Cranial Anatomy Notes

Cranial Cavity

Cranium

Neurocranium:
- Composed of 8 bones (2 paired, 4 unpaired).
- Calvaria: The skullcap.
- Intramembranous ossification: Bones formed through this process.
- Cranial Base: The floor of the cranial cavity.
- Endochondral ossification: Bones formed through this process.
Viscerocranium:
- Composed of 15 bones (6 paired, 3 unpaired).
- Intramembranous ossification: Bones formed through this process.
- Formed from mesenchyme of pharyngeal arches.

External Cranial Landmarks

Frontal bone:
- Superciliary arch.
- Glabella.
- Nasion.
- Supra-orbital notch (foramen).
- Zygomatic process (of frontal bone)
Nasal bone
Frontal process (of maxilla)
Zygomatic bone
Maxilla
- Zygomatic process (of maxilla).
- Infra-orbital foramen.
- Nasal crest
- Anterior nasal spine.
- Alveolar process.
- Piriform aperture
Inferior nasal concha
Mandible
- Ramus of mandible.
- Alveolar part of mandible.
- Body of mandible.
- Mental foramen.
- Mental protuberance.
- Mental tubercle.
- Angle of mandible.
Parietal bone
- Sagittal suture
Occipital bone
- External occipital protuberance.
- Superior nuchal line.
- Inferior nuchal line.
- External occipital crest.
- Inion
Temporal bone
- Mastoid process.
- Mastoid notch.
- Oblique line.

Lateral Cranial Landmarks

Frontal bone
- Coronal suture.
- Bregma
Parietal bone
- Sagittal suture.
- Squamous suture.
- Lambdoid suture.
- Parietal foramen
Occipital bone
- Lambdoid suture.
- Lambda
Temporal bone
- Squamous part (of temporal bone).
- Mastoid part of temporal bone
- Tympanic part (of temporal bone).
- Styloid process
- Zygomatic process (of temporal bone).
- Parietomastoic suture
- Asterion
Sphenoid bone
- Greater wing (of sphenoid bone).
- Sphenosquamous suture.
- Sphenoparietal suture.
Zygomatic bone *Zygomaticofacial foramen *Temporal process (of zygomatic bone)
- Zygomaticotemporal foramen (on deep surface of zygomatic bone).
Lacrimal bone
Nasal bone
Maxilla
- Alveolar part
Mandible
- Body of mandible
- Mental foramen.
- Ramus of mandible.
- Angle
- Condylar process
- Coronoid process
Pterion

Inferior Cranial Landmarks

Maxilla
- Hard palate (maxilla).
- Incisive fossa.
- Alveolar arch.
Palatine bone
- Hard palate (palatine bone).
- Greater palatine foramen.
- Lesser palatine foramen.
- Pyramidal process of palatine bone
Sphenoid bone
- Body of sphenoid.
- Greater wing (of sphenoid bone).
- Pterygoid process.
- Medial plate of pterygoid process.
- Lateral plate of pterygoid process.
- Scaphoid fossa.
- Foramen lacerum.
- Foramen ovale.
- Foramen spinosum.
- Opening of pterygoid canal
Vomer
Temporal bone
- Mandibular fossa.
- Articular tubercle.
- Groove for auditory tube.
- Petrous part of temporal bone.
- Carotid canal.
- Stylomastoid foramen.
- Squamous part of temporal bone.
- Mastoid process.
- Mastoid notch.
- Styloid process.
- Jugular foramen
Occipital bone
- Basilar part of occipital bone.
- Pharyngeal tubercle.
- Occipital condyle.
- Hypoglossal canal.
- Foramen magnum.
- External occipital crest.
- Inferior nuchal line.
- Superior nuchal line.
- External occipital protuberance.
Posterior nasal aperture (choana)
Posterior nasal spine
Hamulus
Pterygoid fossa

Cranial Tables

Internal & external cortical bone tables
Separated by diploë trabecular bone
Buttresses: Thicker areas of cranial bone help transmit forces around weaker areas of bone
Cranial walls are thinner where muscles cover the skull
Thinnest walls at Pterion

Meningeal Arteries

Middle meningeal artery:
- Position related to pterion.
- Branch of the maxillary artery.
Anterior meningeal arteries: from ethmoidal arteries.
Posterior meningeal artery: from ascending pharyngeal artery.
Meningeal branch: from ascending pharyngeal artery.
Meningeal branch: from occipital artery.
Meningeal branch: from vertebral artery.

Cranial Fractures

Le Fort fractures:
- Le Fort I
- Le Fort II
- Le Fort III
Mandible fractures
- Condylar process
- Coronoid process
- Ramus
- Angle
- Body
- Alveolar process
- Mental foramen
- Mental protuberance

Cranial Development

Face grows extensively.
$1/8$ of cranium in children to $1/3$ in adults.
Sinuses, teeth, nose.
Fontanelles
- Anterior, Posterior, Sphenoidal, & Mastoidal.
- Bregma, lambda, pterion, asterion.
Fontanelle closure
Suture obliteration ( $\sim$ 30-40 yrs. of age)
Metopic suture
Persistent frontal suture

Craniosynostosis

Premature suture closure.
1 in 2,000 births
Scaphocephaly: Premature closure of sagittal suture.
- Increased A-P dimension.
Oxycephaly/Turricephaly: Premature coronal suture closure.
- Increased superior to inferior dimension.
Plagiocephaly: Premature closure of coronal or lambdoidal suture on one side only.
- Twisted or asymmetrical skull shape.

Air Sinuses

Pneumatic sinuses
Frontal
Maxillary
Sphenoidal
Ethmoidal

Scalp

Layers of the scalp:
- Skin
- Connective tissue (dense CT), blood vessels & nerves
- Aponeurosis of occipitofrontalis
- Loose areolar tissue
- Pericranium/periosteum

Cranial Meninges

Dura mater
- External periosteal layer.
- Internal meningeal layer.
Arachnoid mater
Subarachnoid space
Arachnoid granulations
Pia mater

Dural Folds

Falx cerebri:
- Runs in longitudinal cerebral fissure.
- Crista galli to internal occipital protuberance.
Tentorium cerebelli:
- Between occipital lobes & cerebellum.
Falx cerebelli:
- Separates cerebellar hemispheres.
Diaphragma sellae:
- Roof over hypophyseal fossa.

Venous Sinuses

Sinuses between dural layers.
Superior sagittal sinus:
- Superior border of falx cerebri.
Inferior sagittal sinus:
- Inferior border of falx cerebri.
Confluence of sinuses:
- Union of inferior sagittal sinus & great cerebral vein.
Paired sinuses:
- Transverse sinus.
- Sigmoid sinus.
- Cavernous sinus:
  - Lateral to sella turcica.
Transverse sinus & sigmoid sinus lead from confluence of sinuses to jugular foramen.
Cavernous sinus contents:
- Hypophyseal fossa
  - CN III, IV, V1, V2, VI, internal carotid artery
  - Orbit, face, meninges, and brain

Innervation

Scalp:
- CN V
- Ventral & dorsal rami of C2 and C3
Dura:
- Meningeal branches of CN V, CN X & dorsal rami of C2 and C3
Trigeminal Nerve (CN V)
- Ophthalmic nerve (V1)
- Maxillary nerve (V2)
- Mandibular nerve (V3)
- Trigeminal ganglion

Arteries

Basilar artery
Right & Left vertebral arteries
Middle meningeal artery:
- Branch of maxillary artery
Internal carotid artery
Scalp is supplied by branches of: *Internal carotid artery * Supratrochlear * Supraorbital
- External carotid artery
  - Superficial temporal
  - Posterior auricular
  - Occipital

Internal Cranial Landmarks

Bones: Ethmoid, Frontal, Occipital, Parietal, Sphenoid, Temporal
Ethmoid bone
- Crista galli of ethmoid bone
- Cribriform plate of ethmoid bone
- Ethmoidal spine
- Ethmoidal foramina: Anterior, Posterior
Frontal bone
- Frontal crest
- Orbital part of frontal bone
Sphenoid bone
- Limbus of sphenoid
- Prechiasmatic sulcus
- Tuberculum sellae
- Hypophysial fossa
- Posterior clinoid process
- Dorsum sellae
- Lesser wing of sphenoid bone
- Optic canal
- Sphenoidal crest
- Superior orbital fissure
- Anterior clinoid process
- Foramen rotundum
- Carotid groove
- Foramen ovale
- Foramen spinosum
- Greater wing of sphenoid bone
Temporal bone
- Superior border of petrous part
- Groove for greater petrosal nerve
- Opening of internal acoustic meatus
- Groove for sigmoid sinus
- Groove for transverse sinus
Occipital bone
- Foramen magnum
- Internal occipital crest
- Internal occipital protuberance
- Hypoglossal canal
- Clivus
Foramen cecum
*Note: The internal carotid artery and its accompanying sympathetic and venous plexuses actually pass horizontally across (rather than vertically through) the area of the foramen lacerum, an artifact of dry crania, which is closed by cartilage in life.

Cranial Nerves

Olfactory nerves (CNI)
Olfactory Bulb
Olfactory Tract
Optic nerve (CN II)
Oculomotor nerve (CN III)
Trochlear nerve (CN IV)
Trigeminal nerve (CN V)
- Ophthalmic nerve (CN V₁)
- Maxillary nerve (CN V2)
- Mandibular nerve (CN V3)
- Trigeminal ganglion
Abducent nerve (CN VI)
Facial nerve (CN VII)
Vestibulocochlear nerve (CN VIII)
Glossopharyngeal nerve (CN IX)
Vagus nerve (CN X)
Spinal accessory nerve (CN XI)
Hypoglossal nerve (CN XII)

Arteries and Sinuses

Internal carotid artery
Basilar artery
Vertebral artery
Middle meningeal artery
Superior petrosal sinus
Sigmoid sinus
Transverse sinus
Superior sagittal sinus
Inferior sagittal sinus

Review Questions

Which of the following is NOT a cranial landmark?
- A. Asterion
- B. Pterion
- C. Inion
- D. Corion
Which of the following is NOT associated with the sphenoid bone?
- A. foramen spinosum
- B. optic canal
- C. pterygoid canal
- D. foramen rotundum
- E. carotid canal
Which of the following is NOT associated with the temporal bone?
- A. stylomastoid foramen
- B. internal acoustic meatus
- C. jugular foramen
- D. carotid canal
Which two sinuses are found within the longitudinal fissure?
- A. transverse sinus and straight sinus
- B. inferior sagittal and superior sagittal sinus
- C. sigmoid sinus and cavernous sinus
- D. there are no sinuses within the longitudinal fissure