One body part that starts with the letter "Q" is the quadratus lumborum muscle. This muscle is found in the lower back behind the kidneys, the pancreas and the horizontal part of the duodenum, which is the first section of the small intestine. It's also called the QL muscle.
The QL muscle has four sides and tapers somewhat at the top. Its functions are to support the stability and the movement of the vertebrae and the pelvis. It also aids the body in breathing by fixing the 12th rib during an expiration.
The QL muscle has been implicated in some patients' episodes of lower back pain.