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Serratus Posterior Inferior Muscle
Muscular System

Serratus Posterior Inferior Muscle

Musculus serratus posterior inferior

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Quick Facts

Origin: Spinous processes of T11-L2 vertebrae.

Insertion: External surfaces of ninth to twelfth ribs.

Action: Depresses ribs at their costovertebral joints.

Innervation: Anterior rami of ninth to twelfth thoracic nerves.

Arterial Supply: Dorsal branches of lower posterior intercostal arteries and subcostal artery.

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The serratus posterior inferior muscle originates from the:

- spinous processes of the eleventh and twelfth thoracic and first and second lumbar vertebrae;

- adjacent supraspinous ligaments.


The fibers of the serratus posterior inferior muscle travel superolaterally and insert, via four separate tendons, onto the external surfaces of the ninth to twelfth ribs. On the ninth to eleventh ribs, these insertion sites are located just lateral to their angles.

Key Features & Anatomical Relations

The serratus posterior inferior muscle is an extrinsic muscle of the back and is found in the lower back region. It is a thin, broad, quadrilateral type of skeletal muscle and its digitations, found at its insertion sites, give the muscle its saw-toothed, or serrated, appearance.

It is located:

- posterior (superficial) to the erector spinae muscles;

- anterior (deep) to the latissimus dorsi muscle.


The serratus posterior inferior muscle depresses the ribs at their costovertebral joints during forced expiration (Sinnatamby, 2011). It may also be involved in proprioception (Moore, Dalley and Agur, 2009).


Moore, K. L., Dalley, A. F. and Agur, A. M. R. (2009) Clinically Oriented Anatomy. Lippincott Williams & Wilkins.

Sinnatamby, C. S. (2011) Last's Anatomy: Regional and Applied. ClinicalKey 2012: Churchill Livingstone/Elsevier.

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