Reptile Anatomy

파충류샵 Reptiles are covered in scales that form armor that enables them to live on land unlike amphibians. They also have a different cardiovascular system.


Like birds and mammals, snakes have a four-chambered heart that can function as a three-chamber heart during contraction. The pulmonary artery from the single ventricle runs to the lungs(s). A tracheal lung may be present as well.


The skulls of reptiles differ from those of amphibians in a number of ways. The reptiles do not have an otic notch and several small bones at the rear of the skull roof are absent. The lower jaws are characterized by the fact that only one of the bones, called the dentary, bears teeth. Behind the dentary a small bone, the articular, forms a joint with the quadrate bone near the back of the skull.

Reptiles that rely on water-based lifestyles have evolved lighter skulls to accommodate the large jaw musculature and lungs required for gaseous exchange. They also have a skull that does not have a complete roof and has vacuities (empty spaces) on each side of the skull, just anterior to the eye orbits. This type of skull is characteristic of the euryapsid reptiles that dominated the land from the Late Carboniferous to the Early Triassic, and gave rise to mammals. Today, some turtles and lizards still possess this type of skull.

A key feature of the euryapsid skull is that it has temporal vacuities (empty spaces) on either side of the skull, guarded by postorbital and squamosal bones above and jugal and quadratojugal bones below. The symphysis that connects the quadrate and squamosal bones is moved forward, creating more space for the attachment of jaw muscles. This is an adaptation for catching and devouring larger prey. The squamosal and parietal bones have moveable joints to permit high amounts of cranial kinesis.


The body of a reptile is covered with a heavily keratinized layer of scales. Scales may be small, such as those on the heads of some lizard species, or large, such as the plates on a crocodile’s skin. All scales contain a unique type of keratin called beta keratin, which makes them resistant to water and other chemicals.

Most reptiles have closed circulation through a three-chamber heart. This design allows them to control the flow of oxygenated and deoxygenated blood, which helps them maintain a stable internal temperature. It also allows them to dive for longer periods of time underwater.

Like most vertebrates, reptiles have a two-part digestive system. The stomach begins the digestion of food, and then the intestines finish it off. Reptiles are the only animals that produce a gas called ethylene, which is produced in the digestive tract and can help to break down protein.

Snakes have hinged upper and lower jaws that can stretch outward when they swallow prey. As a result, the mouth can be much larger than in most other vertebrates. This allows snakes to digest much bigger prey items before it reaches the stomach, where its acid can break down proteins more effectively.

Like other tetrapods, reptiles have a pair of eyes that can sense light and movement, known as lateral lines. However, some lizards (such as the chamaeleonids) have a third eye, located on top of the head. This third eye is similar to the lateral line of vision in other reptiles, but it is used for light detection rather than movement perception.


The evolutionary pressures that led to snakes’ losing legs are twofold. First, as they got larger and bigger, it became more difficult for their leg muscles to bear their body weight while retaining a lizard-like stance. Second, many of their ancient ancestors spent a lot of time in aquatic environments and found that a long, lithe body is better for speed and maneuverability in water than are large, limb-based lizards.

The fossil reptile Dinilysia patagonica, which lived about 85 million years ago in the Late Cretaceous period, is believed to be the first snake to lose its limbs. Researchers have excavated an amazingly well-preserved skeleton of this animal, which was as long as a human. It preserved a pelvic girdle, but no limb bones and no toes. Another fossil snake, Pachyrhachis, also lacked toe bones and lacks a pelvic girdle.

While most snakes are limbless, some species such as pythons and boas still retain vestigial remnants of their ancient limbs near the bottom of their bodies. These limbs are not used for movement, but serve as claspers during mating. Like all reptiles, snakes breathe air through lungs. The lungs are simple, compared to those of mammals and birds. The pulmonary system consists of a single cavity (the coelomic cavity) with one or more lobes. In most snakes, the left lung has regressed into a vestigial structure; this helps the animal conserve body heat.


The skin of reptiles is covered in rough, horny scales or bony plates that are shed regularly, to maintain good health. The scales are made of a material called keratin, which is also found in nails and hair and the claws of some species of snakes.

Underneath the epidermis are blood and lymph vessels, nerves and skin muscles. In lizards and snakes, the dermis is supported by special cells known as chromatophores. These have the ability to change color in response to light. The chromatophores are filled with pigment cells that can alter the space between crystals, changing the overall color of the skin.

In addition to the normal skin layer, some reptiles have a subcutaneous fat layer that provides insulation and buoyancy. It is poorly developed in most reptiles but some, such as the tail of a gecko, have substantial deposits.

Most reptiles can be spotted by their coloration, which is designed to blend in with the kind of environment in which they live. In addition, some reptiles can change their skin color. This is done by adjusting the space between pigment cells, which contain guanine crystals. This process is called chromatophoresis. This is the same mechanism that allows chameleons to shift their colors, based on the wavelength of the light they are exposed to. The underlying skin is changed by the movement of the chromatophores, so that the chameleon can adapt to its environment.