The vocal sac is the flexible

membrane A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. B ...

of skin possessed by most male

frog A frog is any member of a diverse and largely Carnivore, carnivorous group of short-bodied, tailless amphibians composing the order (biology), order Anura (ανοὐρά, literally ''without tail'' in Ancient Greek). The oldest fossil "proto-f ...

s and

toad Toad is a common name for certain frogs, especially of the family Bufonidae, that are characterized by dry, leathery skin, short legs, and large bumps covering the parotoid glands. A distinction between frogs and toads is not made in scientif ...

s. 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 or toad in many species; taking frogs as an example; The vocal sac is open to the mouth cavity of the frog, with two slits on either side of the tongue. To call, the frog inflates its lungs and shuts its nose and mouth. Air is then expelled from the lungs, through the

larynx The larynx (), commonly called the voice box, is an organ in the top of the neck involved in breathing, producing sound and protecting the trachea against food aspiration. The opening of larynx into pharynx known as the laryngeal inlet is about ...

, and into the vocal sac. The vibrations of the larynx emits a sound, which resonates 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 forth between the lungs and vocal sac.

Development

The development of the vocal sac is different in most species, however they mostly follow the same process. The development of the unilobular vocal sac begins with two small growths on the floor of the mouth. These grow until they form two small pouches, which expand until they meet in the centre of the mouth and form one large cavity, which then grows until it is fully developed.

Purpose

The primary purpose of the vocal sac is to amplify the advertisement call of the male, and attract females from as large an area as possible. Species of frog without vocal sacs may only be heard within a radius of a few metres, whereas some species with vocal sacs can be heard over away. Modern frog species (

neobatrachia The Neobatrachia (New Latin ''neo-'' ("new") + ''batrachia'' ("frogs")) are a suborder of the Anura, the order of frogs and toads. This suborder is the most advanced and apomorphic of the three anuran suborders alive today, hence its name, whi ...

ns and some

mesobatrachia The Mesobatrachia (Ancient Greek ''μέσος'' (mésos, "middle") + ''batrachia'' ("frogs")) is a paraphyletic group of relatively primitive frogs. At the end of 2016, it contained 3 superfamilies ( Pelobatoidea, Pelodytoidea and Pipoidea), 6 ...

ns) which lack vocal sacs tend to inhabit areas close to flowing water. The sound of the flowing water overpowers the advertisement call, so they must advertise by other means. An alternative use of the vocal sac is employed by the frogs of the family

Rhinodermatidae Rhinodermatidae, also known as Darwin's frogs, mouth-breeding frogs or mouth-brooding frogs, is a small family of frogs found in temperate forests of southern Chile and adjacent Argentina. They are a unique and evolutionary significant group of ...

. The males of the two species of this family scoop recently hatched tadpoles into their mouth, where they move into the vocal sac. The tadpoles of

Darwin's frog Darwin’s frog (''Rhinoderma darwinii''), also called the Southern Darwin's frog, is a species of Chilean/Argentinian frog of the family Rhinodermatidae. It was discovered by Charles Darwin during his voyage on voyage on HMS ''Beagle''. on a ...

(''Rhinoderma darwinii'') remain in the vocal sac until

metamorphosis Metamorphosis is a biological process by which an animal physically develops including birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some inse ...

, whereas the

Chile Darwin's frog The Chile Darwin's frog (''Rhinoderma rufum''), also called the northern Darwin's frog, is one of only two members of the family Rhinodermatidae. It is endemic to central Chile, although it might well be extinct. Description The Chile Darwin's ...

(''Rhinoderma rufum'') will transport the tadpoles to a water source.

References

* * * * *{{cite web, title=Anurans – Vocal, url=http://cal.man.ac.uk/student_projects/2000/mnzo7cas/vocal.htm, access-date=2006-06-19, archive-url=https://web.archive.org/web/20040822114000/http://cal.man.ac.uk/student_projects/2000/mnzo7cas/vocal.htm, archive-date=2004-08-22, url-status=dead Amphibian anatomy Animal communication Frogs

Development

Purpose

See also

References