Posterior Inferior Serratus, Posterior View

Description

Posterior superficial back musculature is presented with the serratus posterior inferior highlighted deep to the latissimus dorsi and inferior to the rhomboid major. Its thin, quadrilateral muscle belly arises from the thoracolumbar fascia and the spinous processes of T11 to L2, then runs superolaterally as digitations to the inferior borders of ribs 9 to 12 near their angles. Medially, the fibers blend with the posterior layer of thoracolumbar fascia adjacent to the erector spinae; laterally they approach the costal attachments under the lower thoracic cage. Connective tissue and tendinous portions appear in white. Fiber direction matters. Serratus posterior inferior is often taught as an accessory muscle of respiration, depressing the lower ribs during forced expiration, but the view is more than a breathing diagram. Its fascial continuity with the thoracolumbar fascia makes it a useful landmark in posterior thoracolumbar approaches and in discussions of myofascial sources of lower rib and flank pain that can mimic renal colic or intercostal neuralgia. Palpation and trigger point referral in the region of ribs 9 to 12, or strain at the costal attachments in athletes performing repetitive trunk rotation, make sense when you can see how far lateral the slips run beneath latissimus dorsi. Use this illustration in gross anatomy and kinesiology coursework to teach layered posterior trunk anatomy, or in radiology and sports medicine materials to orient readers before correlating with axial CT and ultrasound over the costal margin. It also fits surgical atlases covering posterolateral thoracoabdominal exposure where the thoracolumbar fascia and inferior rib attachments guide dissection planes. Anatomical accuracy verified by SciePro's Medical Advisory Board.