The back comprises the dorsal part of the neck and the torso (dorsal body cavity) from the occipital bone to the top of the tailbone. The muscles of the back can be divided in three main groups according to their anatomical position and function. The superficial muscles participate in the movements of the upper limb, the intermediate muscles support the respiratory function, and the deep muscles are involved in the posture and rotation of the vertebral column. The first two groups include the extrinsic muscles, which are innervated by the anterior branches of the spinal nerves, while intrinsic muscles of the latter group are innervated by the posterior branches. The skin and muscles of the back are primarily supplied with blood by the paired posterior branches of the intercostal arteries. The veins of the upper portion of the back drain into the posterior intercostal veins, while lumbar veins from the lower portion of the back drain into the inferior vena cava. Similarly, the intercostal lymph nodes receive drainage from the thoracic portion of the back, while the inguinal lymph nodes drain from the lumbar back.
Two muscles (the serratus posterior superior and inferior) belong to the intermediate group of back muscles. They are immediately deep to the muscles in the superficial group and pass obliquely outward from the vertebral column to attach to the ribs. These muscles support the respiratory function and are also covered under chest wall muscles in the “Chest wall” article.