Bones of the Skull & Head - Learn the Skeletal System

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Individual Bone Information

Frontal Bone

General Information
The frontal bone is the single convex bone that makes up the forehead. Inferiorly beneath the eyebrows it forms the palpable supra-orbital margins and in the midline it projects downwards to form a small portion of the bridge of the nose. Two plates of the frontal bone lie horizontally and form the roofs of the orbits, the orbital plates. The frontal sinuses lie within the frontal bone above and behind the superciliary arches.

Articulations
It articulates posteriorly with the parietal bones at the coronal suture and with the sphenoid, ethmoid, lacrimal, nasal, maxillary, zygomatic and temporal bones.

Muscle attachments
It gives attachment to two muscles of facial expression, orbicularis oculi and corrugator supercilii.
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Parietal Bones

General information
The two parietal bones form the bulk of the vault of the skull behind the frontal bone.

Each bone is quadrilateral in shape and forms a curved plate. Inferior and superior temporal lines are faint curves on the external surface, indicating the attachment of temporalis and the temporal fascia respectively. Grooves for the middle meningeal vessels run on the concave internal surface and a groove for the superior sagittal sinus runs along the sagittal margin.

Articulations
The two parietal bones meet to form the sagittal suture. They articulate with the frontal bones at the coronal suture, with the occipital bones at the lambdoid suture and with the temporal and sphenoid bones to form the squamous sutures. Wormian bones may appear along these sutures.

Muscle attachments
The parietal bones give attachment to temporalis.
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Supra Orbital Foramen

The supra-orbital notch is found in the center of the supra-orbital margin, beneath the eyebrows and may close to form a foramen. It transmits the supratrochlear nerve and vessels from the orbit onto the forehead.
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Temporal Bones

General Information
There are two temporal bones; each bone contributes to the base and to the lower lateral aspect of the skull.

The temporal bone can be described as four parts;
Squamous part - thin and translucent, it forms the anterior and upper part of the bone, its outer surface is smooth and convex and provides attachment for temporalis.
Petrous part - a solid, wedge of bone that forms most of the posterior and inferior portions and houses the middle and inner ear cavities.
Mastoid part - lies below the squamous and behind the tympanic parts.
Tympanic part - a semicircular plate of bone that forms the bony boundaries of the external acoustic meatus.

Articulations
The temporal bone articulates with the sphenoid and parietal bones at the squamous suture and with the occipital bone at the occipitomastoid suture. The zygomatic process articulates with the zygomatic bone and the mandibular fossa articulates with the mandible at the temporomandibular joint.

Squamous part
A zygomatic process projects from the lower part of the squama to articulate anteriorly with the temporal process of the zygomatic bone, forming the zygomatic arch. Inferiorly is the mandibular fossa, an oval depression for the reception of the condyle of the mandible.

Attachments
The outer surface provides attachment for temporalis, masseter and the temporomandibular ligament.

Petrous part;
The internal aspect is divided into anterior and posterior surfaces by a ridge running along its superior margin. The anterior surface forms the posterior boundary of the middle cranial fossa and is related to the temporal lobe of the brain. The posterior surface constitutes the anterior portion of the posterior cranial fossa and is related to the cerebellum. The orifice of the internal acoustic meatus can be seen opening into the posterior cranial fossa. Its inferior surface contributes to the external surface of the cranial base.

Attachments
It gives attachment to the cartilaginous part of the auditory tube and levator veli palatini.

Mastoid part;
It bears the mastoid process, a heavy, inferior conical projection that is easily palpated behind the earlobe. This process is hollowed out into a number of mastoid air cells. On its medial side is a deep groove termed the mastoid notch, which gives attachment to the digastric muscle. The main feature on the internal surface of the mastoid part is a deep and curved groove that lodges part of the sigmoid and transverse sinuses.

Attachments
The external surface gives attachment to the occipital belly of the epicranius, posterior auricularis, sternocleidomastoid, splenius capitis, longissimus capitis and digastric.

Tympanic part;
Inferior to the meatus, it presents an inferiorly projecting, pointed spine, called the styloid process.

Attachments
The tympanic part gives attachment to the tympanic membrane and the cartilaginous part of the external acoustic meatus.
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Sphenoid Bone

The greater wings of the sphenoid are two strong processes of bone, which arise from the sides of the body, and are curved upward, lateral ward, and backward. Each greater wing has cerebral, orbital, maxillary, infratemporal and temporal surfaces.

The superior, cerebral surfaces form part of the middle fossae of the skull and house the temporal lobes of the brain. The orbital surfaces form the posterior part of the lateral wall of the orbit and the lateral border of the inferior orbital fissure. The infratemporal surface forms part of the infratemporal fossa and the temporal surface part of the temporal fossa.

Attachments
The temporal portion gives attachment to temporalis and the infratemporal surface gives attachment to the lateral pterygoid.
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Nasal Bones

General information
The paired nasal bones meet in the midline to form the bridge of the nose. Inferiorly they give attachment to the lateral nasal cartilages.

Articulations
They articulate with the frontal, maxillary and ethmoid bones.

Muscle attachments
The nasal bones give attachment to procerus.
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Lacrimal Bones

General Information
The paired lacrimal bones are small, thin and rectangular, and each lie in the anterior part of the medial wall of the orbit. A depression, the lacrimal fossa can be found medially; it houses the lacrimal sac, which collects tears from the eyes via the nasolacrimal duct and empties them into the nasal cavity.

Articulation
The lacrimal bones articulate with the maxilla, ethmoid and frontal bones.
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Supra Orbital Margins

Inferiorly the squamous part and orbital parts of the frontal bone meet to form the supra-orbital margins which lie under the eyebrows. The lateral two-thirds of each supra-orbital margin are sharp whereas the medial third is rounded. The supra-orbital margin projects laterally as the zygomatic process of the frontal bone. This process articulates with the frontal process of the zygomatic bone.
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Zygomatic Procesess

The zygomatic process of the maxilla projects laterally from the body. It is pyramidal in shape and articulates with the zygomatic bone.
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Maxillae

General Information
The paired maxillary bones support the teeth of the upper jaw and contribute to much of the skeleton of the upper face. Its main bulk is pyramidal-shaped and known as the body. The maxillary sinuses lie within the bodies of the maxillae and are the largest of the paranasal sinuses.

Extending inferiorly from the body is the alveolar process that supports the teeth within the bony sockets. Projecting laterally from the body is the zygomatic process that articulates with the zygomatic bone. The palatine process projects horizontally from the medial surface of the maxilla to meet its opposite at the median palatine suture. Posteriorly the palatine process articulates with the horizontal plate of the palatine bone at the transverse palatine suture.

Articulation
It articulates with the nasal, frontal, zygomatic, vomer, inferior nasal conchae, lacrimal, and ethmoid bones and with the nasal and septal cartilages.

Muscle attachments
It gives attachment to a number of muscles of facial expression, these include, orbicularis oculi, levator labii superioris, levator anguli oris, nasalis and incisivus labii superioris. It also gives attachment to buccinator, a muscle of mastication.
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Occipital Bone

General information
The occipital bone forms the back and base of the skull enclosing the foramen magnum and can be described as three parts;

Squamous part - the expanded plate of bone posterosuperior to the foramen magnum.
Basilar part - thick, it extends anteriorly from the foramen magnum to the sphenoid bone.
Lateral parts - each extending laterally from the foramen magnum, joining the basilar and occipital parts.

Articulations
The squamous part articulates with the parietal bones at the lambdoid suture and the temporal bones at the occipitomastoid suture. The occipital condyles articulate inferiorly with the atlas (C1) at the occipito-atlantal joint.

Squamous part;
The external surface of the squamous part is convex and in the midline is a projection termed the 'external occipital protuberance'. A thin ridge called the external occipital crest passes downwards from the protuberance and from this the upper, middle and lowest nuchal lines run laterally. The internal surface is concave and marked by grooves that house the venous sinuses that drain the brain. It is related to the occipital lobes of the brain and the inferior surface of the cerebellum.

Attachments
On its external surface it gives attachment to the: ligamentum nuchae, epicranial aponeurosis, trapezius and sternocleidomastoid. On its internal surface it gives attachment to layers of the meninges of the brain.

Basilar part;
The basilar part extends antero-superiorly from the foramen magnum to fuse with the sphenoid bone. Anterior to the foramen magnum is the pharyngeal tubercle. The superior (internal) surface forms part of the clivus, lateral to which are grooves for the inferior petrosal sinus.

Attachments
Longus capitis attaches to the pharyngeal tubercle.

Lateral parts;
The lateral parts lay either side of the foramen magnum, a large ovoid opening in the cranial floor that transmits the vertebral arteries, and is where the spinal cord becomes continuous with the medulla oblongata. Directly lateral to the foramen magnum are the oval convex occipital condyles for articulation for the superior facets of the atlas (C1).
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Vomer

General Information
The vomer is a single thin plate, shaped like a 'ploughshare'. It forms the postero-inferior portion of the nasal septum and rests inferiorly along the midline of the maxilla and palatine bones.

Articulations
The vomer articulates with the ethmoid, sphenoid, maxilla, palatine and nasal bones.
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Ethmoid Bones

General Information
The ethmoid is a single bone that forms parts of the nasal septum, medial wall of the orbital cavity and the roof and lateral wall of the nose.

Superiorly is the cribriform plate, which forms a large part of the nasal roof and has many olfactory foramina. Projecting upwards from the cribriform plate is the crista galli which gives attachment to the falx cerebri (cranial meninges). A thin, quadrilateral plate, known as the perpendicular plate descends vertically from the midline of the cribriform plate to form the superior part of the nasal septum. Networks of chambers, called ethmoidal labyrinths, descend vertically from the lateral margins of the cribriform plate; the medial surfaces form part of the lateral wall of the nose.

The ethmoid bone gives rise to the superior and middle nasal concha, thin, scroll-like plates of bone that hang down from the upper lateral wall and lower lateral wall of the nose respectively. They are covered in mucous membrane and contain receptor cells for smell.

Articulation
It articulates with the frontal, sphenoid, nasal, vomer and lacrimal bones.
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Infra Orbital Foramen

Each infra-orbital foramen is the anterior opening of the infra-orbital canal and can be found on the anterior surface of the maxilla, above the canine fossa.

Structures transmitted
It transmits the infra-orbital vessels and nerves.
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Zygomatic Bones

General Information
The two zygomatic bones form the skeleton of the cheeks and the inferior and lateral walls of the orbit. It has a trapezoidal-shaped body with frontal and temporal processes projecting from its posterior margin. The frontal process forms the lateral margin of the orbit and articulates with the frontal bone. The temporal process forms the prominent zygomatic arch and articulates with the temporal bone.

Articulations
The zygomatic bones articulate with the frontal, temporal, maxilla and sphenoid bones.

Muscle attachments
It gives attachment zygomatic major and minor, muscles of facial expression and masseter, a muscle of mastication.
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Mandible: Rami

The ramus is the quadrilateral, vertical portion of the mandible. The superior border is formed by the coronoid and condylar processes which lie anteriorly and posteriorly, separated by the mandibular notch. The coronoid process gives attachment to temporalis and the condylar process articulates with the mandibular fossa of the temporal bone.

In the center of the medial surface of the ramus lies the mandibular foramen, from which the mylohyoid groove runs anteriorly towards the midline of the body.

Structures transmitted
Transmitted through the mandibular foramen and canal is the inferior alveolar nerve and vessels.

Attachments
The rami give attachment to masseter, the sphenomandibular ligament, medial pterygoid and mylohyoid.
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Aveolar Processes

The alveolar processes of the maxilla extend inferiorly from the body of the maxilla and support the teeth within bony sockets.
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Mandible: Body

The body of the mandible is U-shaped and forms the main bulk of the bone. It has important features on both its internal and external surfaces.

External (anterior and lateral) surface
Mandibular symphysis - anterior midline ridge.
Mental protuberance - distinct anterior midline triangular prominence.
Mental tubercles - anterior tubercles, lateral to the midline.
Incisive fossae - shallow depressions above tubercles.
Mental foramina - in the region of the premolar teeth (transmits mental nerves and vessels)
Alveolus - forms the superior margin of the body.

Internal (posterior and medial) surface
Digastric fossae - shallow depressions close to the midline (anterior bellies of the digastric attach here).
Genial (superior) tubercles - attachment for genioglossus muscles.
Genial (inferior) tubercles - attachment for geniohyoid muscles.
Mylohyoid (internal oblique) line - a prominent ridge for the attachment of mylohyoid muscle.
Sublingual fossa - a shallow depression above and in front of the mylohyoid line in which the sublingual salivary gland lays.
Submandibular fossa - a shallow concavity below the mylohyoid line in which the superficial portion of the submandibular salivary gland lays.
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Mandible Protuberance

The mental protuberance is the triangular prominence in the midline of the anterior aspect of the mandible, which forms the point of the chin.
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Mandible: Mental Foramina

The mental foramen lies below the premolar teeth and is the opening of the mandibular canal. This canal passes upwards and backwards through the mandible to emerge on its medial surface as the mandibular foramen.

Structures transmitted
The mental nerve from the mandibular division of the trigeminal nerve and accompanying vessels.
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Mandible: Coronoid Processes

The coronoid process is a triangular plate of bone that projects upwards and slightly forwards from the anterior part of the rami of the mandible.

Attachments
It gives attachment to temporalis and masseter.
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Superior Temporal Lines

The inferior temporal lines curve in an antero-posterior direction along the middle of the external surface of the temporal bone.

Attachments
The inferior temporal line gives attachment to temporalis.
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Inferior Temporal Lines

Mastoid Processes

The mastoid process is a large prominence located immediately behind the external acoustic meatus. It is hollowed out into a number of mastoid air cells which communicate with the middle ear cavity.

Attachments
It gives attachment to the sternocleidomastoid muscle.
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Condylar Processes

The convex condylar processes emerge superiorly from the posterior part of the mandible rami. They articulate with the mandibular fossa of the temporal bone to form the temporomandibular joint.
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Head and Skull