Expansion
Serratus posterior superior elevates the upper ribs, serratus posterior inferior depresses the lower ribs
Expansion
- Serratus posterior superior - from the lower cervical and upper thoracic spines to ribs 2 to 5. Elevates the upper ribs; a weak muscle of inspiration
- Serratus posterior inferior - from the lower thoracic and upper lumbar spines to ribs 9 to 12. Depresses the lower ribs and anchors them against the pull of the diaphragm
- Levatores costarum - twelve small fan-shaped muscles from the transverse processes to the rib below. Elevate the ribs
Both serratus posterior muscles are supplied by intercostal nerves, which marks them out from the true muscles of the back; they are displaced thoracic wall muscles, not intrinsic back muscles, and they lie in the intermediate layer.
Their contribution to respiration is minor, and their main significance is anatomical orientation during dissection of the back.