Carotid canal (canalis caroticus)
Canalis caroticus begins with the external aperture (apertura externa canalis carotici) on the inferior surface of the petrous part of the temporal bone and ends with the internal aperture (apertura interna) at the apex of the petrous part. The external opening is located adjacent to the jugular fossa (fossa jugularis), serving as a landmark when identifying the canal on a specimen.
The canal transmits the internal carotid artery (arteria carotis interna) and the accompanying internal carotid sympathetic plexus. 2–4 caroticotympanic canaliculi (canaliculi caroticotympanici), which open on the anterior wall of the tympanic cavity, branch off from the posterior wall of the canal; these transmit the caroticotympanic nerves.
Facial canal (canalis nervi facialis)
The canal begins at the fundus of the internal acoustic meatus (porus acusticus internus) and ends at the stylomastoid foramen (foramen stylomastoideum). It is Z-shaped and divided into three parts:
- Labyrinthine part — from the internal acoustic meatus to the genu;
- Tympanic part — runs along the medial wall of the tympanic cavity;
- Mastoid part — runs vertically downward to the stylomastoid foramen.
The transition from the labyrinthine part to the tympanic part forms the genu of the facial nerve (geniculum canalis nervi facialis). The canal transmits the facial nerve (nervus facialis), intermediate nerve (nervus intermedius), and the stylomastoid artery and vein.
Canaliculus of the chorda tympani (canaliculus chordae tympani)
Branches off from the facial canal slightly below the genu, passes through the tympanic cavity, and opens into the petrotympanic fissure (fissura petrotympanica), also known as the Glaserian fissure. The canaliculus transmits the chorda tympani — a branch of the intermediate nerve that carries taste fibers to the anterior two-thirds of the tongue and preganglionic parasympathetic fibers to the submandibular and sublingual ganglia.
Mastoid canaliculus (canaliculus mastoideus)
Begins at the floor of the jugular fossa and ends in the tympanomastoid fissure (fissura tympanomastoidea). The canaliculus transmits the auricular branch of the vagus nerve (ramus auricularis nervi vagi). To locate the canaliculus on a specimen, use the stylomastoid foramen and external acoustic meatus as landmarks.
Tympanic canaliculus (canaliculus tympanicus)
Begins as a small aperture in the petrosal fossa (fossula petrosa), located between the external opening of the carotid canal and the jugular fossa. The canaliculus ends at the hiatus for the lesser petrosal nerve — hiatus canalis nervi petrosi minoris. It transmits the tympanic nerve (nervus tympanicus), a branch of the glossopharyngeal nerve, which emerges onto the anterior surface of the petrous pyramid to continue as the lesser petrosal nerve.
Musculotubular canal (canalis musculotubarius)
The canal begins at the anterior border of the petrous pyramid lateral to the external opening of the carotid canal and ends with two separate openings on the anterior wall of the tympanic cavity. A horizontal bony septum divides the canal into two semicanals:
- Semicanalis musculi tensoris tympani — the upper semicanal, contains the tensor tympani muscle;
- Semicanalis tubae auditivae — the lower semicanal, contains the bony part of the pharyngotympanic (auditory) tube.
Algorithm for identifying canals on a specimen
On a dissected temporal bone, work systematically: first, locate the jugular fossa as a key landmark, and adjacent to it, the external opening of the carotid canal. Rotating the bone reveals the internal opening and the porus acusticus internus — the beginning of the facial canal. Lateral to the carotid canal lies the musculotubular canal, and on the inferior surface of the pyramid is the petrosal fossa with the entrance to the tympanic canaliculus. The stylomastoid foramen is located at the base of the styloid process and serves as a landmark for the termination of the facial canal and the entrance to the mastoid canaliculus.
Key points
- The carotid canal transmits the internal carotid artery (a. carotis interna) and gives rise to the caroticotympanic canaliculi.
- The facial canal has three parts — labyrinthine, tympanic, and mastoid, with a genu between the first two.
- The canaliculus of the chorda tympani opens into the petrotympanic (Glaserian) fissure.
- The mastoid canaliculus begins in the jugular fossa and ends in the tympanomastoid fissure; it transmits the auricular branch of the vagus nerve (n. vagus).
- The tympanic canaliculus begins in the petrosal fossa and ends at the hiatus canalis n. petrosi minoris.
- The musculotubular canal is divided into the semicanal for the tensor tympani muscle (m. tensor tympani) and the semicanal for the auditory tube.
- All listed canals open into or communicate with the tympanic cavity, providing its innervation and connection to the nasopharynx.
- Key landmarks for most canals on a specimen are the jugular fossa and the external opening of the carotid canal.