The innermost intercostals are a muscle of the thoracic wall. They are the deepest of the intercostal muscles. Their fibres are orientated in an inferior and posterior direction. Attachments: Originates from the medial edge of the costal groove and inserts onto the superior surface of the rib below. Actions: Stablises the position of the ribs during normal respiration. Depresses the ribs and decreases the thoracic volume during forced expiration. Innervation: Intercostal nerves (T1-T11) Blood supply: Anterior and posterior intercostal arteries By TeachMeSeries Ltd (2025) Fig 2View of the internal aspect of the thoracic wall. The internal intercostal and transverse thoracis muscles are visible. Pro Feature - 3D Model You've Discovered a Pro Feature Access our 3D Model Library Explore, cut, dissect, annotate and manipulate our 3D models to visualise anatomy in a dynamic, interactive way. Learn More Print Article Rate This Article