Gas exchange between the air and bloodstream occurs in three locations in the frog: 1) the skin, 2) the lining of the mouth and 3) the lungs.

1. The throat moves down drawing air into the mouth through the nostils.
2. The nostrils close and the throat moves up, forcing air into the lungs.
3. The throat moves down drawing air back out of the lungs.
4. The nostrils open and the throat moves up, forcing air out of the frog.
Repeat.