The medial branches of the posterior primary divisions of all the lumbar nerves end in the multifidus spinse and those of the three lower nerves send very small branches to the skin of the sacral region.
The lateral branches of the upper three nerves pass obliquely lateralward, supplying twigs to the adjacent muscles, pierce the posterior layer of the lumbar aponeurosis at the lateral border of the sacro-spinalis (erector spinse) and enter the subcutaneous tissue. They are, for the most part, cutaneous, forming the superior clunial nerves, which cross the crest of the iUum and pass downward to occupy different planes in the thick superficial fascia which covers the upper part of the gluteus medius.
The branch from the first lumbar nerve is comparatively small, and occupies the most superficial plane. The second occupies an intermediate position. The lateral branch from the third nerve is the largest of the three, and occupies the lowest position; it distributes branches over the gluteus maximus as far as the great trochanter. The three nerves anastomose with one another and also with the cutaneous branches from the posterior primary divisions of the two upper sacral nerves.
The lateral branch of the fourth lumbar nerve is of small size and ends in the lower part of the sacro-spinalis (erector spinas). That of the fifth lumbar is distributed to the sacro-spinalis and communicates with the first sacral nerve.