Final answer:
The diaphragm is the muscle that contracts to aid in drawing air into the lungs in mammals, increasing volume and decreasing pressure in the thoracic cavity to allow air to flow in.
Step-by-step explanation:
The structure that aids in drawing air into the lungs of mammals as it contracts is the diaphragm. This dome-shaped muscle is located at the bottom of the chest cavity, beneath the lungs. During inhalation, the diaphragm contracts and flattens, increasing the volume inside the thoracic cavity and creating negative pressure, which allows air to flow into the lungs. The alveoli, tiny air sacs in the lungs, then facilitate gas exchange with the surrounding blood vessels. When the diaphragm relaxes during exhalation, the volume decreases, the pressure increases, and air is expelled from the lungs