Foramen Magnum – Location, Anatomy and Structures passing through it


Foramen Magnum Definition: The large orifice in the base of the skull through which the spinal cord passes to the cranial cavity and becomes continuous with the medulla oblongata. It is basically that large opening at the base of skull where the spinal cord exits the cranial vault.

Foramen Magnum

Where is Foramen Magnum located?

It is situated in the occipital bone, and it forms around the base of medulla oblongata. Four individual parts of the occipital join together to form the Foramen Magnum – pars squama, left and right pars lateralis, and pars basilaris. There are two important points in the foramen, including opisthion (the midpoint on posterior line of the foramen) and basion (the midpoint on anterior margin of the foramen).

What are the structures passing through Foramen Magnum?

The structures passing through the large foramen magnum include:

  • Spinal cord as an extension of medulla exits the cranial vault through this foramen
  • Vertebral arteries
  • Anterior spinal arteries
  • Posterior spinal arteries
  • Tectorial membranes
  • Alar ligaments
  • Spinal component of accessory nerve into the skull

The other important foramina of skull include Foramen ovale, supraorbital foramen, infraorbital foramen, foramen ovale, foramen rotundum and foramen lacerum among others.

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