[Location] Localized in the prone position or in the erect sitting position with the elbows resting on a table, on the back. on the posterior median line, in the depression below the spinous process of the third thoracic vertebra. (Fig.69)
 
[Regional Anatomy] Skin→subcutaneous tissue→the supraspinal ligament→the interspinal ligament. Superficial layer, the distribution of the medial cutaneous branch of the posterior rami of the third thoracic 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 branch of the posterior rami of the third thoracic nerves, the branches or the subordiantial ramus of the dorsal branch of the third posterior intercostal artery and vein.