-Occurs through the skin
-Because it is moist and has a rich supply of blood capillaries
-Oxygen uptake through the skin is almost constant throughout the year
-In cold weather, it supplies almost all the oxygen required by the animal in warm weather, when animals are most active it may represent only a quarter of the frog’s need.
-Visible bucco-pharyngeal movement of the throat maintain a constant exchange of gases between the buccal cavity and the atmosphere
-For inhalation to occur the mouth and the glottis must be closed
-The nostril open and the floor of the buccal cavity is lowered
Contraction is achieved by sternohynoid muscles attached to the hyoid cartilage
-The buccal cavity is lined with moist, heavily vascularized epithelium and it is here that gaseous exchange occurs
-Exhalation follows when petrohynoid muscles contract
Raising the floor of buccal cavity
-The lungs are a pair of hollow sacs
-Their surface is extremely folded
-Surface area is relatively small compared to that of mammals
-Ventilation movement is as follows:
*With the mouth closed, the nostril open and glottis closed, the floor of the buccal cavity is lowered. Air enters the buccopharynx
*The nostril close, the glottis open. Air from the lungs is forced into the buccopharynx by muscle action and elastic recoil of the lungs thus fixing it with freshly inhaled air.
*The floor of the buccal cavity is raised; this forces the mixed air into the lungs. When the lungs are full, the glottis closes and air is trapped there for some time. Gas exchange between the blood capillaries in the epithelium of the lungs and the inspired air occurs.
*After a short interval, exhalation occurs the nostrils close, the glottis opens and the floor of the buccal cavity is once again lowered. The nostril open, the glottis closes and the floor of the buccal cavity is raised this force air out of the body via the nostrils.