Anterior cranial fossa
The anterior cranial fossa (Fossa cranii anterior) occupies the anterior part of the internal cranial base.
Boundaries:
- Anteriorly: conventionally bounded by the frontal squama (squama frontalis). The main landmark here is the origin of the frontal crest (crista frontalis).
- Posteriorly: laterally, the boundary is formed by the lesser wings of the sphenoid bone (Alae minores ossis sphenoidalis), and along the midline, the boundary is the prechiasmatic sulcus (Sulcus prechiasmaticus).
Messages: From this fossa, one can enter the nasal cavity. This occurs via the cribriform foramina (Foramina cribrosa), located on the ethmoid bone, as well as through the foramen caecum of the frontal bone (Foramen caecum).
Middle cranial fossa
The middle cranial fossa (Fossa cranii media) lies posterior to the anterior cranial fossa and features the most complex system of apertures.
Boundaries:
- Anteriorly: completely duplicates the posterior boundary of the anterior fossa (lesser wings of the sphenoid bone laterally and the prechiasmatic sulcus centrally).
- Posteriorly: laterally bounded by the superior border of the petrous part of the temporal bone (Margo superior partis petrosae) or the sulcus for the superior petrosal sinus (Sulcus sinus petrosi superioris) running along it. Along the midline, the boundary is the dorsum sellae (Dorsum sellae).
Communications with other cavities:
- With the orbit: via the optic canal (Canalis opticus) and the superior orbital fissure (Fissura orbitalis superior).
- With the pterygopalatine fossa: via the foramen rotundum (Foramen rotundum).
- With the external cranial base: via the oval (Foramen ovale) and spinous (Foramen spinosum) foramina, the carotid canal (Canalis caroticus), and also through the foramen lacerum (Foramen lacerum). Note: in the living skull, the foramen lacerum is filled with the sphenopetrosal synchondrosis (Fissura sphenopetrosa) and is visible as a "hole" only on a dried (macerated) specimen.
- Additional pathways: via the hiatuses for the greater and lesser petrosal nerves (Hiatus canalis nervi petrosi majoris/minoris), the fossa communicates with the facial canal and tympanic canaliculus, respectively.
Posterior cranial fossa
The posterior cranial fossa (Fossa cranii posterior) is the most posterior compartment, formed primarily by the occipital and temporal bones.
Boundaries:
- Anteriorly: coincides with the posterior boundary of the middle fossa (dorsum sellae centrally, superior border of the petrous part of the temporal bone laterally).
- Posteriorly: along the midline, the landmark is the cruciform eminence (Eminentia cruciformis), also known as the internal occipital protuberance (Protuberantia occipitalis interna). Laterally, the boundary runs along the sulcus for the transverse sinus (Sulcus sinus transversi).
Communications with the external cranial base and inner ear:
- Within the occipital bone: located here are the foramen magnum (Foramen magnum), condylar canal (Canalis condylaris), and hypoglossal canal (Canalis nervi hypoglossi).
- Within the temporal bone: the mastoid foramen (Foramen mastoideum) and internal acoustic meatus (Meatus acusticus internus) open here, which further continues into the facial canal.
- Between the occipital and temporal bones: are the jugular foramen (Foramen jugulare) and the petro-occipital fissure (Fissura petrooccipitalis), which is clearly visible on a macerated skull at the level of the sulcus for the inferior petrosal sinus (Sulcus sinus petrosi inferioris).
- With the internal ear cavities: the fossa communicates via the external aperture of the vestibular canaliculus (Apertura canaliculi vestibuli) and the apertures of the cochlear canaliculus (Aperturae canaliculi cochleae).
Briefly: answers to topical questions
What passes through the superior orbital fissure?
Cranial nerves and venous vessels pass through the superior orbital fissure into the middle cranial fossa. These include the ophthalmic nerve, oculomotor nerve, trochlear nerve, and abducens nerve. The superior ophthalmic vein and sometimes anterior meningeal branches from the ophthalmic artery also pass through this fissure.
What passes through the foramen rotundum?
The foramen rotundum provides communication from the middle cranial fossa to the pterygopalatine fossa. The maxillary nerve, which is the second branch of the trigeminal nerve, enters the cavity of the pterygopalatine fossa through this foramen.
What passes through the jugular foramen?
Cranial nerves and blood vessels pass through the jugular foramen, located in the posterior cranial fossa between the occipital and temporal bones. Specifically, the glossopharyngeal nerve, vagus nerve, and accessory nerve exit through it, along with veins. Additionally, the posterior meningeal artery enters the cranial cavity through the jugular foramen.
What passes through the foramen spinosum?
The middle meningeal artery, branching from the maxillary artery, passes through the foramen spinosum from the middle cranial fossa to the external cranial base. A vein and a branch of the mandibular nerve also pass through it.
What passes through the internal acoustic meatus?
Cranial nerves and inner ear vessels pass through the internal acoustic meatus of the posterior cranial fossa. Its contents include the facial nerve, intermediate nerve, and vestibulocochlear nerve, as well as labyrinthine arteries and veins.
What passes through the optic canal?
The optic canal of the middle cranial fossa provides communication with the orbit. Passing through this canal are the optic nerve, the ophthalmic artery (a branch of the internal carotid artery), and the central retinal artery.
The boundaries of the fossae can be remembered using the "domino" principle: the posterior boundary of the anterior fossa is precisely the anterior boundary of the middle fossa, and the posterior boundary of the middle fossa serves as the anterior boundary for the posterior fossa.
Class and exam questions
Which structure forms the posterior boundary of the middle cranial fossa along the midline?
The dorsum sellae (Dorsum sellae), which belongs to the body of the sphenoid bone.
How does the middle cranial fossa communicate with the pterygopalatine fossa?
Through a single foramen only — the foramen rotundum.
Why cannot the foramen lacerum be considered a true foramen in a living person?
Because in life this area is occupied by a permanent synchondrosis (cartilaginous tissue) forming the sphenopetrosal fissure (Fissura sphenopetrosa). The open foramen is visible only on a dry bone specimen.
Through which foramina is the posterior cranial fossa connected to the inner ear?
Connection with the inner ear is provided via the aperture of the vestibular canaliculus and the apertures of the cochlear canaliculus.
What else to study on this topic
- Detailed topography of the facial canal and its branches
- Synchondroses of the cranial base and their age-related changes
- Contents of the jugular foramen and foramen magnum
- Topography of the optic canal and superior orbital fissure
Study the complete topic in the Anatomy course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on the "Internal cranial base" and 1,363 other subject pages
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 295 video lessons by subject
Other topics in the "Skull" section
Free video lessons: AnatomyShort lessons with study notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.