Ligament · Neck

Posterior atlanto occipital membrane

Membrana atlantooccipitalis posterior

A broad thin membrane running from the back of the atlas up to the rear margin of the foramen magnum, closing the space between skull and first vertebra from behind, and the topmost member of the ligamentum flavum series. Its distinguishing feature is at the side: the membrane arches over the groove on the atlas in which the vertebral artery lies, converting that groove into an opening through which the artery and the first cervical nerve pass on their way into the skull. That arch is sometimes ossified into a complete bony bridge, a well-recognised variant of the atlas.