The skeletal system consists of a backbone and 160 - 435 vertebrae. A pair of ribs is attached to each vertebra, but variation in number of vertebrae can be seen in different species. These vertebrae are joined together by several separate articulations i.e. any two adjoining vertebrae are always linked by five separate joints. This special arrangement of vertebrae provides stability, strength and flexibility to the extremely long and elastic backbone. This also enables their body to expand and contract and facilitates the constriction process in many snakes.

The ribs are very thin and elastic. They are larger in the neck region as compared to the tail. The lower surface of the ribs is attached to the ventral scales and during locomotion the rib raises the scales of the belly above the ground, thus helping the snakes to move easily on any type of surface with great speed.

The skull is present at the anterior end of the first spinal vertebra. The skeleton is not only equipped to facilitate different modes of locomotion, it also helps in feeding, courtship and defense behaviours. For example, burrowing species have a thick, blunt skull, whereas arboreal species possesses a light and flexible skull. In the same way, ribs are flattened out in some species to facilitate different functions. As seen in cobras the ribs of the neck are long and flattened out to form a hood like structure, which it spreads in times of danger. Besides this, cobras raise the anterior part of their bodies in a vertical position, while they are excited.

The Head and Its Parts

The head consists of two round or oval openings of the external nostrils, a pair of eyes covered with a scale and a mouth. At the time of danger, snakes expel air through these nostrils with immense force and produce a hissing sound.

The Tooth / Fang Arrangement

The teeth are pointed and recurved. The teeth are fixed into the supporting bones of the two halves of the lower jaws, which are joined by an elastic ligament. The teeth and fangs of snakes vary in structure and arrangement, depending on the family they belong to. Poisonous snakes possess two fully developed hollow fangs attached to the anterior part of the upper jaw and laced with poisonous saliva or venom, which travels through a tube from a gland to the fangs. The fangs are shed and replaced at regular intervals. The snakes have four basic tooth (fang) arrangement patterns.

The Tongue

The tongue is long, round and sticky, its anterior part is bifurcated and pointed, while the posterior part lies in a sac. Snake repeatedly flicks its tongue in and out. When a snake points its tongue in the air or rubs it on the ground, it collects tiny particles present in the air and gathers them in a hollow cavity in the roof of mouth, known as Jacobsons Organ. In this cavity, particles are analyzed and information is sent to the brain. This way the snake is able to identify its surrounding and can analyze whether the environment is favourable or that there is danger near by.

The Ears and Eyes

Contrary to prevalent belief, its sense of hearing is very poor and can only respond to low frequency ground and airborne vibrations. The eyes are different from other animals in terms of focussing on far and near objects. Snakes can identify moving objects with accuracy but are not able to recognize far and stationary objects. Eyesight is well developed but varies in sharpness, as some species are blind e.g. burrowing snakes. The eyes are covered with a thick scale known as Spectacle or Brille , which performs the function of an eyelid. The shape of the pupil varies from specie to specie for example the pupil of the snakes of family Colubridae e.g. Xenochrophis piscator (Checkered Keelback) and family Elapidae e.g. Naja naja naja (Indian Cobra) is round in shape, while those of Viperidae family e.g. Echis carinatus (Saw Scaled Viper) posses vertical pupil. In brightness the pupil shrinks and becomes short but in darkness it stretches to control the amount of light and protect the eye from damage.

The Venom

The venom, present in a small sac, is a very complex chemical compound. It contains many proteinous enzymes, salts and water. Since the snakes swallow the prey whole, the venom plays an important role by destroying the tissues and muscles of the prey. The proteinous nature makes it effective only when it directly enters into the lymphatic, blood circulatory system or the body tissues of the victim.

The venom is a golden tasteless, odourless viscous liquid. Fresh venom is granular in appearance; on evaporation it changes into brown crystals. It is acidic in nature. At high temperature i.e. more than 90ºC it looses its poisonous effect.

The bites of poisonous and non-poisonous snakes leave different imprints on the skin of the victim. The fangs of the poisonous snake penetrate deep into the skin and leave two deep and distinct punctures. On the other hand, non-poisonous snakes leave a series of less deeper punctures. The bite of a poisonous snake causes swelling, heavy bleeding and discolouration of the skin while that of a non-poisonous snake does not cause any reaction.

Morphological Differences between Poisonous and Non-Poisonous Snakes

One can distinguish between poisonous and non-poisonous snake on the basis of the following morphological characteristics.

• The scales present on the ventral surface of the poisonous snakes are large and plate like while those of non-poisonous snakes are small in size.

• The head of the poisonous snakes possesses small scales, large shield and a pit, present between the eye and nostril. No such characteristic is found in non-poisonous snakes.

• In poisonous snakes the hard shield of the upper lip touches the shield of the eye and nose. No such arrangement of shield is present in non-poisonous snakes.

Locomotion in Snakes

Locomotion patterns differ from specie to specie, depending on their habitat. The special arrangement of bones and muscles helps them to lengthen, coil, contract and squeeze their bodies around the prey, enabling them to move easily in different and difficult habitats.

The ventral scales are geared to support the locomotion in snakes. Internally these scales are attached to the muscles of the body. During locomotion, the ventral muscles of the body expand and contract, producing a wave like motion throughout the body, which in turn pushes the body in the forward direction. This peculiar type of locomotion is known as serpentine locomotion. The thin and long snakes can move faster than the thick-bodied snakes, as waves produced in thin-bodied snakes are quicker.

In the deserts, the non-consistent or loose particles of sand do not support the contraction of the body. Therefore the desert species have to lift or raise their ventral surface from both sides. This type of locomotion has been seen in thin non-poisonous desert species of the family Colubridae such as Xenochrophis piscator (Checkered Keelback).

The poisonous species of the desert snakes that possess stout and thick bodies, move in a very peculiar way. This locomotion pattern is known as side winding. In this type of movement the twist is produced only on one side of the body, which is buried or sunk in the sand. The snakes retain their one side of the body on the surface while the other side is lifted above the ground. When the whole body passes through one position to other, the neck of the snake moves first in the forward direction, followed by the tail. This movement produces parallel lines on loose sandy ground. This mode of locomotion can be seen in snakes of the family Viperidae such as Echis carinatus (Saw Scaled Viper).

Some species of snake can glide also for example Chrysopelea ornate, which is found in the thick forests of Java and Sumatra. This specie lives on tall trees, lays eggs on branches or under the barks of tree.

Snakes are cold-blooded and are not able to maintain their body temperature, which also affect their speed. The snakes can maintain their fast speed for 3 - 5 minutes. They have to revitalise their energy to move again with the same speed.

Food and Feeding Behaviour

Snakes are either carnivores or caniblasts. Insects, rats, frogs, birds, lizards, eggs, fishes, deer are the preferred food of the carnivorous species, while the cannibalistic species feed on other species of the snakes, Echis carinatus (Saw Scale Viper) is a very good example of the caniblastic species.

Feeding patterns largely depend on the size and taste of a snake for example species like pythons and boas prefer birds and mammals. Other species such as pipesnakes feed on lizards and eels. Typical blind and thread snakes mainly feed on ants and insects. Snakes feed occasionally that one full meal last for two to three weeks (duration can vary from specie to specie). This digested food is deposited in the form of fat and provides nourishment during winter sleep or hibernation.

Feeding behaviour also varies from specie to specie; pythons and boas have an excellent ability to catch their prey, they follow their targets with a strong determination and strike with an acute precision. The prey is caught and immobilized first with their sharp teeth and later killed by the constriction process. Venomous snakes of which cobras and vipers are examples catch and kill their prey by injecting venom into them. Once the prey is dead, it is swallowed whole. Elasticity of jaws enables them to extend their mouth over prey larger than their heads. The digestive system is weak and poorly developed but in poisonous snakes, the venom contains a powerful enzyme, which softens the tissues of the victim and helps in digestion.

Courtship and Reproduction in Snakes

The duration and occurrence of the mating season vary greatly from specie to specie, depending on their geographical conditions and the family they belong to. Usually, subtropical snakes mate in spring; just after the winter sleep, while in tropical areas mating takes places in summer or spring season. However, there are few species that mate in any season. Naja naja naja (Indian cobra) is an example of this exception, they are capable of mating almost through out the year between December to August (from Sept to Nov they go into hibernation).

In Pakistan, the mating of snakes usually takes place in early summer; March or April but some species prefer to mate in mid summer or in the rainy season. Courtship behaviour is triggered by a number of stimuli, such as excessive exposure to sunlight, increased supply of food or water and release of pheromones by the female. Mating usually takes place once a year but there are some species known to mate twice a year, for example Lycodon striatus (Northern Wolf Snake), Amphiesma stolata (Striped Keelback) and Echis carinatus (Saw Scaled Viper).

Apart from the size, no other visible distinction in different sexes of snakes can be noticed; adult female snake is larger than the male. Male snakes possess a pair of reproductive organ known as Hempenis, found in the posterior part of the tail, whereas in female snakes, sex organ is termed as Cloaca which is located in the anus. Mating always takes place between the snakes of the same family.

As mating season arrives, the female snake starts secreting a scent hormone, which attracts the male of the same specie. Many adult males outnumber the female but they are not as territorial as lizards, and very few fight for the female. After the procurement of the female, copulation takes place immediately but in some species it may take place after a while. Copulation continues from a few minutes to several days, in which male inserts its Hemipenis, into the female's copulatory organ and transfers sperms into it. After the successful fertilization, the female snake gets pregnant. During this period the female becomes inactive and avoids food. It deposits eggs in a dry and warm place. Hatching usually takes 30 - 50 days but this period may vary from one specie to another, depending on the climatic conditions. There are some species known to give birth to young ones, these species are called viviparous and snakes of the families Viperidea and Hydrophidea are the examples of this group. Theses species have long gestation and hatching periods than oviparous species.

Eggs are covered either with a tough membrane or a strong case. They are oblong in shape and contain a large quantity of yolk.

Generally, snakes do not look after their young ones or eggs after hatching. It has been seen that oviparous snakes only ensure the secure hatching by laying eggs in a suitable and protected place however in case of viviparous species, a quick departure of the young ones from their parents has been observed. On contrary to this, rattle snakes, cobras, pythons all show a remarkable caring behaviour towards their eggs or young ones.

Ecdysis or Change of Slough

Like all other reptiles, snakes also go through the shedding process known as ecdysis . The number of times ecdysis occurs varies from specie to specie and largely depends on factors such as age, availability of food, surrounding temperature, and skin cell division.

As Ecdysis begins, the skin pattern becomes dull and changes into a soft, transparent form due to secretion of keratin, which covers the whole body and obscures vision. At this stage the upper layer becomes frail and ready to tear out. Beneath, the new layer has not yet fully-developed. In this condition, the snakes normally become inactive and hide into burrows or in any other resting-places. They also become quite restless and refuse to eat, and this condition may last for one to two weeks. The slough becomes soft and is shed off by rubbing the nose against the surrounding surface. The skin begins to tear from the mouth to the tail in one piece (sometimes it may comes out in pieces). As the process comes to an end, the snake becomes active and is able to see and move. Since they do not eat during ecdysis, they are very hungry and quickly go in search of food. The cast skin breaks into pieces and soon decomposes.

Economic and Ecological Importance of Snakes

Snakes instill fear in man. Contrary to their reputation however, they are very inoffensive and shy by nature. People are eager to know about them, but also kill them ruthlessly wherever and whenever they appear due to the myths and dangers associated with them. Hindus worship them, even in some countries snakes are eaten by people for protein.

An increasing number of studies and researches have unveiled the medicinal importance of the venom as a remedy for some dreadful diseases. Locally, snake's skin and fat are used for the treatment of a number of diseases such as asthma, tuberculosis, gonorrhea and sexual weakness. Economically, they are considered as a potential source of skins, meat and venom. Ecologically they occupy a very important place, as they act as predators to species such as rats and other rodents and protect crops from these menaces, therefore keeping the ecosystem in balance. Though herpetologists and naturalists are trying to learn more about their habits and habitats, structure, nature and economic importance, much work needs to be done in this context .One thing is certain, that this creature is neither useless nor as aggressive as was once thought.

Threats to Snakes

Wild snakes are shy by nature and have a number of potential predators. They have to struggle hard for their survival and for food. Following are some of threats faced by this reptile:

• Though all carnivores are considered potential predators of snakes; mongoose, fox, jackal, hyena, owls, falcons and other birds of prey hunt snakes for food. Some snake species are also fond of eating other snakes but this predation can not be regarded as a threat to snakes. As it is a natural ecological cycle, which is a part of the ecosystem since its creation. However, this predation change into a threat when this ecological cycle gets disturbed or when the population of predator exceeds as compares to its prey. Unfortunately, in the Indian subcontinent, this practice is promoted by villagers to keep their surrounding protected from snakes. Usually large number of mongoose is introduced that limits the population of snakes at an alarming rate.

• Illegal trading for different purposes, is one of the biggest challenge faced by the population of snakes: in southern part of Asia snake charmers catch these snakes for show or exhibition in different cities, moreover fight between snake and mongoose is a favourite past time of the people, which often results in the death of the snake.

Steps for the Conservation of Snakes

In the light of the above threats, following steps are suggested for the conservation of this creature.

• Captive breeding should be promoted in Pakistan as this population could be used for export and research purpose. The skin as well as the alive snakes both can be exported to foreign countries where they are in demand. More attention should be given to poisonous snakes because their venom is used as an important component in the preparation of medicines such as antivenom vaccines and other useful drugs. Beside its economical value, this method also gives an opportunity to observe and study various behaviours and habits of the snakes closely.

• Snakes are caught and captured for their venom, but unfortunately, after taking the venom they are not returned to their natural or preferred environment. This practice is a great threat to snakes and many rare species are endangered because of this. Therefore it is required, that they should either be provided with a natural environment, proper food and care or should be released to their natural habitat, so that population remains undisturbed and equilibrium is maintained.

• Bans should be imposed on illegal catching and export of snakes and people involved in these activities, should be sternly dealt with.

• Awareness programmes and informative literature should be developed with relevant facts to convince the villagers and local people in order for them to better understand this creature.