Nerve · Thoracic spine

Dorsal rami

Rami dorsales

The smaller of the two branches every spinal nerve splits into, and the one that turns backwards. Each dorsal ramus passes behind the facet joints of its own level and fans out into the deep muscles running alongside the spine and the skin over them — so the back is supplied segment by segment by nerves of its own, while everything in front of it is left to the ventral rami, which in the limbs are first rewoven into a plexus. Most divide into a medial branch, which supplies the facet joints and the muscles closest to the midline, and a lateral branch running further out. One small nerve therefore accounts for both the muscle beside a vertebra and the surface of skin above it, which is what makes the back's nerve supply so tightly tied to a single spinal level.