The anterior atlantoöccipital membrane (anterior atlantoöccipital ligament) is broad and composed of densely woven fibers, which pass between the anterior margin of the foramen magnum above, and the upper border of the anterior arch of the atlas

Atlas (anatomy)

In anatomy, the atlas is the most superior cervical vertebra of the spine.It is named for the Atlas of Greek mythology, because it supports the globe of the head....

 below.

Laterally, it is continuous with the articular capsules.

In front, it is strengthened in the middle line by a strong, rounded cord, which connects the basilar part of the occipital bone

Occipital bone

The occipital bone, a saucer-shaped membrane bone situated at the back and lower part of the cranium, is trapezoidal in shape and curved on itself...

 to the tubercle on the anterior arch of the atlas.

This membrane is in relation in front with the Recti capitis anteriores, behind with the alar ligaments.