Surfactants are generally lipoproteins and reduce the resistance to lung expansion as well as the energy needed to fill the lungs. The larynx is the primary organ that functions in producing sound. The larynx is supported caudally by the cricoid cartilage, dorsally by the arytenoid cartilage, and by the addition of the thyroid cartilage in mammals. The vocal cords themselves are flaps of epithelium supported by cartilage, and produces bursts of air that can be modified by the pharynx, lips, and tongue to produce speech. In amphibians, ventilation of the lungs occurs through external nares and choanae rather than the mouth.
Air is drawn into the pharynx by muscle contraction that lowers the pharynx floor.
In reptiles, muscle action against the ribs helps to change internal air pressure, causing inspiration. The action is assisted by contraction of die diaphragmatic muscle, which is DZ the same thing as the diaphragm. In birds, the lungs are half the size of the lungs of a similarly sized mammal. However, the lungs connect to a system of air sacs in the bones, which increases the capacity to 2 - 3 times that of a similarly sized mammal. The result is to decrease overall body mass, but still maintain respiratory efficiency.