foramina

Foramina are natural openings in bones or other structures through which nerves, blood vessels, and other passing structures travel. The term is the plural of foramen. Foramina can be simple holes or part of larger passages, and their size and shape often reflect the vessels and nerves they convey. They are distinct from canals, which are longer passages, and from fissures, which are elongated slits.

In the skull, many foramina provide essential routes for cranial nerves and vessels. Notable examples include the foramen magnum, through which the medulla oblongata and the vertebral arteries enter the cranial cavity; the optic canal for the optic nerve; the cribriform foramina for olfactory nerve fibers; the foramina for the branches of the trigeminal nerve (such as the foramen rotundum, ovale, and spinosum); the internal acoustic meatus for facial and vestibulocochlear nerves; the jugular foramen for cranial nerves IX–XI and the internal jugular vein; the hypoglossal canal for cranial nerve XII; the infraorbital foramen for the infraorbital nerve and vessels; and the mental foramen for the mental nerve and vessels.

In the vertebral column, the intervertebral foramina are lateral openings formed by adjacent pedicles. They transmit spinal nerve roots and accompanying vessels, and their size can vary with movement or pathology.

In the pelvis and limbs, the obturator foramen is a large opening mostly closed by a membrane; the greater and lesser sciatic foramina permit passage of nerves and vessels between the pelvis and the gluteal region and thigh; sacral foramina transmit sacral nerves.

Other notable contexts include the foramina in the cribriform plate for the olfactory nerves and the fetal foramen ovale in the heart, which typically closes after birth. The diaphragm contains major openings, such as the caval opening, esophageal hiatus, and aortic hiatus, through which major vessels pass.