Noun
vocal sac (plural vocal sacs)
The flexible membrane of skin possessed by most male frogs, used for amplification of the voice.
Call seeAlso A male Dendropsophus microcephalus displaying its vocal sac during its call. Source: Internet
When the tadpoles are about to hatch, they are engulfed by the male, which carries them around inside his much-enlarged vocal sac. Source: Internet