The cruciate (cruciform) ligament of the atlas is a ligamentous complex located at the level of the atlanto-occipital joint and atlanto-axial joint. It is composed of two distinct parts that go in different directions.

The horizontal portion of the cruciform ligament is formed by the transverse ligament of the atlas, while the vertical part is formed by additional fibers known as the longitudinal bands. The longitudinal bands extend above and below the transverse ligament. They can be further subdivided into two smaller components called the superior longitudinal band and the inferior longitudinal band.

The transverse ligament of the atlas and both longitudinal bands are arranged in two different directions. As mentioned earlier, the transverse ligament is horizontally oriented, while the longitudinal bands are vertically positioned. The layout of the cruciform ligament resembles a cross, and therefore, it has such a name.

The transverse ligament of the atlas (transverse atlantal ligament) is a strong and broad ligament that extends between two small tubercles found on the medial aspects of the lateral masses of the atlas (C1). It fixates the dens of the axis (C2) to the posterior part of the anterior arch of the atlas. The anterior arch of the atlas and transverse atlantal ligament forms the osteo-ligamentous ring, which is an articulating component of the atlanto-axial joint. It encloses the dens of the axis.
The superior longitudinal band stretches from the superior aspect of the transverse ligament to the anterior border of the foramen magnum and clivus of the occipital bone. It is positioned between the apical ligament of the dens anteriorly and the tectorial membrane posteriorly. The primary function of the superior longitudinal band is to hold the transverse ligament in its anatomical position. Therefore, it aids the transverse ligament in holding the atlas (C1) against the dens of the axis (C2).
The inferior longitudinal band goes from the inferior aspect of the transverse ligament to the posterior surface of the body of the axis (C2). It prevents the transverse ligament from extending too far superiorly.

The transverse ligament of the atlas and the alar ligaments are the primary stabilizers of the atlanto-axial joint.

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Cruciate ligament of atlas