External Intercostal Muscles, Gross Anatomy

Description

Running obliquely infero-anterior from the rib tubercles toward the costochondral junctions, the external intercostal muscles occupy the intercostal spaces as paired sheets spanning much of the thoracic cage. Individual ribs are rendered with partial transparency, so you can track the fibers from the posterior angles of the ribs toward their more anterior aponeurotic transition near the costal cartilages. Laterally, the slips lie deep to the scapular region and adjacent proximal humerus, with thoracic vertebrae visible posteriorly as a reference for rib head and neck orientation. Clear segmental patterning. External intercostals are the easiest intercostal layer to misread in the lab because their fibers change apparent direction with rib curvature, and they give way anteriorly where parasternal intercostal membrane replaces muscle. That matters in procedures that traverse the chest wall: chest tube thoracostomy in the 4th or 5th intercostal space at the anterior or mid-axillary line, intercostal nerve blocks, and VATS port placement all depend on a correct mental model of intercostal space boundaries and the position of the neurovascular bundle on the inferior border of the rib. Fiber orientation also helps distinguish external intercostals from internal intercostals during layered dissection. Use this plate for gross anatomy teaching of the thoracic wall, for surgical education modules on safe pleural access, and for publisher layouts covering mechanics of respiration and chest wall surface anatomy in adult male reference. Anatomical accuracy verified by SciePro's Medical Advisory Board.