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Serratus posteriorMusculi serrati posteriores

Two thin sheets of muscle (superior and inferior) connecting the spine to the ribs under the rhomboids and latissimus dorsi, with a minor role in breathing.

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LatinMusculi serrati posteriores
Origin
  • Superior: lower part of the ligamentum nuchae, spinous processes of C7–T3 and the supraspinous ligament
  • Inferior: spinous processes of T11–L2 and the supraspinous ligament, through an aponeurosis blended with the thoracolumbar fascia
Insertion
  • Superior: upper borders of ribs 2–5, just lateral to their angles
  • Inferior: lower borders of ribs 9–12, just lateral to their angles
Action
  • Superior: elevates ribs 2–5 (assists breathing in)
  • Inferior: draws ribs 9–12 down and back
NerveIntercostal nerves (ventral rami of the thoracic spinal nerves) (T2–T5 (superior); T9–T12 (inferior))
NameLatin serratus, 'saw-toothed', from its tooth-like slips onto the ribs.

Palpation

  1. Client prone; stand beside the table.
  2. Superior: it lies under the rhomboids. Let the arm hang off the table so the scapula slides out, then feel the upper ribs just medial to the medial border of the scapula.
  3. Inferior: place the fingers over the lower ribs at the level of T11–L2, lateral to the erector spinae and deep to latissimus dorsi.
  4. Neither part can be felt apart from the muscles over it; ask the client to take a deep breath in and feel the tension change across the ribs.

Landmarks: Medial border of scapula · C7 spinous process

This entry covers both serratus posterior muscles. The superior one lies under Rhomboid major and Rhomboid minor. The inferior one lies under Latissimus dorsi at the junction of the thoracic and lumbar spine. Both are thin and lie over Erector spinae. In a back massage you work them indirectly, through the muscles above them.

The sources disagree about the inferior part. Wikipedia says it pulls the lower ribs down to help breathing out; Gray’s (1918) calls it a muscle of breathing in, because it fixes the lower ribs against the pull of the Diaphragm. They also differ on its origin: T11–L2 in Wikipedia, and the lower two thoracic and upper two or three lumbar vertebrae in Gray’s.

Techniques

  • Circular friction — Small circles made with the finger or thumb pads that move the skin over the deeper tissue without sliding, to work a specific spot.
  • Myofascial release — Slow, sustained, low-load pressure or stretch into the skin and fascia, held without sliding until the tissue is felt to soften, then followed as it gives.

Works with

  • Scalenes — Three paired muscles (anterior, middle and posterior) at the side of the neck that side-bend the neck and lift the first two ribs in deep breathing.
  • Intercostals — Three thin layers of muscle filling the spaces between the ribs that move the ribcage during breathing and keep the chest wall firm.
  • Diaphragm — Dome-shaped sheet of muscle separating the chest from the abdomen that is the main muscle of breathing in.
  • Quadratus lumborum — Deep, four-sided muscle between the iliac crest, the 12th rib and the lumbar spine that side-bends the lower back and hitches the hip.

Sources

  1. Wikipedia, Serratus posterior superior muscle
  2. Wikipedia, Serratus posterior inferior muscle
  3. Gray's Anatomy (1918), IV. Myology 6c: The Muscles of the Thorax (Public domain; Bartleby edition read via the Internet Archive.)