Innermost Intercostals, Posterior View

Description

Seen from a posterior perspective, the thoracic cage is opened to the deep intercostal layer, with slips of innermost intercostal muscle (musculi intercostales intimi) spanning the intercostal spaces along the lateral thoracic wall. Posteriorly, the thoracic vertebrae and adjacent rib angles sit medial to the muscle fibers, and the ribs (costae) curve laterally away from their costovertebral joints toward the axillary line. A characteristic finding is emphasized: the intimi become sparse or absent near the most posterior rib segments, where the intercostal space is occupied instead by membranes and the neurovascular bundle tracks in the costal groove. That gap matters. For teaching layered thoracic wall anatomy, this posterior view helps distinguish the innermost intercostals from internal intercostals and from the subcostales that cross more than one intercostal space near the rib angles. The posterior deficiency of the intima is clinically relevant when planning posterior or posterolateral thoracotomy and during chest tube placement in the “safe triangle,” because the intercostal neurovascular bundle remains at risk even where muscle coverage thins, and the plane between internal and innermost intercostals is where the collateral branches may be encountered. Regional anesthesia also depends on this detail, since an intercostal nerve block targets the neurovascular plane along the inferior rib margin, not the patchy muscle slips. Use this artwork in gross anatomy lab manuals, respiratory mechanics lectures, and surgical atlases that need a clear posterior map of intercostal layering around the thoracic spine and rib angles in an adult male. It also supports thoracic surgery and anesthesia teaching files that explain why “between the ribs” is not a uniform muscular wall from vertebra to sternum. Anatomical accuracy verified by SciePro's Medical Advisory Board.