The iliocostalis thoracis is a muscle located in the lower back, part of the larger group known as the erector spinae. It plays a crucial role in maintaining posture and supporting the spine during movement. This muscle extends from the lower ribs to the upper ribs, helping to stabilize the thoracic region. Functionally, the iliocostalis thoracis assists in lateral flexion and extension of the spine. It works in conjunction with other muscles in the erector spinae group, such as the longissimus thoracis and spinalis thoracis, to facilitate various movements and maintain an upright position.