External Intercostal Muscle Beneath the Skin, Posterior View

Description

Posterior thoracic skin is rendered semi-transparently to reveal the external intercostal muscles spanning the intercostal spaces between adjacent ribs on either side of the vertebral column. Rib contours and the posterior rib angles frame the fiber direction, which runs infero-anteriorly from the inferior border of each rib toward the superior border of the rib below, becoming aponeurotic near the costal cartilages laterally and anteriorly. Midline, the spinous processes mark the posterior median line, with ribs arcing laterally from the thoracic vertebrae and defining the interspaces occupied by the intercostal layer. External intercostals are the main inspiratory intercostals, elevating the ribs to increase thoracic volume, so a posterior view helps clarify where their muscular portion is most substantial, near the rib angles and posterior thoracic wall. That matters in blunt trauma and rib fracture patterns, where focal pain at the posterolateral chest often reflects irritation of the intercostal neurovascular bundle that runs inferior to each rib in the costal groove, deep to the intercostal musculature. It is also the anatomy you want in mind when planning or explaining a posterior intercostal nerve block, where needle trajectory and depth must respect rib position and the pleura deep to the intercostal spaces. Educators can drop this plate directly into gross anatomy and respiratory mechanics modules to connect rib kinematics with muscle fiber orientation, without losing the surface landmarks students palpate on the back. It also fits thoracic surgery, anesthesia, and emergency medicine teaching materials that cover rib fractures, posterior chest wall pain, and regional analgesia at the thoracic level. Anatomical accuracy verified by SciePro's Medical Advisory Board.