Iliocostalis muscle has a common origin from the iliac crest, the sacrum, the thoracolumbar fascia, and the spinous processes of the vertebrae from T11 to L5.

[1] Iliocostalis cervicis (cervicalis ascendens) arises from the angles of the third, fourth, fifth, and sixth ribs, and is inserted into the posterior tubercles of the transverse processes of the fourth, fifth, and sixth cervical vertebrae.

Iliocostalis thoracis (musculus accessorius; iliocostalis thoracis) arises by flattened tendons from the upper borders of the angles of the lower six ribs medial to the tendons of insertion of the iliocostalis lumborum; these become muscular, and are inserted into the upper borders of the angles of the upper six ribs and into the back of the transverse process of the seventh cervical vertebra.

[1] Iliocostalis muscle is supplied by the dorsal rami of spinal nerves.

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