Osteology

Temporal Bones

Temporal Bones Terminology

The temporal bone is so named because of its contribution to the temporal region.

Temporal Bones Side Determination

1. To distinguish superior and inferior, the following features are to be noted:

• A thin plate-like squamous part is directed upwards and lies in para- the sagittal plane.
• Styloid and mastoid processes occupy the lower part of the bone and are directed downwards.

2. To distinguish external and internal aspects, one should consider the following features:

• The outer surface of the squamous part is very smooth.
• The zygomatic process is directed forward.
• The zygomatic process is present on the external aspect of bone.
• External acoustic meatus (present below the posterior part of the zygomatic process) opens externally.
• The apex of the petrous temporal is directed medially and a little forward.

3. To distinguish anterior from posterior, the following criteria should be taken into account:

1. The zygomatic process is directed forward.
2. The mandibular fossa and external acoustic meatus are present below the posterior part of the zygomatic process. Relatively, the mandibular fossa is anterior to the external acoustic meatus.

Temporal Bones Features And Attachments

Morphologically temporal bone is divided into four parts.

1. Squamous part.
2. Petromastoid part.
3. Tympanic part.
4. Styloid process.

For descriptive purposes, the petromastoid part is further subdivided into the mastoid part and the petrous part.

Temporal Bones Squamous Part

It is thin and plate-like and occupies the anterior and superior parts of the temporal bone. It has two surfaces (temporal and cerebral) and two borders (superior and anteroinferior).

1. Surfaces

• Temporal Surface
  1. It is the outer surface.
  2. It is smooth and slightly convex.
  3. It contributes to the temporal fossa, the origin of the temporalis muscle.
  4. The middle temporal artery grooves the surface, just above the external acoustic meatus.
  5. The supramastoid crest runs backwards and upwards across its posterior part. Temporal fascia is attached to this crest.
  6. Squamomastoid suture marks the junction between squamous and mastoid parts. It is situated 1.5 cm. below the supramastoid crest.
  7. Macewen’s Triangle (Suprameatal Triangle)
     • It is a triangular depression posterosuperior to the external acoustic meatus.
     • It is bounded by the posterosuperior margin of the external acoustic meatus, supramastoid crest and a vertical line tangent to the posterior border of the external acoustic meatus.
     • The spine of Henle is a sharp, spur-like projection in the supramental triangle.
     • The mastoid antrum is situated 12.5 mm deep to the surface of the supramental triangle in adults.
  8. Zygomatic Process
     • It is a forward projection from the lower part of the temporal surface.
     • Its anterior end articulates with the temporal process of zygomatic bone to complete the zygomatic arch or zygoma.
     • The anterior part of the zygomatic process has two surfaces (lateral and medial) and two borders (superior and inferior). Masseter originates from its medial surface and inferior border. The temporal fascia is attached to its superior border. Its lateral surface is subcutaneous.
     • Its posterior part is triangular having superior and inferior surfaces.
     • The inferior surface of the posterior part of the zygomatic process is bounded by two roots (anterior and posterior) which converge at the tubercle of the root of the zygoma. The lateral ligament of the temporomandibular joint is attached to this tubercle.
     • The anterior root extends medially from the tubercle of the root of the zygoma and is also called the articular tubercle.
  9. Mandibular Fossa
     • It is situated behind the articular tubercle.
     • Only the anterior part of the mandibular fossa is articular and contributed by the squamous part of the temporal bone.
     • Articular tubercle and anterior part of mandibular fossa is related to the superior surface of articular disc of temporomandibular joint.
     • The posterior part of the mandibular fossa is non-articular and contributed by the tympanic part of the temporal bone. This part is related to the parotid gland.
  10. Squamotympanic Fissure
      • It is situated in the mandibular fossa and marks the junction of squamous and tympanic parts of the temporal bone.
      • The medial part of this fissure is divided into petrosquamous and petrotympanic fissures by the projection of the tegmen tympani of the petrous part of the temporal bone.
      • Three structures pass through petrotympanic fissure, i.e. chorda tympani nerve, anterior tympanic artery and anterior ligament of the malleus.
      • Note: To remember the structures passing through petrotympanic fissure think of a ‘CAT’ in which the C-Chorda tympani nerve, A-Anterior ligament of malleus and T-Tympanic artery.
      • A petrotympanic fissure leads into the middle ear.
• Cerebral Surface
  • It is the inner surface.
  • It is grooved by middle meningeal vessels.
  • It has impressions for the sulci and gyri of the temporal lobe of the cerebrum.

2. Borders

• Superior border
  • It articulates with the parietal bone.
• Temporal Bones
  • It articulates with the greater wing of the sphenoid bone.

Temporal Bones Mastoid Part

It forms the posterior part of the temporal bone. It consists of two surfaces (outer and inner), two borders (superior and posterior) and a downward projecting part called the mastoid process.

1. Surfaces

• Outer Surface
  • The auricularis posterior and occipital belly of occipitofrontalis are attached to this surface.
  • The mastoid foramen is an infrequent opening near the posterior border. When present this foramen transmits an emissary vein from the sigmoid sinus and a branch from the occipital artery.
• Inner surface
  • The sigmoid sulcus is a deep groove on the inner surface. It is meant for the sigmoid sinus.
  • Mastoid foramen opens in the upper part of sigmoid sulcus.

2. Borders

1. Superior Border
   • It articulates with the occipital bone at occipitomastoid suture.
2. Posterior Border
   • It articulates with the occipital bone at occipitomastoid suture.

3. Mastoid process

It possesses a lateral and a medial surface.

1. Lateral surface
   • It gives insertions to the following three muscles from above downwards:
     1. Sternomastoid.
     2. Splenius capitis.
     3. Longissimus capitis.
2. Medial surface
   • It is marked by a deep groove called a mastoid notch, from which originates the posterior belly of the digastric.
   • The occipital groove is observed medial to mastoid notch. This groove lodges the occipital artery.

Temporal Bones Petrous Part

Petrous is a Latin word which means strong or rock-like. It is a strong part of the temporal bone and protects the internal ear within it.

The petrous part is comprised of a base, an apex, three surfaces (anterior, posterior and inferior) and three borders (superior, anterior and posterior).

1. Base

• It is directed laterally.
• It fuses with the squamous part at petrosquamosal suture which disappears soon after birth.
• The base also fuses with the mastoid part.
• The base is separated from the squamous and mastoid parts by an air-filled space called the mastoid antrum.

2. Apex

• It projects medially and slightly forward.
• It is situated between the greater wing of the sphenoid and the basilar part of the occipital bone.
• It forms the posterolateral boundary of the foramen lacerum.
• It possesses an anterior orifice of the carotid canal.

3. Surfaces

• Anterior surface
  1. It contributes to the middle cranial fossa.
  2. This surface shows the following features if one goes from apex to base:
     • Trigeminal impression: It is a depression for the trigeminal ganglion adjacent to the apex.
     • The roof of the internal acoustic meatus: Is another depressed area behind the ridge.
     • Arcuate eminence: It is a prominent elevation produced by the superior semicircular canal. Its posterior sloping lies over lateral and posterior semicircular canals.
  3. Area anterolateral to trigeminal impression forms the roof of the anterior part of the carotid canal.
  4. Area anterolateral to arcuate eminence forms the roof of the vestibule and the beginning of the facial canal.
  5. A thin plate of bone between the squamous part (cerebral surface) of the temporal bone and the features described above is called tegmen tympani.
  6. It forms the roof of the mastoid antrum, middle ear and canal for tensor tympani from posterior to anterior.
  7. Tegmen tympani projects downwards to form lateral walls of the canal for tensor tympani and bony Eustachian tube and appears in the squamotympanic fissure.
  8. A hiatus (opening) lateral to arcuate eminence leads into a groove for greater superficial petrosal nerve which runs towards the foramen lacerum on the tegmen tympani.
  9. Lateral to the groove for the greater superficial petrosal nerve presents a groove for the lesser petrosal nerve which runs towards the foramen ovale.
• Posterior Surface
  1. It contributes to the posterior cranial fossa.
  2. Internal acoustic meatus is present in the centre of this surface. It transmits facial and vestibulocochlear nerves and labyrinthine vessels. It is about 1 cm in length.
  3. The fundus of the internal acoustic meatus is a plate of bone at its lateral end. This plate is divided into upper and lower areas by a transverse ridge called crista falciformis.
     • The upper area is further divided into anterior and posterior areas by a vertical crest called Bill’s bar. The anterior area shows a facial canal for the facial nerve.
     • The posterior area is called the superior vestibular area which presents a number of small openings for the nerve fibres supplying the utricle and superior and lateral semicircular ducts.
     • Below the transverse crest, anteriorly is the cochlear area (which possesses a number of foramina called tractus spiralis for aminosus) and posteriorly is the inferior vestibular area.
     • Fibres of the cochlear nerve enter the cochlear area while nerve fibres supplying the saccule enter the inferior vestibular area.
     • Below and behind the inferior vestibular area is the foramen singular for the passage of the nerve to the posterior semicircular duct.
  4. A slit behind the internal acoustic meatus leads into the aqueduct of the vestibule which contains the saccus and ductus endolymph phatic along with a small artery and vein.
  5. An irregular depression called the subarcuate fossa is located above and between the openings of the internal acoustic meatus and the aqueduct of the vestibule. It lodges a process of dura mater.
• Inferior Surface
  1. It is rough and triangular.
  2. It is divided into four areas from apex to base.
     • The quadrilateral area near the apex provides attachment to the levator palate muscle.
     • The Carotid canal (lower opening) is present behind the quadrilateral area. It transmits the internal carotid artery along with its sympathetic and venous plexuses.
     • The jugular fossa is a depression behind the carotid canal. It lodges the superior bulb of the internal jugular vein.
     • The jugular surface is a quadrilateral area behind the jugular fossa. It articulates with the jugular process of the occipital bone.
  3. A triangular depression in front of the medial part of the jugular fossa lodges the inferior ganglion of the glossopharyngeal nerve. The apex of this triangular depression is marked by an opening leading into the cochlear canaliculus which is traversed by:
     • Perilymphatic duct
     • Prolongation of dura mater
     • A vein from the cochlea drains into the internal jugular vein.
  4. The canaliculus for the tympanic nerve (a branch of the glossopharyngeal nerve) is situated on the bony ridge between the carotid canal and the jugular fossa.
  5. The mastoid canaliculus is present in the lateral wall of the jugular fossa. It transmits the auricular branch of the vagus.

4. Borders

• Superior border
  • It is grooved by the superior petrosal sinus.
  • Margins of the groove provide attachment to tentorium cerebelli.
• Anterior border
  • It is divided into medial and lateral parts.
  • The medial part articulates with the greater wing of the sphenoid.
  • The lateral part joins the squamous part at petrosquamosal suture which disappears soon after birth.
• Posterior border
  • It can be divided into medial and lateral parts.
  • The medial part has a sulcus which with a similar sulcus on the occipital bone forms a groove for the inferior petrosal sinus.
  • The lateral part is occupied by a larger jugular fossa laterally and a smaller glossophary deal notch medially. The lateral part forms the anterior boundary of the jugular foramen whose posterior boundary is formed by the jugular notch of the occipital bone.

Temporal Bones Tympanic Part

It is a curved bony plate situated below the squamous part and in front of the mastoid part of the temporal bone.

• It joins the squamous part at squamotympanic fissure and mastoid part at tympanomastoid fissure. Auricular branch of vagus emerges through the tympanomastoid fissure.
• The tympanic part has two surfaces (anterior and posterior) and three borders (lateral, upper and lower).

1. Surfaces

• Anterior Surface
  • It forms the posterior nonarticular part of the mandibular fossa.
  • It is related to the parotid gland.
• Posterior Surface
  • It forms the anterior wall, floor and the lower part of the posterior wall of the external acoustic meatus.
  • Its medial end is marked by a groove called the tympanic sulcus. This sulcus provides attachment to the circumferential of the tympanic membrane.

2. Borders

• Lateral Border
  • It is free.
  • It continues with the cartilaginous part of the external acoustic meatus.
• Upper border
  • Laterally it fuses with the postglenoid tubercle.
  • Medially it forms the posterior boundary of the petrotympanic fissure.
• Lower Border
  • Medially it extends up to the carotid canal.
  • Laterally it splits to form the veginal process which encloses the root of the styloid process.

Temporal Bones Styloid Process

1. The styloid process is divisible into two parts:
   • Proximal or tympanohyal part
     • It is surrounded by a bony sheath derived from the lower border of the tympanic part of the temporal bone.
   • Distal Or Stylohyal Part
     • It is visible lower part. It is this part which is described below.
2. The styloid process is a conical projection directed downwards, forwards and slightly medially.
3. It provides attachments to five structures (3 muscles and 2 ligaments):
   • Medially: Stylopharyngeus muscle.
   • Anteriorly: Styloglossus muscle.
   • Posteriorly: Stylohyoid muscle.
   • Laterally: Stylomandibular ligament.
   • At the tip: Stylohyoid ligament.
4. Some important relations are as follows:
   • It is interposed between two important structures, the parotid gland (laterally) and the internal jugular vein (medially).
   • The external carotid artery crosses the tip of the styloid process superficially
   • The facial nerve crosses the base of the styloid process laterally.
5. Stylomastoid foramen is situated behind its base (between it and the mastoid process). The following structures pass through this foramen:
   • Facial nerve.
   • Stylomastoid artery.

Temporal Bones Spaces And Canals External acoustic meatus

1. The bony part of the external acoustic meatus is about 16 mm long. This contribution is about 2/3rd of the total length (24 mm).
2. It is directed medially, downwards and slightly forward.
3. The tympanic part of the temporal bone contributes to its anterior wall, floor and lower part of the posterior wall.
4. The squamous part of the temporal bone forms its roof and the upper part of the posterior wall.

Middle Ear Space (Tympanic Cavity)

• Parts
  1. The tympanic cavity consists of three parts:
  2. Tympanic cavity proper (mesotympanum): Opposite the tympanic membrane.
  3. Epitympanic recess (epitympanum): Above the level of the tympanic membrane.
  4. Hypotympanum: Below the level of the tympanic membrane.
• Measurements
  1. Vertical diameter – 15 mm.
  2. Anteroposterior diameter – 15 mm.
  3. Transverse diameters:
  4. Upper part – 6 mm.
  5. Lower part – 4 mm.
  6. Opposite the centre of the tympanic membrane 2 mm.
• Boundaries
  1. Roof
     • It is formed by tegmen tympani which separates the middle ear from the middle cranial fossa.
  2. Floor
     • It is formed by a thin plate of bone which separates the cavity from the superior bulb of the internal jugular vein.
  3. Lateral wall
     • It is formed mainly by the tympanic membrane.
     • Close to the circumference of the tympanic membrane, there are three small apertures:
       1. Petrotympanic fissure: It is located. anteriorly.
       2. Anterior canaliculus for chorda tympani: It is located at the medial end of the petrotympanic fissure.
       3. Posterior canaliculus for chorda tympani It is located posteriorly.
  4. Medial wall
     • It is the lateral wall of the internal ear.
     • It has a rounded elevation called promontory produced by the basal turn of the cochlea.
     • Promontory is grooved by the nerves of tympanic plexus.
     • A depression behind the promontory, the sinus tympani, indicates the position of the ampulla of the posterior semicircular canal.
     • Fenestra vestibuli is a reniform opening posterosuperior to the promontory. It
       connects the tympanic cavity to the vestibule of the internal ear.
     • Fenestra cochlea is a rounded opening in the posteroinferior part of the promontory. It connects the tympanic cavity with the scala tympani of the cochlea.
     • Above and posterior to the fenestra vestibuli there is an elevation produced by the facial nerve canal.
  5. Posterior wall
     • Aditus to the mastoid antrum is an opening in the upper part of the posterior wall. It connects the epitympanic recess with the mastoid antrum.
     • The medial wall of the aditus to mastoid antrum shows an elevation produced by the lateral semicircular canal.
     • The facial nerve canal lies vertically in the posterior wall anterior to which is a pyramidal eminence projecting into the middle ear cavity.
     • Pyramidal eminence is occupied by the stapedius muscle.
     • Fossa includes a small depression in the posteroinferior part of the epitympanic recess. It contains the short process of incus.
  6. Anterior wall
     • Its lower part is formed by a thin plate of bone which separates the middle ear from the carotid canal.
     • Its upper part is occupied by two openings. An upper opening leads into the canal for the tensor tympaní. The lower opening leads into the osseous part of the Eustachian tube. These two canals are visible from the apex side of the petrous temporal at petrosquamosal junction.
     • The septum between the aforementioned canals runs on the medial wall and just above the fenestra vestibuli its posterior end curves laterally to form processus cochleariformis.

Mastoid Antrum

1. It is an air sinus in the petrous part of the temporal bone.
2. It is well developed at birth and is almost of adult size.
3. The mastoid antrum is a spherical sinus.
4. In adults, the mastoid antrum has a capacity of about 1 ml.
5. Aditus ad antrum is an opening in the upper part of the anterior wall of the mastoid antrum. It connects the antrum with the epitympanic recess of the middle ear.
6. The roof of the antrum is formed by tegmen tympani.
7. Posteriorly the antrum is closely related to the sigmoid sinus.
8. The medial wall is related to the posterior semicircular canal.
9. Anteroinferiorly the antrum is related to the canal for the facial nerve.
10. The floor has multiple apertures which connect the mastoid antrum with mastoid air cells.
11. The lateral wall of the antrum corresponds to the supramental triangle. This wall is 1 mm thick at birth and increases at a rate of 1 mm per year until it reaches the adult thickness of about 12.5 mm.

Mastoid Air Cells

1. These are very small intercommunicating spaces in the temporal bone continuous
   with mastoid antrum.
2. At birth neither mastoid air cells nor mastoid process are present. Only after birth do mastoid air cells grow out of the mastoid antrum into the mastoid process.
3. The mastoid air cells are mainly seen in the mastoid process but may extend into the surrounding bones like petrous or squamous parts of the temporal bone or even zygomatic bone and the jugular process of the occipital bone.
4. Some common groups of air cells are as follows:
   • Tip cells.
   • Perisinus cells.
   • Retrofacial cells.
   • Periantral cells.
   • Perilabyrinthine cells.
   • Petrous cells.
   • Zygomatic cells.
5. Depending upon the pneumatization, the mastoid process may be of three types:

• • Pneumatic or cellular.
  • Sclerotic or acellular.
  • Diploeic or mixed.

Bony Labyrinth (Osseous Labyrinth)

It consists of three parts, vestibule, semi-circular canals and cochlea.

1. Vestibule

• 1. It is the central part of the bony labyrinth.
  2. In its lateral wall, there is an opening of fenestra vestibuli (oval window) occupied by a foot plate of stapes in life.
  3. Its medial wall corresponds to the fundus of the internal acoustic meatus.
  4. The anterior part of the medial wall has a spherical recess for the saccule. This recess has multiple perforations which correspond to the openings in the inferior vestibular area of the fundus of the internal acoustic meatus.
  5. Posterosuperior to spherical recess is an elliptical recess which lodges the utricle. This recess also has a number of foramina which correspond to openings in the superior vestibular area of the fundus.
  6. Below the elliptical recess is the opening of the aqueduct of the vestibule which passes ductus endolymphaticus.

2. Semicircular Canals

1. They lie posterosuperior to the vestibule.
2. There are three semicircular canals.
   • Anterior or superior.
   • Lateral or horizontal.
   • Posterior.
3. Ipsilateral semicircular canals lie in three planes at right angles to each other.
4. Each canal is about two-thirds of a circle.
5. The superior semicircular canal is placed in a vertical plane perpendicular to the long axis of the petrous bone at about 45° with the sagittal plane.
6. The posterior semicircular canal is placed in a vertical plane in the long axis of the petrous bone. This also makes an angle of 45° with the sagittal plane.
7. The lateral semicircular canal makes an angle of 30° with the horizontal plane. This canal lies horizontally if the head is bent forward for 30°.
8. One end of each canal is dilated called the ampulla.
9. Both the ends of each canal open into the vestibule. Since non-ampullated ends of superior and posterior semicircular canals have a common opening in the vestibule, only five openings connect the three canals with the cavity of the vestibule.

3. Cochlea

1. It is conical in shape and consists of two and three-quarter spiral turns of a tapering cylindrical canal.
2. The axial bone around which the canal spirals is called modiolus.
3. The basal turn of the cochlea produces promontory on the medial wall of the middle ear.
4. From the modiolus a shelf of bone projects into the canal. Since the shelf follows the spiral path of the canal, this is called the spiral lamina.
5. The spiral lamina forms a hook-like structure (called hamulus) at the apex of the modiolus.
6. The basal turn of the cochlea shows two holes:
   • The fenestra cochleae
   • It is closed in life by a secondary tympanic membrane.
   • The opening of the aqueduct of cochlea
   • It leads downwards to reach the apex of the glossopharyngeal notch.
7. The base of the modiolus is perforated by spirally arranged foramina. This area corresponds to the cochlear area of the fundus of the internal acoustic meatus.

Temporal Bones Ossification

1. Temporal bone ossifies partly in cartilage and partly in membrane.
2. Squamous and tympanic parts ossify in the membrane.
3. The petromastoid part and the styloid process ossify in cartilage.
4. Appearance of centres
   1. Squamous part
      • The single centre appears near the root of the zygomatic process during the 8th week of intrauterine life.
   2. Petromastoid part
      • As many as 14 centres may appear in the cartilaginous mass (otic capsule) around the developing internal ear during the 5th month of intrauterine life. These centres fuse by the 6th month of intrauterine life.
   3. Tympanic part
      • Single centre appears during the 12th week of intrauterine life. At birth, a tympanic ring represents the tympanic part.
   4. Styloid process
      • It develops from the cranial end of the 2nd arch cartilage. It ossifies from two centres. Centre for tympanohyal appears before birth and for stylohyal appears after birth.
   5. Fusion
      • The squamous part fuses with the tympanic part just before birth.
      • The petromastoid part fuses with the squamous part and tympanohyal during 1st year.
      • Stylohyal fuses with the tympanohyal after puberty.

Temporal Bones Applied Anatomy

1. At birth, the tympanic cavity, tympanic membrane, mastoid antrum, ear ossicles and internal ear are all of adult size.
2. At birth the mastoid process is absent and the facial nerve lies on the surface at its exit from the stylomastoid foramen. This makes the postauricular incision a risky procedure in newborns.
3. A very long styloid process may lead to multiple complications and in such cases, it has to be removed by surgery.
4. In the majority of people, the pneumatization of the temporal bone is adequate. In 20% of cases, the pneumatization may be arrested in childhood.
5. This is easily pointed out in X-ray and is called sclerotic or acellular mastoid, a condition which is prone to inflammation.
6. Infections of the middle ear (otitis media) invariably lead to infections of the mastoid antrum and mastoid air cells.
7. The suprameatal triangle is clinically very important as it helps in localizing the mastoid antrum. The mastoid antrum is located 1.25 cm deep to the surface of this triangle.
8. Gross fractures of temporal bones are divided into longitudinal and transverse in relation to the long axis of the petrous temporal bone.
9. Longitudinal fractures are common and are due to blows to the temporal or parietal areas. Transverse fractures are less common and are due to blows in the occipital region.
10. Zygomatic arches form the prominences of the face and, therefore, are prone to facial injuries.
11. Fractures of the zygomatic process of the temporal bone may involve the lateral wall of the orbit and injure the eye.
12. The squamous part of the temporal bone contributes to the vault and, therefore, is prone to both fissured and depressed fractures. The petrous part contributes to the base of the skull and thus invariably shows a linear fracture.
13. Fracture of the tegmen tympani might connect the subarachnoid space with the middle ear leading to CSF leakage into the middle ear.
14. If the tympanic membrane is also damaged then the CSF will appear as a discharge through the external acoustic meatus. This condition is called CSF otorrhoea. The passage may also act as a portal for sepsis of the meninges and brain.
15. Since the petrous part of the temporal bone is very strong, most fracture lines end here without making a tear in it.
16. The indications of the fracture of the petrous part of the temporal bone are as follows:
    • CSF otorrhoea.
    • Tear of tympanic membrane.
    • Collection of blood in the middle ear.
17. Discolouration and oedema of the tissue over the mastoid process (Battle’s sign) is an indication of sigmoid sinus damage.
18. Fracture of the petrous temporal may damage the facial nerve and result in facial paralysis.
19. Involvement of vestibulocochlear nerve in petrous fracture will lead to hearing loss, vertigo and nystagmus.

Orbital Cavity Definition

Orbits are two bony sockets which lodge the eyeballs and the associated structures.

Orbital Cavity Shape And Parts

Each orbit is pyramidal in shape having an anterior base (orbital opening), posterior apex and four walls (medial, lateral, roof and floor).

Orbital Cavity Bony Contributions

• Orbital Opening (Base)

It consists of four margins (supraorbital, infraorbital, lateral and medial).

• • Supraorbital Margin
    1. It is formed by the frontal bone.
    2. The supraorbital notch (or foramen) is situated at the junction of its medial 1/3rd. (rounded) and lateral 2/3rd (sharp) parts.
    3. Supraorbital notch transmits:
       1. Supraorbital nerve.
       2. Supraorbital artery.
       3. Communicating veins between angular and superior ophthalmic veins.
  • Infraorbital Margin
    • It is formed by maxilla medially and zygomatic bone laterally.
  • Lateral orbital margin
    • It is formed by the frontal process of the zygomatic bone below and the zygomatic process of the frontal bone above.
  • Medial Orbital Margin
    • It is formed by the frontal bone above and the lacrimal crest of the frontal process of the maxilla below.
• Apex

1. It forms the posterior end of the orbit.
2. It is contributed by sphenoid.
3. Usually, the medial end of the superior orbital fissure is said to mark the apex.

• Medial Wall
  • It is formed by the following bones from anterior to posterior:
    1. Posterior part of the frontal process of the maxilla.
    2. Lacrimal bone.
    3. The orbital plate of ethmoid.
    4. Body of sphenoid.
• Lateral Wall
  • It is contributed by:
    1. Greater wing of sphenoid bone posteriorly.
    2. Orbital surface of the zygomatic bone and medial aspect of its frontal process anteriorly.
• Roof
  • It is formed by:
    1. Orbital plate of frontal bone anteriorly.
    2. Lesser wing of sphenoid posteriorly.
• Floor
  • It is formed by:
    1. Orbital surface of maxilla medially. It is the major contribution.
    2. Orbital surface of the zygomatic bone.
    3. Orbital process of the palatine bone. It is an insignificant contribution near the posterior end at the junction of the medial wall and floor.

Orbital Cavity Communications

The orbit communicates through several passages with adjacent regions as shown
below.

Orbital Cavity Measurements

1. Length of medial wall – 50 mm.
2. Length of lateral wall – 50 mm.
3. Width of orbital opening, i.e. the distance between medial and lateral orbital margins – 40 mm.
4. Distance between two lateral orbital margins – 100 mm.
5. Distance between two medial orbital margins – 25 mm.
6. The angle between two lateral walls – 90°.
7. The angle between the lateral and medial walls of each orbit is – 45°.
8. The angle between the long axis of the orbit and the anteroposterior axis of the eyeball – 23.
9. Distance between medial orbital margin and coronal plane passing through lateral orbital margins – 20 mm.
10. Measurements of the optic canal:

• • Length – 3 – 9 mm.
  • Diameter – 5 mm.
  • Distance between orbital openings of optic canals – 30 mm.
  • Distance between cranial openings of optic canals – 25 mm.

Orbital Cavity Features

1. The anterolateral part of the roof is slightly hollowed out to form a fossa for the lacrimal gland.

2. The anteromedial part of the roof near the orbital opening is marked by the trochlear fovea or spine for the attachment of a fibrocartilaginous pulley meant for the tendon of the superior oblique muscle.

3. The optic canal is present at the posterior end of the junction of the roof and medial wall. The optic nerve and ophthalmic artery pass through the optic canal.

4. The posterior part of the junction of the lateral wall and floor is marked by an inferior orbital fissure. It transmits the following structures:

• Maxillary nerve.
• Infraorbital vessels.
• Zygomatic nerve.
• A branch from an inferior ophthalmic vein.
• Some twigs (orbital branches) from the pterygopalatine ganglion.

Boundaries of the inferior orbital fissure are as follows:

• Superiorly – Greater wing of sphenoid.
• Inferiorly – Body of maxilla and orbital process of palatine bone
• Laterally Zygomatic bone.

5. The maxillary part of the floor is marked by a groove (infraorbital groove) in the posterior part.

• This groove is directed forward and continues with the infraorbital canal in the anterior part of the floor and ultimately opens on the face as an infraorbital foramen.
• The infraorbital groove, canal and foramen are meant for the passage of infraorbital nerve and vessels.

6. In the anterior part of the medial wall, the posterior part of the frontal process of the maxilla (behind the anterior lacrimal crest).

• Anterior part of lacrimal bone (anterior to posterior lacrimal crest) form a vertical fossa called lacrimal fossa.
• This fossa continues down with the beginning of the nasolacrimal canal. The fossa and canal are meant for the lacrimal sac and nasolacrimal duct respectively.

7. Anterior lacrimal crest provides attachments to:

• Lacrimal fascia.
• Medial palpebral ligament.
• Orbicularis oculi.

8. Posterior lacrimal crest gives attachments to:

• Lacrimal fascia.
• Lacrimal part of orbicularis occuli.

9. The junction of the orbital plate of the frontal bone (roof) and an orbital plate of the ethmoid (medial wall) shows two openings which lead into anterior and posterior ethmoidal canals. These transmit corresponding ethmoidal nerves and vessels.

10. The orbital surface of the zygomatic bone in the lateral wall possesses zygomatic-orbital foramina meant for the passage of zygomaticotemporal and zygomaticofacial nerves and zygomatic branches of the lacrimal artery.

11. Superior Orbital Fissure

• Location
  • It is located at the junction of the roof and lateral wall of the orbit.
• Shape
  • It is triangular in shape with a base medially and apex laterally.
• Communication
  • It connects the orbit with the middle cranial fossa.
• Boundaries
  • Medial: Body of sphenoid bone.
  • Apex: Frontal bone.
  • Superior: Lesser wing of sphenoid.
  • Inferior: Greater wing of sphenoid.
• Common annular tendon
  • The lower margin of the fissure presents a bony projection for the attachment of the common tendinous ring (common annular tendon) for the attachment of the recti of the eyeball.
• Structures passing through
  • The common annular tendon divides the fissure into three compartments for the passage of a number of structures as shown below.
  • Lateral part
    1. Lacrimal nerve.
    2. Frontal nerve.
    3. Trochlear nerve.
    4. Superior ophthalmic vein.
    5. Meningeal branch of the lacrimal artery.
    6. Orbital branch of the middle meningeal artery.
  • Part within the tendinous ring
    1. Upper and lower divisions of the oculomotor nerve.
    2. Nasociliary nerve.
    3. Abducent nerve.
  • The part below the tendinous ring
    1. Inferior ophthalmic vein
    2. Sympathetic twigs.

12. The lateral wall of the orbit near the lateral orbital margin presents an ill-defined Whitnall’s tubercle.

• It is located on the orbital surface of the frontal process of the zygomatic bone about 1 cm below the frontozygomatic suture.
• The following structures are attached to this tubercle:
• Lateral palapebral ligament.
• Lateral check ligament.
• Suspensory ligament of the eyeball.
• Aponeurosis of levator palpebrae superioris.

Orbital Cavity Applied Anatomy

1. Maxillectomy should be performed below the attachments of check ligaments to avoid the sagging of the eyeball.

2. A normal amount of orbital fat stabilizes the eyeball from behind. An increase in the orbital fat as observed in hyperthyroidism, will push the eyeball forward leading to exophthalmos (bulging of the eye).

3. The floor and medial wall of the orbit are relatively thin therefore tumours arising from ethmoidal and maxillary sinuses may push into the orbital cavity and displace the eyeball.

4. In Graves’ disease there is hypertrophy of extraocular muscles which is responsible for increased intraorbital pressure and exophthalmos.

5. Eyeball occupies the anterior half of the orbit and it is joined by the optic nerve from behind. The optic nerve runs a tortuous course to allow the movements of the eyeball without being damaged. Inflammation of the optic nerve is called retrobulbar neuritis.

6. There may be an isolated fracture of a single orbital margin or wall or there can be involvement of multiple margins or walls in different combinations.

7. Fracture of the orbital plate of the frontal bone causes haemorrhage into the orbit. The haemorrhage acquires a triangular shape under the conjunctiva whose apex is towards the corneoscleral junction and base towards the orbital margin.

8. A severe impact on the nasal bridge may involve the medial wall of the orbit. The involvement of the lacrimal bone will damage the lacrimal passage.

9. A fracture of the sphenoid may lacerate the optic nerve in the optic canal resulting in blindness.

10. Frontozygomatic suture located in the lateral orbital margin forms an important landmark in the treatment of maxillofacial injuries.

11. Fracture of the frontal process of the zygomatic bone may occur in conjunction with a comminuted fracture of the orbital rim and frontal bone.

12. Orbit is an anatomical region which is of great clinical and surgical interest due to many disciplines in its surrounding relations.

13. The floor of the orbit is very thin and further weakened by the presence of an infraorbital groove. A fracture which is common in this part, invariably involves the infraorbital nerve and vessels.

14. Le Fort (2 and 3) fractures of the midfacial skeleton involve the walls of the orbit. The fracture line in the case of Le Fort 2 fracture crosses the lower part of the frontal process of the maxilla and lacrimal bone. In Lé Fort 3 fracture both medial and lateral walls are involved near the roof.

15. For optic nerve decompression in the optic canal, the posterior lacrimal crest, ethmoid and sphenoid are infractured to reach the medial wall of the optic canal.

16. Lacrimal bone is very fragile therefore an extra precaution should be taken to avoid trauma in cases of surgery of the lacrimal system.

17. A penetrating object will enter the orbit through an orbital opening and damage the adjacent regions depending upon its directions, for example:

• Directed upwards and medially: It will enter the frontal sinus in the anterior part and anterior cranial fossa more posteriorly.
• Directed towards the floor: It will enter the maxillary sinus.
• Directed backwards: It will enter the middle cranial fossa through the superior orbital fissure and damage the temporal lobe.

18. Ethmoidal malignancy may erode the optic canal and compress the optic nerve.

19. Tumours in the adjacent regions may enter the orbit through large communications. From the middle cranial fossa, it passes through the superior orbital fissure while from the temporal fossa, it traverses the inferior orbital fissure.

20. An orbital tumour will push the eyeball forward producing exophthalmos.

21. Since the lateral orbital margin lies relatively more posteriorly than the medial orbital margin, a lateral approach is preferred for the operations on the eyeball.

Nasal Cavity

The nasal cavity is the beginning of the respiratory system. It is divided into right and left halves by a midline partition called nasal septum.

To study the cavity, a sagittal section of the skull is considered in which one and a half of the skull shows a lateral wall of the nasal cavity and the second half shows a nasal septum.

Nasal Cavity Features

Each half of the nasal cavity consists of a roof, floor, medial wall, and lateral wall.

1. Roof

It has anterior and posterior slopings and a middle horizontal part.

• Anterior Sloping
  • It is formed by the nasal bone and nasal spine of the frontal bone.
• Posterior Sloping
  • It is formed by the following bones from anterior to posterior:
    1. The anterior surface of the body of the sphenoid.
    2. Ala of the vomer.
    3. Sphenoidal process of palatine bone.
  • It possesses an opening of the sphenoidal sinus.
• Middle Horizontal Part
  • It is formed by the cribriform plate of the ethmoid bone.
  • The number of foramina in it provides passages for filaments of the olfactory nerve.
  • One of these perforations in its anterior part transmits the anterior ethmoidal nerve and vessels.

2. Floor

• It is formed by the superior surface of the bony palate, i.e. palatine process of the maxilla and horizontal plate of the palatine bone.
• Anteriorly near the septum, a small infundibular opening leads into an incisive canal.
• The nasopalatine nerve and greater palatine vessels traverse the incisive canal.

3. Medial wall

• It is formed by bony septum in a dried skull.
• The posteroinferior part of the bony septum is contributed by vomer.
• Its anterosuperior part is formed by a perpendicular plate of ethmoid.
• The nasal crest (below), sphenoidal crest, and rostrum (above and behind) provide minor contributions to the bony septum.
• A groove on each side of the vomer descends downwards and forwards towards the incisive canal. It lodges the nasopalatine nerve.

4. Lateral wall

1. This is very irregular.
2. This is marked by three bracket-like projections that run anteroposteriorly and lie one above the other. These projections are named from above downwards, superior, middle, and inferior conchae.
3. Each concha forms the medial wall and roof of the corresponding meatus. Therefore, there are three meatus, superior, middle, and inferior.
4. The part of the lateral wall above the superior concha is called sphenoethmoidal
   recess.
5. The main bony contributions in the lateral wall are as follows:
   • Below and in the front nasal surface of the maxilla.
   • Behind-Perpendicular plate of palatine bone.
   • Above-Ethmoidal labyrinth (with superior and middle conchae).
   • Below-Inferior concha (an independent bone).
6. Inferior meatus
   1. It lies below and lateral to the inferior concha.
   2. It receives an opening of the nasolacrimal duct in its anterior part.
7. Middle meatus
   • It is situated between the middle and inferior conchae.
   • A rounded elevation in its upper part is called ethmoidal bulla produced by middle ethmoidal air cells.
   • On the surface or just above the bulla is the opening of the middle ethmoidal sinus.
   • Behind the bulla is the opening of the maxillary sinus.
   • Anteroinferior to bulla is a curved, thin bony projection called the uncinate process of ethmoid.
   • The uncertain process passes backward and encloses a curved gap between it and the bulla. This gap is called hiatus semilunaris.
   • Upper end of hiatus semilunaris continues with ethmoidal infundibulum.
   • The infundibulum of the ethmoid receives the opening of the anterior ethmoidal sinus and itself continues up as the frontonasal duct reaches the frontal sinus.
8. Superior meatus
   • It is situated between the superior and middle conchae.
   • The opening of the posterior ethmoidal sinus is located in the superior meatus.
9. Sphenoethmoidal recess
   • It is situated between the roof and the superior concha.
   • It receives the opening of the sphenoidal air sinus.
10. Sphenopalatine foramen
    • It is located just behind the superior concha.
    • It transmits the sphenopalatine artery and nasal branches of the pterygopalatine ganglion.

Nasal Cavity Applied Anatomy

1. Fracture of the base of the skull involving the anterior cranial fossa might lead to communication between the nasal cavity and subarachnoid space resulting in CSF leak into the nose. This condition is called CSF rhinorrhoea.

2. An impact on the nasal bridge will lead to fracture and displacement of the nasal septum.

3. Fracture of the cribriform plate will result in anosmia (loss of smell sensation) due to damage to olfactory nerve filaments.

4. Fracture of the cribriform plate may cause infection to enter the cranial cavity from the nasal cavity resulting in meningitis.

5. Le Fort fractures of the mid-facial skeleton always involve the nasal septum.

6. All the bones of the nasal cavity are clothed in the mucosa, therefore, their fractures open to the nasal cavity with the potential risk of infection.

7. The bones of the nasal cavity receive adequate blood supply from periosteal arteries and, therefore, all the fragments of fractured bone retain a periosteal blood supply.

8. Bony septum is papery thin and does not resist much to forces responsible for fracture.

9. The floor of the nasal cavity may be fractured in an uncommon central split of the palate. It is actually paramedian in nature because median sutures (intermaxillary and interpalatine) are relatively strong.

10. Nasal ethmoidostomy (an artificial opening to drain the ethmoidal air cell) is a common practice in several surgical procedures involving ethmoidal labyrinth.

11. Lacrimal bone is very fragile therefore an extra precaution should be taken to avoid trauma in cases of surgery of the lacrimal system.

12. In the management of congenital lacrimal defect, in fracture of the inferior concha is sometimes needed.

13. In cases of obstruction of the lacrimal sac or nasolacrimal duct, dacryocystorhinostomy is performed. In this operation, an artificial passage is made by breaking the lacrimal bone.

14. Congenital atresia of the choanae is an uncommon condition in which there is occlusion of the posterior naris by a bony or membranous diaphragm.

15. Antral puncture is a common procedure performed by ENT surgeons to wash out infected fluid in the maxillary sinus (antral lavage). The antrum is punctured through the inferior meatus by a trocar and cannula.

16. Deviation of nasal septum (DNS) is a common condition that may be developmental in origin or may arise from trauma.

17. A perforated septum may be due to septal surgery or syphilis or tuberculosis.

18. Sometimes a permanent opening is made in the inferior meatus to encourage the drainage of the pus in the maxillary sinus. This operation is called intranasal antrostomy.

Norma Basalis

Norma Basalis Definition

Observation of the cranium (skull without mandible) from the inferior aspect is called norma basalis.

Norma Basalis Boundaries

• Anterior: Incisor teeth.
• Posterior: Superior nuchal line.
• Lateral (side):
  • Rest of teeth.
  • Zygomatic arch.
  • Posterior root of zygoma.
  • Mastoid process.

Norma Basalis Subdivisions

For the sake of convenience, norma basalis is divided into anterior, middle and posterior parts. The hard palate and alveolar arch are included in the anterior part.

An imaginary horizontal line passing through the anterior margin of the foramen magnum separates the posterior part from the middle part of the norma basalis.

Norma Basalis Features And Attachments

 

1. Anterior Part Of Norma Basalis

• The posterior border of the hard palate
  • It forms the junction of the anterior and middle parts of norma basalis.
  • The posterior nasal spine is a spinous projection from its middle in the median plane.
  • Musculus uvulae is attached to the posterior nasal spine.
• Alveolar arch
  • It possesses sockets for the roots of the upper teeth.
  • The number of sockets depends upon the number of roots. There is a single socket for each of the incisors, canines and premolars. There are three sockets for each of the upper molars.
• Bones contributing to hard palate
  • Palatine processes of two maxillae contribute to the anterior 2/3rd of the hard palate.
  • The posterior 1/3rd of the hard palate is formed by the horizontal plates of palatine bones.
  • The bony palate is marked by several depressions produced by palatine glands.
• Cruciform suture
  • It is formed by the following three sutures.
  • Intermaxillary suture.
  • Interpalatine suture.
  • Palatomaxillary sutures.
• Incisive fossa
  • It is present anteriorly in the median plane of the hard palate.
  • Incisive foramen (right and left) pierces its corresponding side.
  • Each incisive foramen is transferred by the nasopalatine nerve and greater palatine vessels.
• Greater palatine foramen
  • It is present behind the lateral part of the palatomaxillary suture.
  • Greater palatine vessels and nerves pass through it.
  • A groove observed between the greater palatine foramen and incisive fossa is meant for greater palatine vessels.
• Lesser palatine foramina
  • These are 1-3 foramina in the pyramidal process of palatine bone and located just behind the greater palatine foramen on each side.
  • Lesser palatine nerves and vessels pass through these foramina.
• Palatine crest
  • It is a curved ridge observed in the hard palate near its posterior border.
  • The palatine aponeurosis is attached to the palatine crest, the posterior border of the hard palate and the area between the two.
• Premaxilla
  • It is a triangular piece of maxilla holding four incisor teeth.
  • It is a separate bone in most vertebrates.

2. Middle part of norma basalis

For the sake of convenience, it is divided into a median area and two lateral areas (right and left).

1. Median area

• Posterior nasal apertures
  • These are also known as choanae.
• The posterior border of the vomer
  • It separates two choanae.
• Alae of vomer
  • These are two bony plates formed by the splitting of vomer superiorly.
  • It articulates with the rostrum of the sphenoid.
• Vomerovaginal canal
  • It is formed between the latter! border of each ala of the vomer and the vaginal process of the medial pterygoid plate.
  • It transmits branches of the pharyngeal nerve and vessels.
• Palatovaginal canal
  • It is a canal between the vaginal process of the medial pterygoid plate and the sphenoidal process of the palatine bone.
  • This canal leads anteriorly into the posterior wall of the pterygopalatine fossa.
  • It transmits pharyngeal branches of the pterygopalatine ganglion and pharyngeal branches of 3rd part of the maxillary artery.

Note: Students are invariably confused as to which is the palatovaginal canal and which one is the vomerovaginal canal.

To differentiate keep in mind that the vaginal process of the medial pterygold plate is common to both but as the palatine bone is anterior to the medial pterygoid plate the palatovaginal canal is relatively anterior to the Domeroenginal canal.

• Broad bar of bone behind the alae
  • It is formed by the continuation of the inferior surface of the body of the sphenoid and that of the basilar part of the occipital bone.
  • It extends up to the foramen magnum.
  • The pharyngeal tubercle is a median elevation just in front of the foramen magnum. It is better felt than seen.
  • Pharyngeal tubercle gives attachments to:
    • Highest fibres of superior constrictor.
    • Pharyngeal raphe
  • Longus capitis is inserted on the basilar part of the occipital bone just lateral to the pharyngeal tubercle.
  • Rectus capitis anterior is inserted on each side just in front of the occipital condyle.

2. Lateral area

• Pterygoid processes
  • Pterygoid processes are located just behind the posterior ends of the alveolar arch.
  • Each pterygoid process descends vertically downwards from the junction of the body and the greater wing of the sphenoid.
  • The pterygoid process consists of a lateral and a medial plate.
  • Pterygoid plates unite anteriorly in the upper part to enclose a fossa called pterygoid fossa.
  • The lower ununited portions form a pterygoid fissure which is filled by the pyramidal process of the palatine bone.
  • The anterior surface of the pterygoid process forms the posterior boundary of the pterygopalatine fossa.
  • The lateral surface of the lateral pterygoid plate forms the medial wall of the infra-temporal fossa and gives origin to the lower head of the lateral pterygoid muscle.
  • The medial surface of the lateral pterygoid plate forms the lateral wall of the pterygoid fossa and gives origin to the deep head of the medial pterygoid muscle.
  • The lateral surface of the medial pterygoid plate forms the medial wall of the pterygoid fossa and is related to the tensor palate muscle.
  • The medial surface of the medial pterygoid plate forms the lateral wall of the corresponding posterior nasal aperture.
  • The posterior border of the medial pterygoid plate shows the following features:
    • At its upper end, it splits to enclose the scaphoid fossa which gives origin to the tensor palati muscle.
    • Its upper end shows a small projection called the pterygoid tubercle which lies immediately below the posterior end of the pterygoid canal.
    • Pharyngobasilar fascia is attached to its whole extent while the superior constrictor arises from its lower part only.
    • A hook-like process at its lower end is called pterygoid hamulus. Tendon of tensor palati winds around this process. Superior constrictor and pterygomandibular raphe are also. attached to it.
    • An angular process projecting from the middle of this margin is called processus tubarius. The posterior border above this process is called the notch of the auditory tube. This process and notch support the medial end of the auditory tube.
• The infratemporal surface of the greater wing of the sphenoid
  • It is pentagonal in shape.
  • It forms roof of infratemporal fossa.
  • It gives origin to the upper head of the lateral pterygoid muscle.
  • It is crossed by deep temporal and masseteric nerves.
  • The spine of the sphenoid is a projection from the posteriormost part of the infratemporal surface.
  • The infratemporal crest is the lateral limit of the infratemporal surface.
  • From the scaphoid fossa to the spine of the sphenoid, four foramina can be noticed, i.e. foramen of Vesalius, foramen ovale, canaliculus innominatus and foramen spinosum.
• Foramen ovale
  • It is an oval foramen.
  • It transmits the mandibular nerve, accessory meningeal artery, lesser petrosal nerve and emissary vein.

Note: For remembering the structures passing through foramen ovale remember MALE, in which M-Mandibular nerve, A-Accessory meningeal artery, L-Lesser petrosal nerve and E-Emissary vein.

• Foramen spinosum
  • It is situated near the spine of the sphenoid, posterolateral to foramen ovale.
  • It transmits the middle meningeal artery, nervus spinosus (meningeal branch of the mandibular nerve) and parietal trunk of the middle meningeal vein.
• Foramen of Vesalius (sphenoidal emissary foramen)
  • It is an infrequently seen foramen between the scaphoid fossa and the foramen ovale.
  • It transmits an emissary vein connecting the cavernous sinus with the pterygoid venous plexus.
• Canaliculus innominatus (foramen innominatum)
  • This is also an infrequently seen foramen between foramen ovale and foramen spinosum.
  • It transmits lesser petrosal nerve.
• Spine of sphenoid
  • It is related laterally to the auriculo-temporal nerve and medially to chorda tympani nerve and the Eustachian tube.
  • The sphenomandibular ligament is attached to its tip.
  • Most posterior fibres of tensor palatini originate from its anterior surface.
• Sulcus tube
  • It is a groove between the posteromedial margin of the infratemporal surface of the greater wing of the sphenoid and the inferior surface of the petrous part of the temporal bone.
  • The cartilaginous part of the Eustachian tube (also called the auditory tube or pharynx-tympanic tube) occupies this sulcus.
• The inferior surface of the petrous part of the temporal bone
  • It is located just behind the infratemporal surface of the greater wing of the sphenoid.
  • Its anteromedial serrated end marks the apex of the petrous part.
  • The quadrilateral area near the apex provides attachment to the levator palati muscle.
  • The lower opening of the carotid canal is located just behind the quadrilateral area. It transmits the internal carotid artery with its sympathetic and venous plexuses.
  • The Carotid canal runs forward and medially in the petrous part and perforates its apex as the upper opening of the carotid canal.
• Foramen lacerum
  • It is located between the sphenoid and apex of the petrous temporal.
  • It is named ‘lacerum’ because of its irregular margins.
  • The carotid canal and pterygoid canal open into it.
  • Posterior part of norma basalis irregular margins. For the sake of convenience, this part can be
  • Only two structures pass through it, i.e. meningeal branch of the ascending pharyngeal artery and the emissary vein.
  • The internal carotid artery traverses its upper part with its sympathetic and venous plexuses.
  • The nerve of the pterygoid canal (Vidian nerve) is formed in its upper part by the union of greater superficial petrosal and deep petrosal nerves.
• The tympanic part of the temporal bone
  • It is a triangular bone which occupies the angle between the petrous and squamous parts of the temporal bone.
  • Its anterior surface is related to the parotid gland.
• The squamous part of the temporal bone

Only a small part of the squamous part of the temporal bone is seen in norma basalis and shows the following features from posterior to anterior:

• • Anterior (articular) part of mandibular fossa.
  • Articular tubercle.
  • Part of the roof of the infratemporal fossa.
• Squamotympanic fissure
  • It marks the junction of squamous and tympanic parts of the temporal bone.
  • The downward edge of the tegmen tympani (a part of the petrous part of the temporal bone) divides the squamotympanic fissure into petrotympanic (posterior) and pterosquamous (anterior) fissures.
  • The Chorda tympani nerve, anterior tympanic artery and anterior ligament of the malleus pass through petrotympanic fissure.

3. Posterior Port Of Norma Basalis

For the sake of convenience, this part can be divided into a median area and two lateral areas (right and left).

• Median area

It consists of foramen magnum, external occipital crest and external occipital protuberance from anterior to posterior.

• • Foramen magnum
    1. It is the largest foramen in the skull.
    2. It is a single foramen located in the lowest part of the posterior cranial fossa.
    3. It is oval in shape.
    4. It is the communication between the cranial cavity and the vertebral canal.
    5. Anterior atlanto-occipital membrane is attached to its anterior margin.
    6. The posterior atlanto-occipital membrane is attached to its posterior margin.
    7. Lateral margins provide attachments to alar ligaments.
    8. The following structures pass through its anterior part:
       • Apical ligament of dens.
       • Superior longitudinal band of cruciform ligament.
       • Membrana tectoria.
    9. The following structures pass through its posterior part:
       • Medulla oblongata.
       • Meninges.
       • Spinal roots of accessory nerves.
       • Meningeal branches of upper cervical nerves (C_1-3).
       • Vertebral arteries.
       • Sympathetic plexuses around vertebral arteries.
       • Anterior and posterior spinal arteries.
  • External occipital crest
    1. It extends from the posterior margin of the foramen magnum to the external occipital protuberance.
    2. The upper margin of ligamentum nuchae is attached to it.
  • External occipital protuberance

Trapezius is attached to it superiorly and ligamentum nuchae inferiorly.

• Lateral area
  • Occipital condyles
    1. These are located lateral to the anterior half of the foramen magnum.
    2. Each is oval and convex to articulate with a concave superior articular process of the atlas.
  • Condylar fossa
    1. It is present just behind the occipital condyle.
    2. It may have a condylar canal for the emissary vein from the sigmoid sinus.
  • Hypoglossal canal
    1. Lateral to the anterior part of the condyle is the outer opening of the hypoglossal canal.
    2. It transmits:
       • Hypoglossal nerve.
       • Meningeal branch of ascending pharyngeal artery.
       • Emissary vein from basilar venous plexus.
  • Squamous part of the occipital bone
    1. The superior nuchal line is a well-defined ridge which extends laterally from the external occipital protuberance on each side. Its medial 1/3rd provides origin to the trapezius while the lateral 1/3rd receives insertions of sternomastoid (above) and splenius capitis (below).
    2. Running laterally on each side from the middle of the external occipital crest is another ridge called the inferior nuchal line.
    3. A vertical line on each side along with the inferior nuchal line divides the region below the superior nuchal line into four areas, each meant for the attachment of a muscle as follows:
       • Upper medial area for semispinalis capitis.
       • Upper lateral area for obliquus capitis superior.
       • Lower medial area for rectus capitis posterior minor.
       • Lower lateral area for rectus capitis posterior major.
  • Jugular foramen
    1. It is an interosseous foramen situated between the anterior margin of the jugular process of the occipital bone and the posterior margin of the petrous part of the temporal bone at the petro-occipital suture.
    2. It is divided into anterior, middle and posterior parts.
    3. 9th, 10th and 11th cranial nerves pass through its middle part.
    4. The inferior petrosal sinus and meningeal branch of the ascending pharyngeal artery pass through its anterior part.
    5. The sigmoid sinus and meningeal branch of the occipital artery traverse through its posterior part.
    6. At its posterior end, the anterior wall (petrous temporal) is hollowed out to form the jugular fossa which lodges the superior bulb of the internal jugular vein.
    7. The mastoid canaliculus is a minute canal in the lateral wall of the jugular fossa which transmits the auricular branch of the vagus.
    8. The glossopharyngeal notch is on the posterior border of the petrous temporal bone near the medial end of the jugular foramen.
    9. The cochlear canaliculus is located at the apex of the glossopharyngeal notch. The aqueduct of the cochlea opens into the cochlear canaliculus.
    10. Tympanic canaliculus is present in the ridge between the jugular fossa and the lower opening of the carotid canal. It transmits the tympanic branch of the glossopharyngeal nerve to the middle ear.
  • Inferior surface of jugular process of occipital bone
    1. It is the area just lateral to the occipital condyle behind the jugular foramen.
    2. It provides attachment to rectus capitislateralis.
  • Styloid process
    1. It is a conical projection just below the tympanic part of the temporal bone.
    2. It is directed downwards, forwards and slightly medially.
    3. It provides attachments to 3 muscles and 2 ligaments. Three muscles attached to it are the styloglossus (anteriorly), stylohyoid (posteriorly) and stylopharyngeus (medially). Two ligaments attached to it are stylomandibular (laterally) and stylohyoid (on the tip).
    4. It is interposed between the parotid gland (laterally) and the internal jugular vein (medially).
    5. Two structures cross it superficially, i.e. facial nerve (near the base) and external carotid artery (near the tip).
  • Mastoid process
    1. It is a prominent projection from the temporal bone posterolateral to the styloid process.
    2. The medial aspect of this process shows a deep groove (digastric notch) which provides attachment to the posterior belly of the digastric.
    3. Medial to the digastric notch, there can be another groove for the occipital artery.
  • Stylomastoid foramen
    1. It is present between styloid and mastoid processes.
    2. The facial nerve and stylomastoid artery pass through this foramen.

Norma Basalis Applied Anatomy

A forceful hit on the forehead causes linear fracture of both vertex and base.

1. Due to the presence of natural thick bony buttresses at the base of the skull, the fracture lines often converge towards the foramen magnum or sella turcica.
2. In the case of basal fractures, the location of structures passing through the basal foramina may complicate the issue.
3. A fracture line passing through the foramen lacerum may tear the internal carotid artery.
4. If the fissure lines involve grooves having a resultant carotid-cavernous fistula. meningeal vessels and dural sinuses, then epidural haematoma might result.
5. Fractures of the skull base are often zig-zag in appearance because the fracture lines avoid thickening and pass through the lines of least resistance.
6. Tumours of the base of the skull
   • Transitional cell carcinoma arising from the mucous membrane of paranasal sinuses or fossa of the Rosenmuller of the nasopharynx usually erodes the skull base.
   • Some of the very rare tumours which may arise from the base of the skull or adjacent tissue are as follows:
     • Osteomas.
     • Chondromas.
     • Giant cell tumours of bone.
   • Many malignant tumours metastasize to the base of skull bones from distant organs, for example. prostate, lung and breast.
7. The bony palate may be fractured in an uncommon central split of the palate. It is actually paramedian in nature because median sutures (intermaxillary and interpalatine) are relatively strong.
8. Clinical signs and symptoms which support the involvement of the base of the skull, are as follows:
   • Discharge of CSF through external acoustic meatus (C.S.F. otorrhoea)
   • Tear of tympanic membrane.
   • Collection of blood in the middle ear.
   • Facial paralysis due to damage of the 7th cranial nerve.
   • Loss of hearing, vertigo and nystagmus due to the involvement of the 8th cranial nerve. The aforementioned signs are indicative of a fracture of the petrous part of the temporal bone.
   • Discolouration and oedema of tissue over the mastoid process is an indication of sigmoid sinus damage.
9. Cranial nerve damage is due to the involvement of foramina in the skull base by the fracture lines.

Exterior Of The Skull

Different views of the skull are considered from the description point of view. These are as follows:

1. Norma vertical: This is the superior view.
2. Norma occipitalis: This is a posterior view.
3. Norma frontalis: This is the anterior view.
4. Norma lateralis: This is a lateral (side) view.
5. Norma basalis: This is the inferior view.

Norma Vertical

Norma Verticalis Definition

Observation of the skull from the superior aspect is called norma verticalis.

Norma Verticalis Shape

Norma’s vertical view of the skull appears ovoid in shape. It is relatively wider posteriorly.

Norma Verticalis Bones

The following bones contribute to the norma verticalis:

1. Frontal bone (frontal squama): It lies anteriorly.
2. Occipital bone (squamous part): It lies posteriorly.
3. Parietal bones (paired): These lie on each side of the midline.

Junctions Of Bones (Sutures)

1. Sutures are the immovable joints of the skull which are fibrous in nature.
2. In norma verticalis following sutures can be seen:

• • Coronal Suture: It is between the frontal and parietal bones.
  • Sagittal Suture: It is between the two parietal bones.
  • Lambdoid Suture: It is between the occipital and two parietal bones.

Norma Verticalis Features

1. Vertex

It is the highest point on the sagittal suture.

2. Vault

It is the arched roof of the skull.

3. Bregma

• It is situated at the intersection between coronal and sagittal sutures.
• Bregma is the site of a membranous gap in the foetal skull. This gap is known as anterior fontanelle.
• Anterior fontanelle closes by 18 months.

4. Lambda

• It is situated at the intersection of sagittal and lambdoid sutures.
• In the foetal skull, there is a membranous gap at the site of lambda. This gap is known as posterior fontanelle.
• Posterior fontanelle closes in 2-3 months.

5. Parietal Foramen

It pierces the parietal bone on each side of the midline about 3.5 cm in front of lambda. An emissary vein passes through it.

6. Obelion

It is the region on the sagittal suture between two parietal foramina.

7. Parietal Eminence

It is the area of maximum convexity of the parietal bone.

8. Temporal Lines

• There are two temporal lines on each side:
  • Superior temporal line.
  • Inferior temporal line.
• Both the temporal lines start as a single line from the zygomatic process of the frontal bone.
• The two lines arch backwards and upwards and cross the frontal bone, coronal suture and parietal bone.
• The superior temporal line fades out in the posterior part of the parietal bone.
• Epicranial aponeurosis and temporal fascia are attached to a superior temporal line.
• The inferior temporal line marks the upper limit of the origin of the temporalis muscle.

Norma Verticalis Applied anatomy

1. Fontanelles serve two important purposes:

• These allow moulding during birth.
• These allow the brain to grow.

2. The presence of anterior fontanelle is both clinically and therapeutically very significant.

• A bulge indicates increased intra-cranial tension (for example. in the case of a brain tumour).
• An abnormal depression indicates excessive loss of fluid (for example. in case of bleeding and dehydration).
• Diagnostic and therapeutic punctures could be carried out through anterior fontanelle.
• Ultrasonography of the brain in infants is performed through anterior fontanelle.

3. The osseous closure of the anterior fontanelle is an important milestone in the normal development of a child.

4. Soft and pliable bones of the neonate can withstand a considerable amount of compression and moulding, a fact clinically important during childbirth.

5. In neonates the flat bones of the vault are very soft and, therefore, a depressed fracture is like a dimple (pond fracture).

6. In adults there is some amount of elasticity in flat vault bones which often prevents fractures in cases of minor trauma. However, if the trauma force exceeds the minimal elasticity, fractures are bound to occur.

7. In adults a depressed fracture always shows an irregular line of fracture at the periphery of the depressed area.

8. Almost invariably all fractures of the vault of the skull in children are associated with the rupture of the dura mater.

9. When the skull is compressed between two hard surfaces an axial shortening takes place along the line of the force and an axial lengthening takes place at a right angle. This results in the fracture of distant poles of the skull far from the actual site of the application of force.

10. Fracture of the skull is usually due to a direct blow. A forceful hit on the forehead may cause a linear fracture of the vertex.

11. Cranium is clinically important because it reflects the size of the brain. Macrocephaly (enlargement of the head) can be due to hydrocephalus. Microcephaly may be hereditary or due to the maldevelopment of the brain.

12. Because of the lack of regenerating capacity of the flat bones of the vault, a gap in it should be filled with tantalum or titanium.

Norma Frontalis

Norma Frontalis Definition

When the skull is observed from the anterior aspect it is known as norma frontalis.

Norma Frontalis Shape

It is oval in shape being wider above than below.

Norma Frontalis Bones

Major bones contributing to the surface features of norma frontalis (excluding bones contributing to deeper orbits, nasal cavity and oral cavity) are as follows:

1. Frontal bone (unpaired).
2. Maxillae (paired).
3. Nasal bones (paired).
4. Zygomatic bones (paired).
5. Mandible ethmoid (unpaired).

Junctions of Bones (Sutures)

1. The junction between the zygomatic process of the frontal bone and the frontal process of the zygomatic bone is called the frontozygomatic suture. It is observed along the lateral margin of the orbital opening.
2. A junction between the nasal part of the frontal bone and the frontal process of the maxilla (frontal-maxillary suture) is observed along the medial margin of the orbital opening in its upper part.
3. The junction between the nasal part of the frontal bone and the nasal bones is called the frontonasal
   sutures.
4. The junction between two nasal bones is a midline suture just above the anterior nasal aperture. This is called internasal suture.
5. The junction between the maxilla and zygomatic bone (zygomaticomaxillary suture) is an oblique suture extending downwards and laterally from the lower border of each orbital opening.
6. The junction between two maxillae is called an intermaxillary suture. It is a midline suture just below the anterior nasal aperture.

Note: Intermaxillary suture is also observed in the hard palate between the palatine processes of two maxillae.

Norma Lateralis

Norma Lateralis Definition

When the skull is observed from the side, it constitutes norma lateralis.

Norma Lateralis Bones

The following bones can be visualized in this view:

1. Frontal
2. Parietal
3. Occipital
4. Nasal
5. Zygomatic
6. Temporal
7. Sphenoid
8. Maxilla

Norma Lateralis Features And Attachments

1. Temporal Lines

There are two temporal lines, superior and inferior.

• Superior Temporal Line
  • It commences at the frontal process of the zygomatic bone.
  • It arches upwards and backwards across the parietal bone.
  • It fades away on the temporal bone.
  • Temporal fascia is attached to it.
• Inferior Temporal Line
  • It commences at the same point.
  • It runs inferior and parallel to the superior temporal line.
  • Posteriorly it curves downwards and forwards on the temporal bone to continue with the supramastoid crest.
  • It limits the attachment of the temporalis muscle.

2. Temporal fossa

• Boundaries
  • Anteriorly: Zygomatic bone.
  • Superiorly: Superior temporal line.
  • Posteriorly: Superior temporal line. Supramastoid crest.
  • Inferiorly: Zygomatic arch.
• Anterior Wall Of The Fossa Is Formed By:
  • The temporal surface of the zygomatic bone
  • The greater wing of the sphenoid
  • Frontal bone
• Its Floor Is Formed By Following Bones:
  • Frontal
  • Parietal
  • Temporal
  • Greater wing of the sphenoid.
• The Temporalis muscle is attached to the floor and inferior temporal line.
• Other Contents Of Fossa Are:
  • Middle temporal artery (a branch of superficial temporal artery).
  • Deep temporal arteries arise from the maxillary artery.
  • A zygomaticotemporal nerve and a minute artery appear from the zygomaticotemporal foramen located on the temporal surface of the zygomatic bone.
  • Deep temporal nerves arise from the mandibular nerve.

3. Pterion

• It is a circular area in the anterior part of the temporal fossa which encloses four bones, frontal, parietal, sphenoid and temporal. These four bones form an ‘H’ shaped suture.
• It is located 4 cm above the zygomatic arch and 3.5 cm behind the front zygomatic suture.
• The middle meningeal vein, anterior branch of the middle meningeal artery and stem of the lateral sulcus of the brain lie deep in the pterion.

4. Zygomatic Arch

• It is formed by the temporal process of the zygomatic bone and the zygomatic process of the temporal bone.
• It has two surfaces (outer and inner) and two borders (upper and lower).
• Its outer surface is subcutaneous and crossed by the following structures from posterior to anterior:
• • Auriculotemporal nerve.
  • Superficial temporal vein.
  • Superficial temporal artery.
• Masseter originates from its inner surface and lower border.
• The temporal fascia is attached to its upper border.
• The posterior end of the lower border is marked by the tubercle of the root of the zygoma. To this is attached the lateral ligament of the temporomandibular joint.
• Roots of the zygomatic arch diverge from the tubercle. The anterior root (articular tubercle) passes medially in front of the mandibular fossa. The posterior root continues with the supramastoid crest.

5. External Acoustic Meatus

• It is located behind the mandibular fossa below the posterior root of the zygoma.
• Its anterior wall, floor and lower part of the posterior wall are formed by the tympanic part while its roof and upper part of the posterior wall are contributed by the squamous part of the temporal bone.
• Margins of the meatus give attachment to the cartilaginous part of the external acoustic
  meatus.

6. MacEwen’s Triangle (Suprameatal Triangle)

• It is situated posterosuperior to the external acoustic meatus.
• The spine of Henle (supramental spine) may be present at the anteroinferior part of the triangle.
• The mastoid antrum is situated about 12.5 mm deep to the supramental triangle.

7. Mastoid Process

• It is a downward projection from the mastoid part of the temporal bone.
• It is present below and behind the external acoustic meatus.
• The muscles attached to it from anterior to posterior are:
  • Sternocleidomastoid.
  • Splenius capitis.
  • Longissimus capitis.
• The posterior belly of the digastric originates from its medial aspect (digastric notch).

8. Styloid Process

• It is a slender, elongated projection below the external acoustic meatus and in front of the mastoid process.
• It provides attachments to the following five structures:
  • Anteriorly: Styloglossus muscle.
  • Posteriorly: Stylohyoid muscle.
  • Medially: Stylopharyngeus muscle.
  • Laterally: Stylomandibular ligament.
  • On the tip: Stylohyoid ligament.

9. Infratemporal Fossa

It is an irregular space below the zygomatic arch.

• Boundaries
  • Anterior – Posterior surface of the body of the maxilla.
  • Medial – Lateral pterygoid plate and pyramidal process of palatine bone.
  • Lateral – Ramus of mandible
  • Roof – Infratemporal surface of the greater wing of the sphenoid.
• Contents
  • Muscles
    • Lateral and medial pterygoids.
    • Temporalis.
  • Arteries
    • Maxillary artery (Ist and 2nd parts) with its branches.
    • Posterior superior alveolar branch of 3rd part of the maxillary artery.
  • Veins
    • Maxillary vein.
    • Pterygoid venous plexus.
    • Posterior superior alveolar vein.
  • Nerves
    • Mandibular nerve and its branches.
    • Chorda tympani.
    • Maxillary nerve.
    • Posterior superior alveolar nerve.
• The anterior wall of the fossa shows two to three perforations for the posterior superior alveolar nerve and vessels.
• The junction of the anterior and medial walls is marked by a fissure (pterygomaxillary fissure) through which it communicates with the pterygopalatine fossa.
• The junction of the roof and anterior wall is marked by the lateral part of the inferior orbital fissure.
• Foramen ovale and foramen supinosum are present in the roof of the fossa.
• The lateral part of the fossa communicates with the temporal fossa through a gap between the zygomatic arch and the side of the skull.

10. Pterygomaxillary Fissure

• It is a gap which leads into the pterygopalatine fossa.
• Boundaries
  • Anterior: Maxilla.
  • Posterior: Pterygoid process.
• The maxillary artery enters the pterygopalatine fossa through the pterygomaxillary fissure.
• The maxillary nerve courses forward through it from the pterygopalatine fossa to enter the orbit through inferior orbital fissures.

11. Pterygopalatine fossa

• Boundaries
  • Anterior: Posterior surface of maxilla.
  • Posterior:
    • Pterygoid process.
    • Greater wing of the sphenoid.
  • Medial: Perpendicular plate of palatine bone.
  • Floor: Fusion of anterior and posterior walls.
• Communications
  • The pterygopalatine fossa communicates with,
  • The orbit, through the inferior orbital fissure.
  • The middle cranial fossa, through foramen rotundum.
  • The infratemporal fossa, through pterymaxillary fissure.
  • The nasal cavity, through the palatovaginal canal and sphenopalatine foramen.
  • The foramen lacerum, through the pterygoid canal.
• Contents
  • The third part of the maxillary artery and its branches.
  • Maxillary nerve with its branches.
  • Pterygopalatine ganglion and its branches.

Norma Lateralis Applied anatomy

1. The spine of Henle is an important surgical landmark for surgery on the mastoid antrum.

2. Pterion is very important clinically because the anterior branch of the middle meningeal artery and accompanying vein lie on its internal aspect and are vulnerable to tearing if there are fractures of bone-forming this region.

3. If the meningeal vessels in the region of the pterion are damaged, an extradural haematoma is formed. Such haematoma may exert pressure on the cerebral cortex.

4. Decompression of the brain in cases of extradural haematoma in the region of pterion can be done by the method of trephining (burr hole) at this site.

5. Temporal fascia is commonly used for making tympanic membrane grafts during surgery for the repair of the ear drum.

6. Deep temporal vessels and nerves along with the tendon of the temporalis muscle, transverse the gap deep to the zygomatic arch whose fracture can involve these structures.

7. An elongated styloid process usually needs surgical correction because it leads to multiple complications in the neck.

8. An oblique line drawn from the frontozygomatic suture to the pterion corresponds with the inferior surface of the frontal lobe. This surface landmark is of great neurosurgical importance.

9. In radiographs of the skull, the diploic canals containing the diploic veins may be mistaken for the fractures of the skull.

10. Calvaria is very thin in the region of the temporal fossa and, therefore, is likely to get fractured because of hard blows to the head.

11. In depressed fractures, the inner table of calvaria is often more extensively fractured than the outer table.

12. Zygomatic fracture is very common in facial injuries due to its prominent position.

13. Fracture of the skull is usually due to direct blows. A forceful hit on the forehead causes linear fractures of both vertex and base.

14. Junctions of frontal and temporal processes of zygomatic bone form surgically important landmarks in the treatment of maxillofacial injuries.

15. The periosteum and attachment of strong temporal fascia limit the displacement of zygomatic bone following injuries.

16. In a depressed fracture of the zygomatico-maxillary complex the maxilla is greatly damaged and there is displacement of the zygomatic bone without its fracture.

17. If a fracture of the zygomatic arch is associated with separation from the temporal fascia, then there occurs a downward displacement of the arch.

18. The weakest point of the zygomatic arch is its middle, just behind the temporo- zygomatic suture. This point is the most common fracture in cases of injuries to the arch.

19. Frontozygomatic suture, the zygomatic prominence, the zygomatic buttress and 1st molar tooth lie in the same vertical line. In the majority of zygomatic-complex
(zygomatic bone + adjacent bones like maxilla and zygomatic process of temporal) fracture, the zygomatic bone rotates along this axis.

Norma Frontalis Features

1. Three Large Apertures

One anterior nasal aperture and two orbital openings form the most striking feature of the norma frontalis.

• Anterior Nasal Aperture
  • It is a midline aperture.
  • It is piriform in shape and wider below than above.
  • Its upper boundary is formed by the lower borders of nasal bones.
  • Its lateral and inferior boundaries are contributed by nasal notches of two maxillae.
  • The anterior nasal spine is a sharp projection at the lower margin of the nasal aperture, in the midline.
  • Rhinion is the lower end of the internasal suture.
  • A notch at the inferior border of the nasal bone is meant for passage of the external nasal nerve.
  • Margins of the aperture give attachments to the nasal cartilages.
• Orbital Openings
  • Each is present above and lateral to the anterior nasal aperture. It is quadrangular in shape and possesses four margins (supraorbital, infraorbital, lateral and medial).
  • Supraorbital margin
    • It is formed by the frontal bone.
    • The supraorbital notch (or foramen) is situated at the junction of the medial 1/3rd (rounded) and lateral 2/3rds (sharp) of the supraorbital margin.
    • The supraorbital notch transmits the supraorbital nerve and artery and a communicating vein between angular and superior ophthalmic veins.
  • Infraorbital margin
    • It is formed by maxilla medially and zygomatic bone laterally.
  • Lateral orbital margin
    • It is formed by the frontal process of the zygomatic bone below and the zygomatic process of the frontal bone above.
  • Medial orbital margin
    • It is formed by the frontal bone above and the lacrimal crest of the frontal process of the maxilla below.

2. Frontal Region

• Superciliary arch
  • It is a curved elevation above the medial part of the supraorbital margin.
• Glabella
  • It is the median elevation between two superciliary arches.
• Nasion
  • It is the junction of internasal and frontonasal sutures.
  • Frontal eminence (frontal tuber)
  • It is a rounded elevation above each superciliary arch.

3. Maxillae

Each maxilla shows the following features:

• Infraorbital Foramen
  • It is situated about 1 cm below the infraorbital margin.
  • Infraorbital nerve and vessels pass through the infraorbital foramen.
• Incisive Fossa
  • It is situated above the incisor teeth.
• Canine Eminence
  • It is produced by the root of the canine tooth.
• Canine fossa
  • It is situated just lateral to canine eminence.
• Frontal Process
  • It is sandwiched between the nasal bone and the lacrimal bone.
• Zygomatic Process
  • It articulates with the zygomatic bone.
• Alveolar Process
  • It bears the sockets for the upper teeth.

4. Zygomatic Bones

• Each bone is situated below and lateral to the orbital opening.
• It is marked by a foramen called zygo- maticofacial foramen.
• Zygomaticofacial nerve traverses the zygomaticofacial foramen.

5. Mandible

• It forms the lower facial skeleton. For details of the features please consult the description of individual bone.
• It is situated just lateral to canine eminence.

Norma Frontalis Attachments

1. Nasal Bone: Procerus
2. Superciliary Arch: Corrugator supercilii
3. Frontal process of maxilla.
   • The orbital part of orbicularis oculi (it is also attached to the nasal part of the frontal bone).
   • Medial palpebral ligament.
   • Levator babii superioris alaeque nasi.
4. Between infraorbital margin and infra-orbital foramen: Levator labii superioris.
5. Below the infraorbital foramen (to canine fossa): Levator anguli oris.
6. Zygomatic bone just below the zygomaticofacial foramen: Zygomaticus minor.
7. Lateral to zygomaticus minor: Zygomaticus major.
8. Adjacent to nasal notch: Nasalis (transverse part above and alar part below).
9. Incisive fossa.
   • Medially: Depressor septi
   • Laterally: Incisivus labii superioris.
10. Alveolar process of maxilla opposite to molar teeth: Buccinator.
11. Mandible: Please consult the description of individual bones.

Norma Frontalis Applied Anatomy

1. In about 8% of adult skulls a remnant of the lower part of the suture between two halves of the frontal bone (metopic suture) may persist. This suture is sometimes confused for a fracture in the radiograph.

2. Superciliary arches are elevated ridges from the surface of bone and any injury in this region will cause laceration of the skin and severe bleeding.

3. Compression of supraorbital nerves causes nerve pain. This fact may be used by anaesthetists to determine the depth of anaesthesia.

4. If the fracture of the frontal bone involves an inner table forming the roof of the frontal sinus, then the air may enter the cranial cavity (aerocele) causing meningitis or brain abscess.

5. An impact on the nose directed in the anteroposterior plane will cause a depression of the nasal bridge due to fracture of nasal bones, frontal processes of maxillae and septal cartilage.

6. A force on the nasal bridge directed from the lateral aspect will result in a deviation of the nasal bridge to the opposite side.

7. Traumatic alteration in the shape of the nose because of fractures of nasal bones is of great clinical importance due to cosmetic reasons, especially in young females.

8. A severe impact on the nasal bridge may involve frontal processes of maxillae.

9. Mid-facial skeleton is commonly involved in facial injuries. It includes maxillae, zygomatic bones, nasal bones and most of the bones which form a nasal cavity.

10. Mid-facial skeleton receives adequate blood supply from periosteal arteries and, therefore, all the fragments of fractured bone retain a periosteal blood supply.

11. Fractures of maxillae and zygomatic bones show a constant pattern. Le Fort has classified such fractures into three types:

• Le Fort 1 fracture (Guerin’s fracture): It shows fractures of the lower 3rd of the nasal septum, maxillae and lower 3rd of pterygoid plates.
• Le Fort 2 fracture: It includes fractures of nasal bones, frontal processes of maxillae, lacrimal bones, ethmoid, vomer and pterygoid plates.
• Le Fort 3 fracture: In this fracture facial skeleton is separated from the skull base. It involves upper parts of nasal bones, frontal processes of maxillae, ethmoid, lesser wings of sphenoid and roots of pterygoid plates.

12. Zygomatic bone is very commonly involved in cases of fractures of the middle 3rd of the face. Fracture of the frontal process of the zygomatic bone may occur in conjunction with a comminuted fracture of the orbital rim and frontal bone.

13. Any of the four margins of the orbit may fracture as an isolated fracture or in combination.

Note: For applied anatomy of the mandible and other bones of norma frontalis, discussion on individual bones may be consulted.

Norma Occipitalis

Norma Occipitalis Definition

When the skull is observed from the posterior aspect, it is known as norma occipitalis.

Norma Occipitalis Shape

Norma occipitalis is convex upwards and flat below.

Norma Occipitalis Bones

The following bones contribute to the norma occipitalis.

1. Parietal bones (paired).
2. Squamous part of occipital bone (unpaired).
3. Mastoid parts of temporal bones (paired).

Norma Occipitalis Sutures

1. Posterior Part Of Sagittal Suture

2. Lambdoid Suture

• It is between the two parietal bones and the occipital bone.
• The lower end of the lambdoid suture meets with the mastoid portion of the temporal bone at a point which forms the junction of occipitomastoid and parietomastoid sutures.

3. Occipitomastoid Suture

It is situated between the occipital bone and the mastoid part of the temporal bone.

4. Parietomastoid Suture

It is situated between the parietal bone and the mastoid part of the temporal bone.

Norma Occipitalis Features

1. External Occipital Protuberance

• It is a midline protuberance on the lower part of norma occipitalis.
• It marks the junction of the head and neck posteriorly.
• Inion is the most prominent point of external occipital protuberance.
• Trapezius originates from the upper part of the external occipital protuberance.
• Ligamentum nuchae is attached to the lower part of this protuberance.

2. Superior Nuchal Lines

• These are curved ridges passing laterally from the external occipital protuberance.
• These form the junction of head and neck posteriorly.
• The trapezius originates from the medial 1/3rd of the superior nuchal line.
• The Sternocleidomastoid is inserted on the lateral part of the superior nuchal line.
• Splenius capitis is also inserted on the lateral part of this line below the attachment of the sternomastoid.

3. Highest Nuchal Lines

• These are situated about a ‘cm’ above the superior nuchal lines.
• The epicranial aponeurosis is attached to their medial parts.
• The occipital belly of occipitofrontalis originates on each side from its lateral 2/3rd.

4. Mastoid Foramen

• It is located near the occipitomastoid suture.
• It opens internally into the sigmoid sulcus.
• The following structures transverse through it:
• Meningeal branch of occipital artery.
• Emissary vein.

5. Occipital Point

• It is situated in the midline a little above the inion.
• It is farthest from the glabella.

Norma Occipitalis Applied anatomy

Craniostenosis is a condition in which there is premature closure of the cranial sutures.

1. When lambdoid and coronal sutures are involved, the skull grows vertically leading to the tower skull.
2. The squamous part of the occipital bone is prone to both fissured and depressed fractures.
3. A crack in the inner table of the squamous part of the occipital bone may damage the large diploic vein and produce a small epidural haematoma.
4. Almost invariably fractures of the occipital squama in children are associated with rupture of the dura mater.
5. A gap in the occipital squama is usually filled with tantalum or titanium due to a lack of regeneration in this part whose periosteum is devoid of a cambium layer.
6. The inner table of cranial vault bones (including the squamous part of the occipital bone) is more brittle than the outer table, therefore, fractures are more extensive in the inner table.

Skull General Features Introduction

1. The skull is the skeleton of the head.
2. Cranium means skull minus the mandible.
3. Neurocranium is the upper part of the skull that encloses the brain.
4. The calvaria is the upper part of the cranium. It is also called the skull cap.
5. The facial skeleton (viscerocranium) is the skull minus the calvaria.
6. The facial skeleton is further divided into an upper facial skeleton and a lower facial skeleton (mandible).

Neurocranium

The bones which constitute the neurocranium can be classified as:

1. Paired Bones

• These include:
• Parietal bones.
• Temporal bones.

2. Unpaired Bones

These include:

• Frontal bone.
• Occipital bone.
• Sphenoid.
• Ethmoid.

Facial Skeleton (Viscerocranium Or Splanchnocranium)

It is composed of the following bones:

1. Paired Bones

These include:

• Maxillae.
• Zygomatic bones.
• Nasal bones.
• Lacrimal bones.
• Palatine bones.
• Inferior conchae.

2. Unpaired Bones

These include:

• Mandible.
• Vomer.

Anatomical Position Of Skull

The skull can be kept in a normal anatomical position by Reid’s baseline or Frankfurt’s horizontal plane.

1. Reid’s Baseline

It is a horizontal line formed by the joining of the infraorbital margin with the center of the external acoustic meatus.

2. Frankfurt’s Horizontal Plane

It is marked by the horizontal line joining the infraorbital margin with the upper margin of the external acoustic meatus.

Note:

• Remember that Reid starts with ‘R’ which also stands for ‘Round’ opening of the external acoustic meatus, thus Reid’s baseline passes through the rounded external acoustic meatus.
• On the other hand ‘Frankfurt’ starts with ‘F’ which also stands for ‘Fly’ and anything that has to fly has to be above, therefore, Frankfurt’s horizontal plane passes above the external acoustic meatus.

Skull Applied Anatomy

Clinically the entire front of the skull is considered to be a facial skeleton. It is further divided into the following three parts:

1. Upper Facial Skeleton

• It forms the skeleton of the forehead.
• It is comprised of frontal bone.

2. Lower Facial Skeleton

• It forms the skeleton of the lower jaw.
• It is comprised of a mandible.

3. Middle Facial Skeleton

It is the complex middle 3rd of the facial skeleton. The region is of great clinical importance because the multiple bones constituting it are frequently involved in fractures.

1. Boundaries

• Upper: Transverse line passing through frontozygomatic, frontomaxillary, and frontonasal sutures.
• Lower: Incisal edge and occlusal plane.
• Posterior: Spheno-ethmoidal junction.

2. Bones Involved In The Fractures Of The Middle 3rd Of The Facial Skeleton Are As Follows:

• Maxillae.
• Palatine bones.
• Zygomatic bones.
• Zygomatic processes of temporal bones.
• Nasal bones.
• Lacrimal bones.
• Vomer.
• Ethmoid.
• Pterygoid processes of sphenoid.

3. Subdivisions

The middle 3rd facial skeleton can be divided into:

• Lateral middle 3rd also called zygomatico- maxillary part.
• Central middle 3rd, which can be further subdivided into:
  • Alveolar part.
  • Dentoalveolar complex.
  • Nasomaxillary part.
  • Nasoethmoidal part.

General Considerations Of Bone Definition

Bone is the hard part of the body providing a dynamic framework for it.

Bone Properties

Bone Functions

1. Bones provide a framework for the body.
2. Bones accord shape to the body.
3. Bones act as levers for muscles and, therefore, help in the movements of the body.
4. Bones provide protection to a number of viscera, for example. brain, lungs and heart.
5. Bone is the site of blood formation.
6. Bone plays an important role in the immune responses of the body by producing cells of the reticuloendothelial system.
7. Bones are storehouses of calcium and phosphorus

Bone Chemical Composition

Bone is one-third organic and two-thirds inorganic. Inorganic calcium salts [calcium phosphate, calcium carbonate and crystals of hydroxyapatite, i.e. Ca₁₀ {P0₄}₄ (OH)₂] make it hard and rigid. the organic connective tissue(collagen fibre) makes it tough and resilient. The collagen protein of collagen fibres is characterised by hydroxyproline amino acid.

Structure Of Bone

1. Macroscopically

There are two types of bones, spongy or cancellous bone and compact or dense bone. The outer part of all bones is made up of compact bone. Cancellous bone fills up the interior of the except the following.

In the shaft of a long bone, it is replaced by a medullary cavity. This is filled with red marrow in newborns but replaced by yellow or fatty marrow in adults.

• In the maxilla, sphenoid, ethmoid and frontal bones, it is replaced by large air spaces called sinuses.
• In many places, the cancellous bone is replaced by marrow. The red marrow is active in hematopoiesis. Yellow marrow is mainly inert and fatty.
• The flat bones of the skull cap (calva) have a spongy bone (diploe) sandwiched between two compact bones called outer and inner tables. Red marrow persists in spongy bone throughout life.

The compact bone is more radio-opaque, while the spongy bone is relatively more radiolucent. In the radiograph, therefore, the compact bone looks whiter than the spongy bone which appears relatively darker.

2. Microscopically

Microscopically the bones can be classified into four types:

• Lamellar Bone: Most of the mature human bones, both compact and spongy, are of this type.
• Fibrous Bone: It is found in early foetuses.
• Dentine: It is found in teeth.
• Enamel: It is found in teeth.

The compact bone shows typical Haversian systems each of which is comprised of a central canal along the long axis of bone surrounded by concentric lamellae.

• Volkmann’s canals connect the adjacent Haversian canals. Osteocytes are located in the small spaces (lacunae) between adjacent lamellae.
• The cytoplasmic processes of osteocytes extend into canaliculi diverging from lacunae. Circumferential lamellae adjoin the surface or medullary cavity of long bones. Interstitial lamellae fill the spaces between Haversian systems.
• Spongy bone differs from ct fa ‘lacking Haversian systems’ and ‘having Spongy bone differs from compact bone in irregularly arranged bony lamellae’.
• Periosteum, the outer covering of bone, consists of an external collagen fibrous layer and an inner osteogenic cellular layer.

Collagen fibres from the periosteum piercing the bone are called Sharpey’s fibres. The periosteum has a rich nerve supply which makes it the most sensitive part of the bone.

Classification Of Bones

Bones may be classified according to their development, shape or location.

1. Phylogenetic classification

From a comparative anatomy point of view skeleton may be classified as:

Exoskeleton

Nails, hairs and enamel of teeth are the only remnants of exoskeleton observed in human beings.

Endoskeleton

It includes most of the bones.

2. Developmental Classification

Developmentally bones may be classified as:

1. Cartilaginous bones.
2. Membranous bones

3. Morphological classification

According to shape, the bones may be classified as:

• Long Bones – Femur, humerus
• Short Bones – Carpal and tarsal bones
• Miniature Long– Metacarpals and bones metatarsals
• Flat Bones – Parietal bone
• Irregular Bones – Hip bone
• Pneumatic Bones – Maxilla, ethmoid, sphenoid and frontal bone.

4. Regional classification

Bones may be classified regionally as:

Axial Bones

It includes 80 bones as shown below.

• Skull bones – 22
• Vertebrae – 26
• Ribs – 24
• Sternum – 1
• Auditory ossicles – 6
• Hyoid – 1

Appendicular Bones

It includes 126 bones which are further subgrouped as:

• Upper limb bones – 64
• Lower limb bones – 62

The total number of bones is 206

5. Miscellaneous classification

Accessory Bones

An accessory bone is a small piece of bone which develops from a separate centre of ossification but fails to unite with the main mass of bone, for example. sutural (Wormian) bones and interparietal bones.

Sesamoid Bones

A sesamoid bone is a bone usually small, developing in the tendon of a muscle, ligament or joint capsule. they ossify after birth and are devoid of periosteum. sesamoid bones possibly resist pressure, they alter the direction of pull of muscle and minimize the friction.

Blood Supply Of Bones

1. Short Bones: These are supplied by numerous periosteal vessels.
2. Vertebrae: The body of the vertebra is supplied by the anterior and posterior vessels. The vertebral arch is supplied by large vessels entering through the bases of transverse processes.
3. Ribs: These are supplied by nutrient and periosteal vessels.
4. Flat Bones: These are supplied by nutrient and periosteal vessels.

Nerve Supply Of Bones

Nerves accompany the blood vessels of bone. Periosteal nerves are sensory (carry pain) while others are vasomotor.

Lymphatic Drainage Of Bones

Lymphatics have not been demonstrated within bone but these are very much present in the periosteum which drains into regional lymph nodes.

Ossification Of Bones

Bones ossify from centres of ossification from where the laying down of long lamellae starts by osteoblasts.

1. Centres of ossification may be primary or secondary. The primary centre appears before birth, usually during the 8th week of intra-uterine life and gives rise to the diaphysis. The secondary centre appears at or after birth and gives rise to epiphysis.
2. Most of the long bones have epiphysis at each end but the growth in length occurs mainly at one end. This end is called the growing end.
3. Here, the epiphysis usually appears earlier and fuses with the body later than that at the non-growing end.

Applied Anatomy Of Bones

1. Organic matter in the bone is greatest in childhood making it more flexible.
2. In rickets and osteomalacia, there is inadequate calcium in bone leading to knocked knees and bowlegs.
3. Metaphysis is the most common site of infection due to rich vascular anastomosis which has relatively fewer lymphocytes and has a hairpin loop arrangement of blood vessels.
4. Capsular relations of metaphysis are clinically important. The inflammation of intra-articular metaphysis may result in septic arthritis, e.g. upper end of the femur.
5. Injury of the growing ends of long bones. is more dangerous in young children because it will directly affect their growth.
6. In certain conditions example. pernicious anaemia) the yellow marrow is replaced by red marrow to enhance the formation of red blood cells.
7. Some interesting facts regarding fractures in young children are as follows:
   • It is more common due to carefree activities.
   • Green-stick fracture (incomplete fracture with bending) is common in children due to excessive elasticity in bone.

In old age, there is generalized skeletal atrophy called osteoporosis which makes the bone very weak. Osteoporosis is relatively more common in females, therefore, fracture of the femoral neck is more common in elderly ladies.

1. In sternal puncture, the needle pierces the compact bone to reach the central spongy bone from where red marrow is aspirated for haematological examination. The same procedure is used for bone marrow transplantation.
2. For perfect healing, the fractured ends of a bone should be properly aligned. This is called reduction. Healing is difficult and defective if the bony ends are mobile. To make them immobile, a hard cast is made around the fractured site and adjacent joints. This is called plaster immobilization.
3. The age of a person can be determined by observing the ossification centres of the bones and their fusion in the radiographs. This is of medicolegal importance.

Part of a bone may be deprived of blood supply after fracture. This leads to avascular necrosis. The best example of avascular necrosis is the head of the femur after a fracture of the neck.

1. A fibrous capsule is the most sensitive structure in a joint.
2. A bone cyst is the most common cause of pathological fracture in children.
3. Increased density in metaphysis is seen in hypervitaminosis.
4. Senile osteoporosis is radiologically manifested only when 30% of the skeleton has been lost.
5. Multiple bone fracture in a newborn is seen in osteogenesis imperfecta.
6. Two interesting facts regarding Ewing’s tumour are:

• • It arises from diaphysis.
  • It is very sensitive to radiotherapy.