 Dear students, in this topic we shall discuss the mechanism of ventilation of lungs in frogs. First we shall discuss the respiratory apparatus of frog that consists of nostrils which are open internally into the buccal cavity. The buccal cavity that leads to the glottis, the trachea, which starts from the glottis and leads to the lungs, the lungs which are balloon shaped. The lungs have alveoli, which are small and thin walled chambers that increase the surface area for gas exchange in lungs. This all is the respiratory apparatus of frogs. Now, we shall discuss the mechanism of breathing or lung ventilation, which has two phases, inspiration and expiration. First we shall discuss inspiration. Inspiration in frogs happens with positive pressure pumping mechanism. In contrast to other vertebrates which have mostly negative pressure, frogs have positive pressure pumping mechanism. In this mechanism, air is pushed into the lungs by the pumping pressure of buccal cavity. This phenomenon is possible because the frog has the capacity to open and close its nears and glottis independently. Glottis or nears both at a time open and close. This is an autonomy which a frog has. Now we shall discuss the steps of inspiration. As a first step, the external nears open and glottis closes. As a result, the floor of mouth is lowered. These actions cause the air to be drawn into the buccal cavity. After this, air comes into the buccal cavity. The next process is to pump air from the buccal cavity. For this process, the nears are closed. Glottis is opened and the buccal floor is raised. This raising of buccal floor provides the force for pumping the air into the lungs. Dear students, in frogs, the process of inspiration is repeated several times in a sequence. The ventilation cycle for expiration begins after many inspirations. Now we shall discuss the process of expiration. Expiration is the complex of frog. It occurs in steps. The lungs are sent to the buccal cavity through a portion of air from the lungs. Because when there is a repeating sequence of inspiration, the glottis is opened every time. The purpose is to push the inspired air through the lungs. This opens the glottis. But this opening encourages the inward air to come out of the buccal cavity. This way, the air expires into the buccal cavity. Now, when there is a buccal floor raised during the inspiration, and the fresh air is pushed into the lungs, the expired air which comes into the buccal cavity is inspired. That is also pumped back. It means that the pulmonary returned air which is low in oxygen and high in carbon dioxide is mixed with fresh air in the buccal cavity. And a mixture of both these is returned to the lungs. After few such cycles, a full ventilation cycle for exhalation happens. In that step, steps of the inhalation are repeated in a reverse order during exhalation.