11. Males have subgular vocal sacs with a slit-like opening in the floor of the mouth. 12. The male has a pair of vocal sacs which are used during the mating season. 13. Air is then expelled from the lungs, through the larynx, and into the vocal sac . 14. This indicates the development of a vocal sac and thus an ability to commence calling behaviour. 15. The male has a median subgular vocal sac . 16. Males have internal vocal sacs and oval flat glands on the inner side of their arms. 17. An alternative use of the vocal sac is employed by the frogs of the Rhinodermatidae family. 18. They also possess a white vocal sac that can be used to produce sounds for mating. 19. Muscles within the body wall force the air back and forth between the lungs and vocal sac . 20. Male with an internal subgular vocal sac .
