🪴 GoDeep
Search
← University Challenge
Portrait of Foramen magnum

Anatomy · Bones

Foramen magnum

The 'big hole' of the skull

Skull · base

The foramen magnum, Latin for big hole, is the large oval opening in the occipital bone at the base of the skull. It is the largest foramen of the skull, and through it the spinal cord becomes continuous with the medulla oblongata of the brainstem. It also transmits the vertebral arteries, the spinal arteries and the spinal roots of the accessory nerve.

How to spot them

  • ▸A large oval opening in the middle of the base of the skull, with a rounded condyle on each side
  • ▸Lies in the deepest part of the posterior cranial fossa, surrounded by the occipital bone
  • ▸Its position under the skull, rather than at the back, is a sign of upright walking in fossil hominins
  • ▸Where the brainstem ends and the spinal cord begins

What to know

The largest hole in the skull, through which the brainstem passes to become the spinal cord

Foramen magnum — Latin for big hole, in the occipital bone.

In 1925 Raymond Dart used the position of this opening in the Taung Child to argue that the creature walked upright

Foramen magnum — a forward position under the skull indicates bipedalism.

Besides the spinal cord, it transmits the vertebral arteries, the spinal arteries and the spinal roots of the accessory nerve

Foramen magnum — with the tectorial membrane and the apical ligament of the dens.

A rounded condyle on each side of this opening articulates with the first cervical vertebra

Foramen magnum — the occipital condyles and the atlas.

If the cerebellar tonsils are pushed down through this opening, as in a Chiari malformation or brain herniation, the brainstem can be compressed

Foramen magnum — tonsillar herniation or 'coning' compresses the medulla.

Its rim is formed in front by the basilar part of the occipital bone, at the sides by the condylar parts and behind by the squamous part

Foramen magnum — surrounded by all three parts of the occipital bone.

Key ideas

  • In humans the opening faces downward and lies below the skull, so the head balances on top of the spine; in quadrupeds it lies further back and faces backward.

Quick-fire facts

  • •The largest foramen of the skull, oval in shape
  • •Lies in the deepest region of the posterior cranial fossa
  • •Transmits the spinal cord and its meninges, vertebral arteries, anterior and posterior spinal arteries, dural veins and the spinal roots of the accessory nerve
  • •The tectorial membrane and the apical ligament of the dens pass through it
  • •Enclosed entirely within the occipital bone
  • •The spinal cord meets the medulla oblongata here
  • •Raised pressure within the skull can force the cerebellar tonsils down through it (tonsillar herniation)
  • •The Taung Child, discovered in 1924 and described by Raymond Dart in 1925, showed a forward foramen magnum

Drill it — 7 cards

1 / 7new card

Sources