Skeleton torso with schematically outlined medial autochthonous back muscles. Autochthonous back muscles are all muscles that are innervated by dorsal rami of spinal nerves. They are also called erector spinae muscles. On a living person there are two visible longitudinal bulges on both sides of the spinal processes that are most developed in the pelvic area. The muscles are located in an osteofibrous canal that consists of vertebral bows, costal processes, and spinal processes. The spinal erectors can be subdivided into a lateral superficial tract and a medial profound tract. The lateral tract extends from the pelvis to the cranium.