Iliocostalis

The iliocostalis is the outermost of the three columns of the erector spinae, the group that forms most of the muscle mass of the back. It attaches to the ribs. (OpenStax A&P 2e, 11.3; StatPearls, Back, Muscles)

FMA77177 · Muscular system

The back muscle model seen from behind, faded, with the iliocostalis of both sides highlighted as long columns running up the back on the outer side of the erector spinae. — The right and left iliocostalis in the back muscle model, seen from behind. Render: ScienceQuest, CC BY 4.0. Meshes: BodyParts3D, © The Database Center for Life Science, CC BY 4.0

The iliocostalis of both sides alone, seen from behind: the lumborum, thoracis and cervicis parts of each side stacked as one long column from the lower back to the neck. — The iliocostalis of both sides alone, from behind. Render: ScienceQuest, CC BY 4.0. Meshes: BodyParts3D, © The Database Center for Life Science, CC BY 4.0

Open it in the Back Muscles Explorer See it alone in 3D

Where is the iliocostalis?

It lies on the outer side of the longissimus, and the spinalis lies nearest the midline. (StatPearls, Back)

The thoracolumbar fascia, the serratus posterior inferior, the rhomboids and the splenius muscles cover the erector spinae. (StatPearls, Back, Muscles)

What are the parts of the iliocostalis?

It has three parts, named by region: the iliocostalis cervicis of the neck, the iliocostalis thoracis of the chest and the iliocostalis lumborum of the lower back. Gray’s 1918 text calls the chest part the iliocostalis dorsi. (OpenStax A&P 2e, 11.3; StatPearls, Back, Muscles; Gray 1918, 6a. Deep Muscles of the Back)

The lumborum arises from the iliac crest and inserts on the transverse processes of L1 to L4, the angles of ribs 4 to 12 and the thoracolumbar fascia. StatPearls names each origin below its insertion, because these muscles are described as if their fibers run upward. (StatPearls, Back, Muscles)

The thoracis, narrow and spindle-shaped, runs from the angles of the lower six ribs to the angles of the upper six ribs and the transverse process of C7. The cervicis runs from the angles of ribs 3 to 6 to the posterior tubercles of the transverse processes of C4 to C6. (StatPearls, Back, Muscles)

What does the iliocostalis do?

Acting on both sides, the erector spinae is the main extensor of the back. Acting on one side, it bends the spine sideways and rotates it. (StatPearls, Back; OpenStax A&P 2e, 11.3)

The group also keeps the lumbar curve and controls flexion of the trunk, including the forward bend that gravity produces. (OpenStax A&P 2e, 11.3; StatPearls, Back, Muscles)

What supplies the iliocostalis, and what lies deep to it?

Like the other true back muscles, it takes its nerves from the dorsal rami of the spinal nerves. At the lumbar level, lateral branches of the dorsal rami supply the iliocostalis. (StatPearls, Back, Muscles)

The deep cervical, posterior intercostal, subcostal or lumbar arteries supply the back muscles, and the pattern varies from person to person. (StatPearls, Back, Muscles)

The transversospinalis group, which includes the multifidus, lies deep to the erector spinae, between the transverse and spinous processes. (StatPearls, Back)

In the lumbar region, three layers of the thoracolumbar fascia surround the erector spinae, the transversospinalis and the quadratus lumborum. (StatPearls, Back)

Iliocostalis at a glance, with sources
Feature	Detail and source
Parts	Iliocostalis lumborum, thoracis and cervicis (OpenStax A&P 2e, 11.3; StatPearls, Back, Muscles; Gray 1918, 6a. Deep Muscles of the Back)
Origin	Iliac crest (lumborum); angles of the lower six ribs (thoracis); angles of ribs 3 to 6 (cervicis) (StatPearls, Back, Muscles)
Insertion	Angles of the ribs; transverse processes of L1 to L4, C7 and C4 to C6; thoracolumbar fascia (StatPearls, Back, Muscles)
Action	Extends the spine when both sides act; bends it to one side and rotates it when one side acts (StatPearls, Back)
Nerve	Lateral branches of the dorsal rami (StatPearls, Back, Muscles)

Touches in this model

Measured on the BodyParts3D meshes: surfaces within 2 mm of the iliocostalis, nearest first, 12 of 80.

Left latissimus dorsi in contact
Left levator scapulae in contact
Left longissimus capitis in contact
Left longissimus cervicis in contact
Left longissimus thoracis in contact
Left multifidus in contact
Left serratus posterior inferior in contact
Left serratus posterior superior in contact
Left splenius cervicis in contact
Right latissimus dorsi in contact
Right levator scapulae in contact
Right longissimus capitis in contact

Sources

OpenStax Anatomy and Physiology 2e, section 11.3, Axial Muscles of the Head, Neck, and Back. CC BY-NC-SA 4.0. Read 2026-10-25.
StatPearls, Anatomy, Back, Muscles. Brandi Henson; Bhavana Kadiyala; Mary Ann Edens. Last update August 14, 2023. CC BY-NC-ND 4.0. Read 2026-10-25.
StatPearls, Anatomy, Back. Robert J. Modes; Sevda Lafci Fahrioglu. Last update February 27, 2023. CC BY-NC-ND 4.0. Read 2026-10-25.
Gray’s Anatomy of the Human Body, 20th US edition (1918), IV. Myology, 6a. The Deep Muscles of the Back (1918 terms: Sacrospinalis for erector spinae, Iliocostalis dorsi for iliocostalis thoracis, Longissimus dorsi for longissimus thoracis). Henry Gray. Public domain. Read 2026-10-25.