External Intercostal Muscles

Description

Across the anterolateral thoracic wall, the external intercostal muscles occupy the intercostal spaces between adjacent ribs, their fibers running inferoanteriorly from the inferior border of the rib above to the superior border of the rib below. Near the sternum, the fleshy muscle bellies taper and give way to the external intercostal membrane, which continues anteriorly toward the costochondral junctions where true muscle fibers are absent. Superficial landmarks likely include the pectoralis major overlying the upper ribs, with the deltoid laterally at the shoulder and the serrated digitations of serratus anterior along the lateral thorax; inferiorly, the external oblique interdigitates with serratus anterior over the lower ribs. This anterior transition from muscle to membrane matters in practice because it changes what you can safely dissect, repair, or traverse during anterior thoracic procedures. The external intercostals contribute to rib elevation during inspiration, but their anterior membrane means force transmission differs near the parasternal region, a point worth emphasizing when teaching chest wall mechanics. It also frames where intercostal neurovascular bundles run in the costal groove deep to the internal intercostal layer, a constant hazard during chest tube placement and parasternal blocks. Use this artwork for gross anatomy and respiratory physiology teaching when you want students to correlate fiber direction with inspiratory mechanics and to understand why the intercostal musculature is not uniform from vertebral column to sternum. It also suits surgical anatomy chapters on thoracostomy, parasternal approaches, and regional anesthesia, where layer recognition and rib space orientation determine technique. Anatomical accuracy verified by SciePro's Medical Advisory Board.