Serratus Posterior Inferior Muscle, Posterior View

Description

Positioned deep to the latissimus dorsi on a posterior view of the male trunk, the serratus posterior inferior is highlighted with its narrow digitations sweeping inferolaterally from the lower thoracic and upper lumbar midline to the inferior borders of ribs 9 to 12. Medially, its aponeurotic origin blends with the thoracolumbar fascia over the spinous processes of approximately T11 to L2, adjacent to the posterior midline of the vertebral column. Laterally, the slips interdigitate with the posterior rib cage while the quadratus lumborum sits deeper and more inferior, spanning from the iliac crest to the 12th rib and lumbar transverse processes. Fiber direction is the key cue. This posterior emphasis matters because serratus posterior inferior is often misunderstood in teaching as a primary muscle of respiration, yet its mechanical advantage is modest and its attachments overlap with structures clinicians palpate and operate around in the thoracolumbar region. Pain referral from the thoracolumbar fascia or irritation of the subcostal nerve (T12) can mimic posterolateral rib pain, and the muscle’s relationship to ribs 11 and 12 provides a useful landmark when differentiating muscular strain from costovertebral or costotransverse joint dysfunction. Clear visualization of its deep position also supports discussions of posterior thoracoabdominal approaches where latissimus dorsi is reflected. Use this artwork in gross anatomy and kinesiology modules covering accessory respiratory muscles, posterior trunk layering, and the thoracolumbar fascia, or in atlases and journal figures addressing lower rib pain, flank incisions, and ultrasound-guided regional anesthesia landmarks around the 12th rib. Anatomical accuracy verified by SciePro's Medical Advisory Board.