出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/03/21 22:01:52」(JST)
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The tail is the section at the rear end of an animal's body; in general, the term refers to a distinct, flexible appendage to the torso. It is the part of the body that corresponds roughly to the sacrum and coccyx in mammals, reptiles, and birds. While tails are primarily a feature of vertebrates, some invertebrates including scorpions and springtails, as well as snails and slugs, have tail-like appendages that are sometimes referred to as tails. Tailed objects are sometimes referred to as "caudate" and the part of the body associated with or proximal to the tail are given the adjective "caudal".
Animal tails are used in a variety of ways. They provide a source of locomotion for fish and some other forms of marine life. Many land animals use their tails to brush away flies and other biting insects. Some species, including cats and kangaroos, use their tails for balance; and some, such as New World monkeys and opossums, have what are known as prehensile tails, which are adapted to allow them to grasp tree branches.
Tails are also used for social signaling. Some deer species flash the white underside of their tails to warn other nearby deer of possible danger, and canids (including domestic dogs) indicate emotions through the positioning and movement of their tails. Some species' tails are armored, and some, such as those of scorpions, contain venom.
Some species of lizard can detach ("cast") their tails from their bodies. This can help them to escape from predators, which are either distracted by the wriggling detached tail, or left with only the tail while the rest of the lizard flees. Tails cast in this manner generally grow back over time, though the replacement is typically darker in colour than the original.
The tails of most birds end in long feathers called rectrices. These feathers are used as a rudder, helping the bird to steer and maneuver in flight; they also help the bird to balance while it is perched. In some species—such as birds of paradise, lyrebirds, and most notably peafowl—modified tail feathers play an important role in courtship displays. The extra-stiff tail feathers of other species, including woodpeckers and woodcreepers, allow them to brace themselves firmly against tree trunks.
The tails of grazing animals, such as horses, are used both to sweep away insects, and positioned or moved in ways that indicate the animal's physical or emotional state.
Human embryos have a tail that measures about one-sixth of the size of the embryo itself.[1] As the embryo develops into a fetus, the tail is absorbed by the growing body. The developmental tail is thus a human vestigial structure.[2][3] Infrequently, a child is born with a "soft tail", which contains no vertebrae, but only blood vessels, muscles, and nerves, although there have been several documented cases of tails containing cartilage or up to five vertebrae.[4]
Humans have a "tail bone" (the coccyx) attached to the pelvis, formed of fused vertebrae, usually four, at the bottom of the vertebral column. It does not protrude externally.
Scorpion
Pig (Sus domestica)
Glyptodon (Glyptodon asper)
Longhorn cowfish (Lactoria cornuta)
Grévy's zebra (Equus grevyi)
Polo pony (Equus ferus caballus)
American alligator (Alligator mississipiensis)
Hippopotamus (Hippopotamus amphibius)
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| 関連記事 | 「appendage」「caudal」 |