Posterior Inferior Serratus Muscle

Description

Positioned on the posterolateral thoracic wall, the serratus posterior inferior lies deep to latissimus dorsi and the superficial layer of the thoracolumbar fascia, spanning from the lower thoracic and upper lumbar midline to the inferior ribs. Fibers arise from the spinous processes and supraspinous ligaments of approximately T11 to L2 (via the thoracolumbar fascia) and run superolaterally to insert by short tendinous slips onto the inferior borders of ribs 9 to 12 near their angles. Medially it approaches the erector spinae mass, while laterally its digitations interdigitate with costal musculature and the posterior abdominal wall fascial planes. Small muscle. Clear attachments. Because the serratus posterior inferior sits at the thoracolumbar junction, this posterior view is useful when teaching the layered anatomy encountered in posterior approaches to the lower thorax and upper lumbar spine. Its rib insertions become relevant when discussing respiration mechanics and the debated role of this muscle in rib depression and proprioception, and when differentiating myofascial pain sources from costovertebral joint irritation or lower rib stress injuries. Clinically, tenderness along the 9th to 12th ribs can be misattributed to latissimus dorsi or quadratus lumborum, so seeing the serratus posterior inferior in situ helps clarify why symptoms may track obliquely from the paraspinal region toward the costal margin. Instructors can drop this asset into gross anatomy lab guides, thoracolumbar fascia lectures, or review materials on posterior trunk dissection planes, and authors will find it fits well in surgical anatomy chapters describing posterior lumbar exposures and flank incisions where fascial layers and rib landmarks matter. Anatomical accuracy verified by SciePro's Medical Advisory Board.