Frog - Morphology and Physiology

Morphology and Physiology

Frogs have no tail, except as larvae, and most have long hind legs, elongated ankle bones, webbed toes, no claws, large eyes and a smooth or warty skin. They have a short vertebral column, with no more than ten free vertebrae and a fused tailbone (urostyle or coccyx). Like other amphibians, oxygen can pass through their highly permeable skins. This unique feature allows them to remain in places without access to the air, respiring through their skins. The ribs are poorly developed so the lungs are filled by buccal pumping and it has been shown that a frog deprived of its lungs can maintain its body functions without them. For the skin to serve as a respiratory organ, it must remain moist. This makes frogs susceptible to various substances they may encounter in the environment, some of which may be toxic and can dissolve in the water film and be passed into their bloodstream. This may be one of the causes of the worldwide decline in frog populations.

Frogs range in size from the recently discovered 7.7 mm (0.30 in) long Paedophryne amauensis of Papua New Guinea to the 300 mm (12 in) goliath frog (Conraua goliath) of Cameroon. The skin hangs loosely on the body because of the lack of loose connective tissue. Frogs have three eyelid membranes: one is transparent to protect the eyes underwater, and two vary from translucent to opaque. They have a tympanum on each side of the head which is involved in hearing and, in some species, is covered by skin. True toads completely lack teeth but most frogs have them, specifically pedicellate teeth in which the crown is separated from the root by fibrous tissue. These are on the edge of the upper jaw and there are also vomerine teeth on the roof of the mouth. There are no teeth in the lower jaw and frogs usually swallow their food whole. The teeth are mainly used to grip the prey and keep it in place till swallowed, a process assisted by retracting the eyes into the head. The African bull frog (Pyxicephalus), which preys on relatively large animals such as mice and other frogs, has cone shaped bony projections called odontoid processes at the front of the lower jaw which function like teeth.