 A line is made from the thoracic spinous process to the fifth lumbar spinous process; tangent lines are then made from the fifth lumbar spinous process to both sides of the pelvic outlet. The dashed lines from the fifth lumbar spine to the right pelvic outlet and the left ilium are distinguished as projections into the right colon, left colon, and rectosigmoid colon. R: Right; L: Left; RS: Rectosigmoid colon.