~ Skeletal System
~ Internal Organs
~ The Dragon's fiery breath
~ Muscular system
~ The Dragon's wing
~ Senses
~ External features

Skeletal System:
The skeleton of the Western dragon is an impressive structure, from an engineering viewpoint. At first glance, it has all the hallmarks traditionally associated with the skeleton of a mammal or a dinosaur (see fig. 3). However, upon closer inspection, the bones are hollow, with thin struts of bone criss-crossing the inside, as in birds (class Aves). This bony strutwork adds strength, as do the high calcium and phosphorous levels. Therefore the Western dragon has bones that are not only strong, but extremely light.
Externally, the main features include the long, cat or dog-like limbs, tipped with razor claws. The tail acts as a rudder and counterbalance and is correspondingly lengthened, however it is not very flexible. This stiffness in the tail is due to small pieces of ossified (bony) ligaments that run lateral to the vertebrae, preventing excessive movement due to crosswinds1 (Long, 1998). The tail is also flattened laterally and expanded dorso-ventrally, decreasing wind resistance while not diminishing its use as a rudder.
The thoracic portion of the skeleton also merits further discussion. Like in Aves, Western dragons possess a deep ribcage, with a large keel running off the ventral surface of the sternum (see Fig. 3). This provides anchorage for the enormous flight muscles. The wings (discussed further down the page) are unusual in that they share an attachment point (with the trunk) with the forelimbs, ie. they both connect on the singly paired scapula. Anterior to the scapula runs the paired clavicles and coracoids, necessary for bracing the wings during flight and also for shock absorption during jumping.

The skull is formidable in appearance, and large relative to the overall size. The cranium is large, the orbits face forward, and the zygomatic arches are huge, anchoring the strong jaw muscles that allow the Western dragon to bite down with immense force. The teeth are equally impressive (see fig. 1). Another feature of the skull is the dip anterior to the orbits that allow the eyesight to be unimpeded by the long muzzle.

Fig. 1: Dentition of a typical Western dragon (lower jaw disarticulated from skull)

Legend: I: Incisor - C: Canine - PM: Premolar - M: Molar

The dental formula is usually a descriptive term for mammals only; of extant (living today) organisms, mammals are the only class that show differentiation in their teeth. Most mammals are therefore heterodont (hetero : different, dont : tooth), meaning a single animal can have several different types of teeth, such as in a dog; some teeth are for tearing, some for nipping, others can crack bones (Strickberger, 2000). In contrast, other vertebrates have teeth that are the same3, ie. a lizard has identical, small conical teeth. Thus a lizard would be a homodont (homo : same, dont : tooth) (Strickberger, 2000). The dental formula for the dragon has been worked out for you further down the page.

Although dragons are not classed as mammals, we have given the Western dragon a heterodont-type dentition. The different tooth types are labeled in fig. 1 above, and colour coded for clarity. The reason the Western dragon has been given this dentition is because it is far more suitable to the lifestyle of the dragon, and also because the dragon is generally thought of as an extremely advanced reptile. Therefore it fits that it should have specialised teeth.

Mammals have only two sets of teeth in their lives, the milk teeth and the adult teeth (Bay Books, 1977). This allows for an accurate fit between the teeth of the upper and lower jaws, which would be disrupted if the teeth were continually being shed. Mammalian teeth (and those of crocodiles and dinosaurs) are set into sockets in the jawbone, meaning they are far more stable than the teeth of, say, a lizard. The teeth in most reptiles are fused to the jawbone itself; they sit on top of it rather than in sockets. Correspondingly, they are far more likely to be shed, so reptiles have a constant supply of teeth, with each tooth being replaced after it falls out (or is pushed out by the replacement tooth).

In dragons, there are two sets of teeth only4. Like in mammals, the teeth are set into sockets in the jaw. There are four tooth types found in dragons. The incisors are short and sharp, used for nipping small pieces off meat from bones, allowing the dragon to glean the last scraps of food from its prey. The canines are most obvious, they are massively long, curved and pointed, tapering to a razor tip. Their purpose is clear- they are used to deliver a killing bite or a suffocating throat hold. The next two types of teeth, the premolars and molars, are usually termed carnassial teeth in carnivorous mammals, and the same terminology may be applied here5. From fig. 1, it is clear that the last premolar of the upper jaw and the first molar of the lower jaw are much larger than the other carnassial teeth. These are specialised to form a carnassial shear- that is, they slice against each other to tear off pieces of meat from a carcass with excellent precision.
From fig. 1, the dental formula of a typical Western dragon can be easily worked out. It is determined by counting the types of each tooth found in one half of the upper jaw, and also in one half of the lower jaw. The reason only one half of each jaw is counted is that each half will be a mirror of the other- it will have the same types and numbers of teeth.
So, a Western dragon has six incisors in the upper jaw, and six in the lower, meaning it has three in each half. There is one canine in each half of each jaw, and four premolars. The molars are the only point of difference between the upper and lower jaws, as you can see, there are two molars in the upper jaw and three in the lower.


Fig. 2: Dental formula of the Western dragon

In fig. 2, the first set of numbers refers to the incisors. The number above the line denotes the number of incisors in the upper jaw, whereas the number below the line shows how many incisors are in the lower jaw. The second set of numbers refers to the canines, the third to the premolars and the last to the molars. The number of teeth an organism has can be worked out from the dental formula. All the numbers from fig. 2 can be added up, to give the total number of teeth in one half of the dragons jaws. This can then be multiplied by two to give the total tooth number. So, in the Western dragon, this would be 42.

Typically, Western dragons are depicted as gargantuan creatures, but in reality, probably wouldn't be anywhere near this. A dog-sized dragon is a definite possibility, though hardly awe-inspiring, and a dragon that could carry a human is improbable, but well worth considering.

In fig. 2, the first set of numbers refers to the incisors. The number above the line denotes the number of incisors in the upper jaw, whereas the number below the line shows how many incisors are in the lower jaw. The second set of numbers refers to the canines, the third to the premolars and the last to the molars. The number of teeth an organism has can be worked out from the dental formula. All the numbers from fig. 2 can be added up, to give the total number of teeth in one half of the dragons jaws. This can then be multiplied by two to give the total tooth number. So, in the Western dragon, this would be 42.

Typically, Western dragons are depicted as gargantuan creatures, but in reality, probably wouldn't be anywhere near this. A dog-sized dragon is a definite possibility, though hardly awe-inspiring, and a dragon that could carry a human is improbable, but well worth considering.


Fig. 3: Skeletal system of the Western Dragon

Note the long tail, used for balance on the ground and in the air, the extremely deep keel that anchors the flight muscles, and the massive, expansive wings, membranous in life. The teeth and claws are well developed, as is the braincase. The large orbits support prominent, sensitive eyes.

Internal Organs:
The Western dragon is always endothermic. It would simply not be able to fly if it was an ectotherm. Western dragons have an internal organ arrangement similar to that of predatory mammals. The extremely advanced nervous system, with a well-developed brain, has an especially large cerebrum (associated with higher functions such as abstract thought, memory, language and learning) (Mader, 2000). A large brain consumes a sizeable proportion of the animals total energy (after endothermy). The brain requires a constant temperature to function optimally, thus a Western dragon simply couldn't be ectothermic.
The hydrocarbon storage gland is located dorsally to the hard palate (see fig. 4). This gland stores the chemicals used for breathing fire, which will be discussed in greater detail later. The Jacobson's organ, located also near the mouth, is used primarily by the male dragon to detect pheromones, and thus allows it to determine if a female is on heat. Jacobson's organ is located in the roof of the mouth, and is mainly a reptilian feature although it does occur more rarely in mammals (Coppard, 1998).

The heart of the Western dragon is extremely large, and is four-chambered as in birds or mammals6, which allows for efficient blood circulation with no mixing of arterial and venous blood (ie. oxygenated and unoxygenated blood is separated) (Mader, 2000). Having a very large heart allows the dragon to supply its muscles with the high amounts of oxygen needed during flight.
The dragon's respiratory tract mimics that of avians. The paired lungs are multi-lobed, with an anterior and posterior pair of air sacs branching off from the lungs proper. This system differs to that of mammals in that air circulates in one direction only, before being exhaled. The gas exchange rate of the dragon is very high among terrestrial vertebrates7.
A diaphragm separates the thoracic and abdominal cavities (see fig. 4). The digestive system is quite short, as meat is relatively easy to digest as opposed to plant materials such as cellulose8.
Western dragons reproduce sexually, with internal fertilisation, and lay eggs like typical reptiles (oviparous), which are incubated by both parents and hatch after a few months (the incubation period differs between species). They don't give birth to live young for the same reason that avians don't; carrying a developing young around in the womb would be cumbersome during flight. Egg laying allows the offspring to develop outside the womb in the safety of a hard-shelled egg.


Fig. 4: Internal organs of a female Western Dragon

In fig. 4 the lungs of the dragon are large and efficient. Air sacs that help to make the creature lighter for flight are visible to the front and back of the lungs, and are also large. The intelligence of the dragon is reflected in the large degree of encephalisation exhibited.

The Dragon's fiery breath:
When a dragon eats, symbiotic archea (microorganisms) in the small intestine, called methanogens, break down food into organic materials such as methane, the simplest hydrocarbon compound. The food is broken down into alkanes (saturated hydrocarbons) which are generally unreactive, but are capable of combustion in the presence of oxygen9. Depending on the species of methanogens each dragon possesses in its gut, slightly different compounds are produced, however their amazing reactive properties remain similar.
These hydrocarbons are stored in the hydrocarbon storage vesicle and are released when fire is needed. Upon expulsion from the mouth, these chemicals are exposed to high levels of oxygen, and also high concentrations of ultra-violet light. These factors cause the chemicals to combust into the familiar flame of the Western dragon.
It should be noted here that if the dragon existed today, it would probably have no reason to possess fire-breathing capabilities at all. It is essentially a top predator, and certainly wouldn't need the extra weight that a hydrocarbon storage gland would impose. In short, a dragon would have no need to breathe fire, as its other weapons would be more than enough to allow it to thrive as a predator.

Muscular System:
Starting from the anterior portion of the body, the jaw muscles (eg. the masseter) of the dragon are most impressive and allow the dragon to bite with enough strength to crush bones. The neck muscles (eg. the trapezius) are also very strong without sacrificing flexibility. As dragons attack prey with their teeth, the need for a strong jaw and neck becomes obvious.
The pectoral and shoulder girdle musculature supports the vast wings, with the main flight muscles attaching to the huge sternal keel (see fig. 5). The fore and hindlimbs are suitably well muscled also, with massive deltoid and biceps brachii muscles in the forelimb and a huge sheet of ilio-tibial muscle powering the hindlimb.
The postanal tail is comparatively stiff compared to the rest of the body. Muscles in this area mainly serve to swing it from side to side for steering purposes during flight.
Different species of Western dragon have slightly different muscle arrangements which can be attributed to the presence or absence of wings and/or limbs. The Wyvern, for example, has no front limbs and thus its thoracic region would of course vary from the four-limbed Western dragon.
On the whole, the Western dragon has a strongly muscled body that is very supple, allowing it to groom itself with ease, important for a fastidiously clean creature.



Fig. 5: Musculature of the Western Dragon

It is easy to see how the dragon gets its legendary strength; the muscles powering its forelegs, neck and chest are huge. The tail is also immensely strong and stiff, able to be used equally well as a rudder during flight or a makeshift weapon.

The Dragon's Wing:
The wing is a notable difference between dragons and other large animals. It usually resembles the wing of a bat (mammalian order Chiroptera), consisting of a flexible leathery material that is very elastic stretched over bones. Most Western dragon species possess wings (an exception is the wyrm).
The Western dragon's wing is easily larger than its body, and this is due to the fact that dragons aren't particularly well constructed for flight, if compared with avians. They have a heavy skull with teeth, rather than a light beak; and also have heavy limbs with large claws. Western dragons also possess an extra pair of limbs, and overall they aren't particular aerodynamic. Indeed, the popular view of a dragon is one of a spectacularly unaerodynamic creature. On top of this, the wing itself, being homologous with a bat wing, isn't as effective an aerofoil as a bird wing10. However, dragons have enormous brute strength, with strong flight muscles and expansive wings, and are thus able to succeed in flight despite their shortcomings. Smaller dragons are much more maneuverable in the air than larger ones, and faster compared to their size (this has to do with the surface area of their wings as compared to their weight, smaller dragons invariably have larger wings compared to their body size).
The wing itself is made of the same bones as the forelimbs, except they are elongated and a cross-section of a bone will reveal that it is flattened like a knife blade to provide less wind resistance. There are usually five phalanges which support the distal edge of the wing membrane, each terminating in a highly reduced claw. The thumb is far shorter than the other digits and supports a small membrane. This is the alula, similar to that found in birds, and reduces the possibility of stalling during takeoff. While in flight, the alula is folded against the wing to reduce drag, and when not in use, the wings can be folded neatly next to the body.

Senses:
The Western dragon has extremely acute senses. Like other animals it responds to "four types of stimuli: chemical, mechanical, temperature and light" (Mader, 2000, p. 348).
First we will deal with the special senses. These are the more familiar senses of sight, smell, balance, hearing and taste (Mader, 2000). Sight in the Western dragon is among the most well developed of all its senses. This is fundamental to being an efficient predator of fast-moving prey. As the eyes face forward, vision is binocular. The dragon has a slit-pupilled eye, the iris being able to dilate or contract a great deal. This allows the Western dragon to finely tune its vision to accommodate differing light levels. The lens of the dragon's eye can change shape enormously, allowing the animal to see across huge distances. Behind the retina, lies a reflective layer of cells, called the tapetum lucidum. This layer captures any light not intercepted by the retina and reflects it back, enhancing the dragon's vision (Coppard, 1998).
Dragons have two types of photoreceptors in their eyes. Rod cells are sensitive to low light levels, and coupled with the tapetum, enable the Western dragon to see in the dark. They are also more sensitive to movement than cone cells and help in periphery vision (Mader, 2000). Cone cells are sensitive to colour, and most Western dragons can see in a full colour range, as they have three different types of cone cells, each sensitive to different light wavelengths. Most diurnal dragons have eyes that can see all colours. Each type of dragon has varying levels of vision acuteness; nocturnal species have enhanced night vision, with more rod cells, and diurnal species have more cone cells and thus better colour vision.
A Western dragon also has a highly evolved sense of smell, with many olfactory cells in the folded nasal membranes. Each olfactory cell functions like a neuron, and each cell has a different type of receptor protein on its surface, which responds to different olfactory stimuli (Mader, 2000). There may be up to one hundred different types of olfactory cells.

The hearing of a Western dragon is also exceptionally acute. The outer ear flap, or pinna, can be articulated in any direction to act as an amplifier for sound. Western dragons can also hear over a very wide frequency range, from the squeaks of rodents to the bass rumbles of elephants. Smaller dragons or juvenile dragons generally can hear higher-pitched sounds than adult dragons, but mature dragons can hear lower-pitched sounds. This accurately reflects the sounds made by different sized-prey animals (smaller animals generally make higher-pitched noises, and smaller dragons are more likely to hunt these small animals).
The inner ear's semicircular canals are responsible for balance, and Western dragons have an excellent sense of balance. Balance is one of the somatic senses, which also include senses that monitor muscles, skin and organ systems (Mader, 2000).

Western dragons also have very sensitive skin, with large amounts of chemoreceptors, mechanoreceptors, and thermoreceptors. Chemoreceptors are nerve endings that respond to pain or itching. Mechanoreceptors are sensitive to touch on the skin, or pressure. Thermoreceptors include Ruffini endings, that respond to temperatures above 45 degrees Celcius, and bulbs of Krause that respond to sub-20 degree temperatures (Mader, 2000).
Another specialised type of nerve ending involved in the Western dragon's senses are proprioreceptors, which are located near muscle cells (Mader, 2000). These nerves allow the dragon to be able to tell where its limbs are without looking at them. The close proximity of proprioreceptors to muscle tissue also mean they are able to balance the body by monitoring how contracted each muscle is.

External Features:
The hide of the Western dragon can be either leathery or smooth in texture (see fig. 6), or it may be covered in a pattern of small scales similar to those of a snake. The heavy, ossified plates seen in popular depictions of dragons would, in all likelihood, render it unable to fly. There is a popular view that dragon scales are used as protection, however a dragon has so many other weapons already it would seem superfluous to have plates as an additional feature.
A dragon's claws and small scales are formed of keratin, the same protein that makes up our hair and fingernails. Fins on the back may be used in sexual display and are also made from keratin. They are, in essence, modified neural spines that project upwards from the spinal column. Capillaries running across their membranes allow the dragon to realease excess heat from its body when needed11. These capillaries also run over the surface of the skin, and on hot days become dilated, exactly like in the dorsal fin.

The colour of the skin itself is, famously, found in a wide range of colours. Co-dominant colour genes include those that code for red (including brown), blue and yellow. If one copy of either gene is found in a dragon's genome, that colour will be expressed in the dragon's phenotype. However, whenever a gene of the alleles of blue and yellow are found in a dragon's genetic makeup, the dragon will be green.
Co-dominance means that if a dragon has one of co-dominant genes (eg. blue and yellow), it will result in green which is a mixture of blue and yellow (Alberts, et al., 1998). Similarly, a copy of each of the red and yellow genes will result in an orange dragon, and copies of the red and blue genes will produce a purple dragon. Note: the genes for red, blue and yellow, the primary colours, are the only genes in the Western dragon genome for hide colour that are co-dominant. This helps explain the vast range of hues the creature is found in.

The white phenotype is coded for by a recessive gene. This means that two copies of the white allele must be found at the locus for hide colour in order for the dragon to be white. As a result, white dragons are rarer than coloured dragons. A white hide is different from albino colouration, because white dragons still have pigmented eyes and may even exhibit colour patterns12. Black (includes grey) Western dragons are usually males. This is because the recessive gene for black colour is found only on the X chromosome. Because a male only has one copy of the X chromosome, it follows that only one copy of the black gene is needed for the animal to be black in colour. Females, having two X chromosomes, therefore need two copies in order to be black. (The allele for black colouring is an example of a sex-linked trait. Other examples include colour blindness in humans, which is more prevalent in males [Alberts, et al., 1998].)

Dragons, like all sexually reproducing organisms, inherit one copy of their nuclear genome from the female parent, and the other from the male parent. This mixing of genes in offspring is crucial for evolution. In contrast, it has been said that dragons inherit certain traits exclusively from a specific parent, however this argument is heavily flawed.
For example, say dragons inherited their appearance from the father, not the mother. Automatically, this means that the genes its mother was carrying for external traits are lost immediately in that single generation. Assuming that the number of females equaled the number of males in the population, the gene pool for a dragon's appearance would be halved. For every generation, genetic variability would be halved. Because genetic variability is what allows evolution to occur in a changing environment, the draconic race would cease to evolve and every dragon would essentially look like a clone of one another. The only genetic material that is passed down faithfully through one parental line is mitochondrial DNA through the maternal line (Alberts, et al., 1998). In addition, sons will always get their mothers X chromosome and their fathers Y. Daughters will always get their fathers X and, randomly, one of their mothers X's, however, crossing over during meiosis as well as random assortment of chromosomes to gametes will help to create more diversity at the time of conception (Alberts, et al., 1998). It should be noted that it is assumed in this essay that dragons have the same sex chromosome configuration as mammals, that is, XX and XY, as opposed to other vertebrate groups. XX denotes a female and XY a male13.

In addition to variations in colours and markings, some small Western dragons possess chromatophores on their skin.
Chromatophores are cells in the skin that possess an 'iris', normally closed. In response to a stimulus, this iris may open, displaying the pigment revealed underneath. The dragon may change its colour in response to an intruder, to attract a mate, or to blend in with its surroundings.


Fig. 6: External features of the Western Dragon

Here is where figs. 3- 5 culminate. When the Western dragon is sheathed in thick leathery skin, we can greater appreciate its strength and prowess as a hunter, even if it does only prowl the recesses of our mind.