Under normal circumstances, the toad gets sufficient oxygen for its skin and buccal cavity. To draw air into the lungs, air is first sucked into the buccal cavity as just described. Then, the nostril are closed, the glottis is opened, and the floor of the buccal cavity is raised. This increases the air pressure in the buccal cavity, forcing air into the lungs through open glottis. The lungs become Inflated as air fills the aveoli. Gaseous exchange occurs between the inhaled air in the alveoli and the blood in the capillaries lining the alveoli.
To expel air from the lungs into the mouth, the floor of buccal cavity is lowered to create a region of low pressure there. When air fills the buccal cavity, the glottis closes and the floor of the buccal cavity is raised. This causes the valves of nostrils to open, allowing air to flow our of the body.
VENTILATION OF LUNGS THROUGH MAMMALS.
In mammals, the structure of the thorax is designed to bring about the ventilation of the lungs. The ribcage, intercostal muscles and diaphragm work together to draw air into and out of the lungs.

VENTILATION IN HUMAN BEINGS
In air breathing vertebrates, gaseous exchange occurs in lungs. These are suspended in the thoracic cavity, which is separated from the abdominal cavity by the diaphragm, a muscular sheet. The lungs are surrounded and protected by the rib cage, and enclosed within a double membrane sac called pleura, which is tight nd waterproof. The set up enables air breathing vertebrates to inhale fresh air from their external environment and exhale uses air from the bodies.
Mammals breath buy moving diaphragm and the rib cage. These respiratory movement bring about inspiration (inhalation) and expiration ( exhalation.