Dragon Anatomy and Physiology

Snake Anatomy

This article contains a review of snake and serpent anatomy for reference in dragon anatomy and physiology. All illustrations in this page have been created by Kylie 'drago' McCormick and should not be removed or otherwise redistributed.

• Snake Classification
• Number of Species and Geographical Distribution
• General Description of Size
• Locomotion and Movement
• Snake Skeletons and Vestigial Features
• The Snake Skull and Jaws
• Shedding Skin
• Chrysopelea: Gliding Serpents
• Considerations on Dragon Anatomy and Physiology

List of Illustrations:

1. Illustration 1. Specialized sidewinding snake locomotion.
2. Illustration 2. Expanded sidewinding movement exhibited by some snakes.
3. Illustration 3. Generalized snake skeleton.
4. Illustration 4. Vestigial hindlimbs on a snake.
5. Illustration 5. Python Skull.
6. Illustration 6. Cobra Skull.
7. Illustration 7. Comparison of Upper Snake Jaws.
8. Illustration 8. A Chrysopelea snake's body before gliding.
9. Illustration 9. A Chrysopelea snake's body flattented while gliding.

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 scales as part of their epidermis. 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 19 Families for snakes, although these tend to change to reflect new species and new research.

Snakes are related to members of the suborder Sauria, or lizards, as well as members of the suborder Amphisbaenia, or the worm-snakes.¹⁰ More distant relationships exist between snakes and members of the orders of Crocodilia (alligators, crocodiles), Testudines (turtles, tortoises), and Sphenodontia (tuatara).¹⁰

Particular serpent traits that relate to the dragon include the following:

• Eyes that do not blink
• Scales
• Sloughing/Shedding of skin as a single unit
• Swallowing large food whole
• Venom
• Locomotion, including in water
• Certain snakes have special abilities, such as gliding

Figuring out "the size" of a snake species can be very difficult, primarily because animals in captivity exhibit different behavior than members of the same species in the wild, so measuring captive snakes may not be accurate. On the other hand, measuring animals in the wild is not necessarily an easy task. Measuring a shed snake skin 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.⁹

Please note that some snakes have far less research than others, so some averages may not be an accurate average size. The larges specimen size is not used here because often the largest individual of a species is not typical, so it will not help illustrate the average size of a snake found in the wild.

Table 1. Analysis of snake sizes by species as listed in Mattison pp. 196-263. (See footnotes)

In short, of the known species of snake, 57.3% of them 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 in the family Viperidae, or Viper. So while the average snake might not be a giant, there are some snakes that are very large and venomous.

Despite seeming like a detriment, snakes live across the world in a variety of habitats.¹¹ The size and species of the snake, the 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.¹¹

Lateral Undulation, or Serpentine Crawling, is the most common form of locomotion for snakes.¹¹ 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.¹¹ This is the same movement used by snakes for swimming, where the snake presses against the resistance of the water.¹¹

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,¹¹ making the iconic serpent with an elongated and gracefully curved body.

Concertina Locomotion is used to move through narrow spaces, especially in the burrowing snake species.¹¹ The snake curves the back half of its body to provide an anchor, while the head and front part of the serpent move ahead. Once the snake has anchored its head and front half through curves, it can bring its back half ahead.¹¹ This is important for crawling vertically or diagonally with a steep slope.

Rectilinear Crawling is an important part of stalking prey in many snakes, as well as a common form of locomotion in the heavy-bodied (thick) snake species, such as boas.¹² 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 to this point, and then again stretch to find a new set of irregularities to hook into.¹² The snake moves in an essentially straight line, which is why it is used during the last part of stalking prey.¹²

Illustration 1. Specialized sidewinding snake locomotion.
© Kylie 'drago' McCormick.

Sidewinding Locomotion is a specialized form of movement, evolved independently by several snake species that live in areas with loose sand and similar surfaces.¹² This movement is particularly hard to describe, since it involves several anchor points used by the snake at different parts of the motion, and the snake moves at a roughly 45° to the direction its head is pointing.¹³

The movement can be described in terms of the following steps:

1. The snake anchors itself using its middle and rear body, then raises its head and neck and throws them sideways.¹²
2. 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.¹³
3. The snake begins again with step 1, usually with little or no rest in between movements.¹³

Illustration 1 (right) shows a three-step movement in sidewinding locomotion, with the arrows indicating movement in order from top-to-bottom. This locomotion is incredibly effective,¹³ 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 motion described above.

Illustration 2 (below) 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.

Illustration 2. Expanded sidewinding movement exhibited by some snakes. © Kylie 'drago' McCormick.

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.

Illustration 3. Generalized snake skeleton. © Kylie 'drago' McCormick.

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.⁵

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.²

Illustration 4. Vestigial hindlimbs on a snake. © Kylie 'drago' McCormick.

Some snakes families retain vestigial parts of the pelvic girdle as well as the hind limbs, such as the families of boas and pythons.³ Small "spurs" might even be visible on some of the snakes, particularly in males.

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.¹⁵ While blindsnakes cannot perceive images, they can sense changes in light, which is particularly useful for these species, since they live underground.¹⁵ Other snakes possess a single, transparent scale over each eye, called a brille.¹⁶ In either case, the snake's eyes rest in the orbit of the skull.

The snake skull has numerous adaptations, such as a touch upper cavity to the jaw to protect the brain during feeding, since even swallowing unmoving prey or eggs whole can cause damage to the snake. Illustration 5 (below) shows the general features of a python's skull, which does not have fangs. Below that illustration is Illustration 6, which is of a cobra's skull. For more information on the terminology used in the labeled graphics, please see the article containing Anatomy and Physiology Terminology.

Illustration 5. Python Skull. © Kylie 'drago' McCormick.

Illustration 6. Cobra Skull. © Kylie 'drago' McCormick.

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.⁴ 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.⁴

Snake's teeth are replaced throughout the entirety of a snake's life, with the new replacement tooth developing 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.⁴ Illustration 7 (below) 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.

Aglyphous snakes are those without fangs.⁴ Opisthoglyphous snakes possess what have been termed rear fangs, which possess fangs further back in the mouth.⁴ Venomous snakes have adapted fangs that have a hollow within, with an inlet at the base of the fang and an outlet near the tip.¹⁴ Most snakes force the venom through the fang, but some species can also spit their venom, notably the species belonging to the genera Naja (approximately twenty to twenty-two species) and Hemachatus (one species).¹⁴

Humans and other mammals lose small particles of their epidermal layer throughout the day, making it impossible to see what discarded the skin particles except through certain microscopic tests. 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.

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 to hold the irregularities of the surface.⁶

The Paradise Tree Snake can glide down at angles of 50 to 60 degrees and travel 65 feet (19.81 meters) and land safely.⁶ It had been assumed for quite some time 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.⁷ The intial assumption that these snakes were poor gliders came from a lack of understanding their undulation movements in the air, which appear wild and unplanned. The undulating movements seem almost 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.⁷

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.⁷

It is unknown what happens to the snake's vital organs during a flattening phase. Although Chrysopelea snakes have been observed with some parts of their body flattened while retaining their normal shape in other areas.

Illustrations 8 & 9. A Chrysopelea snake's body before gliding (left) and flattented while gliding (right).
© Kylie 'drago' McCormick.

The specialized locomotion of serpents, for swimming, climbing, descending, and even gliding, are particularly important when considering dragon physiology and anatomy for types like Great Serpents (which would be essentially gigantic snakes), Lindorms, and Wurms.

1. Mattison 10
2. Mattison 11
3. Mattison 12
4. Mattison 52
5. Mattison 55
6. Whitfield 461
7. Socha, John J., Tony O'Dempsey, and Michael LaBarbera. "A 3-D kinematic analysis of gliding in a flying snake, Chrysopelea paradisi." Journal of Experimental Biology 208 (9 March 2005): 1817-1833.
8. Mattison 195
9. Ricciuti 85
10. Mattison 9
11. Mattison 39
12. Mattison 40
13. Mattison 41
14. Mattison 53
15. Ricciuti 46
16. Mattison 13

For more information on footnotes and references, please see the Bibliography.