Reptile Anatomy

Reptiles have a number of unique characteristics which set them apart from other vertebrates. Their skin is covered with scales made from a special kind of keratin known as beta-keratin.


Their heavily keratinized skin prevents water loss, and reflects their commitment to land living. They also have a four-chambered heart which can act as a three chambered one during diving.


The skull of a reptile is very different from the skulls of amphibians and mammals. The bones that make up the skull are not fused together, and the lower jaw muscles can move in a wider range of positions. The skull is also much more compact.

Among the squamates, snakes are highly derived and have evolved to consume large prey items. This has involved extensive modification of the skull. In snakes, the bone that forms the skull’s roof can hinge in two places, allowing the mouth to stretch wide to take in large meals. Also, the frontal and parietal bones are less fused together than in most other squamates.

In addition, some of the skull bones that make up the palate have moved to the back of the head and now correspond to the malleus and incus in mammals, enabling them to detect higher frequency sounds. Thus, snakes have a more complex palate than fish, amphibians, and most other reptiles.


Reptiles have a dry outer covering of hard keratin scales, which prevent water loss, a feature essential to their terrestrial existence. Their skin also has few or no glands, which sets it apart from the hairs and feathers of mammals and amphibians.

In some types of reptile, such as snakes and crocodiles, the bones of the limbs are modified into fins or flippers. Other species, such as extinct marine reptiles such as ichthyosaurs and plesiosaurs, have lost their limbs altogether and have evolved a long tail that serves to balance the body.

The cellular architecture of reptilian scales has been studied extensively, but a thorough understanding of the specific kinetics involved in the formation of these localized growth zones remains elusive. It will be interesting to study the pattern of cell proliferation and death within these pits, which resemble the invagination of follicles that occur in the formation of hairs and feathers.


The skin of most reptiles is covered with overlapping epidermal scales that distinguish them from other amniotes. These scales, called scutes or keratinized plates, protect the animal and help it regulate its body temperature by reflecting heat back to its environment. In some species, the scales are modified to serve particular functions; for example, ridged snake skin helps it grip its prey, while platelike lizard scutes have infrared receptors that enable them to detect heat emitted from other reptiles.

The dermis of a reptile is composed of fibrous connective tissue, blood and lymphatic vessels, nerves, and pigmentary cells. Bony plates of dermal bone, called osteoderms, are located under the keratinized epidermis in some reptiles, including crocodilians and many lizards.

A transitory epidermal placode, shared by avian and mammalian skin, initiates development of scales in all reptiles that possess them. In situ hybridization analysis demonstrates that the epidermal placode in squamate reptiles, like those of avian and mammals, exhibits early spatially restricted expression of the epidermal markers used to mark anatomical placodes, as well as conserved dermal Bmp4 expression.


Reptiles are a class of vertebrates that include snakes, lizards, turtles and crocodiles. They have bony skeletons, scales and lay eggs.

The mouth of a snake has many adaptations to allow it to swallow large prey. The lower jaw hinges loosely with the skull rostrally and the mandibular symphysis can separate, called dislocating. The lower teeth also have a ‘jaw lock’ which can be activated by rubbing the corners of the mouth on an abrasive surface, causing them to come apart and allow more room for eating.

The heart of reptiles is very different from that of mammals and this can cause difficulty in using pulse oximetry on them. Reptiles have high circulating levels of methemoglobin and can often give falsely low readings on a monitor. Therefore it is important for veterinary nurses to have sufficient knowledge of normal reptile cardiac anatomy. This will enable them to understand why a reading might be abnormal and interpret the results correctly.


Reptile teeth vary widely among species, depending on what they eat. For example, snakes that eat rodents tend to have more specialized teeth that are more pointed and able to puncture skin. Lizards that eat insects have simpler, more conical adult teeth that are better suited to crushing their prey’s hard exoskeletons.

Some reptiles, like the venomous lizard Heloderma, have anterior and posterior grooves on their teeth that are thought to enhance venom introduction into the target animal’s gastrointestinal tract. These ridges are also present in the molars of Komodo monitors and other varanids.

Most lizards have a dentition of pleurodont teeth, which do not fuse to the jaw bone on the cheek side and are weakly attached with ligaments. The teeth grow throughout life and are replaced when lost. They are located on the palatines, pterygoids and occasionally the premaxillae. Some lizards, such as pit vipers and elapids have fangs that fold caudodorsally when not in use, and they lie sheathed in a membranous flap when closed.

Digestive System

Reptiles are vertebrates that include snakes, lizards, turtles and crocodilians. They have a bony skeleton, scales, leathery or hard shelled eggs and the ability to conserve water.

Herbivorous reptiles have short digestive tracts, so they require few meals and have slow metabolisms. They also use rocks and pebbles to grind plant matter in their mouths, much like birds.

Snakes have a special adaptation that helps them swallow whole prey items. The two halves of the lower jaw hinge only loosely together rostrally and are able to separate and then re-position themselves over the head. This allows the pharynx (a muscular tube that communicates with the respiratory system) to close, and prevents food or ‘cud’ from entering the lungs.

Snakes do not have a diaphragm, although some species such as crocodiles have an analogous muscle. They breathe using a combination of rib and abdominal muscles, and the elastic recoil of the lungs themselves.