The posterior divisions of the sacral nerves (rami posteriores) are small, and diminish in size from above downward; they emerge, except the last, through the posterior sacral foramina. The upper three are covered at their points of exit by the Multifidus, and divide into medial and lateral branches. The posterior divisions of the lower two sacral nerves are small and lie below the Multifidus. They do not divide into medial and lateral branches, but unite with each other and with the posterior division of the coccygeal nerve to form loops on the back of the sacrum; filaments from these loops supply the skin over the coccyx.
The posterior division of the coccygeal nerve(ramus posterior) does not divide into a medial and a lateral branch, but receives, as already stated, a communicating branch from the last sacral; it is distributed to the skin over the back of the coccyx.