- origin: spinous processes of T11 to L2 vertebrae and supraspinous ligament
- insertion: inferior border of 9th to 12th ribs
- innervation: intercostal nerves
- arterial supply: intercostal arteries
- action: depresses ribs
The serratus posterior inferior muscle forms from a thin, broad aponeurosis which is attached to the spinous processes of T11 to L2 vertebrae, and the intervening supraspinous ligament. It passes superolaterally and inserts onto the inferior border, just lateral to the angles of the 9th to 12th ribs 1-3. It is separated from the serratus posterior superior muscle by a wide interval.
The serratus posterior inferior muscle receives motor supply from the ventral rami of the 9th to 12th thoracic spinal nerves (intercostal nerves) 1.
This muscle depresses the inferior ribs which aids in expiration.