Quick Facts
Origin: Spinous processes of L1-L5 vertebrae, dorsal surface of sacrum, and Iliac crest.
Insertion: Transverse processes of lumbar and thoracic vertebrae, and second to twelfth ribs.
Action: Extends and laterally flexes trunk.
Innervation: Lateral branches of posterior rami of thoracic and lumbar nerves.
Arterial Supply: Dorsal branches of posterior intercostal and lumbar arteries, lateral sacral arteries.
Related parts of the anatomy
Origin
The longissimus thoracis muscle originates from the:
- spinous processes of all lumbar vertebrae;
- dorsal surface of sacrum;
- posterior end of iliac crest.
There can be variations between individuals regarding the origin sites for the longissimus thoracis muscle (Tubbs, Shoja and Loukas, 2016).
Insertion
The fibers of the longissimus thoracis muscle travel superiorly along the back and insert onto the:
- transverse processes of all thoracic and lumbar vertebrae;
- dorsal aspects of the posterior ends of the shafts of all twelve ribs.
There can be variations between individuals regarding the insertion sites for the longissimus thoracis muscle (Tubbs, Shoja and Loukas, 2016).
Key Features & Anatomical Relations
In general, the longissimus muscles are the central-most muscles of the erector spinae. They are intrinsic muscles of the back and are found along the entire length of the back and posterior neck regions. They are long, flat skeletal muscles that are composed of three parts:
- longissimus capitis, which is the superior portion;
- longissimus colli, which is the middle portion;
- longissimus thoracis, which is the large, inferior portion.
The longissimus muscles are located:
- superficial to the ribs, and the external intercostal, levatores costarum breves, and levatores costarum longi muscles;
- deep to the sternocleidomastoid, splenius capitis, serratus posterior superior, rhomboid major, trapezius, latissimus dorsi, and serratus posterior inferior muscles, and the thoracolumbar fascia;
- medial to the iliocostalis muscle;
- lateral to the spinalis muscle.
Actions
The longissimus thoracis muscle is involved in multiple actions:
- during unilateral contraction, it laterally flexes the trunk to the same side;
- during bilateral contraction, it extends the trunk (Moore, Dalley and Agur, 2009).
References
Moore, K. L., Dalley, A. F. and Agur, A. M. R. (2009) Clinically Oriented Anatomy. Lippincott Williams & Wilkins.
Tubbs, R. S., Shoja, M. M. and Loukas, M. (2016) Bergman's Comprehensive Encyclopedia of Human Anatomic Variation. Wiley.
