Skull Structure and Development

Structure of the Skull

• The bones of the head form the skull.
• Sutures interconnect most skull bones, creating immovable fibrous joints known as syndesmoses.
• There exists only three synovial joints in the head.
• The temporomandibular joint is the largest synovial joint, positioned between the lower jaw (mandible) and temporal bone.
• Two other synovial joints are between the malleus, incus, and stapes which are three tiny bones located in the middle ear.

Skull Development

• Large membranous, unossified gaps (fontanelles) between the skull bones exists in fetuses and newborns.
• Fontanelles located between the large flat bones of the cranial cavity's top provides the head to deform during birth and enable postnatal growth.
• Fontanelles usually close during the first year of life.
• Ossification of thin connective tissue ligaments separating skull bones via suture lines begins in the late twenties.
• Full ossification is generally completed in the fifth decade of life.

Fontanelles

• The anterior fontanel is unpaired and the largest, situated between the frontal and two parietal bones.
• The posterior fontanel is unpaired, located at the junction of the parietal and occipital bones.
• The anterolateral (pterygoid) fontanel is paired, is at the junction of the frontal, sphenoid, parietal, and temporal bones.
• The posterior-lateral (mastoid) fontanel is paired, situated at the junction of the parietal, temporal, and occipital bones.

Bones of the Skull

• The skull consists of 22 bones.
• 8 cranial bones form the skull.
• 14 bones make up the face.
• There are also 7 associated bones.

Cranium

• The neurocranium is formed by flat bones with irregular edges that protect the brain.
• It features a base (basis) where the brain rests and a vault (calvaria) enclosing it.
• Bones in cranium have perforations for nerves, blood vessels, and lymph vessels.
• The neurocranium includes one frontal bone, two parietal bones, two temporal bones, one occipital bone, one sphenoid bone, and one ethmoid bone.

Anterior View of the Skull

• The anterior skull view comprises 8 bones, both single and paired.
• Sutures join these bones together.
• Bones featured are the frontal bone, 2 zygomatic bones, 2 maxillas, 2 nasal bones, and the mandible.

Lateral View of the Skull

• The the most notable bones in this view are the frontal, parietal, temporal, occipital, sphenoid, zygomatic, maxilla, nasal bone, and mandible.

Posterior View of the Skull

• This section of skull comprises 2 parietal bones, 2 temporal, and the occipital.

Superior View of the Skull

• The viewed section is of 2 parietal bones, the frontal, and occipital.

Internal Surface of Calvaria

• Specific features are visible in the superior view of the internal surface.

Inferior View of the Skull

• Incisive foramina contain nasopalatine nerve; sphenopalatine vessels
• Greater palatine foramen encompass greater palatine nerve and vessels
• Lesser palatine foramina houses lesser palatine nerves and vessels
• Pterygoid canal allows pterygoid nerve and vessels
• Foramen ovale serves the mandibular nerve [V3]
• Foramen spinosum serves the middle meningeal artery
• The foramen lacerum is Filled with cartilage while the carotid canal serves the internal carotid artery and nerve plexus
• The foramen magnum is a continuation of brain and spinal cord; vertebral arteries and nerve plexuses; anterior spinal a., posterior spinal a.; roots of accessory nerve [XI]; meninges
• The condylar canal serves the emissary veins
• The hypoglossal canal contains the hypoglossal nerve [XII] and vessels
• Jugular foramen contains internal jugular vein; inferior petrosal sinus
• Stylomastoid foramen serves the facial nerve [VII]
• The inferior view of the skull consists of 2 temporal, occipital, sphenoid, 2 zygomatic, 2 maxillas, and 2 palatines.

Inferior Wall of the Skull

• The maxilla (palatine process) in hard palate.
• The palatine bone (horizontal plate) in hard palate.
• The zygomatic and temporal bones (zygomatic process).

Bones of the Calvaria

• Frontal bone consists of frontal squama, frontal tuberosity, orbital part (orbital surface), supraorbital margin, supraorbital notch, zygomatic process, temporal line, superciliary arch and its glabella (frontal crest (internal Surface) and superior sagittal sinus groove).
• The two air-filled cavities (frontal sinuses) inside the frontal squama are divided by the septum of the frontal sinuses.
• The coronal suture connects the frontal with the parietal bones.
• Parietal bones constitute the sides and bottom of the skull vault.
• The inner, concave surface has grooves for blood vessels.
• Parietal bones are interconnected by the sagittal suture.
• They're joined by the coronal suture to the frontal bone.
• The lambdoid suture joins the occipital bone and squamous suture joins the temporal bone.
• The superior saggital sinus groove is part of the parietal bone.

Temporal Bones

• They form sutures with the parietal, occipital, sphenoid and zygomatic bones.
• The bone has a widened squamous section that forms a suture with the parietal bone.
• The zygomatic process connects with the zygomatic bone, forming the zygomatic arch (cheekbone)

Base of the Temporal Bone

• The petrous forms part of the skull base.
• The part includes elements of the middle and inner ear, and thus the organs of hearing and balance.
• The mastoid process is behind the auditory canal, contains mastoid cells, and small air-filled spaces lined with epithelium communicating with the middle ear.
• Usually the styloid process contains muscles of the pharynx and larynx.
• The carotid canal transmits the internal carotid artery.
• There is a stylomastoid foramen, located between the mastoid and stylomastoid processes.
• The facial nerve runs through the foramen.
• The tympanic portion contains a tympanic ring and the external auditory foramen and canal

Occipital Bone

• It connects to the parietal, temporal, and sphenoid bones.
• The bone has a squamous aspect, with cerebral and cerebellar fossae.
• Includes internal and external occipital protuberance, along with transverse, sigmoid, and sagittal sinuses and confluence of sinuses.
• Basal part presents foramen magnum to connect with the spinal canal.
• Features occipital condyles for lateral basis, hypoglossal nerve canal for XII cranial nerve, body with pharyngeal tubercle for external aspects, and clivus for slope on the internal side.
• Lateral basioccipital joints form.
• The atlanto-occipital joint (articulatio atlantooccipitalis) is a condylar (ellipsoidal) and biaxial joint.
• Articular surfaces include the occipital condyles of the occipital bone and surfaces of the altas.
• The posterior and anterior atlantooccipital membranes connects the anterior and posterior arch of the atlas with the occipital bone and supports it.
• Flexion and extension, and lateral and medial rotation movements are possible.
• The range of flexion and extension totals 30 degrees, and rotation is limited to 5 degrees.

Sphenoid Bone

• The sphenoid features a hypophysial fossa on the sella turcica that is visibly limited by the dorsum sellae.
• The body contains sphenoid sinuses.
• Parts include the greater and lesser wing below optic canal, with a pterygoid process on the outer surface where muscles attach.
• The central part of the skull base combines the occipital, frontal, temporal and parietal bones.
• It’s a connection between neurocranium and viscerocranium.

Ethmoid Bone

• It occupies the anterior skull base and contributes to forming orbits, nasal septum, and cavity lateral walls.
• The cribriform plate in the roof of the nasal cavity next to the frontal bone is integral.
• The olfactory nerves passing through its cribriform foramina, while the crista galli anchors attachment of the cerebral falx.
• Labyrinths of ethmoid form cells within paranasal sinuses.

Anterior Cranial Fossa

• It is limited by a squamous portion of the frontal bone in front; lesser wings of the sphenoid bone at the back.
• Made up of orbital parts of the frontal bone, cribriform plate of the ethmoid bone, and the anterior clinoid processes.

Middle Cranial Fossa

• It is limited by: Lesser wings and body of the sphenoid bone in front; the dorsum sellae and the petrous part of the temporal bone posteriorly.
• It also includes Squamous parts of the parietal and temporal bones.
• Made up of hypophysial fossa and greater wing of the sphenoid bone, petrous part of the temporal bone.

Posterior Cranial Fossa

• It is limited by the body of the occipital bone along with clivus, and petrous part of the temporal bone in the front.
• It then is enclosed by the squamous part of the occipital bone from behind and squamous part parietal bones laterally.
• Made up of the basal part of occipital bone.

Viscerocranium

• The structure consists of 2 zygomatic, 2 maxillas, 2 nasal, 2 lacrimal, 1 vomer, 2 palatine and 2 inferior nasal conchas.

Zygomatic Bones

• The zygomatic makes up the lateral surface of the skull face, forming the cheek.
• It connects the temporal, maxillary, frontal, and sphenoid.
• Forms the floors and walls of orbit.

Maxilla

• It makes up the lateral walls of the nasal cavity and parts of the floor of the orbits.
• It includes the anterior alveolar process where teeth are set.
• The body holds maxillary sinuses.
• The infraorbital foramen and canal transmit the infraorbital nerve.

Nasal Bones

• Small flat bones construct upper bridge surfaces of the nose.

Lacrimal Bone

• It lies between the nasal bone and frontal maxilla parts, forming an orbit bondary.
• The bone contains the lacrimal sac fossa which leads to the nasolacrimal duct carrying tears from the conjunctival sac into the nasal cavity.

Vomer

• The vomer projects superiorly to merge with the sphenoid body, forming the primary lower section of the nasal septum.

Palatine Bone

• The bone presents as L-shaped.
• Its horizontal lamina forms the posterior hard palate area while the vertical builds nasal cavity lateral walls.
• The bone further contributes to the orbital floor with a foramen that transfers nerves out from the fossae to into a cavity.

Inferior Nasal Concha

• Resembles a scroll, which lines the nasal cavity lateral wall by concaving directly under a middle concha.
• Superior/middle are components of ethmoid.
• Purpose is to expand surface area in nasal passageway, improving airflow.

Mandible

• Made of three parts of a singular bone.

• Contains the arch that houses teeth.

• The rami contains a coronoid process for muscle attachments and condylar process joining with the temporal area at the TMJ(temperomandibular joint)

• The inner mandibular surface hosts the mandibular canal through lingula with spinal joint.

• Mylohyoid lines help support muscles.

• Also have the digastric and sublingual fossas that help provide salivary movement as well as attachments as well as spine regions.

Hyoid Bones

• Located in soft tissue within the neck above vocal box below a horseshoe form.
• Attaches no other bone yet is affixed by ligments linked with vocal region including muscle group at various spots.

Additional Information

• Facial elements provide protection in both cavity section or the resiratory area.
• Processes at alveolar bone allow for an embedding process to form.
• With jaws, food particles pass by the musclular section to allow chewing
• Furthermore, the brain section is protected via the neurocranium.
• The orbita contains muscular movements about with temporal that support inner ear parts that provides sound processing via nasal movement.
• The skeletal framework of of oral structures is temporal, palatine, and other portions that provide passage.
• Fossa sections to create oral components are also integrated into a portion of the skull from both anterior to areas are supported via processes in order for jaw or cran areas for structure.