 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 frog has the capacity to open and close its nears and glottis independently. Glottis and nears open at a time and close either of them. This is an autonomy which a frog has. Now we shall discuss the steps of inspiration. The 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 is pumped into the buccal cavity and the air is pumped into the air. Now for this process, the nears close. Glottis is opened and buccal floor is raised. This raising of buccal floor provides the force for pumping the air into the lungs. For frog, the process of inspiration is repeated several times in a sequence. Expiration is a ventilation cycle that begins after many inspirations. Now we shall discuss the process of expiration. Expiration frog is complex. It occurs in steps. Lungs are sent to the buccal cavity through a portion of air lung during every breathing cycle. Because when there is a repeating sequence of inspiration, the glottis opens every time which means that the inspired air has to be pushed through the buccal cavity into the lungs. This is why the glottis opens but the opening of the glottis encourages the inward air to come out of the buccal cavity. This way the air expires into the buccal cavity. Now when the buccal floor is raised and the fresh air is pushed into the lungs, the expired air which comes into the buccal cavity is also 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.