Posterior cranial fossa
The posterior cranial fossa (latin: fossa cranii posterior) lies at the lowest level of the internal cranial base and is the largest of the three cranial fossae.
The boundaries of the posterior cranial fossa are formed anteriorly by the dorsum sellae, posterior aspects of the body of the sphenoid and the basilar part of occipital bone; posteriorly by the squamous part of the occipital bone; laterally by the petrous and mastoid parts of the temporal bone and by the lateral parts of the occipital bone.
The base or floor of the posterior cranial fossa is formed by the occipital bone, the posterior surface of the petrosal part of the temporal bone, and the mastoid angle of the parietal bone.
The borders of the posterior cranial fossa ar the following:
- anteromedial: dorsum sellae of the sphenoid;
- anterolateral: superior border of the petrous part of the temporal bone;
- posterior: squamous part of the occipital bone, groove for transverse sinus, internal occipital protuberance;
- inferior: mastoid part of the temporal bone, the squamous, condylar and basilar parts of the occipital bone.
The posterior cranial fossa accommodates the following parts of the brain:
There are several opening connecting the posterior cranial fossa with other parts of the skull, these are as following:
- inner acoustic meatus,
- opening of vestibular canaliculus,
- mastoid foramen,
- foramen magnum,
- hypoglossal canal,
- condylar canal,
- jugular foramen.
The first three openings mentioned above - inner acoustic meatus, opening of the vestibular canaliculus and mastoid foramen - are located in the temporal bone.
The inner acoustic meatus is a paired canal connecting the posterior cranial fossa and the facial canal. It transmits the facial nerve and the vestibulocochlear nerve, and also the labyrinthine artery.
The opening of the vestibular canaliculus connects the posterior cranial fossa with the vestibule of the internal ear. The vestibular canaliculus carries the vestibular aqueduct.
The mastoid foramen leads from the posterior cranial fossa to the external cranial base and transmits the mastoid emissary vein, a small branch of the occipital artery, and the posterior meningeal artery.
Three openings of the posterior cranial fossa are located in the occipital bone, these are the foramen magnum, hypoglossal canal, and condylar canal.
The foramen magnum is the largest opening in the skull base connecting the posterior cranial fossa with the external cranial base. The foramen magnum transmits the lower end of the medulla oblongata, the vertebral artery, the spinal root of the accessory nerve and the anterior and posterior spinal arteries.
The paired hypoglossal canal leads to the external cranial base and carries the hypoglossal nerve
The paired condylar canal also leads to the external surface of the cranial base and conducts the occipital emissary vein.
The jugular foramen forms bilaterally between the occipital and temporal bones in the posterior cranial fossa and leads to the external surface of the cranial base. The jugular foramen transmits the inferior petrosal and sigmoid sinuses, and the glossopharyngeal, vagus, and accessory nerves.