meatus
    It is the largest meatus. Its highest point is the junction of anterior and middle 1/3rd. Nasolacrimal duct opens in the inferior meatus, just anterior to its highest point (it is closed by a mucosal flap called Hasner's valve.
  2. Middle meatus
    It lies below the middle turbinate (middle concha), i.e. between middle turbinate and inferior turbinate. The important structures in middle meatus are:-
    1. Hiatus semilunaris
    2. Ethmoidal infundibulum: - Frontal sinus, maxillary sinus and the anterior ethmoidal sinuses drain into it.
    3. Anterior / Posterior fontanelle: - Accessory ostia are found mostly in the posterior fontanelle.
    4. Uncinate process: - It partly covers the opening of maxillary sinus.
    5. Bulla ethmoidalis: Middle ethmoidal sinuses open on or above.
      Atrium is a shallow depression in front of the middle turbinate. Aggernasi is an elevation just anterior to the attachment of middle turbinate.
  3. Superior meatus
    It lies below the superior turbinate and posterior ethmoidal sinuses open into.
  4. Spheno-ethmoidal recess
    It lies above the superior turbinate and receives the opening of sphenoid sinus.

Additional points:

Sometimes e fourth turbinate is also present just above superior turbinate. This fourth turbinate is known as supreme turbinate. Supreme (fourth) turbinate is found in 30% of population. The middle, superior and supreme turbinates are part of ethmoidal complex; accordingly they may be called "ethmoidal turbinates". On the other hand, inferior turbinate is a maxilloturbinale because it is part of maxillary bone:

Osteomeatal complex

Osteomeatal complex is an area in the lateral nasal wall which is bounded by the middle turbinate medially, the lamina papyracea laterally, and the basal lamella superiorly and posteriorly. The inferior and anterior borders of the osteomeatal complex are open. Osteomeatal complex is a narrow anatomical region consisting of:-

  1. Multiple bony structures (middle turbinate, uncinate process, Bulla ethmoidalis.
  2. Air spaces (frontal recess, ethmoidal infundibulum, middle meatus)
  3. Ostia of anterior ethmoidal, maxillary and frontal sinuses therefore, connects theses sinuses to nasal cavity.

Medial nasal wall or Nasal septum

  1. Nasal septum is the osseocartilaginous partition between the two halves of the nasal cavity.
  2. Nasal septum consists of:-
    1. Columellarseptum: - It is formed by columella containing the medial crura of alar cartilages united together by fibrous tissue.
    2. Membranous septum: - It consists of double layer of skin with no bony or cartilaginous support.
    3. Septum proper: - This forms the major portion of nasal septum and consists of osteocartilaginous framework which is covered by mucous membrane. Its constituents are :-
      1. Osseous part
        • The vomer
        • Perpendicular plate of ethmoid
        • Nasal spine of frontal bone
        • Rostrum and crest of sphenoid
        • Nasal crest of nasal bone
        • Nasal crest of palatine bone
        • Nasal crest of maxillary bone
      2. Cartilaginous part
        Septal (Quadrilateral) cartilage
  3. Amongst all above, the nasal septum is mainly formed by vomer, perpendicular plate of ethmoid and septal cartilage.

Blood supply of nose

  • The blood supply to nose is derived from both the internal and external carotid arteries.
  • Both these arteries supply the septum and lateral nasal wall.
  1. Nasal septum
    1. Internal carotid system
      1. Anterior ethmoidal artery    
      2. Posterior ethmoidal artery Branches of ophthalmic artery
    2. External Carotid System
      1. Sphenopalatine artery (branch of maxillary artery) gives nasopalatine and posterior medial nasal branches.
      2. Septal branch of greater palatine artery (Br. of maxillary artery).
      3. Septal branch of superior labial artery (Br. of facial artery)
  2. Lateral wall
    1. Internal Carotid system
      1. Anterior ethmoidal              
      2. ​Posterior ethmoidal   Branches of ophthalmic artery
    2. External carotid system
      1. Posterior lateral nasal branches
      2. Greater palatine artery
      3. Nasal branch of anterior superior dental
      4. Branches of facial artery to nasal vestibule
  • Most of the lower part of nasal cavity and nasal septum is supplied by external carotid artery.
  • The top of the nasal cavity and nasal septum is supplied by internal carotid artery.


Little's area : -

Situated in the anterior inferior part of nasal septum, just above the vestibule.


Four arteries supply this area:

  1. Anterior ethmoidal artery
  2. Septal branch of superior labial artery (Branch of facial A)
  3. Septal branch of sphenopalatine artery (Branch of maxillary A).
  4. Greater palatine artery (Branch of maxillary A).

These arteries anastomose to form a vascular plexus called "Kiesselbach's plexus".

Woodruff's area: -

  1. It is situated under the posterior end of inferior turbinate.
  2. Sphenopalatine artery anastomoses with posterior pharyngeal artery here.
  3. Posterior epistaxis occurs in this area.

Eye Ball And Associated Structures


Bony Orbit

  1. Orbital cavity is a pyramidal shaped space protecting the eye ball, associated muscles, nerves, vessels and lacrimal apparatus. Orbit has an apex, a base and four walls (floor, roof, lateral wall, medial wall).
  2. Base is the quadrangular orbital opening and is made of four margins. Supraorbital margin is formed by frontal bone and presents supraorbital foramen at the junction of its medial 1/3 and lateral 2/3. Infraorbital margin is formed by maxilla (medially) and zygomatic bone (laterally). Infraorbital foramen lies 1 cm below the infraorbital margin, in line with supraorbital foramen. Lateral orbital margin is formed by frontal process of zygomatic tic and zygomatic process of frontal bone. Medial orbital margin is formed by frontal process of maxilla and frontal bone.
  3. Apex is formed by medial end of superior orbital fissure.
  4. Roof is formed mainly by orbital plate of frontal bone and lesser wing of sphenoid.
  5. Floor is formed by orbital surface of maxilla (mainly), orbital surface of zygomatic and orbital process of palatine.
  6. Lateral wall is thickest and is formed by frontal process of zygomatic and greater wing of sphenoid.
  7. Medial wall is thinnest and is formed by frontal process of maxilla, lacrimal bone, orbital plate of ethmoid and body of sphenoid.
  8. Inferior orbital fissure occupies the posterior part of junction between lateral wall and floor. Superior orbital fissure occupies the posterior part of the junction between lateral wall and roof.
  9. Optic canal lying more posteriorly at junction of medial wall and roof, and is enclosed by lesser wing of sphenoid and body of sphenoid.

Extraocular Muscles


  1. Involuntary muscles
    Besides seven voluntary extraocular muscles, three small involuntary muscles are there :-
    1. Orbitalis (Orbital muscle of muller):- Fills the inferior orbital fissure.
    2. Superior tarsal muscle (of muller):- Assists in elevating the upper eyelid.
    3. Inferior tarsal muscle: - Depresses the lower eyelid.

These three muscles are supplied by postganglionic sympathetic fibers from superior cervical sympathetic ganglion.

Various muscle groups

Depending on the action of muscles in relation to other, muscles can be grouped into-

  1. Synergists. It refers to the muscles having the same primary action in the same eye. e.g., superior rectus and inferior oblique of the same eye act as synergistic elevators.
  2. Antagonists. These are the muscles having opposite actions in the same eye. For example, medial and lateral recti, superior and inferior recti and superior and inferior obliques are antagonists to each other in the same eye.
  3. Yoke muscles (contralateral synergists). It refers to the pair of muscles (one from each eye) which contract
  4. Simultaneously during, vision movements. For example, right lateral rectus and left medial rectus act as yoke muscles for dextroversion movements. Other pairs of yoke muscles are: right MR and left LR, right LR and Left
  5. MR, right SR and left IO; right IR and left SO, right SO ad left IR, and right IO and Left SR.
  6. Contralateral antagonists. These are a pair of muscles (one from each eye) having opposite action for example, right LR and left LR, right MR and left MR.




  1. The eyeball is made up of three coats :-
    1. Fibrous coat (outermost layer): - Anterior 1/6th is transparent and called cornea. Posterior 5/6th is opaque and called sclera.
    2. Vascular coat (middle layer): - Middle layer consists of, from anterior to posterior, Iris, ciliary body and choroid.
    3. Nervous coat (inner most layers): - It consists of retina. 
  2. Within these coats are the aqueous humor (in anterior segments), the lens, and the vitreous humor (in posterior segment).

Important facts

  1. Anteroposterior diameter of eye ball is 24 mm and horizontal diameter is 23.5 mm.
  2. Inner surface of choroid lies in contact with pigmented epithelium of retina
  3. Sclera is thinnest just posterior to the rectus muscle insertion and thickest at posterior pole.
  4. Sclerocorneal function is called limbus.
  5. Cornea (anterior surface) is the most important refractive surface of eye.
  6. Epithelium lining of conjunctiva and cornea is stratified squamous non-keratinized epithelium.
  7. Cornea receives its nutrition from aqueous humor and from air through tear film.
  8. Lens receives its nutrition mostly from aqueous humor.
  9. Aqueous humor is secreted by ciliary body. 
  10. Lamina cribrosa is a sieve like perforation in the posterior part of sclera, which allows passage of axons of retinal ganglion cells and central retinal vessels. It is the weakest part of sclera.
  11. Absence of lamina cribrosa is feature of Morning glory syndrome.

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