It is the longest subdivision of the erector spinae muscles that extends forward into the transverse processes of the posterior cervical vertebrae.

The longissimus thoracis et lumborum is the intermediate and largest of the continuations of the erector spinae.

In the lumbar region (longissimus lumborum), where it is as yet blended with the iliocostalis, some of its fibers are attached to the whole length of the posterior surfaces of the transverse processes and the accessory processes of the lumbar vertebrae, and to the anterior layer of the lumbodorsal fascia.

The longissimus cervicis (transversalis cervicis), situated medial to the longissimus thoracis, arises by long, thin tendons from the summits of the transverse processes of thoracic vertebræ 1–5, and is inserted by similar tendons into the posterior tubercles of the transverse processes of cervical vertebrae 2–6.

This article incorporates text in the public domain from page 399 of the 20th edition of Gray's Anatomy (1918)