External Intercostal Muscles

Description

Prominent external intercostal muscles occupy the intercostal spaces on the right lateral thoracic wall, with fibers coursing inferoanteromedially from the inferior border of each rib toward the superior border of the rib below. Their muscular bellies extend anteriorly almost to the costochondral junction, where they transition to the external intercostal membrane over the costal cartilages. Superficially, portions of pectoralis major and the anterior axillary fold may overlap the upper ribs, while the serratus anterior digitations can be inferred along the lateral rib cage; the ribs and costal cartilages define the deep boundary. Fiber direction is the story. External intercostals are the primary rib elevators during quiet inspiration, and a lateral view makes their “hands-in-pockets” orientation easy to teach in relation to rib motion at the costovertebral and sternocostal joints. Clinically, their position between ribs matters during thoracostomy and intercostal nerve blocks: a safe approach stays just superior to the rib to avoid the intercostal neurovascular bundle (VAN) running in the costal groove on the inferior rib margin, deep to the internal intercostal. This perspective also supports exam-room reasoning about intercostal muscle strain and focal pain after coughing, and why injuries near the costochondral junction behave differently than those near the rib angles. Use this artwork in gross anatomy and respiratory mechanics teaching, in surgical education materials covering chest tube placement through the “safe triangle,” or in patient-facing explanations of rib fractures and intercostal neuralgia. It also fits well in textbooks and journal figures discussing thoracic wall layers and the transition from muscular intercostals to anterior membranes. Anatomical accuracy verified by SciePro's Medical Advisory Board.