External Intercostals, Gross Anatomy

Description

Running obliquely between adjacent ribs, the external intercostal muscles form superficial, banded slips that descend infero-anteriorly from the inferior border of each rib to the superior border of the rib below, occupying the intercostal spaces along the lateral thoracic wall. A lateral male torso perspective also brings the posterior rib angles and thoracic vertebrae into alignment, so the muscle fiber direction can be read against the costovertebral region and the natural kyphosis of the thoracic spine. Inferiorly, the lower ribs approach the costal margin as the thorax transitions toward the visible iliac crest and pelvic girdle. Fiber orientation is the point. External intercostals are the classic teaching example for identifying intercostal layers, since their fibers run opposite to the internal intercostals, and their muscular portion typically gives way to an external intercostal membrane anteriorly near the costochondral junction. That distinction matters in thoracic procedures: intercostal nerve blocks, thoracostomy tube placement, and video-assisted thoracoscopic surgery all require you to anticipate where muscle becomes membrane and to respect the neurovascular bundle coursing in the costal groove along the inferior margin of each rib. Palpation and incision planning often reference the rib angle and midaxillary line, where this lateral view maps neatly onto surface anatomy. Use this artwork in gross anatomy and respiratory mechanics modules to reinforce rib orientation, interspace boundaries, and the infero-anterior fiber direction that contributes to rib elevation during inspiration. It also fits surgical anatomy chapters and patient-education materials explaining intercostal strain from coughing or athletic overuse, and why pain localizes to a specific interspace. Anatomical accuracy verified by SciePro's Medical Advisory Board.