Endocranial Surface
Formed by
- Ethmoid bone
- Sphenoid bone
- Frontal bone
Divided into
Medial portions
- Anteriorly
- Crista galli and the cribriform plate
- Covering the upper nasal cavity and the sphenoid sinus
- Posteriorly
- Planum of the sphenoid body
Lateral portions
- Formed by the frontal bone and the lesser wing of the sphenoid bone, which blends medially into the anterior clinoid process
- Covers the orbit and the optic canal
- Perforations
- Foramen caecum
- Emissary vein
- Cribriform plate
- Filaments of the olfactory nerve.
- Optic canal
- Optic nerve
- Ophthalmic artery.
It for surface for
- Frontal lobes with the gyri recti medially and the orbital gyri laterally
- Branches of the anterior cerebral arteries medially and middle cerebral arteries laterally.
Exocranial Surface
Divided into
Medial part
- Ethmoidal bone
- Ethmoidal sinuses
- Ant 2/3
- Formed by
- Cribriform plate
- With the olfactory fila traveling through it,
- Perpendicular plate
- Joins the vomer in forming the nasal septum, and
- 2 lateral plates
- Located in the medial walls of the orbits.
- Separate the lateral wall of the nasal cavity and the orbit.
- Superior turbinate
- An appendage of the ethmoid bone
- Projects into the superior part of the nasal cavity.
- Sphenoid bone
- Sphenoid sinuses
- Just below the planum sphenoidale
- Post 1/3
- Nasal cavity
- Images
- The frontal, ethmoidal, and sphenoid sinuses and the nasal cavity lie below the medial part of the anterior cranial base.
- The orbit and maxilla are located below the lateral part of the anterior cranial base.
- The sphenoid sinus and sella are located in the medial part of the middle cranial base, and the infratemporal and pterygopalatine fossa are located below the lateral part of the middle cranial base.
- The carotid arteries pass upward on the medial part of the middle cranial base and are intimately related to the sphenoid and cavernous sinuses.
- The infratemporal fossa, which contains branches of the mandibular nerve, pterygoid muscles, pterygoid venous plexus, and maxillary artery, is located below the middle cranial base and greater sphenoid wing.
- The alveolar process of the maxilla, which encloses the roots of the upper teeth, has been preserved on the left side.
- The maxillary nerve enters the pterygopalatine fossa, which is located medial to the infratemporal fossa between the posterior wall of the maxilla and the pterygoid process of the sphenoid bone.
- The infratemporal fossa is located posterolateral to the maxilla.
- The right ethmoid air cells are exposed on the medial side of the right orbit.
- The nasal cavity extends upward between the ethmoidal sinuses.
- The walls of the right maxillary sinus form the floor of the orbit, much of the lateral wall of the nasal cavity, and the anterior wall of the pterygopalatine and infratemporal fossa.
- On the left side, the mandibular nerve enters the infratemporal fossa.
- The maxillary nerve enters the pterygopalatine fossa, which is located in the lateral wall of the nasal cavity and contains the maxillary nerve, pterygopalatine ganglion, and terminal branches of the maxillary artery.
- The orbital apex is located above the pterygopalatine fossa.
- The frontal branch of the ophthalmic nerve passes along the roof of the orbit, and the infraorbital branch of the maxillary nerve courses in the floor of the orbit.
- The posterior ethmoid air cells are located medial to the orbital apex.
- The vomer forms the posterior part of the nasal septum and attaches to the maxilla and palatine bones below and to the body of the sphenoid bone above.
- The sphenoid sinus is located in the middle cranial base below the sella turcica.
- The upper brainstem is seen in the posterior part of the exposure.
Lateral part
- Orbit
- Borders
- Orbital roof formed by
- Lesser sphenoid wing
- Orbital plate of the frontal bone;
- Lateral wall is formed by
- Greater sphenoid wing
- Zygomatic bone
- Inferior wall is formed by
- Zygomatic bone
- Maxillary bone
- Palatine bones
- Medial wall is formed by
- Maxillary
- Lacrimal
- Ethmoid bones
- Covered with periorbita and filled with a great amount of fat,
- Divided into
- Anterior space
- Globe is located
- Posterior space
- Nerves, vessels, and muscles behind the globe
- Annular tendon of Zinn
- A fibrous ring that surrounds the central part of the superior orbital fissure and the optic canal
- Gives attachment to
- Superior rectus muscles
- Medial rectus muscles
- Inferior rectus muscles
- Lateral rectus muscles
- Superior oblique attaches above the annular tendon
- Inferior oblique arises from the inferomedial orbital wall just behind the rim
- Oculomotor foramen
- Located inside the annular tendon
- Transmit
- Oculomotor nerve
- Located between the upper and lower attachment of the lateral rectus muscle.
- Maxilla
Foramina
- Anterior and posterior ethmoidal foramen
- Located in the superomedial orbital wall,
- Transmit
- Anterior ethmoidal nerves and arteries
- Posterior ethmoidal nerves and arteries
- Supraorbital and supratrochlear notches or foramina,
- Transmit
- Arteries and nerves of the same name;
- Optic canal
- Transmit
- Optic nerve
- Ophthalmic artery
- Superior orbital fissure
- Located between
- Lesser and greater wing of the sphenoid bone on the lateral side of the optic canal.
- Inferior orbital fissure
- Located between
- The greater sphenoid wing behind and the maxillary and palatine bones anteriorly
- Is closed by a fibrous tissue and orbital muscle.
Contents
Nerve
- Optic nerve
- Passes superior and medial from the globe to reach the optic canal and divides the retro-orbital space into medial and lateral parts.
- Ophthalmic nerve
- Divides just behind the annular tendon into
- Lacrimal nerve
- Pass outside the annular tendon
- Frontal nerves
- Pass outside the annular tendon
- Nasociliary nerve
- Pass through the annular tendon.
- Gives rise to the
- Long ciliary nerves
- Conveys the sympathetic pupillomotor fibers
- Sensory root to the ciliary ganglion;
- Latter conveys corneal sensation.
- Trochlear nerve
- Passes above and outside the superomedial edge of the annular tendon.
Artery
- Ophthalmic artery
- Main arterial supply to the orbit
- This artery courses below the optic nerve in the optic canal, crosses to the lateral side of the nerve at the orbital apex, and then courses from lateral to medial above the optic nerve.
- Main branches
- Central retinal artery
- Lacrimal arteries
- Ciliary arteries
- Ethmoidal arteries
- Supraorbital arteries
- Dorsal nasal arteries
- Numerous muscular branches.
Vein
- Superior and inferior ophthalmic veins
- Main venous drainage of the orbit
- Exit the orbit by passing outside the annular tendon and through the superior orbital fissure.
Gland
- Lacrimal gland
- Located in the superolateral part of the orbit
- Neuronal
- Sensory innervation from the lacrimal nerve
- Parasympathetic and sympathetic innervation from the greater and deep petrosal nerves.
- The petrosal nerves join to form the vidian nerve that enters the pterygopalatine ganglion, which sends branches to the zygomatic nerve that anastomoses with the lacrimal nerve to reach the gland.
Lateral view of the anterior, middle, and posterior cranial base
A., artery; Car., carotid; CN, cranial nerve; Eust., eustachian; Front., frontal; Gr., greater; Inf., inferior; Infraorb., infraorbital; Infratemp., infratemporal; Int., internal; Jug., jugular; Lat., lateral; M., muscle; Max., maxillary; N., nerve; Ped., peduncle; Pet., petrosal; Pterygopal., pterygopalatine; Rec., rectus; Semicirc., semicircular; Sphen., sphenoid; Temp., temporal; V., vein; Vert., vertebral
- The orbit and maxillary sinus are located below the anterior cranial base.
- The infratemporal and pterygopalatine fossae and the parapharyngeal space are located below the middle cranial base, and the suboccipital area is located below the temporal and occipital bones.
- The first trigeminal division is related to the upper part of the orbit.
- The second trigeminal branch is related to the lower part of the orbit and maxilla.
- The mandibular nerve exits the cranium through the foramen ovale and enters the infratemporal fossa.
- The pterygoid and levator and tensor veli palatini muscles have been removed to expose the eustachian tube and its opening into the nasal pharynx.
- The petrous carotid passes upward and turns medially below the cochlea.
- The sigmoid sinus turns downward under the semicircular canals and vestibule where the jugular bulb is located.
- The segment of the vertebral artery passing behind the atlanto-occipital joint is located below the posterior cranial base.
The lateral part of the temporal bone has been removed to expose the cochlea, vestibule, and semicircular canals.
- The dura has been opened to show the relationships of the frontal and temporal lobes and the cerebellum to the cranial base.
- The orbit is exposed below the frontal lobe. The pterygopalatine and infratemporal fossae and the temporal bone are located below the temporal lobe.
- The jugular bulb and internal jugular vein have been removed to show Cranial Nerves IX through XII exiting the jugular foramen.
- GSPN into vidian nerve
Anterior fossa, orbit, and perinasal sinuses
A., artery; A.C.A., anterior cerebral artery; Ant., anterior; Car., carotid; Cav., cavernous; Clin., clinoid; CN, cranial nerve; Crib., cribriform; Eth., ethmoid, ethmoidal; Front., frontal; Lac., lacrimal; Less., lesser; Lev., levator; M., muscle; M.C.A., middle cerebral artery; Med., medial; N., nerve; Nasocil., nasociliary; Obl., oblique; Olf., olfactory; Ophth., ophthalmic; Post., posterior; Rec., rectus; Seg., segment; Sphen., sphenoid; Sup., superior; Supraorb., supraorbital; Supratroch., supratrochlear; Tr., tract; V., vein.
- The anterior cranial fossa is formed by the frontal, ethmoid, and sphenoid bones.
- The frontal bone splits anteriorly into two laminae, which enclose the frontal sinus.
- The ethmoid bones, which contain the ethmoid air cells and are the site of the crista galli and cribriform plate, are interposed between the frontal bones.
- Posteriorly, the frontal and ethmoid bones join the sphenoid bone, which encloses the sphenoid sinus and has the pituitary fossa on its upper surface.
- The olfactory bulbs and tracts have been preserved.
- The roof of the right orbit has been removed to expose the periorbita.
- The right anterior clinoid process and roof of the optic canal have been removed to expose the optic nerve enclosed within the optic sheath as it passes through the optic canal to reach the orbital apex.
- The orbital fat has been removed and the sphenoid sinus opened.
- The frontal branch of the ophthalmic nerve courses above the levator muscle.
- The ophthalmic artery, nasociliary nerve, and superior ophthalmic vein are located medially in the anterior part of the orbit and cross between the optic nerve and superior rectus muscle to be situated on the lateral side of the optic nerve at the orbital apex.
- The superior oblique muscle has been retracted medially to expose the anterior and posterior ethmoidal branches of the ophthalmic artery and nasociliary nerve entering the anterior and posterior ethmoidal canal.
- The trochlea of the superior oblique muscle is attached to the superomedial margin of the orbit just behind the orbital rim. The frontal nerve divides into supraorbital and supratrochlear branches.
- The levator and superior rectus muscle have been retracted posteriorly to expose the nasociliary nerve, ophthalmic artery, and superior ophthalmic vein passing above the optic nerve.
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