Spinal groove

From Spanking Art
George Rennie's Cupid Rekindling the Torch of Hymen.

The spinal groove or spinal furrow is a groove-like depression in the skin that runs vertically along the human back along the spine. In most people it is not visible along the entire length of the spine but only in the middle part, from between the shoulderblades to somewhere at the lumbar vertebrae. It fades out at the Rhombus of Michaelis, or at the sacral triangle.

The spinal groove is often emphasized in visual art such as painting, drawing, or sculpture, because it structures the back nicely and shows the curved form of the spine.