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Serratus Posterior Inferior Origin, Insertion, Action

Serratus Posterior Inferior Anatomy

Serratus Posterior Inferior Muscle

Origin: The spinous processes of the T11 to L2/L3 and their corresponding supraspinous ligaments, blending with the lumbar part of the thoracolumbar fascia
Insertion: Inferior borders and outer surfaces of the lower four ribs (9th -12th), lateral to their angles
Actions: Forced expiration
Innervation: Ventral primary rami of T9 – T12
Blood Supply: Dorsal branches of the subcostal arteries

Primary Actions of the Serratus Posterior Inferior


  • Transversus abdominis


  • Serratus posterior superior
  • Levatores costarum brevis
  • Levatores costarum longi

Rectus abdominis, external oblique, and internal oblique assist with forced expiration.