More than 8,600 species of animals adapted to flight belong to the bird class. More than 400 species of these animals are known in Ukraine. All species of birds have a short streamline body covered with feather cover. Their forelimbs turned into wings, and the rear legs serve to move on the ground, plant branches or swimming in the water. Homeotherm, ability to fly and a fairly high level of development of the nervous system determined the identity of this group of vertebrates.
The body of the birds is divided into the same sections as in the reptiles, but the tail section is shortened. Birds have a more or less elongated flexible neck. Due to this, they can turn their heads 180 ° or more (for example, owls – by 270 °). On the head are the eyes, protected by three centuries (upper, lower and ciliated membrane), nostrils and auditory holes. The beak consists of the upper part – the superglue and the lower – we connect. At the base of the beak of bird species (for example, pigeons) is a soft skin bundle – a wax.
The forelimbs are wings adapted to flight. They have only three fingers, covered with leather. Birds are two-legged animals. The legs basically have four toes. Three of them are forward, and one – back. This allows the birds to cover the branches and creates a support while traveling on the ground. But in birds that can run fast (for example, ostriches), the number of toes can be reduced to three or even two (for example, in an African ostrich).
Birds, like reptiles, have dry skin, almost devoid of glands. Only the base of the tail in many species opens the ducts of the coccygeal gland. The secret of this gland (fat-like substances) birds are smeared with a beak feather cover, which makes it elastic and waterproof. The skin of the birds forms various horny derivatives: this is the already known hindlegs and subclavian, as well as claws at the fingertips and horny scales covering the lower part of the legs.
A derivative of the skin of birds is also a variety of feathers. Feathers, like scales on legs, consist of horny substance. The individual feathers consist of a rod, from which numerous fine outgrowths – beards – extend in both directions. The totality of the beards is called the fan. The empty part of the rod is aimed at the skin, not the beard. Outline contour and down feathers.