The thoracic nerves are the spinal nerves emerging from the thoracic vertebrae. Branches also exit the spine and go directly to the Sympathetic Chain Ganglia of the Autonomic Nervous System where they are involved in the functions of organs and glands in the head, neck, thorax and abdomen.
The medial branches (ramus medialis; internal branch) of the posterior divisions of the upper six thoracic nerves run between the Semispinalis dorsi and Multifidus, which they supply; they then pierce the Rhomboidei and Trapezius, and reach the skin by the sides of the spinous processes. This sensitive branch is called medial cutaneous ramus.
The medial branches of the lower six are distributed chiefly to the Multifidus and Longissimus dorsi, occasionally they give off filaments to the skin near the middle line. This sensitive branch is called posterior cutaneous ramus.
Areas of distribution of the cutaneous branches of the posterior divisions of the spinal nerves.
Diagram of the course and branches of a typical intercostal nerve.
Intercostal nerves, the superficial muscles having been removed.