The body of a frog can be divided into 3 parts: head, trunk and limbs. Frogs have four toes on their front feet, five toes on their back feet, and webbing. On the sides of the frog's head there are two small, slightly bulging bags. These are the frog's eardrums, through which the frog can hear sounds. The frog's back is green, very smooth, soft, and patterned, and its belly is white. This allows it to hide in the grass, making it easier to catch pests and protect itself. Its skin also helps it breathe. It has an air sac, which only male frogs have. The frog hunts with its tongue, which has mucus on it.

Head

The frog's head is flattened and slightly triangular, with a slightly pointed muzzle end. The mouth is wide, transverse, and consists of upper and lower jaws. There is an external nostril at the dorsal front of the upper jaw, and the outer edge of the external nostril has a nasal valve. The eyes are large and prominent, on the right and left sides of the head, with upper and lower eyelids; the lower eyelid has a translucent transient membrane on the inner side. When the eyelids are closed, there is a round tympanic membrane behind each eye (the tympanic membranes of toads are smaller. There is a pair of oval elevations above the back of the eyes and tympanic membrane called postauricular glands, i.e., venom glands). Male frogs have a light brown membrane folds at the back of each of the corners of the mouth for the vocal sacs, which bulge into bubbles when they call.

The carapace

The carapace follows the tympanum. The frog's trunk is short and wide, and there is a small hole for the cloaca between the two legs at the back end of the trunk, favoring the dorsal side.

Limbs

The forelimbs are short, consisting of five parts: upper arm, forearm, wrist, palm, and fingers. Four fingers, no webbing between the fingers. During the reproductive season, the male frog has an inflated protrusion on the inside of the base of the first finger, called the wedding tumor, which is used for holding the pair. The hind limbs are long and developed, divided into five parts: femur, tibia, tarsus, metatarsus and toe. Five toes, webbed between the toes. On the inside of the first toe there is a harder keratinized spur.

Frog feeding

The frog's tongue is different from the human tongue, the root of the tongue grows in the bottom of the mouth at the top, but the tongue is stretched to the inside of the mouth, long and wide, the front end of the forked polyp-like, covered with mucus. When an insect flies, the tongue is quickly flipped out, sticking the insect into the mouth.

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Species evolution

With the continuous evolution of frogs, there are a variety of frighteningly grotesque frogs, some of which secrete venom from their skin in order to prevent predators, living in the rainforests of the Amazon River Basin in a kind of tree frogs, known as poisonous frogs, and its secretions were used by local Indians to make poisonous arrows, see the blood to seal the throat.

The ancestors of frogs were originally living in the water, and then due to changes in the living environment, some rivers, lakes into the land, the ancestors of frogs with the change in the environment also gradually from the water to the land development, the change in the living environment forced the ancestors of frogs on their own body organs to make the corresponding "adjustments" to adapt to the environmental changes. The change of living environment forced the ancestors of frogs to "adjust" their body organs accordingly in order to adapt to the environmental changes. Some species that were able to adapt to life on land survived, and their locomotor organs changed from the tail that swam in the water to limbs that could move both on land and in the water, and their respiratory organs changed from gills to lungs. Some of the transition from aquatic to terrestrial in the ancestors of frogs was not quite complete, and so it showed in the development of frog larvae. The difference between tadpoles and frogs is the legacy of the frog ancestor.