PMC4724954_01
Photograph of specimen A shows a posterior view of the sub-occipital region showing the atlas with symmetrical complete bilateral dorsal osseous bridges; the lateral osseofibrous bridge; and the oval opening between the two bridges. Also, the passage of VA through the tunnel formed by the dorsal and lateral bridges. The sub-occipitall nerve (C1 dorsal ramus) along with branches of vertebral artery emerging from the oval opening. 1. Dorsal bridge; 2. Vertebral artery; 3. C1 dorsal ramus; 4. Lateral bridge; 5. Rectus capitis posterior minor; 6. C2 dorsal root ganglion; 7. C2 dorsal ramus; 8. C2 ventral ramus; 9. Branches of VA; 10. Dorsal tubercle of atlas; 11. Dorsal arch of atlas
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PMC4724954_01_12998_2016_82_Fig1_HTML.jpg
Fig1
Visual observations were preserved with digital photography and dimension measurements were recorded (Figs. 1, 2, 3 and 4).
A higher magnification of specimen A of the right posterolateral aspect of sub-occipital region showing the atlas with complete dorsal and lateral bridges; and the oval opening between the two bridges. Also, the passage of vertebral artery through the tunnel formed by the posterior and lateral bridges. The sub-occipital nerve (C1 dorsal ramus) along with branches of VA emerging from the oval opening. 1. Dorsal bridge; 2. Vertebral artery; 3. C1 dorsal ramus; 4. Lateral bridge; 5. Denticulate ligament; 6. C2 dorsal root ganglion; 7. C2 dorsal ramus; 8. C2 ventral ramus; 9. Branches of VA; 10. Dorsal tubercle of atlas; 11. Dorsal arch of atlas
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PMC4724954_01_12998_2016_82_Fig2_HTML.jpg
Fig2
Visual observations were preserved with digital photography and dimension measurements were recorded (Figs. 1, 2, 3 and 4).
Schematic drawing corresponding to Figs. 1 and 2 showing the dimension measurements associated with the dorsal arch of the atlas: D 1 = 2.5 mm, D 4 = 3.8 mm, D 7 = 5 mm, D 10 = 18 mm, D 2 = 7.5 mm, D 5 = 10 mm, D 8 = 13 mm, D 11 = 85 mm, D 3 = 14 mm, D 6 = 5 mm, D 9 = 6 mm. LDPP = Left dorsal ponticulus posticus; LLPP = Left lateral ponsiculus posticus; RDPP = Right dorsal ponticulus posticus; RLPP = Right lateral ponticulus posticus; DAT = Dorsal arch of atlas; DTA = Dorsal tubercle of atlas; VAG = Vertebral artery groove; VA = Vertebral artery
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PMC4724954_01_12998_2016_82_Fig3_HTML.jpg
Fig3
Visual observations were preserved with digital photography and dimension measurements were recorded (Figs. 1, 2, 3 and 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
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PMC4724954_01_12998_2016_82_Fig4_HTML.jpg
Fig4
Visual observations were preserved with digital photography and dimension measurements were recorded (Figs. 1, 2, 3 and 4).
Frontal radiographic view of C1 and C2 vertebrae demonstrating complete lateral ponticle (arrow) on right and incomplete on the left. Linear bar represent 10 mm
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PMC4724954_01_12998_2016_82_Fig5_HTML.jpg
Fig5
Radiographic images were obtained in the frontal, bilateral oblique and neutral lateral (right and left) positions of the prosected suboccipital region of Specimen A to compare the visual effects of this variation (Figs. 5 and 6).
Lateral radiographic view of C1 and C2 vertebrae demonstrating complete ossification of membrane (arrow) forming an arcuate foramen. Linear bar represent 10 mm
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PMC4724954_01_12998_2016_82_Fig6_HTML.jpg
Fig6
Radiographic images were obtained in the frontal, bilateral oblique and neutral lateral (right and left) positions of the prosected suboccipital region of Specimen A to compare the visual effects of this variation (Figs. 5 and 6).