ABSTRACT
Spinal nerves arise from the spinal cord by a ventral root and a dorsal root, including the spinal ganglion. Both roots are joined to a mixed spinal nerve. There are 31 pairs of spinal nerves: cervical, dorsal, lumbar, sacral and coccygeal. These mixed nerves divide into a ventral and a dorsal division. The ventral divisions are large and form general plexuses: cervical, brachial, lumbar, sacral and pudendal. The branches of the dorsal division are smaller. The dorsal branches of the thoracic roots pass over the transverse processes medial to the costotransversal ligament and intertransversal muscle, which is often missing. The dorsal branches of the thoracic roots divide into medial and lateral branches. Above the level of the T6, the cutaneous branches originate from the medial branches. They emerge in the groove between spinalis and longissimus muscle, pursue a rightangled course through the multifidus spinae muscle and supply the skin of the back (Figure 29.1). The lateral branches supply the longissimus and iliocostalis muscles. Below the T6, the medial branches supply the rotatores, multifidus, spinalis and semispinalis muscles, and lateral branches supply the skin of the rest part of the back. The lateral branches emerge in the groove between the longissimus and iliocostalis muscles.
