Autochtonous back musculature
The true back musculature stems from the epaxial portion of the myotome and in the adult lies under that of the externally visible muscles that do not count as being autochtonous back musculature. The deep portions of the autochtonous back musculature are ordered in a strictly segmental fashion. The innervation then occurs according to the dorsal branches of the spinal nerves. The superficial muscle blastemas of the autochtonous back musculature form segment-overlapping, long muscles.
The externally visible, superficial back musculature (e.g., the latissimus dorsi muscle) stems from the hypaxial portion of the myotome. Originally, it belongs to the arm musculature and secondarily it is again shifted back to the thorax. Their original innervation (brachial plexus) is retained, however. A further, more prominent superficial back muscle, the trapezes muscle, which has a cranial origin (innervation by the N. XI), forms the upper contour of the back.