Major canals
Among the canals of the temporal bone, three main (major) ones are distinguished.
- Carotid canal (Canalis caroticus)
- Origin: external aperture on the inferior surface of the petrous part.
- Course: runs anteriorly and medially, then forms a bend (genu) and directs superiorly.
- Termination: internal aperture at the apex of the petrous part.
- Contents: internal carotid artery, venous plexus, and sympathetic nerves.
- Facial canal (Canalis nervi facialis)
- Origin: fundus of the internal acoustic meatus.
- Course: has a complex trajectory. First runs perpendicularly to the axis of the petrous part up to the genu (Geniculum), then turns and runs parallel to the axis posteriorly (forming a prominence in the tympanic cavity), after which it descends vertically.
- Termination: stylomastoid foramen (Foramen stylomastoideum).
- Contents: facial nerve, nervus intermedius, and blood vessels.
- Musculotubal canal (Canalis musculotubarius)
- Origin: lateral to the carotid canal, closer to the apex of the petrous part.
- Course: penetrates the thickness of the petrous part, divided by a bony septum into two semicanals (for the tensor tympani muscle and the pharyngotympanic tube).
- Termination: opens on the anterior wall of the tympanic cavity.
Minor canals (canalicular systems)
In addition to the major canals, there are four small canaliculi running through the temporal bone.
- Caroticotympanic canaliculi (Canaliculi caroticotympanici). Originate from the posterior wall of the carotid canal (usually 2–4 openings) and terminate on the anterior wall of the tympanic cavity. They transmit the corresponding nerves and vessels.
- Canaliculus of the chorda tympani (Canaliculus chordae tympani). Originates from the descending part of the facial canal (near the stylomastoid foramen). Passes in transit through the tympanic cavity and exits via the petrotympanic fissure (Fissura petrotympanica). Inside is a branch of the nervus intermedius — the chorda tympani.
- Tympanic canaliculus (Canaliculus tympanicus). Begins in the petrosal fossa (Fossula petrosa) on the inferior surface of the petrous part. Ascends and opens via the hiatus for the lesser petrosal nerve on the anterior surface of the petrous part.
- Mastoid canaliculus (Canaliculus mastoideus). Starts from the floor of the jugular fossa (Fossa jugularis) and terminates in the tympanomastoid fissure. Transmits the auricular branch of the vagus nerve.
Topographical landmarks
For a quick search of canals on a skull specimen, key landmarks are used:
- Jugular notch, external aperture of the carotid canal, and aperture of the cochlear canaliculus form a triangle, inside of which lies the entrance to the tympanic canaliculus.
- Stylomastoid foramen is the main landmark for finding the exit of the facial nerve canal and the origin of the canaliculus of the chorda tympani.
- Hiatuses/apertures on the anterior surface of the petrous part (hiatuses of the channels for the greater and lesser petrosal nerves) indicate the level of the geniculum of the facial nerve.
Briefly: answers to topical questions
Which specific nerves and vessels pass through the caroticotympanic canaliculi?
The caroticotympanic canaliculi transmit the nerves of the same name, as well as vascular branches that are not specifically named.
- Caroticotympanic nerves serve as a landmark that helps quickly find the connections between the carotid canal and the tympanic cavity.
- Vascular branches accompany the nerves, but their exact names are not detailed in the provided materials.
The canaliculi themselves originate from the posterior wall of the carotid canal and open on the anterior wall of the tympanic cavity.
Which exact blood vessels accompany the facial nerve in its canal?
Arteries and veins, whose exact names are not detailed, pass through the facial nerve canal itself, but upon exiting the canal, the nerve is accompanied by a specific vessel.
- Stylomastoid vein (v. stylomastoidea) accompanies the facial nerve as it exits the stylomastoid foramen.
- Arteries and veins are mentioned as contents of the facial nerve canal without specifying exact names.
The texts also mention the stylomastoid artery (a. stylomastoidea), but its course directly inside the canal along with the nerve is not described.
Class and exam questions
Is the internal acoustic meatus considered a canal of the temporal bone?
No, the internal and external acoustic meatuses, as well as the vestibular and cochlear aqueducts, are not classified as true canals of the temporal bone in the international nomenclature.
What passes through the carotid canal?
It transmits the internal carotid artery, accompanying veins, and a plexus of sympathetic nerve fibers.
What parts does the facial nerve canal consist of?
The facial nerve canal consists of three parts: labyrinthine (runs perpendicular to the axis of the petrous part), tympanic (parallel to the axis), and mastoid (descending).
Where does the musculotubal canal open?
The musculotubal canal and both of its semicanals open on the anterior wall of the tympanic cavity (in the middle ear cavity).
What else to study on this topic
- Detailed course of the facial nerve within the petrous part
- Walls of the tympanic cavity and the canals opening into it
- Topography of the slits on the external cranial base (petrotympanic, petrosquamous)
- Relationship of the inner ear structures with the canals of the temporal bone
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