The
long thoracic nerve (
external respiratory nerve of Bell;
posterior thoracic nerve) supplies the
serratus anterior muscle. This nerve characteristically arises from the
anterior rami of three spinal
nerve roots: the fifth, sixth, and seventh
cervical nerves (C5-C7) although the root from C7 may be absent. The roots from C5 and C6 pierce through the
scalenus medius, while the C7 root passes in front of the muscle.