[Location] Localized in the prone position. On the lumbar region, on the posterior median line, in the depression below the spinous process of the fourth lumbar vertebra. (Fig.69)
 
[Regional Anatomy] Skin→Subcutaneous tissue→the supraspinal ligament→the interspinal ligament→the ligamenta tiara. Superficial layer, the distribution of the medial branch of the posterior rami of the fourth lumbar nerves and the artery and vein along with it; deep layer, there are the external (posterior) vertebral venous plexus between the adjacent spinous processes, the branches of the posterior branches of the 4th lumbar nerves and the branches or tributaries of the dorsal branches of the 4th lumbar artery and vein.