Transversus Thoracis Under the Skin

Description

Beneath the anterior thoracic wall, the transversus thoracis (sternocostalis) lies deep to pectoralis major and the costal cartilages, fanning superolaterally from the posterior surface of the sternum and xiphoid process toward the internal surfaces of the 2nd to 6th costal cartilages. Slips of intercostalis internus occupy the intercostal spaces lateral to the parasternal region, while the ribs and their cartilaginous continuations form the rigid boundary of the rib cage. Inferiorly, the diaphragm attaches along the costal margin and lower ribs, its muscular fibers converging on the central tendon as it separates thoracic from abdominal cavities. Orientation is anterior, with structures described in anatomical position. For teaching and operative planning, this is the layer where the internal thoracic artery and veins course vertically just lateral to the sternum, with transversus thoracis forming part of their deep bed. Surgeons harvesting the internal thoracic artery for coronary artery bypass grafting work in close proximity to these muscle slips and adjacent pleura; clear appreciation of the parasternal planes helps explain where bleeding, pleural breach, or postoperative anterior chest wall pain can arise. The relationship to the costal cartilages also matters during anterior thoracotomy and during placement of parasternal chest drains, where staying superficial or deep to this plane changes what you risk. Use this illustration in gross anatomy and respiratory mechanics modules to contrast the subtle transversus thoracis with the dominant diaphragm, and in cardiothoracic texts discussing internal thoracic vessel exposure and median sternotomy closure planes. It also fits clinical teaching files on CABG conduit harvest and parasternal interventions where accurate layer-by-layer anatomy prevents complications. Anatomical accuracy verified by SciePro's Medical Advisory Board.