[Location] Localized in the prone position. In the region of the sacrum, medial and inferior to BL32 (Ciliao), in the third posterior sacral foramen. (Fig.62)
 
[Regional Anatomy] Skin→subcutaneous tissue→the gluteus maximus→the erector spinae. Superficial layer, the distribution of the intermediate gluteal cutaneous nerve; deep layer, the third sacral nerve, and the posterior branches of the lateral sacral artery and vein.