Fig. 4

A photograph of a specimen B shows a left posterolateral view of the sub-occipital region showing vertebral artery passage from lateral to medial under the oblique inferior boarder of the atlanto-occipital membrane. This part of atlanto-occipital membrane extends from the posteromedial aspect of the superior articular process of the atlas to the medial boarder of vertebral artery groove. It is this oblique ligament that ossifies and forms the posterior complete or incomplete arcuate foramen. Note this specimen has a partial ossification of the superior aspect of the atlanto-occipital membrane. 1. Oblique part of atlanto-occipital membrane with partial ossification superiorly; 2. Vertebral artery; 3. C1 dorsal ramus; 4. C2 Dorsal root ganglia; 5. C2 Ventral Ramus; 6. C2 dorsal ramus; 7. Dorsal arch of atlas; 8. Dorsal tubercle of atlas; 9. Rectus Capitis Posterior Minor; 10. Lamina of axis; 11. Atlanto-occipital membrane