Nares are another word for nostrils. Frogs have two types of nares: external and internal. These two types of nostrils work together to provide oxygen to frogs when they're not in the water. In addition to nares, frogs can also breathe through their skin when submerged in water.
How Frogs Breathe
A frog controls its breathing by pulsating its throat, and it always breathes with its mouth closed. The movements made by the throat pull oxygen into its body through its nares and into its lungs. Exhaled air is forced out when the body contracts.
External nares are located on the top of a frog's snout, and look like small slits. These make it possible for the frog to float on the surface of the water, leaving its external nares above the water level for inhaling oxygen.
Internal nares are on the roof of a frog's mouth. Air passes from the external nares into the mouth through these openings. They can be closed using a sphincter muscle when the frog is submerged under water to prevent water from entering the mouth and therefore the lungs.
Breathing Without Nares
A frog also can breathe by absorbing oxygen through its skin. Small blood vessels called capillaries that are under the outer skin layer absorb oxygen from the water. Some frogs use this method of breathing when they must be submerged for longer periods of time, such as during breeding seasons.