Intercostal Muscles Beneath the Skin, Anterior View

Description

Running between adjacent ribs on the anterior thoracic wall, the external intercostal muscles occupy the intercostal spaces from the costal cartilages laterally toward the rib angles, where their fibers continue as the external intercostal membrane. Deep to them, the internal intercostals and innermost intercostals form a second and third layer, with fiber direction generally perpendicular to the external layer and oriented to depress the ribs during forced expiration. Superficial landmarks remain apparent under the skin, including pectoralis major superiorly and rectus abdominis and the external oblique inferiorly, framing the costal margin and upper abdomen. Respiratory mechanics are easier to teach from an anterior perspective because the anterior intercostal spaces sit adjacent to the sternum and costal cartilages, where rib elevation and bucket handle motion translate into measurable changes in thoracic volume. This is the layer-by-layer anatomy clinicians rely on when placing a chest tube or performing needle decompression for tension pneumothorax, because the intercostal neurovascular bundle (VAN) runs in the costal groove along the inferior border of each rib and is best avoided by entering just superior to the rib below. Small errors here matter. Intercostal muscle strain and costochondral pain syndromes also localize to these spaces and can mimic pleuritic pathology. Ideal use cases include undergraduate thoracic wall labs, anesthesia and emergency medicine teaching on intercostal space identification, and surgical atlases describing anterior approaches for thoracostomy, parasternal blocks, or costal cartilage exposure. Medical publishers will also find it suitable for pairing with cross-sectional imaging discussions of pleura and intercostal spaces. Anatomical accuracy verified by SciePro's Medical Advisory Board.