posterior arch of the atlas

It emerges between the posterior arch of the atlas and the lamina of the axis, below the Obliquus inferior.

At the C1 level, the vertebral arteries travel across the posterior arch of the atlas through the suboccipital triangle before entering the foramen magnum.

The posterior division of the first cervical or suboccipital nerve is larger than the anterior division, and emerges above the posterior arch of the atlas and beneath the vertebral artery.

The posterior atlantoaxial ligament is a broad, thin membrane attached, above, to the lower border of the posterior arch of the atlas; below, to the upper edges of the laminæ of the axis.