The origin of the iliocostalis lumborum includes which structures?

• A. Spinous processes of lower thoracic vertebrae.
• B. Transverse processes of lumbar vertebrae.
• C. Iliac crest, sacrum, and thoracolumbar fascia.
• D. Ribs 7-12.

Answer: (C)

The main idea is where the iliocostalis lumborum originates. This part of the erector spinae group has its origin from the posterior iliac crest and sacrum, via the thoracolumbar fascia. It then fibers upward to attach to the angles of the lower ribs. So the structures that form its origin are the iliac crest, sacrum, and thoracolumbar fascia, making that option correct.

Spinous processes of lower thoracic vertebrae aren’t the starting point for this muscle’s fibers, and the transverse processes of lumbar vertebrae are not the primary origin of iliocostalis lumborum. The ribs themselves (7–12) serve as the insertion, not origin, for this muscle.