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Skull

The human skull (Latin: cranium) is the skeleton of the head composed of 22 separate bones joined together primarily by sutures. Most of the bones have pairs. 

Human skull, four views (anterior, lateral, inferior, posterior)
The skull by Anatomy Next

 

The brain is located within the skull and connected with other anatomical structures by the nerves and blood vessels going through many foramina (openings), and the largest foramen of the skull called the foramen magnum.

The primary function of the skull is to provide protection for the brain and the sensory organs connected with it. 

The skull also incorporates the upper parts of the digestive (oral cavity, mouth) and respiratory tracts (nasal cavity, nose). It also supports the soft tissue and facial anatomical structures of the head.

 

Learn more about "Visual Guide to The Anatomy of The Skull"

Parts of the skull

The human skull consists of two main parts:

  • the braincase called the neurocranium,
  • and the facial skeleton called the viscerocranium

Several bones forming the neurocranium and viscerocranium contain air-filled cavities called the paranasal sinuses. These sinuses help to create resonance with the voice and aid in warming and moistening of the inhailed air. 

The skull may also be divided into a skullcap (or calvaria, skull vault) and cranial base

 

Neurocranium

The neurocranium encloses the brain, including the cerebrum, cerebellum, brainstem, and sensory organs connected with the brain.

Bones of the neurocranium contain grooves for arteries, as well as depressions visible on the inner surfaces corresponding to the convolutions of the brain (cerebral gyri), and these depressions are called the digitate impressions and impressions of cerebral gyri.

 

Colored bones of neurocranium, part of skull
Bones of the neurocranium by Anatomy Next

 

Bones of neurocranium

The neurocranium is formed by two paired and four unpaired bones.

 

The unpaired bones are:

  • Sphenoid - situated in the middle of the skull towards the front, it forms a rear of the orbit;
  • Frontal bone - forms the forehead;
  • Occipital bone - forms the base part of the skull;
  • Ethmoid - located in front of the skull and separating the nasal cavity from the brain. 

The paired bones of the neurocranium are:

  • Temporal bones - located to the base and sides of the skull,
  • Parietal bones - superior to temporal bones, make up the roof part and sides of the skull.

The sphenoid, frontal, and ethmoid bones contain sinuses.

 

Viscerocranium

The viscerocranium is the part situated anteriorly from the neurocranium. It forms the facial skeleton and supports the soft tissue of the face.

Colored bones of viscerocranium, facial skeleton, part of skull, frontal view
Bones of the viscerocranium by Anatomy Next

 

Bones of viscerocranium

The viscerocranium is formed by six paired and two unpaired bones.

The paired bones of the viscerocranium are:

  • Lacrimal bones - these are the smallest bones of the face, and they form the medial wall of the orbit;
  • Nasal bones - located in the midline of the face and form the bridge part of the nose;
  • Inferior nasal conchae - located within the nasal cavity;
  • Zygomatic bones - form the cheeks and also contribute to the orbits;
  • Maxillae - also located in the midline of the face, both bones are fused in a single bone called the maxilla, which forms the upper jaw and contributes to the hard palate;
  • Palatine bones - both bones fuse in the midline and participate in forming the hard palate, which forms the floor of the nasal cavity and the roof of the mouth.

And the unpaired bones of the viscerocranium are:

  • Vomer - forms the posterior part of the nasal septum;
  • Mandible - forms the lower jaw and is connected to the skull with the temporomandibular joint.

The maxilla contains a paranasal sinus (maxillary sinus), and it is the most prominent immovable bone of the facial skeleton.

Sometimes the unpaired hyoid bone is also classified as a bone of the viscerocranium, although located in the upper neck region, and it is connected with the skull with the help of ligaments. 

So together with the hyoid bone, 23 bones form the skull (not including the tiny bones of the middle ear - the auditory ossicles).

 

Calvaria

As mentioned above, the skull may also be divided into the skullcap or cranial roof called the calvaria and the cranial base

The calvaria is the top part of the neurocranium and covers the cranial cavity, which contains the brain.  

The calvaria is robust and surrounds and protects the brain, while the cranial base is more delicate, composed mainly of thin-walled bones.

The skullcap is formed by the parietal, frontal, and occipital bones joined together with sutures. To be more precise, the squamous part of the frontal, squamous part of occipital bone above the superior nuchal line, parietal bones, squamous portion of the temporal bone, and the great wing of sphenoid bone - these are the structures forming the calvaria.

 

Boundary between calvaria and cranial base

The following structures mark the border between the calvaria and cranial base:

  • Supraorbital margin of the frontal bone
  • Zygomatic process of the frontal bone
  • Infratemporal crest on the greater wing of the sphenoid
  • Zygomatic process of the temporal bone
  • Mastoid process of the temporal bone
  • Superior nuchal line of the occipital bone
  • External occipital protuberance

 

Cranial cavity

The space within the skull is known as the cranial cavity or the intracranial space

Cranial cavity, skull, calvaria removed
Cranial cavity by Anatomy Next

The cranial cavity contains the brain, the intracranial portions of the cranial nerves, blood vessels supplying the brain with arterial blood (arteries) and draining the venous blood (veins), the meninges covering the brain, and the cerebrospinal fluid.

 

Auditory ossicles

There are also three tiny bones called the auditory ossicles. They are known as the malleus, incus, and stapes, and they are located within each middle ear housed in the skull, specifically within the right and left temporal bones.

The smallest bone in the human body is the stapes.

As mentioned above, the skull is formed by 22 bones. Including the hyoid bone, it is 23 bones. 

Then, actually, if auditory ossicles are also included, in total, there are 29 bones forming the skull, as there are three pairs of auditory ossicles (22+1(hyoid bone) + 6 (3 pairs of auditory ossicles)).

 

Junctions of skull

The human skull contains two main junction types:

  • Synarthroses or synarthrodial joints - junstions that allow no movement;
  • Diarthroses or diarthrodial joints, allowing free activities.

Sutures and synchondroses (cartilaginous joints) are classified as a synarthrodial joint type, while the only joint with free movements called the temporomandibular joint belongs to diarthrodial joints.

Sutures

Almost all bones of the skull are connected with the help of fibrous junctions called sutures. Sutures are rigid joints between two or more bones. Only the skull contains sutures.

The bones grow and fuse during fetal and childhood development, forming a single skull. However, the mandible remains separate from the rest of the skull.

There are around 33 sutures in the human skull. 

Sutures of the skull (coloerd), postero-lateral aspect of skull
Most important sutures of the skull by Anatomy Next

The most important sutures in the skull are the following:

  • Coronal suture - between the frontal and the two parietal bones;
  • Sagittal suture - a median suture situated between the right and left parietal bones;
  • Lambdoid suture - between the occipital and the two parietal bones;
  • Squamous suture - between the parietal bone and temporal bone.

 

Sutures of the skull (colored), posterior view of skull
Most important sutures on the posterior side of the skull by Anatomy Next

Most sutures between bones forming the viscerocranium are called plane sutures, as the edges of the articulating bones are relatively smooth. 

For example, the bony base of the hard palate is formed by two horizontal plates of palatine bone and two palatine processes of the maxilla. Both parts are connected by a sagittal oriented median suture in the midline and frontal oriented transverse palatine suture located between the anterior two-thirds and posterior one-third of the hard palate.

Other sutures of the skull include the following: 

  • Spheno-zygomatic suture
  • Sphenofrontal suture
  • Spheno-squamous suture
  • Frontonasal suture
  • Lacrimomaxillary suture
  • Nasomaxillary suture
  • Frontozygomatic suture

 

Fontanelles

In newborn babies, sutures are fused incompletely, and between the bones are membranous gaps called the fontanelles allowing the child to pass through the birth canal. 

The fontanelles slowly close by a process called intramembranous ossification.

Fontanelles can be divided into two groups - major and minor fontanelles.

Major fontanelles

There are two major fontanelles.

The frontal or anterior fontanelle is the largest one, and it resembles a diamond- shape. It is located at the junction of the sagittal and coronal sutures. It stays open until the age two.

The occipital or posterior fontanelle is triangular-shaped. It is situated at the junction of the lambdoid and sagittal sutures. It closes during the first three months after birth.

Minor fontanelles

Smaller fontanelles are situated on the sides of the skull. These are the sphenoidal and mastoid fontanelles.

The sphenoid fontanelle is located between the sphenoid, temporal, frontal, and parietal bones. 

But the mastoid fontanelle is located between the temporal, occipital, and parietal bones. 

Both mentioned fontanelles have pairs.

 

Temporomandibular joint

There is only one synovial joint between the bones of the skull, and it is the temporomandibular joint (TMJ) formed between the head of the mandible and the mandibular fossa, and the articular tubercle of the temporal bone. 

 

Temporomandibular joint (TMJ), lateral aspect of skull
Temporomandibular joint (TMJ) by Anatomy Next

 

The temporomandibular joint is classified as the diarthrodial joint of the skull.

It is located anterior to the outer ear, to be more precise - anterior to the tragus of the ear on the lateral side of the face.

An articular disc separates the articular surfaces, so they do not have contact with each other. With the help of the disc, the joint is divided into two cavities or compartments. And a fibrous articular capsule surrounds the joint.

Several ligaments help in joint stabilization and fixation. They are the lateral ligament, sphenomandibular ligament, as well as the stylomandibular and temporomandibular ligaments.

The TMJ is divided into two floors, and the movement takes place in both, so it acts as a multi-axis joint.

The movements permitted by the TMJ include depression and elevation of the lower jawmoving the jaw forward and backwardside to side, as well as rotating movements, for example, for chewing.

 

Synchondroses

Besides sutures and the temporomandibular joint described above, the skull also contains several synchondroses between skull-forming bones.

Synchondroses are cartilaginous joints and belong to synarthrodial joint type.

For example, there is a synchondrosis between the sphenoid and occipital bone, which is called the sphene-occipital synchondrosis

Other synchondroses of the skull include:

  • Spheno-petrosal synchondrosis
  • Petro-occipital synchondrosis
  • Spheno-ethmoidal synchondrosis
  • Inter-sphenoid synchondrosis
  • Anterior intra-occipital synchondrosis
  • Posterior intra-occipital synchondrosis

 

Muscle attachments on skull

The bones of the skull provide attachment for muscles of the head and neck. 

The facial muscles arise from the bones of the facial skeleton. 

But the base of the skull serves as attachment site for the following muscle groups:

  • Masticatory muscles
  • Extrinsic muscles of the tongue
  • Superior constrictor of the pharynx
  • Muscles of the soft palate

 

Paranasal sinuses

Several bones of the skull contain air-filled spaces surrounding the nasal cavity known as the paranasal sinuses.

There are four sets of paired paranasal sinuses named according to the bone they are located, and these are:

  • Maxillary sinus - the most significant sinus, it surrounds the nasal cavity as it is located under the orbits laterally to the nasal cavities;
  • Frontal sinus - triangular-shaped and located within the frontal bones in the forehead above the eyes, the most superior sinus;
  • Sphenoidal sinus - located within the body of the sphenoid bone therefore located behind the eyes and nasal cavity, the most posterior located sinus;
  • Ethmoid sinus (known as ethmoidal air cells) - situated within the ethmoid bone, between the orbits and in the superior aspect of the nose.

 

Frontal view of skull, paranasal sinuses (maxillary, frontal)
Paranasal sinuses (maxillary sinus and frontal sinus) by Anatomy Next

 

Functions of paranasal sinuses

The paranasal sinuses are extensions of the respiratory tract, and they all open with apertures in the walls of the nasal cavity. 

Functions of the paranasal sinuses include:

  • Reducing weight of the front of the skull and bones of the face;
  • Humidifying and heating inspired air;
  • Buffering against blows;
  • Regulation of gas pressures;
  • Defense against various antigens;
  • Aiding in voice resonance.

 

Openings of skull

The skull is rich with openings, including foramina and canals that serve primarily as passages for cranial nerves, branches, and accompanying blood vessels allowing them to connect one anatomical structure with another. 

Nerves and vessels form neurovascular bundles, which may be harmed at the sites of skull openings by pathological process or trauma.

The frontal, sphenoid, ethmoid, temporal, occipital, palatine bones, and the maxilla contain these foramina.

The largest opening of the skull is the foramen magnum in the cranial base, through which the spinal cord as an extension of the medulla oblongata exits the cranial cavity. 

The foramen magnum is a single opening, while most of the foramina of the skull are two (bilateral). Some are multiple in number, for example, the foramina of the cribriform plate.

Listed below are essential openings in bones of the skull, with the parts of the skull they connect and the structures they carry.

Frontal bone:

  • Supraorbital foramen or notch - located at the central portion of the superior orbital margin; connects the cranial cavity with the forehead region on the external face; transmits the supraorbital nerve, artery, and vein.
  • Frontal foramen or notch - located medially to the supraorbital foramen; it transmits the supratrochlear artery and medial branch of the supraorbital nerve.
  • Foramen cecum - connects the cranial cavity with the nose region; transmits an emissary vein from the nose to the superior sagittal sinus.

Ethmoid bone:

  • Foramina of the cribriform plate  - small openings in the cribriform plate; connect the nasal cavity with the anterior cranial fossa; transmits bundles of the olfactory nerves (CN I).
  • Anterior ethmoidal foramen - connects the anterior cranial fossa with the orbit; transmits the anterior ethmoid nerve, artery, and vein.
  • Posterior ethmoidal foramen - connects the anterior cranial fossa with the orbit; transmits the posterior ethmoidal nerve, artery, and vein.

Sphenoid bone:

  • Optic canal - in the lesser wings; connects the middle cranial fossa with the orbit; transmits the optic nerve (CN II) and ophthalmic artery.
  • Superior orbital fissure - between the body, lesser and greater wing; connects the middle cranial fossa with the orbit; transmits the superior ophthalmic vein (a branch of the inferior ophthalmic vein) and several nerves including the oculomotor (CN III), trochlear (CN IV), lacrimal, frontal and nasociliary nerves arising from the ophthalmic nerve (CN V1), as well as the abducens nerve (CN VI).
  • Foramen rotundum - in the anterior part of the greater wing of the sphenoid; connects the middle cranial fossa with the pterygopalatine fossa; transmits the maxillary nerve (CN V2).
  • Foramen ovale - posterior from the foramen rotundum in the greater wing; connects the middle cranial fossa with the infratemporal fossa; transmits the mandibular nerve (CN V3), lesser petrosal nerve, accessory meningeal artery, emissary vein connecting the cavernous sinus with the pterygoid plexus.
  • Foramen spinosum - posterior and on sides from the foramen ovale in the greater wing of the sphenoid, connects the middle cranial fossa with the infratemporal fossa; transmits the spinous branch of the mandibular nerve (CN V3), as well as the middle meningeal artery, and vein.

Temporal bone:

  • Internal acoustic meatus - in the petrosal part; connects the posterior cranial fossa with the inner ear; transmits the facial nerve (CN VII), vestibulocochlear nerve (CN VIII), vestibular ganglion, and the labyrinthine artery.
  • Stylomastoid foramen - in the petrosal part between the styloid and mastoid processes; connects the posterior cranial fossa with the external cranial base; transmits the facial nerve (CN VII) and the stylomastoid artery.
  • Carotid foramen - in the petrosal part; connects the middle cranial fossa with the external cranial base; transmits the internal carotid artery and the carotid plexus of nerves.

Occipital bone:

  • Hypoglossal canal - located in the condylar part of the occipital bone; connects posterior cranial fossa with external cranial base; transmits hypoglossal nerve (CN XII).
  • Foramen magnum - the most inferior part of the occipital bone; connects the posterior cranial fossa with the external cranial base; transmits the rostral part of the medulla oblongata with three meninges, ascending fibers of the spinal root of the accessory nerve (CN XI), anterior and posterior spinal arteries, vertebral arteries, tectorial membrane, and alar ligaments.

Maxilla:

  • Incisive foramen - in the palatine process of the maxilla on the median line posterior to incisor teeth, leads to the incisive canal that connects the oral cavity with the nasal cavity; transmits the nasopalatine nerve (branch of CN V2), greater palatine artery, and vein.
  • Infraorbital foramen - located in the body part of the maxilla under the infraorbital margin, opens on the external face; transmits the infraorbital nerve, artery, and vein.
  • Alveolar foramina - located in the body part of the maxilla; contain alveolar canals through which nerves and vessels pass to reach the teeth.

Palatine bone:

  • Greater palatine foramen - located in the horizontal plate of the palatine bone; connects the oral cavity with the pterygopalatine fossa; transmits the greater palatine nerve, artery, and vein.
  • Lesser palatine foramina - located in the horizontal plate of the palatine bone posterior to the greater palatine foramen; connects the oral cavity and the pterygopalatine fossa; transmits the lesser palatine nerves, arteries, and veins.

Mixed bones:

  • Sphenopalatine foramen - formed between the sphenoid and palatine bones; connects the nasal cavity with the pterygopalatine fossa; transmits the nasopalatine nerve (branch of CN V2), superior posterior nasal branches of the maxillary nerve (CN V2), sphenopalatine artery, and vein.
  • Inferior orbital fissure - located inferior to the superior orbital fissure in the floor of the orbit; formed between the sphenoid bone and maxilla; connects the orbit with the pterygopalatine and infratemporal fossae; transmits the infraorbital nerve (branch of the maxillary nerve, CN V2), zygomatic nerve (branch of CN V2), orbital branches of the pterygopalatine ganglion (originating from CN V2), inferior ophthalmic vein, emissary veins connecting the previous vein with pterygoid venous plexus, infraorbital artery, and vein.
  • Foramen lacerum - between the sphenoid, temporal bone, and basilar part of occipital bone; connects the middle cranial fossa with the external cranial base; transmits the nerve and artery of the pterygoid canal, meningeal branch of the ascending pharyngeal artery, emissary veins from the cavernous sinus to the pterygoid venous plexus.
  • Jugular foramen - formed between the petrous part of the temporal bone and the occipital bone; connects the posterior cranial fossa with the external cranial base; transmits the glossopharyngeal nerve (CN IX), vagus nerve (CN X), accessory nerve (CN XI), inferior petrosal sinus, sigmoid sinus, and meningeal branches from the occipital and ascending pharyngeal arteries.

 

Skull topography

The skull is divided into several important topographical regions, including the:

  • Cranial base (divided into internal and external)
  • Temporal fossa
  • Infratemporal fossa
  • Pterygopalatine fossa
  • Orbit
  • Nasal cavity

Most of these regions are formed by different cranial fossae.

 

Cranial base

The cranial base, also known as the base of the skull or skull base, is the most inferior part of the skull forming the floor of the cranial cavity. 

The cranial base is formed by six different bones - the ethmoid, sphenoid, occipital, frontal, paired parietal and temporal bones. 

The cranial base can be inspected from two sides - from inside and outside. 

The inner aspect of the skull base is known as the internal cranial base and is topographically divided further into three regions - cranial fossae

The outside of the cranial base is called the external cranial base.

 

Internal cranial base

The internal cranial base is bounded anteriorly by parts of the frontal, sphenoid and ethmoid bones. 

Laterally, it borders with the parietal and temporal bones and posteriorly with the squamous part of the occipital bone. 

The internal cranial base contains the brain, the intracranial parts of cranial and spinal nerves, meninges, blood vessels, and cerebrospinal fluid.

The internal cranial base is subdivided into three distinct regions or fossae:

  • Anterior cranial fossa
  • Middle cranial fossa
  • Posterior cranial fossa

Each cranial fossa houses a different part of the brain.

Internal cranial base, cranial fossae (anterior, middle, posterior)
Internal cranial base and cranial fossae by Anatomy Next

 

Anterior cranial fossa

The anterior cranial fossa lies at the highest and most anterior level of the internal cranial base. It is made of three bones: ethmoid, frontal, sphenoid.

It is formed by the cribriform plate of the ethmoid bone, the orbital part of the frontal bone, and the lesser wings of the sphenoid.

Boundary line

  • Anteriorly and laterally, the anterior cranial fossa is bounded by the inner surface of the frontal bone;
  • Posteriorly, it is bounded by the sphenoid bone;
  • Postero-medially it is bounded by the anterior border of the chiasmatic sulcus and postero-lateral by the lesser wings of the sphenoid.

Content of the fossa

The anterior cranial fossa contains the frontal lobe of the cerebral cortex, the olfactory bulb and olfactory tract, and the orbital gyri.

Foramina

The anterior cranial fossa presents the following openings:

  • Cribriform foramina or the olfactory foramina
  • Foramen cecum 
  • Anterior and posterior ethmoidal foramina

 

Middle cranial fossa

The middle cranial fossa lies deeper within the skull base. It is wider than the anterior cranial fossa. It is butterfly-shaped and located in the center of the cranial floor. The middle cranial fossa is made up of sphenoid and temporal bones.

The middle cranial fossa is formed by the body and greater wings of the sphenoid, the squamous part of the temporal bone, and the anterior surface of the petrous portion of the temporal bone.

Boundary line

The borders of the middle cranial fossa are formed anteriorly by the anterior margin of the chiasmatic groove, posterior margins of the lesser wings, and part of the body of the sphenoid.

Posteriorly, it is bounded by the superior borders of the petrous part of the temporal bone and the dorsum sellae of the sphenoid.

Laterally, the boundary line goes along the squamous part of the temporal bones, greater wings of the sphenoid bone, and part of parietal bones.

Content of the fossa

The middle cranial fossa of the skull accommodates the pituitary gland and the temporal lobes of the cerebral cortex.

Foramina

The middle cranial fossa contains the following openings:

  • Optic canal
  • Superior orbital fissure
  • Foramen rotundum
  • Foramen ovale
  • Foramen spinosum
  • Carotid canal
  • Foramen lacerum
  • Hiatus of the greater petrosal nerve
  • Hiatus of the lesser petrosal nerve

 

Posterior cranial fossa

The posterior cranial fossa lies at the lowest level of the internal cranial base and is the largest of the three cranial fossae. It is made of the occipital, temporal, and parietal bones.

It is formed by all parts of the occipital bone, the posterior surface of the petrous portion of the temporal bone, and the mastoid angle of the parietal bone.

Boundary line

The posterior cranial fossa is bounded anteriorly by the dorsum sellae, the superior margin of the petrous part of the temporal bone.

Posteriorly, it is bounded by the squamous part and internal occipital protuberance of the occipital bone and the groove for the transverse sinus.

Laterally, the boundary line goes by the petrous and mastoid parts of the temporal bone and by the lateral parts of the occipital bone.

Content of the fossa

The brainstem and cerebellum lie within the posterior cranial fossa of the skull.

Foramina

The posterior cranial fossa contains several openings:

  • Foramen magnum
  • Hypoglossal canal
  • Condyloid foramen
  • Jugular foramina
  • Mastoid foramen
  • Internal acoustic meatus
  • Opening of the vestibular canaliculus

 

External cranial base

The external cranial base is the outer aspect of the skull base extending from the superior incisor teeth to the superior nuchal line of the occipital bone. 

External cranial base with anatomical landmarks
External cranial base by Anatomy Next

The external cranial base can be subdivided into anterior, middle, posterior, and two lateral parts.

Anterior part

The anterior part of the external cranial base is comprised of the superior alveolar arch, the bony palate, and the choanae. 

  • Superior alveolar arch. The alveolar process of the maxilla forms the superior alveolar arch, and it contains the dental alveoli or sockets for the teeth.  
  • Bony palate. The bony palate is formed by the palatine process of the maxillae anteriorly and horizontal plates of the palatine bones posteriorly, median palatine suture in the midline, and the frontally oriented transverse palatine suture located between the anterior two-thirds and posterior one-third of the hard palate. The hard palate forms the roof of the oral cavity and the inferior wall of the nasal cavity.Openings presented on the bony palate include the incisive foramen and greater and lesser palatine foramina
  • Choanae. The choana is a paired posterior aperture of the nasal cavity that opens into the nasopharynx. It is delimited by the horizontal plate of the palatine bone, a medial plate of the pterygoid process, the body of the sphenoid, and the vomer.

Middle part

The middle part of the external cranial base is formed by the body of the sphenoid, the petrous portion of the temporal bones, and the basilar part of the occipital bone. 

It extends from the choanae anteriorly to the anterior margin of the foramen magnum posteriorly. 

The middle part of the external cranial base presents with several openings, including the foramen lacerum, pterygopalatine fissure, foramen ovale, foramen spinosum, and the carotid canal.

Posterior part

The occipital bone mainly forms the posterior part of the external cranial base

It features such openings as the single foramen magnum and the paired jugular foramen, hypoglossal canal, condylar canal, as well small openings - the mastoid canaliculus and the canaliculus for the tympanic nerve.

Lateral parts

Each lateral part of the external cranial base consists of the zygomatic arch and the infratemporal fossa anterior, but the mandibular fossa, the tympanic part of the temporal bone, and the styloid and mastoid processes are located posteriorly. 

The lateral parts of the external cranial base present such openings as the external acoustic meatus, petro-tympanic fissure, stylomastoid foramen, and other smaller apertures.

 

Temporal fossa

The temporal fossa is a depressed area on each side of the skull bounded by the temporal lines and the zygomatic arch

It is formed by the temporal, sphenoid, parietal, and frontal bones.

The temporal fossa is located superiorly to the infratemporal fossa.

Boundary line

The area known as the temporal fossa is bordered anteriorly by the frontal process of the zygomatic bone and the zygomatic process of the frontal bone.

Superiorly and posteriorly, this fossa is bounded by both temporal lines (superior and inferior) but inferiorly - by the infratemporal crest on the greater wing of the sphenoid and the zygomatic arch.

Laterally, the fossa is bounded by the temporal fascia.

Medially, it borders with the frontal, parietal, temporal, and sphenoid bones.

The anterior wall is formed by the temporal surface of the frontal bone and the temporal surface of the zygomatic bone.

The medial wall is formed by the temporal surface of the frontal, parietal, and temporal bones and the temporal surface of the greater wing of the sphenoid bone. 

The zygomatic arch forms the lateral wall of the temporal fossa.

Content of the fossa

The temporal fossa contains the temporal muscle, as well as several nerves and blood vessels

The nerves found in this area include the zygomaticotemporal nerve, deep temporal nerves, and the temporal branch of the facial nerve

The deep temporal arteries, superficial temporal artery, superior temporal artery, and corresponding veins are also found in the temporal fossa.

The temporal fascia has an attachment to the superior temporal line, while the temporal muscle attaches to the inferior temporal line.

Foramina

The temporal fossa contains the zygomaticotemporal foramen.

 

Infratemporal fossa

The infratemporal fossa is an irregular-shaped space situated on each side of the skull below the temporal fossa and deep to the ramus of the mandible. 

Skull with infratemporal fossa (borders marked in red)
Infratemporal fossa by Anatomy Next

It is located between the base of the skull, lateral pharyngeal wall, and ramus of the mandible.

The infratemporal fossa communicates with the temporal fossa via space to the zygomatic arch. 

It also communicates with the pterygopalatine fossa via the pterygomaxillary fissure.

Boundary lines

Superiorly, the infratemporal fossa is bordered by the infratemporal surfaces of the temporal bone and the greater wing of the sphenoid but inferiorly by the medial pterygoid muscle.

Laterally, it is bounded by the zygomatic arch, medial surface, and condylar process of the ramus of the mandible, and medially by the lateral plate of the pterygoid process and the tensor veli palatini, levator veli palatini, and superior constrictor muscles. 

Posteriorly, the infratemporal fossa is bounded by the carotid sheath, while anteriorly - by the posterior border of the maxillary sinus.

The anterior wall of the infratemporal fossa is formed by the infratemporal surface of the maxilla, the superior wall - by the infratemporal surface of the greater wing of the sphenoid bone. 

The lateral wall is formed by the zygomatic arch and ramus of the mandible.

Content of the fossa

The infratemporal fossa serves as a passageway for several neurovascular structures traveling from the cranial cavity through the temporal fossa and infratemporal fossa to the pterygopalatine fossa. 

The neural structures include major branches of the mandibular nerve, chorda tympani arising from the facial nerve, and the otic ganglion, several sensory branches of the trigeminal nerve such as the lingual, buccal, inferior alveolar, and auriculotemporal nerves.

Blood vessels crossing this region include the maxillary artery and the pterygoid venous plexus, middle meningeal, and maxillary veins

The infratemporal fossa also contains several muscles of mastication, such as the medial and lateral pterygoids, as well as the tendon of the temporal muscle.

Foramina

Several openings found in the walls of the infratemporal fossa connect it with different areas of the cranial cavity.

These openings include:

  • Foramen ovale
  • Foramen spinosum
  • Pterygomaxillary fissure
  • Inferior orbital fissure
  • Alveolar canals or apertures 
  • Mandibular foramen

These openings transmit particular nerves and blood vessels.

 

Pterygopalatine fossa

The pterygopalatine fossa, also known as the sphenopalatine fossa, is a cone-shaped, bilateral depression below the apex of the orbit on the lateral side of the skull. 

Skull with pterygopalatine fossa (boundaries marked in red)
Pterygopalatine fossa by Anatomy Next

It is located between the maxilla anteriorly, the sphenoid bone posteriorly, and the palatine bones.

Boundary lines

Different bony structures form the walls and borders of the pterygopalatine fossa. 

The pterygopalatine fossa is bounded by:

  • Anteriorly - the superomedial part of the infratemporal surface of the maxilla;
  • Posteriorly - the root of the pterygoid process and the adjacent anterior surface of the greater wing of the sphenoid bone;
  • Inferiorly - the palatine bone;
  • Superiorly - the maxillary surface of the greater wing of the sphenoid bone, inferior orbital fissure;
  • Medially - the perpendicular plate of the palatine bone, and the orbital and sphenoidal processes of the palatine bone;
  • Laterally - by the pterygomaxillary fissure.

Content of the fossa

The pterygopalatine fossa accommodates the pterygopalatine ganglion. It also serves as a passageway for the maxillary nerve, many of its branches (infraorbital, nasopalatine, zygomatic, pharyngeal, superior alveolar, lesser and greater palatine nerves), and the third part of the maxillary artery, including its branches - the sphenopalatine, descending palatine, infraorbital and posterior superior alveolar arteries.

Foramina

The walls of the pterygopalatine fossa present several canals and foramina connecting the fossa with other regions of the skull like the orbit, nasal and oral cavities, middle cranial fossa, and infratemporal fossa. 

These openings transmit particular nerves and blood vessels. 

Openings, seen in the pterygopalatine fossa, include the following:

  • Sphenopalatine foramen
  • Inferior orbital fissure
  • Pterygomaxillary fissure
  • Greater palatine canal
  • Foramen rotundum 
  • Pterygoid canal
  • Pharyngeal canal (also known as the palatovaginal canal)

 

Orbit

The orbit or orbital compartment is a pyramid-shaped paired skeletal cavity located in the skull on either side of the root of the nose. Its base opens anteriorly in the central part of the face and next to the midline. Its apex is pointed backward. 

The orbit is a bony cavity housing and protecting the eye, its appendages, and its accessory structures

Bony orbit, bones forming orbit (colored), anterior view of skull
Bones forming the orbit by Anatomy Next

 

Margins and walls of orbit

The orbit is formed by seven bones - frontal, zygomatic, ethmoid, lacrimal, sphenoid, palatine bones, and maxilla.

The bony orbital compartment has a roof (superior wall), floor (inferior wall), lateral and medial walls surrounding the orbital cavity and its content. 

The orbit has four margins:

  • Supraorbital - formed by the frontal bone;
  • Medial - formed by the frontal process of the maxilla;
  • Lateral - made by the zygomatic process of the frontal bone and the zygomatic bone;
  • Infraorbital - formed by the zygomatic process of the maxilla and the zygomatic bone.

The roof of the orbit is formed anteriorly by the supraorbital margin and orbital surface of the frontal bone and posteriorly by the orbital plate of the lesser wing of the sphenoid. 

The medial wall of the orbit is formed by the:

  • Lacrimal bone
  • Orbital plate of the ethmoid bone
  • Lesser wing of the sphenoid bone
  • Frontal process of the maxilla

The lateral wall of the orbit is formed anteriorly by the frontal process of the zygomatic bone and posteriorly by the orbital surface of the greater wing of the sphenoid. 

The floor of the orbit is formed anteromedially by the orbital surface of the maxilla and anterolaterally by the orbital surface of the zygomatic bone, palatine bone.

Content of orbit

The orbits contain the eyeballs and their associated structures, such as nerves (optic nerve, oculomotor nerve, trochlear, trigeminal, and abducens nerve), blood vessels (ophthalmic artery and superior and inferior ophthalmic veins), lacrimal apparatus, orbital fascia, and extraocular muscles

Any space within the orbit that is not occupied with specific structures is filled with orbital fat that cushions the eyes and stabilizes the extraocular muscles.

Foramina

Several openings are connecting the orbit with the cranial cavity and transmit nerves and blood vessels. 

These include:

  • Superior orbital fissure
  • Inferior orbital fissure
  • Optic canal
  • Anterior and posterior ethmoidal foramina
  • Nasolacrimal canal
  • Infraorbital canal

 

Nasal cavity

The nasal cavity or cavity of the nose is an irregular, bilateral air-filled space located within the skull above the roof of the mouth, forming the internal part of the nose. 

Inside of the skull, frontal view, nasal cavity, nasal conchae and meatuses
Nasal cavity by Anatomy Next

The nasal cavity serves as the initial part of the respiratory tract

It is lined with a mucous membrane, which also houses olfactory receptors

Bones forming the nasal cavity are the sphenoid, palatine, lacrimal, ethmoid, nasal bones, vomer, and maxilla.

Walls of nasal cavity

The nasal cavity is a bony compartment that is split into two symmetric compartments by the nasal septum

It has a roof, a floor, and four walls formed by bones of the skull.  

The roof of the nasal cavity is formed by the cribriform plate of the ethmoid and the anterior aspect of the body of sphenoid. 

The floor is formed by the bony palate (made by the palatine processes of the maxillae and horizontal plate of the palatine bone).

The medial wall of the nasal cavity is represented by the bony nasal septum composed of the vomer and the perpendicular plate of the ethmoid. The vomer is a small, thin bone forming the posterior part of the nasal septum. The vomer is attached to the rostrum of the sphenoid.

The following structures form each lateral wall of the nasal cavity:

  • Nasal surface of the maxilla
  • Perpendicular plate of the palatine bone
  • Ethmoidal labyrinth and superior and middle nasal conchae
  • Lacrimal bone
  • Medial plate of the pterygoid process of the sphenoid
  • Inferior nasal concha

The nasal bones form the anterior wall. On each side, it opens with an anterior nasal aperture

The posterior wall of the nasal cavity is formed by the anterior surface of the body of the sphenoid, and it presents a pair of openings called the choanae. 

Nasal conchae

There are three bony formations in each lateral wall of the nasal cavity that resemble curved shelves called the nasal conchaesuperior, middle, and inferior

They project into the nasal cavity creating five pathways called meatuses

These are the superior, middle, inferior, and common nasal meatuses, and the nasopharyngeal meatus

Content of the nasal cavity

Like other skull regions, the nasal cavity serves as a passageway for several nerves and blood vessels of the head.

Foramina and openings

The nasal cavity presents many openings in its bony walls, such as 

  • Foramina of the cribriform plate
  • Sphenopalatine foramen
  • Incisive canal
  • Opening of the nasolacrimal canal

The nasal cavity is also connected with the paranasal sinuses with openings to the frontal, maxillary and sphenoidal sinuses, and the ethmoidal air cells.

 

Periosteum

The periosteum is a layer of dense connective tissue covering the surfaces of bones, and that includes the skull. The periosteum that covers the skull bones is also known as the pericranium.

The periosteum has a significant role in bone repair and growth and impacts the blood supply of the bone.

It consists of two layers:

  • Outer fibrous layer
  • Inner layer (also known as the cambium)

The outer layer of the periosteum is a tough fibrous layer formed by collagen fibers that can be subdivided into a superficial and deep portion.

Both contain collagen and elastic fibers, but the deep portion is is known as the fibroelastic layer as it has many elastic fibers and is highly collagenous. This layer also contains many nerve endings - therefore, pain sensation can be triggered by the damage to this layer.  

The inner layer contains many blood vessels and cells and is highly vascular and cellular. 

The periosteum of the skull is also the innermost layer of the scalp

The layers of the scalp from the most superficial to the innermost are the:

  • Epidermis of the skin with hair follicles and sebaceous glands;
  • Dermis containing dense connective tissue with nerves, lymphatics, blood vessels;
  • Epicranial aponeurosis (also known as the galea aponeurotica)- immobile connective tissue layer;
  • Loose connective tissue;
  • Periosteum, also known as the pericranium in the skull.

 

Functions of the skull

The primary function of the skull is to provide protection for the brain and the sensory organs connected with it. It also incorporates the upper part of the digestive and respiratory tracts. The skull supports the soft tissue of the head and facial anatomical structures.

The skull also provides:

  • Head movement
  • Formation of the face framework
  • Passage for cranial nerves and vessels
  • Housing organs that provide special senses (vision, hearing, taste, smell)
  • Supporting the muscles moving various parts of the head and providing facial expressions
  • Attaching with the inner surfaces to the meninges that stabilize the brain, blood vessels, and nerves
  • Protection of the eyeballs and attachment for muscles moving them
  • Chewing and digestion - provided by the maxilla and mandible; these bones also contain alveolar processes with sockets that house the teeth
  • Storage of calcium
  • Hematopoiesis
Learn more about "Visual Guide to The Anatomy of The Skull"

Summary on skull

What are the parts of the skull?

The human skull consists of two main parts. One part is the braincase, also called the neurocranium. But other is the facial skeleton called the viscerocranium.

Where is the skull?

The skull is the most superior part of the human body. It is the skeleton of the head; therefore, it surrounds the brain.

What is the medical term for the skull?

The skull in medical terminology is known as the cranium.

What is neurocranium?

The neurocranium is one of two parts forming the human skull. It is also known as the braincase. It encloses the brain, brain stem, and sensory organs connected with it.

What is viscerocranium?

The viscerocranium is one of two parts forming the human skull. It is also known as the facial skeleton as it creates it and supports the soft tissue of the face.

How many bones are in the viscerocranium?

Viscerocranium is formed by six paired and two unpaired bones, in total 14 bones.

Which is the smallest bone of the human body?

The smallest bone of the human body is the stapes located in the middle ear.

Which bones of the neurocranium are paired?

Paired bones of the neurocranium are the temporal and parietal bones.

What are the 22 bones of the skull?

The 22 bones of the skull are temporal (2), parietal (2), frontal, sphenoid, ethmoid, occipital, lacrimal (2), nasal (2), zygomatic (2), palatine bones (2), and mandible, inferior nasal conchae (2), maxilla (2), vomer.

What are the 29 bones of the skull?

The 29 bones of the skull are temporal (2), parietal (2), frontal, sphenoid, ethmoid, occipital, lacrimal (2), nasal (2), zygomatic (2), palatine bones (2), and mandible, inferior nasal conchae (2), maxilla (2), vomer, hyoid bone, the malleus (2), incus (2), and stapes (2).

What are the 14 facial bones called?

Fourteen facial bones are called the viscerocranium.

Which is the only bone of the skull that can move?

The only bone of the skull that can move is the mandible.

Which aspect of the frontal bone is thin-walled and forms the forehead?

The squamous part of the frontal bone forms the forehead.

Does the ethmoid bone have a sinus?

Yes, the ethmoid bone has a sinus or sinuses called the ethmoidal air cells.

What is the most prominent immovable bone of the face?

The maxilla is the most prominent immovable bone of the face.

Does the frontal bone have a sinus?

Yes, the frontal bone has a sinus - the frontal sinus.

Does the sphenoid bone have a sinus?

Yes, the sphenoid has a sinus - the sphenoidal sinus.

Which facial bone is associated with the tear ducts?

The lacrimal bone is associated with the tear duct.

How many sinuses are in the skull?

The skull contains four sets of paired paranasal sinuses.

Why are the sinuses important?

The paranasal sinuses reduce the weight of the front of the skull and bones of the face. They humidify and heat inspired air, buffer against blows, regulate gas pressures, aid in voice resonance and defense against various antigens.

What is the name of the bone that makes up most of the temple?

Most of the temple is made of the temporal bone.

What is inferior nasal concha?

The inferior nasal concha is a paired bone of the facial skeleton or viscerocranium. It is located in the lateral wall of the nasal cavity and resembles a curved shelve.

Why are skull bones not moveable?

The primary function of the skull is to provide protection for the brain and the sensory organs connected with it. Therefore, the skull is a single whole. This is realized by sutures that connect the bones of the skull and do not allow movement.

Is the skull supposed to be smooth?

No, the skull is not smooth as it contains many tubercles, grooves, foramina, apertures, and many more minor anatomical structures.

Do cranial bones move?

The only moveable joint of the cranial bones is the temporomandibular joint formed between the mandible and temporal bone.

What are the two types of joints found in the skull?

The skull contains the synarthrodial and diarthrodial joints.

What is the name of the movable joint in the skull?

The only movable joint in the skull is called the temporomandibular joint. It is a synovial joint, which belongs to the diarthrodial joint type.

What are the major sutures of the skull?

The major sutures of the skull are the coronal, sagittal, lambdoid, and squamous sutures.

Are sutures found only in the skull?

Yes, the sutures are only found in the skull.

What does fontanelle mean?

In newborn babies, sutures are fused incompletely, and between the bones are membranous gaps called the fontanelles allowing the child to pass through the birth canal. 

What is the function of fontanelles?

Fontanelles allow the head of the child to pass through the birth canal, as they make the bony plates of the skull more flexible.

How many fontanelles are there?

The skull of a baby has six fontanelles - two paired and two unpaired.

Where are fontanelles located?

The anterior or frontal fontanelle is located at the junction of the sagittal and coronal sutures. 

The occipital or posterior fontanelle is situated at the junction of the lambdoid and sagittal sutures. 

The sphenoid fontanelle is located between the sphenoid, temporal, frontal, and parietal bones.

But the mastoid fontanelle is situated between the temporal, occipital, and parietal bones.

What age do fontanelles close?

Fontanelles start to close by three months after birth, and the largest fontanelle stays open until the age of two.

What is the top of the skull called?

The top of the skull is called the calvaria.

Which bone is considered to be a part of the skull?

The hyoid bone is considered to be a part of the skull, although located in the neck.

Why is the human skull important?

The human skull provides protection for the brain and the sensory organs connected with it. 

The skull incorporates the upper parts of the digestive and respiratory tracts. It supports the soft tissue and facial anatomical structures of the head.

What is the posterior cranial fossa?

The posterior cranial fossa is a part of the internal cranial base - the inner part of the skull base. It lies at the lowest level of the internal cranial base and is the largest of the three fossae (anterior, middle, posterior). 

It is formed by all parts of the occipital, the posterior surface of the petrous portion of the temporal bone, and the mastoid angle of the parietal bone.

What is pericranium?

The pericranium is the periosteum of the skull, a layer of dense connective tissue covering the surfaces of bones.