Foramina and Fissures of the Skull
The major foramina and fissures of the skull are dotted about within the neurocranium and the viscerocranium in the most illogical way one can imagine. The human body is an earthly miracle and functions to perfection when under ideal conditions, however for the anatomy enthusiast, it is only through dedication and long hours that the anatomical landmarks of the skull can be correctly recalled. In spite of the previous observations, this article aims to simplify this complex and extremely detailed topic as much as can be allowed. Below the cranial foramina and fissures are grouped by the bones that contain them.
Landmarks that are situated between two or more bones
- The foramen caecum can be found between the frontal bone and the ethmoid bone and it carries the emissary vein from the nasal cavity to the superior sagittal sinus.
- The anterior ethmoid foramen is also found between the frontal bone and the ethmoid bone and it encapsulates the anterior ethmoid nerve and its corresponding vessels.
- Lastly, the posterior ethmoid foramen falls between the frontal and ethmoidal bones and encircles the posterior ethmoidal nerve and its corresponding vessels.
- The foramen lacerum is situated between several articulations, including the greater wing and the body of the sphenoid bone, as well as the petrous portion of the temporal bone and the basilar portion of the occipital bone. It doesn’t carry any vessels, but it is filled with fibrous cartilage and has an anterior opening for the pterygoid canal and a posterior opening for the carotid canal.
- The temporal bone and the sphenoid bone surround the opening of the auditory tube which houses the cartilaginous portion of the auditory tube.
- The jugular foramen is surrounded by the petrous portion of the temporal bone and the occipital bone. It allows many structures to pass through it, including the glossopharyngeal nerve (CN IX), the vagus nerve (CN X), the spinal accessory nerve (CN XI), the inferior petrosal sinus, the sigmoid sinus and the posterior meningeal artery.
- Lastly, the inferior orbital fissure runs between the greater wing of the sphenoid bone, the maxilla and the orbital portion of the palatine bones. It houses the maxillary division of the trigeminal nerve (CN V/II), the zygomatic nerve and the infraorbital vessels.
The Frontal Bone
The supraorbital foramen contains the supraorbital nerve and its corresponding vessels and is the only anatomical landmark that is purely within the frontal bone.
The Sphenoid Bone
The optic canal encircles the optic nerve and the ophthalmic artery.
The greater and lesser wings of the sphenoid bone hold the superior orbital fissure which allows many structures to pass through the skull including the nasociliary branch, the frontal branch and the lacrimal branch of the ophthalmic division of the trigeminal nerve (CN V/I), the oculomotor nerve (CN III), the trochlear nerve (CN IV), the abducent nerve (CN VI) and the superior and inferior ophthalmic veins.
The foramen rotundum surrounds the maxillary division of the trigeminal nerve (CN V/II). • The foramen ovale houses the mandibular division of the trigeminal nerve (CN V/III), the accessory meningeal artery, the lesser petrosal nerve and the emissary vein.
The foramen spinosum encircles the middle meningeal vessels and the meningeal branch of the mandibular division of the trigeminal nerve (CN V/III).
The sphenoid foramen contains the emissary vein.
The Zygomaticofacial foramen is the Zygomatic bone’s lone anatomical landmark and contains the zygomaticofacial nerve and its corresponding vessels.
The incisive foramen is found on the palatine process of the maxilla and holds the nasopalatine nerve and the sphenopalatine artery.
The Infraorbital foramen is found on the frontal part of the maxilla and contains the infraorbital nerve, along with its corresponding vessels.
The mandible has 2 mental foramina and each encapsulates the mental nerve as well as the metal artery and vein.
The Palatine Bone
The greater palatine foramen contains the greater palatine artery, vein and nerve.
The lesser palatine foramen houses the lesser palatine vessels and nerve.
The Occipital Bone
The condylar canal contains the emissary vein and the meningeal branches of the ascending pharyngeal artery.
The hypoglossal canal encircles the hypoglossal nerve (CN XII).
The foramen magnum is the largest foramen in the entire cranium and contains the medulla oblongata, the vertebral arteries and the spinal roots of the spinal accessory nerves (CN XI).
The Temporal Bone
The carotid canal can be found in the petrous portion of the temporal bone and contains the internal carotid artery and the internal carotid nerve plexus which contains sympathetic fibers.
The hiatus for the lesser petrosal nerve in the petrous portion of the bone houses the lesser petrosal nerve.
The hiatus for the greater petrosal nerve also in the petrous part of the bone similarly contains the greater petrosal nerve.
Finally, the last landmark of the petrous part of the temporal bone is the opening of the vestibular aqueduct, which includes the endolymphatic duct.
The mastoid portion of the temporal bone has the mastoid foramen which contains the emissary vein and sometimes branches of the occipital artery.
The tympanic canaliculus houses the tympanic branch of the glossopharyngeal nerve (CN IX) and resides within the jugular foramen of the temporal bone.
The petrotympanic fissure includes the chorda tympani and the anterior tympanic artery.
The stylomastoid foramen houses the facial nerve (CN VII) and the stylomastoid artery.
Finally, the tympanomastoid fissure holds the auricular branch of the vagus nerve (CN X).
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