The shape of a body is very various. The amphibious having a tail are similar more to fishes, have the trunk squeezed from sides and a long veslovidny tail; at others a trunk roundish or flat, and the tail absolutely is absent. Some amphibians absolutely have no extremities, at others they are developed very poorly, at the third, on the contrary, are strongly developed.
The digestive channel is rather short and simply arranged; it consists of a long gullet, a simple thick-walled stomach and a back gut. At all amphibians a bladed liver, a gall bladder, a pancreas, kidneys and a bladder.
The brain of the amphibious has the simple device. It has the extended form and consists of two forward hemispheres, the midbrain and a cerebellum representing only the cross bridge and oblong. The spinal cord is developed much more strongly, than head.
Feature of the amphibious consists in lack of any firm external covers why they also are called as naked reptiles. Really, at them is not present, as at fishes and reptiles, neither feathers, nor wool, as at mammals; the majority are covered outside only with naked skin, and only the very few on skin have some traces or similarity of horn educations. But in skin of the amphibious some educations which other vertebrata do not have are had.
Except for extreme polar regions, a frog and toads are widespread on all Earth, but they are most numerous in tropical America where there lives about a half of all of types known now. The way of life of frogs is various, depending on their residence: they live both in water, and on coast, and on meadows, in forest and shrubby thickets and nearby the human dwelling, say, everywhere where can find dampness and suitable food.
Everything that was told about reptiles of rather insignificant extent of their activity, is quite applicable to amphibious which also have cold blood. Public life at them is so poorly developed; however, the care of posterity at them is noticeable a little more, than at reptiles.
In a connecting tkannom a skin layer some amphibians have small caps filled with jellylike substance; at others it is formed the voluminous cavities adapted for development and initial storage of germs. At last, at some in skin sometimes appear ossification or the firm plates similar partly to fish scales. The top layer of skin is very thin and various dyes often consist in it.
The device of a skull happens variously; here it is possible to notice gradual complication and increase in bone educations at the expense of cartilaginous and connecting. A characteristic sign of all class amphibious are two sochlenovy heads on occipital part of a skull which correspond to two dimples of the first cervical vertebra. A skull always flat, wide, eye hollows are very great. The cranium consists of two occipital bones, two frontal, the main bone. In skull sidewalls mostly ossification does not happen absolutely, or the cartilage okostenevat partly. Palatal bones are not movably connected to a skull; on them, in the same way as on a soshnik and on a maple bone, teeth sometimes sit. The lower jaw consists of two or more parts and never okostenevat quite.
The majority of amphibians lead a nocturnalism, since a sunset and till the morning. In the afternoon many of them creep somewhere in cracks or under stones and sit not movably, others use solar warmth and spend day half-asleep.
On a way of life and on an exterior the amphibious have a strong likeness, on the one hand, with reptiles, and with another, it is even more - with fishes; the larval stage makes them as if transition between these two groups.