Working Mechanism of lungs of Frog
In incoming and outgoing of the air from the lung is brought about by the action of the floor of the buccal cavity. It actually acts as a buccal force pump. Two sets of muscles called the sternohyal and the petrohyal muscles help in the action of buccal cavity. The sternohyal muscles arise from the coracoids and clavicle and run towards the lower surface of hyoid, apparatus located in the floor of the buccal cavity below the tongue. The petrohyal muscles arises from the outer side of the auditory capsule and run towards the upper surface of the hyoid apparatus. During pulmonary respiration the air is forced into the lungs. This is aided by the movable premaxillae bones of the upper jaw situated just below the external nares. When the sternohyal muscles contract, the floor of buccal cavity is lowered and the air enters the cavity through the external nares. Now the permaxillae are raised due to which the external nares are being closed. At the same time the petrohyal muscles contract, this results in lifting the hyoid apparatus along with the floor of the buccal cavity. This forces the air to enter into the lungs through the glottis. During this activity the mouth, external nares and gullet remains closed. This drawing in of air into the lungs is called inspiration. The process of inspirations immediately followed by expiration. It is just reversed process which is brought about by the contraction of lungs itself and the abdominal muscles. In this process, the external nares are closed and floor of the buccal cavity is lowered due to the contraction of sternohyal muscles. The air from the lungs rushed into the buccal cavity through the glottis and finally the glottis is closed and premaxillae come back into their original position, opening the external nares. Now the floor of the buccal cavity is raised due to the contraction of petrohyal muscles. This forces the air to go out through the external nares and bring about expiration.