Final answer:
The internal intercostal muscles are responsible for contracting to decrease the volume of the thoracic cavity during expiration. They are part of the thoracic muscles that play a vital role in breathing along with the diaphragm and external intercostal muscles.
Step-by-step explanation:
The muscle that is found on the inner surface of the rib cage, originating on the margin of the sternum, with fibers coursing to the inner chondral surface of ribs 2 through 6, is one of the internal intercostal muscles. These muscles assist in the process of expiration. When the internal intercostal muscles contract, they draw the ribs together, which constricts the rib cage and decreases the volume of the thoracic cavity, thereby increasing the pressure within the pleural cavities and pushing air out of the lungs.
The thoracic muscles are essential for proper breathing, including the diaphragm and intercostal muscles. The diaphragm contracts and flattens, increasing the volume inside the pleural cavities and decreasing the pressure to allow air to flow into the lungs. External intercostal muscles aid in raising the rib cage during inspiration, while the internal intercostal muscles work during expiration.