The spinalis thoracis is a muscle located in the back, part of the erector spinae group. It runs along the spine, connecting the upper and lower thoracic vertebrae. This muscle plays a crucial role in maintaining posture and supporting the spine during movement. Functionally, the spinalis thoracis helps extend the back and allows for lateral flexion. It works in conjunction with other muscles in the erector spinae group, such as the longissimus and iliocostalis, to stabilize the spine and facilitate various movements of the torso.