foramen

Foramen is a term used in anatomy to describe a natural opening or passage in a bone or other structure that allows the transit of nerves, blood vessels, or other structures. The plural form is foramina. Foramen openings occur throughout the skeleton and soft tissues, and their shape and size reflect the structures they transmit.

In the skull, numerous foramina provide routes for cranial nerves and vessels. The foramen magnum in the occipital bone is a large opening through which the brainstem continues as the spinal cord and which transmits the accessory nerve roots and vertebral arteries. The optic canal (foramen) in the sphenoid bone transmits the optic nerve and ophthalmic artery. The foramina ovale, rotundum, and spinosum transmit branches of the trigeminal nerve and meningeal vessels. The jugular foramen, between the temporal and occipital bones, transmits the internal jugular vein as well as cranial nerves IX, X, and XI. Other facial foramina include the infraorbital foramen in the maxilla and the mental foramen in the mandible, which convey facial nerves and vessels.

Beyond the skull, the vertebral foramina are openings in each vertebra that align to form the vertebral (spinal) canal, housing the spinal cord and meninges. The obturator foramen in the pelvic bone is a large opening largely closed by a fibrous membrane in life, through which nerves and vessels pass.

Foramen differ from canals and fissures, which are elongated openings. The term derives from Latin for “hole.”