REPTILES : ANATOMY on Yahoo! Kids

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Anatomy
All reptiles are vertebrates, animals with backbones. Their bodies are covered with dry, horny scales or plates (called scutes). They are low to the ground, and all except snakes and a few lizards have four legs. Each of the main groups found in North America—alligators, turtles, lizards, and snakes—has its own unique characteristics.

Turtle Anatomy
Turtles and tortoises have scales on the head and the legs, but the rest of the body is encased in a rounded, bony shell. The upper portion of the shell, called the carapace, includes the spine and the ribs. It is joined to the lower part, the plastron, by a bridge of bone. Most turtles and tortoises can easily pull their heads straight back into their shells.

A turtle’s top shell, shown here from the inside, includes the rib cage. Turtles are the only animals with their legs inside the rib cage. © Brian Kenney

Blanding’s Turtle © Allen Blake Sheldon

Sealed Up
The bottom shell of some turtles, such as box turtles and Blanding’s Turtle, is hinged and can be pulled up against the top shell, sealing the turtle safely inside.

Blanding’s Turtle © Allen Blake Sheldon

Wood Turtle © Allen Blake Sheldon

Scutes
The individual plates on a turtle’s shell, like those on the Wood Turtle, are called scutes. The scutes on the bottom shell of some turtles can be quite colorful.

Painted Turtle © James H. Harding

Crocodilian Bodies
Both the American Alligator and American Crocodile have torpedo-shaped bodies, well made for life in the water. They are keen-sighted and have sharp hearing. When they dive under, their nostrils close up and a clear membrane closes sideways across their eyes. A wide flap closes the rear of the throat so that they don't drown when they're pulling prey underwater. The nostrils and eyes of crocodilians are perched on top of their heads, so they are able to see and breathe while almost entirely submerged.

Crocodilians have tough skin with large ridged scales. © Brian Kenney

American Alligator © Stephen G. Maka

Lizard Anatomy
Lizards come in all shapes and sizes. Different species have developed special features to help them survive in different habitats. The Gila Monster has a stout body and beadlike scales and stores fat in its thick tail; it can survive without food for several months in its harsh desert environment. Some lizards, especially burrowing forms, have very small legs or no legs at all. Glass lizards are an example of legless lizards. They look like snakes but have movable eyelids, as do most lizards. Skinks are recognized by their shiny, smooth, overlapping scales, short legs, and pointed snouts.

Great Plains Skink © Brian Kenney

Lizard Senses
Most lizards see and hear well. They have external ear openings and their eyes have movable eyelids (unlike snakes).

The Collared Lizard has the typical lizard shape (like a miniature dinosaur): big head, long tail, plump body covered with granular scales, and four feet with five clawed toes on each. © Rod Planck - Photo Researchers, Inc.

Texas Horned Lizard scales and spines. © Karl H. Switak

Gila Monster beadlike scales. © Brian Kenney

Scaly Skin
In some lizards the scales are small and grainlike, while in others they are large and platelike. The scales may be smooth or they may have little ridges called keels or they may even have developed into spines.

Fringe-toed lizard foot. © Dan Suzio

Collared Lizard, top of head. © Karl H. Switak

Head to Toe
The “fringes” on the feet of fringe-toed lizards help them to walk on sand. Some lizards have a "third eye," a tiny, light-sensitive, transparent structure on top of the head that helps them regulate how long they stay in the sun.

Snake Anatomy
Snakes are marvels of nature. They have no eyelids, external ears, or legs, yet they live successfully without these body parts. Their slender shape means that the insides of their bodies are different from those of other vertebrates as well. In most snakes, the left lung is very tiny or absent and the left kidney is positioned behind the right one instead of side by side.

Snakes have an extremely long spine, with 200 to 400 vertebrae. (Humans have 32 to 34 vertebrae.) It takes a very complicated set of interconnected muscles to move all these bones. © David M. Dennis

Snake Skin
Snakes shed the outer layer of their skin two or three times a year. This permits them to grow and also to discard the worn and damaged outer coat of skin. The old layer isn't shed until a new layer of skin has formed completely underneath it. Snakes often shed their skin in one piece. After the skin on the snout splits, the skin peels off inside out as the snake moves forward.

Snake Eyes
Transparent eye caps protect the lidless eyes of snakes. Racers, whipsnakes, indigos, and some other species that are active during the day have excellent vision. Blind snakes can distinguish only light and dark. Most nocturnal snakes, such as Copperheads, Night Snakes, and rattlesnakes, have vertical pupils that expand in low light.

Snake Scales
Snakes have large scales across the belly and smaller scales on the back. The back scales may have a smooth, polished appearance, or they may have a dull finish and a rough texture. The scales on water snakes have ridges, or keels, which help them move through water. Snakes that spend a lot of time burrowing have smooth scales, which enable them to move more easliy through the soil.

Smelling with Forked Tongue
Snakes cannot hear airborne sounds, but their other senses make up for that. By flicking their forked tongues they pick up chemicals left by other animals from the air or ground. These chemicals are carried to an organ in the mouth that helps the snake figure out what (or whom) they came from. Guided by their tongues, snakes can trail food, follow one of their kind, or return to their shelter.

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