Serratus posterior inferior muscle

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.
Details
Origin	Vertebrae: Spinous processes of T11 - L2
Insertion	The inferior borders of the 9th through 12th ribs
Artery	Intercostal arteries
Nerve	Intercostal nerves T9 through T12
Actions	Depress the lower ribs 9-12, aiding in expiration
Identifiers
Latin	Musculus serratus posterior inferior
TA	A04.3.01.010
FMA	13402
	Anatomical terms of muscle

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

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.

Function

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

Position of the serratus posterior inferior (shown in red). Animation.
Close up. The muscle arises from the vertebrae T11 through L2 and inserted into lower border of the 9th through 12th ribs.
Lumbar triangle

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References

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

External links

Anatomy figure: 01:05-04 at Human Anatomy Online, SUNY Downstate Medical Center - "Intermediate layer of the extrinsic muscles of the back, deep muscles."
Cross section image: pembody/body8a—Plastination Laboratory at the Medical University of Vienna

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