Corpus: Iliocostalis muscle
1. Definition
The iliocostalis muscles are part of the sacrospinal system within the autochthonous back musculature, forming a component of the erector spinae muscle group.
2. Classification
The iliocostalis muscles are divided into three parts:
- Iliocostalis lumborum
- Iliocostalis thoracis
- Iliocostalis cervicis
3. Course
3.1. Origin
The iliocostalis lumborum muscle originates from the outer lip of the iliac crest, the dorsal surface of the sacral bone, the thoracolumbar fascia, and the spinous processes of the lumbar vertebrae. The iliocostalis thoracis muscle originates from the costal angle of the six lower ribs. The iliocostalis cervicis muscle originates from the costal angle of the 3rd to 6th ribs.
3.2. Insertion
The iliocostalis lumborum muscle inserts at the costal angle of the 5th or 6th to 12th ribs. The iliocostalis thoracis muscle attaches to the costal angle of the six upper ribs. The iliocostalis cervicis muscle attaches to the posterior tubercles of the transverse processes of the 4th to 6th cervical vertebrae.
4. Innervation
The iliocostalis muscles are innervated by the lateral branches of the posterior rami from the respective segmental spinal nerves.
5. Function
The iliocostalis lumborum and iliocostalis thoracis muscles function to extend and laterally flex the thoracic and lumbar spine, and they also support expiration. The iliocostalis cervicis muscle is involved in dorsiflexion and lateral flexion of the cervical spine and assists in inspiration.