The five sacral nerves emerge from the sacrum. Although the vertebral components of the sacrum are fused into a single bone, the sacral vertebrae are still used to number the sacral nerves. Posteriorly, they emerge from the posterior sacral foramina, and form the posterior branches of sacral nerves. Anteriorly, they emerge from the anterior sacral foramina, and contribute to the sacral plexus (S1-S4) and coccygeal plexus. [ http://en.wikipedia.org/wiki/Sacral_nerves ]