FIG 7. Axial CT scan (A) and corresponding gross anatomic section (B) showing the L5 posterior ramus (white arrow) located into a groove bounded medially by the superior articular process of S1 (black arrow) and laterally by the ala of the sacrum (as). The gross anatomic section was dissected to better show the whole course of the posterior ramus into the bony groove. S1, first sacral vertebrae; SG, spinal ganglia.