Читать книгу Dragons of the Air: An Account of Extinct Flying Reptiles - H. G. Seeley - Страница 8

Between one class of animals and another the differences in the condition of the skin are more or less distinctive. In a few amphibians there are some bones in the skin on the under side of the body, though the skin is usually naked, and in frogs is said to transmit air to the blood, so as to exercise a respiratory function of a minor kind. This naked condition, so unlike the armoured skin of the true Reptilia, appears to have been paralleled by a number of extinct groups of fossils of the Secondary rocks, such as Ichthyosaurs and Plesiosaurs, which were aquatic, and probably also by some Dinosauria, which were terrestrial.

Living reptiles are usually defended with some kind of protection to the skin. Among snakes and lizards the skin has commonly a covering of overlapping scales, usually of horny or bony texture. The tortoise and turtle tribe shut up the animal in a true box of bone, which is cased with an armour of horny plates. Crocodiles have a thick skin embedding a less continuous coat of mail. Thus the skin of a reptile does not at first suggest anything which might become an organ of flight; and its dermal appendages, or scales, may seem further removed from the feathers which ensure flying powers to the bird than from the naked skin of a frog.