INDIAN BULLFROG WITH FULLY DISTENDED VOCAL SAC
The vocal sac is the flexible membrane of skin possessed by the most male frogs. The purpose of the vocal sac is usually as an amplification of their mating or advertisement call. The presence or development of the vocal sac is one way of externally determining the sex of a frog in many species.
The vocal sac is open to the mouth cavity of the bullfrog, with two slits on either side of the tongue. To call, the frog inflates it’s lungs and shuts it’s nose and mouth. Air is then expelled from the lungs, through the larynx and into the vocal sac. The vibrations of the larynx emits sounds, Which resonate on the elastic membrane of the vocal sac. The resonance causes the sound to be amplified and allows the call to carry further. Muscles within the body wall force the air back and force between the lungs and vocal sac.