External Intercostal Muscles, Posterior View

Description

Seen from the posterior thoracic wall, the external intercostal muscles occupy the intercostal spaces between adjacent ribs, their fibers running infero-anteriorly from the inferior border of each rib toward the superior border of the rib below. Medially, the muscle slips approach the rib angles and posterior ribs near their articulations with the thoracic vertebrae, with the thoracic spinous processes centered in the midline. Superiorly, the upper rib cage sits deep to the scapulae, and inferiorly the muscle field tapers toward the costal margin and upper lumbar region. Posterior emphasis matters because the external intercostals reach their greatest thickness near the rib angles, the same region where rib fractures commonly occur and where pain and splinting can measurably reduce thoracic excursion. Their fiber direction contrasts with the internal intercostals, a teaching point that becomes concrete when you relate it to mechanics of inspiration and to how accessory and intrinsic chest wall muscles contribute during increased ventilatory demand. Clear rib-to-vertebra relationships also help orient procedures that traverse the posterior thorax, including posterior thoracotomy planning and needle trajectories for intercostal nerve blocks, where the neurovascular bundle runs in the costal groove along the inferior rib margin. Anatomy faculty can drop this into gross anatomy labs, respiratory mechanics lectures, or surface anatomy sessions that connect rib motion to muscle fiber direction, and publishers will find it suitable for atlas plates contrasting external and internal intercostal layers. It also fits clinical education on rib fracture management, thoracic wall pain patterns, and procedural anatomy for regional anesthesia of the intercostal spaces. Anatomical accuracy verified by SciePro's Medical Advisory Board.