Foramen magnum

The foramen magnum is the large opening in the base of the skull through which the brainstem continues as the spinal cord. It also transmits blood vessels and nerves between the skull and vertebral canal.

Occipital bone: The skull bone that forms the back and base of the cranium and surrounds the foramen magnum. Its basilar, lateral, and squamous parts form the margins of the opening.
Medulla oblongata: The lowest part of the brainstem, continuous with the spinal cord. It crosses the foramen magnum before continuing as the spinal cord.
Chiari malformation: A group of structural abnormalities in which parts of the cerebellum extend downward through the foramen magnum. The opening is the site where cerebellar tissue may descend into the spinal canal.
Australopithecus afarensis: An extinct hominin species known from fossils including the partial skeleton nicknamed Lucy. The position of its foramen magnum helps assess its habitual posture and bipedal locomotion.
Jugular foramen: An opening in the skull base through which the internal jugular vein and several cranial nerves pass. Unlike the foramen magnum, it transmits major veins and cranial nerves rather than the brainstem.
Brainstem: The central nervous system structure connecting the brain with the spinal cord. It passes through the opening and becomes continuous with the spinal cord.
Vertebral arteries: Paired arteries that ascend through the neck and supply the brain and spinal cord. They enter the cranial cavity through the foramen magnum.
Foramen magnum decompression: A neurosurgical procedure that removes bone around the foramen magnum to create more space at the craniovertebral junction. It can relieve crowding associated with Chiari malformation.
Homo erectus: An extinct human species that lived across Africa and parts of Eurasia. Its skull anatomy provides evidence for the evolution of the hominin craniovertebral junction.
Hypoglossal canal: A short canal in the occipital bone that transmits the hypoglossal nerve. It lies beside the foramen magnum but carries a single cranial nerve.

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