Now, the diaphragm is actually connected to the chest cavity, our thoracic cavity. And as the diaphragm flattens down, it increases the space inside our chest cavity. It increases the volume inside that chest cavity. Now, as the external intercostal muscles contract, they also increase the space inside our chest cavity. And that's because as these muscles contract, they essentially increase our rib cage size. They move the ribcage outward, and that increases the overall space inside our thoracic cavity, inside the chest cavity.