Serratus posterior inferior muscle

The Serratus posterior inferior muscle (or posterior serratus) is a muscle of the human body.

Serratus posterior inferior muscle
Muscles connecting the upper extremity to the vertebral column (serratus posterior inferior labeled at center right).
Serratus posterior inferior (red) seen from back.
OriginVertebrae: Spinous processes of T11 - L2
InsertionThe inferior borders of the 9th through 12th ribs
ArteryIntercostal arteries
NerveIntercostal nerves T9 through T12
ActionsDepress the lower ribs 9-12, aiding in expiration
LatinMusculus serratus posterior inferior
Anatomical terms of muscle

Origin and insertion

The muscle lies at the junction of the thoracic and lumbar regions. The origin arises from the vertebrae T11 through L2. The muscle's insertion is the lower border of the 9th through 12th ribs.

It is situated at the junction of the thoracic and lumbar regions: it is of an irregularly quadrilateral form, broader than the serratus posterior superior muscle, and separated from it by a wide interval.

It arises by a thin aponeurosis from the spinous processes of the lower two thoracic and upper two or three lumbar vertebrae, and from the supraspinal ligament.

Passing obliquely upward and lateralward, it becomes fleshy, and divides into four flat digitations, which are inserted into the inferior borders of the lower four ribs, a little beyond their angles.

The thin aponeurosis of origin is intimately blended with the lumbodorsal fascia, and aponeurosis of the Latissimus dorsi.


The serratus posterior inferior draws the lower ribs backward and downward to assist in rotation and extension of the trunk. This movement of the ribs also contributes to forced expiration of air from the lungs.

Additional images

See also


This article incorporates text in the public domain from page 404 of the 20th edition of Gray's Anatomy (1918)

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