Serratus posterior inferior muscle
The serratus posterior inferior muscle is a muscle of the mid back that connects the
rib cage to the
spine. It attaches to the
rib cage over the 9th to 12th
ribs. It is divided up into four sections, and receives blood supply from the intercostal artery.
The serratus posterior inferior compresses the rib cage down and toward the
spine. Having the rib cage pulled to the back allows a better range of motion for the upper body, giving it the ability to rotate and extend. This also assists in breathing, acting as a balance to the pull on the
rib cage caused by the
diaphragm.
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Origin
The serratus posterior inferior originates from the
supraspinous ligament and the
spinous processes of the last two
thoracic vertebrae, T11 and T12, and the first two
lumbar vertebrae, L1, and L2.
Insertion
The serratus posterior inferior inserts on the
posterior side of the four lowest
ribs, 9-12.
Word origin
-
Serratus means saw tooth, in the same way as in
serrated knife, referring to the back-and-forth pattern the
muscle makes as it attaches to each
rib.
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Posterior, meaning on the back side, distinguishes it from the
serratus anterior muscle - a similar
muscle on the front side of the
rib cage.
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Inferior distinguishes it from the
serratus posterior superior muscle, which sits above it.