Diagram 1. The scientific classification of snakes.
Snakes are part of the Animalia Kingdom and the Chordata phylum, which refers to vertebrates and a few closely related invertebrate species. Snakes belong to the class of Reptilia, or Reptiles, and the order of Squamata, which is for reptiles that have epidermal scales. Snakes can be found in the suborder Ophidia, also called Serpentes. Depending on the classification used and the date of the research, Ophidia has approximately nineteen Families of snakes, but research and new species discovery change this.
Snakes are related to members of the suborder Sauria, or lizards, as well as members of the suborder Amphisbaenia, or the worm-snakes.  More distant relationships exist between snakes and members of the orders of Crocodilia, which includes alligators and crocodiles; Testudines, which includes turtles and tortoises; and Sphenodontia, which includes the tuatara. 
Number of Species and Geographical Distribution
While research continues on snakes and new species are being discovered all the time, there are approximately 2,875 snake species known to science.  Snakes appear all over the world, with the exception of certain extreme climates, such as the Arctic Circle and Antarctica, and the exception of some islands, such as Ireland.
Particular Traits to Consider
Dragons and serpents are connected in mythology; some dragons are described as giant snakes, while others are other manifestations of large snakes with additional limbs. Due to this connection, it is important to explore as much about snakes as possible, including the wide variety of snakes that exist in the world today.
Particular serpent traits that relate to the dragon include the following:
- Eyes that do not blink
- Sloughing/Shedding of skin as a single unit
- Swallowing large food whole
- Specialized locomotion, including movement across desert sands, swimming, and gliding
- Specialized abilities, such as gliding and spitting venom
General Description of Size
With the diversity of snakes that exist in the world, it would be impossible to describe each species or family here in terms of size, due to extreme variation and the difficulty of researching certain species of snake. To get a general idea of the size of snakes across species, the following table counts the number of small, medium, and large snakes in each family, based on average size of individuals.
Figuring out the size of a snake species can be very difficult. Animals in captivity exhibit different behavior than members of the same species in the wild, so measuring captive snakes might not produce an accurate size.
Measuring animals in the wild has its own issues. Finding a reasonable number of appropriately mature subjects to size can be difficult, and handling them can be very dangerous. Measuring a shed snakeskin can be misleading, since stretching may occur during the sloughing process, causing the skin to be up to an additional one quarter of its original size. 
Please note that some snakes have far less research than others, so some sizes may not be an accurate average. The largest specimen size is not used here because often the largest individual of a species is not typical.
|Sizes (English)||< 2.5 ft.||2.5 ft. – 5 ft.||> 5ft.|
|Sizes (Metric)||< 76.2cm||76.2cm – 1.52m||> 1.52m|
Table 1. Analysis of snake sizes by species as listed in Mattison pp. 196-263. (See footnotes)
In summary, of the known species of snake, 57.3% of species average a length of less than 2.5 ft. (76.2 cm), and 93% of all snake species average a length of less than 5 ft. (1.52m). Only 7% of species average a length greater than 5 ft.
In short, most snakes are far from giants. On the other hand, there are some very large species of snake, at least some of which are poisonous.
Locomotion and Movement
Particular interest in snake movement comes from their apparent lack of limbs. Most snakes rely on particular belly scales to push against either resistance or fixed points. There are some species that have developed very particular locomotion, such as the gliding tree snakes, but even they need the ability to move across the ground and up trees.
Despite seeming like a detriment, limblessness presents snakes with locomotion in a variety of habitats.  The size of the snake, its current location, and its overall habitat contribute to the type of locomotion the snake uses. Many species can switch from one form of movement to the other, as needed. 
Concertina locomotion is used to move through narrow spaces, especially in burrowing species.  The snake curves the back half of its body to provide an anchor, while the front part of the serpent moves ahead. Once the snake has anchored its head and front half through curves, it can bring its back half ahead.  This is important for crawling vertically or diagonally with a steep slope.
Locomotion: Lateral Undulation / Serpentine Crawling
Lateral undulation is the most common form of locomotion for snakes.  Generally exhibited by small or medium-sized serpents, lateral undulation is used when a snake is moving across uneven ground or rough terrain, such as dense undergrowth.  This is the same movement used by snakes for swimming, where the snake presses against the resistance of the water. 
Using irregularities of the surface or surrounding area, the snake pushes against these points with the sides of its body. Despite the seeming awkwardness of this method, the serpent moves forward quite fluidly,  which displays the iconic serpent with an elongated and gracefully curved body.
Locomotion: Rectilinear crawling
Rectilinear crawling is an important part of stalking prey for many snakes, as well as a common form of locomotion in the thick, heavy-bodied snake species, such as boas.  The snake stretches itself forward and hooks the edges of its scales on irregularities of the surface. Once the underbelly scales have hooked in, the snake can pull its body forward, and again stretch to find a new set of irregularities to hook into.  The snake moves in an essentially straight line, which is why it is used during the last part of stalking prey. 
Sidewinding locomotion is a specialized form of movement, evolved independently by several snake species that live in areas with loose sand and similar surfaces.  This movement is particularly hard to describe, since it involves several anchor points used by the snake at different points of the motion. The snake moves at a roughly 45° to the direction its head is pointing. 
The movement can be described in terms of the following steps:
- The snake anchors itself using its middle and rear body, then raises its head and neck and throws them sideways. 
- Once the head and neck touch the ground again, they become the anchor for the rest of the body (which may be a single movement of the body or a two movements of the body and the final part of the tail) to catch up. 
- The snake begins again with step 1, usually with little or no rest in between movements. 
Illustration 1 shows a three-step movement in sidewinding locomotion, with the arrows indicating movement in order from top-to-bottom. This locomotion is incredibly effective,  using a looping maneuver to move the serpent across areas that have loose sand or other irregularities that would be impossible to use with the other forms of serpent motion.
Illustration 2 shows the same three-step movement in sidewinding locomotion as Illustration 1, but with an expanded view of the serpent's physical position. The set of movements are in order and indicated by arrows from top-to-bottom and left-to-right.
Despite a lack of limbs, snakes can move through a diverse range of habitats in many locations. They can climb trees, crawl through burrows, and swim. For more information on gliding serpent locomotion, see Chrysopelea: Gliding Serpents.
Snake Skeletons and Vestigial Features
Snakes of all species have a reduced skeleton from their closest relatives, the lizards. The entire skeleton is comprised of skull, vertebra, and ribs, with the exception of a few families of snakes that retain vestigial features of the pelvic girdle. No known species of snake possess vestigial features of the forelimbs.
Illustration 3. Generalized snake skeleton. © Kylie 'drago' McCormick.
The above illustration is a generalized skeleton that reflects the basic layout of snake's skeletal structures. The vertebral column consists of different kinds of vertebra running from the atlas, the first vertebra under the skull, down to the tip of the caudal tail. Ribs run for almost the entire length of the snake, unconnected to a breastbone.
The fact that the ribs do not connect to a breastbone gives snakes the possibility to move in extremely supple body forms, such as creating an S-shape or coiling around something. 
The reduction of skeletal bones can be explained by the reduction of limbs. Snakes are not the only reptile to evolve leglessness as an adaptation; several other unrelated lizard families have also independently evolved leglessness. 
Illustration 4. Vestigial hindlimbs on a snake. © Kylie 'drago' McCormick.
Some snake species possess vestigial hindlimbs, or the remainder of the pelvis and back legs. The Ilium, which is the uppermost and largest part of the pelvis in mammals, is still present, along with three small bones that make the hindlimb, or spur, in some snakes.
Some snakes families retain vestigial parts of the pelvic girdle as well as the hindlimbs, such as the families of boas and pythons.  Small spurs might be visible on some of the snakes, particularly in males.
The Snake Skull and Jaws
Snakes have far more loosely articulated skulls than their closest relatives, the lizards; meaning, the connections formed by joints and ligaments in snake skulls possess a wider range of motion than lizards.  This development can be explained by their particular feeding habits. Many animals chew food before swallowing it, but snakes generally swallow their prey whole, creating a need for more elasticity of the jaws. 
Most snakes use sight as a sense, although some snakes are considered blind. They are called blindsnakes because a tough, cloudy scale covers each of their eyes for protection, since snakes lack mobile eyelids.  While blindsnakes cannot perceive images, they can sense changes in light, which is particularly useful for these species, since they live underground.  Other snakes possess a single, transparent scale over each eye, called a brille.  In either case, the snake's eyes rest in the orbit of the skull.
The snake skull has numerous adaptations, such as a tough upper cavity to the jaw to protect the brain during feeding, since even swallowing unmoving prey or eggs whole can be dangerous. Illustration 5 shows the general features of a python's skull, which does not have fangs. Illustration 6 shows a cobra's skull. For more information on the terminology, see Anatomy and Physiology Terminology.
Another important aspect of snake skulls is the type of teeth. Some snakes have no teeth, while others have pleurodont teeth, meaning they attach to the inner edges of the jawbone, not to the top of the bone.  Teeth are commonly lost or shed during hunting or eating prey, and in most cases shed teeth are swallowed and pass undigested to the snake's feces. 
Snake's teeth are replaced throughout the entirety of it's life. The new replacement tooth develops at the base of the existing tooth. When a snake sheds a tooth, the replacement is already ready to be pushed down and sideways (or up and sideways, depending on the part of the jaw) to replace the lost tooth.  Illustration 7 demonstrates the differences in the upper jaw of snakes with fangs to those without fangs.
Illustration 7. Comparison of Upper Snake Jaws. © Kylie 'drago' McCormick.
A generalized view of the upper portion of jaws of non-venomous (left) and venomous (right) snakes. Teeth distribution varies from species to species, and some snakes have no teeth at all.  Many species have many teeth across the palatum and maxilla. In venomous species, the maxilla is generally shortened to feature a fang, or hollowed tooth, with a replacement fang.
Aglyphous snakes are those without fangs.  Opisthoglyphous snakes possess what have been termed rear fangs, which possess fangs further back in the mouth.  Venomous snakes have adapted fangs that have a hollow, with an inlet at the base of the fang and an outlet near the tip.  Most snakes force the venom through the fang, but some species also spit their venom, notably the species belonging to the genera Naja (approximately twenty-two species) and Hemachatus (one species). 
Skin shedding is not unique to snakes. Replaces the outermost part of the epidermis is an important process in most animal species. Lizards and other reptiles also shed their skin, as well as mammals and birds. The primary reason for the highlighted nature of a snake's shed skin is the fact that the skin comes off in essentially a single unit.
Humans and other mammals lose small particles of their epidermal layer throughout the day. Lizards and other reptiles generally shed in a similar manner, and those that do shed an outer layer all at once still leave only large pieces, not a single shed skin. This is because joints and appendages make it possible to scratch or preen the outer layer off more quickly if the animal chooses, and they also make it very difficult for a single layer of skin to fall off as a unit. Snakes do not have this problem, so the entire outermost layer, including that of the brille over their eyes and the layer over their tongue, is shed at once in one unit.
Chrysopelea: Gliding Serpents
Species of the Genus Chrysopelea possess gliding abilities. One species is Paradise Tree Snake (Chrysopelea paradisi), which lives in parts of Southeast Asia, primarily in forests.  They grow up to 4 feet (1.22 meters) long and lay eggs in clutches up to twelve. 
These snakes also have ridged scales that run along their belly, making it possible to climb almost vertically up things like tree trunks by enabling the snake to grasp and hold the irregularities of the surface. 
The Paradise Tree Snake can glide down at angles of fifty to sixty degrees and travel up to 65 ft. (19.81 m) and land safely.  It had been assumed that all gliding serpents were poor gliders and poor navigator during glides, but recent research has shown Chrysopelea species, specifically the Paradise Tree Snake, to be very good gliders.  The initial assumption that these snakes were poor gliders came from their undulation movements in the air, which appear wild and unplanned, making it seem as if the snake is swimming through the air.
New research and modeling, however, reveals that Chrysopelea gliding matches or even exceeds the performance of other gliding animals, such as flying squirrels. 
An important part of Chrysopelea gliding is the flattening of the serpent's body. After jumping from a high place, the snake puffs out its ribs, drawing its body into a rough C-formation, with its ridged belly scale becoming the lower, shorter surface and the back of the snake and ribs forming the higher, longer surface. 
It is unknown what happens to the snake's vital organs during a flattening phase. Chrysopelea snakes have been observed with some parts of their body flattened while retaining their normal shape in areas.
Illustration 8 & 9. A Chrysopelea snake's body before gliding (left) and flattened while gliding (right).
Considerations on Dragon Anatomy and Physiology
Snakes have a long history of awe with humankind, since they have excellent locomotion skills without limbs, the ability to swallow items larger than their own head, and exist in a number of shapes, sizes, and colors all across the world. They can be found in water, in trees, on the ground, underground, and even gliding through the air. The fact serpent eyes appear to be open all the time give it an associate it with wisdom and knowledge, since they appear remain perceptive at all times.
The specialized locomotion tactics of serpents, for swimming, climbing, descending, and gliding, are particularly important when considering dragon physiology and anatomy for types like Great Serpents, Lindorms, and Wurms.
- Mattison 10
- Mattison 11
- Mattison 12
- Mattison 52
- Mattison 55
- Whitfield 461
- Socha, John J., Tony O'Dempsey, and Michael LaBarbera. 'A 3-D kinematic analysis of gliding in a flying snake, Chrysopelea paradisi.'
- Mattison 195
- Ricciuti 85
- Mattison 9
- Mattison 39
- Mattison 40
- Mattison 41
- Mattison 53
- Ricciuti 46
- Mattison 13
For more information on footnotes and references, please see the bibliography.