This is situated on the sides of the spines of the dorsal and lumbar vertebrae, and extends along their entire length from the sacrum to the neck. It is made up of a number of short slips passing obliquely upward and forward.

Origin. - 1. From the sacrum behind. 2. From the articular processes of the lumbar vertebrae. 3. From the transverse processes of the dorsal vertebrae.

Insertion. - Each slip becomes inserted into the spinous process of the third or fourth vertebra in front of the one from which it arises.

Action. - To fix the bones during the action of the large spinal muscle, and to assist in extending the spine.