The iliocostalis muscle is one of the erector spinae group of the back. It runs from the iliac crest to the ribs. Classically, it is divided into three parts with differing origins and insertions:
- iliocostalis lumborum
- iliocostalis thoracis
- iliocostalis cervicis
Iliocostalis is the most lateral of the three parts of erector spinae. It forms part of the intermediate layer of intrinsic back muscles.
In concert with the other erector spinae muscles, its unilateral action is to laterally flex the spine; bilaterally, it extends the spine.
It is innervated by the dorsal primary rami of the segmental spinal nerves.