Muscle · Thoracic spine

Serratus posterior inferior

Musculus serratus posterior inferior

The lower partner of the same pair — a thin sheet at the thoracolumbar junction, deep to latissimus dorsi, running upward and outward from the thoracolumbar fascia to the lower borders of the last four ribs. It is one of the few muscles that attaches directly into the thoracolumbar fascia, which makes it a small mechanical link between the low back and the bottom of the rib cage. Its named action is to draw the lower ribs down and back, resisting the pull of the diaphragm on them during a breath in; like its upper partner it is thin, and its real contribution is closer to steadying than to moving.