When frogs left the ocean, many parts of their anatomy changed. One of the parts of their bodies that changed the most was their skin. Their skin contains two parts: the epidermis (outer skin) and the dermis (inner skin). The epidermis contains many layers of cells, and is covered by an outer layer of , dead cells that protects the other cells and prevents moisture loss which is called the stratum corneum. This layer of dead cells is one of the frog's adaptations to land. Frogs and toads shed this skin at various times and a new layer forms. The dermis is a thinner layer that serves as a respiratory organ. The pigment that colors the frog's skin is usually found in this layer. Depending on the species, a frog may have poison glands in its skin. A frog's skin does not have scales.
The frog's digestive system starts in the mouth with its tongue. For the most part, frog tongues art attached near the back of the jaw and folded on the base of the mouth with the tip of the tongue pointing back toward its throat. Their tongues can be flipped out very rapidly and accurately in order to catch an insect or other tasty treat (mucus glands in the mouth produce a sticky substance that helps to catch prey). Some toads are toothless, but most frogs do have tooth-like structures which are attached to the jaw and aid in breaking up the food so that it can be digested. The food then goes down their short esophagus into the stomach, where the food is digested. The waste goes into the coiled, winding intestines where it can be later removed.
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