The erector spinae muscles are the second layer of intrinsic, or “true,” back muscles and like their more superficial counterparts, the splenius muscles, their muscle fibers span many vertebral levels. Unlike the splenius muscles, the erector spinae muscle group spans the entire length of the vertebral column. Beginning on the posterior surface of the sacrum, the muscle group terminates on the back of the cranium. The erector spinae is divided into three parts, which from medial to lateral are the spinalis muscle, the longissimus muscle, and the iliocostalis muscle. This strong group of epaxial muscles consists of muscle fibers that course vertically and somewhat laterally as they cross multiple vertebral levels. They function as primary extensors of the vertebral column and are key postural muscles for the maintenance of the upright bipedal posture. Like all epaxial muscles, they are innervated by the posterior (dorsal) ramus of the spinal nerves.

Musculus erector spinae

Muscle érecteur du rachis