GENERAL ADAPTATIONS IN SNAKES

GENERAL ADAPTATIONS IN SNAKES

Snakes (suborderOphidia ) are elongated, limbless, flexible reptiles. There are about 2,900 species of snakes. Of these, 375 are venomous.

Snakes are found throughout the world except Antarctica, Iceland, Ireland, Greenland and New Zealand. Most snakes are found in tropical regions. Snakes are found in many habitats including in the land , water,forests, deserts and grass lands.They are nocturnal and carnivorousSnakes have long ,slender , cylindrical body. They lack limbs and girdles .

Some snakes like pythons possess vestigial hind limbs and girdles .

Skin bears rows of scales (smooth and keeled) that over lap, they prevent slipping during locomotionHead bears a pair of eyes, which is covered by a transparent scale which enables the snake to give a steady ,un-winking stare which helps in paralyzing the prey with fear

Ear opening and tympanum is absent ,internal ear is present.Auditory apparatus consists of a semi-cartilagenous columella auris attached to quadrate bone.Snakes cannot perceive air-borne sound but high to earth borne sound or vibratationsThe two halves of lower jaw are connected by a ligament. The palate bones (maxilla ,palatines and pterygoids ) are freely movable and the quadrate is loosely attached to cranium and lower jaw . This enables the snake to open their mouth very wide and swallow prey larger diameter than their own bodies

Snake swallowing prey

Sternum and epi-sternum absent ,so the ribs are free ventrally, this permits great expansion of thorax to accommodate large prey .

To cause further expansion there is soft elastic skin between the scalesCranium is strong and compact.The brain is protected from mechanical injury during swallowing by massive para -sphenoid and extensions of frontals and parietalsTeeth present at jaw margins and also on the palate. Teeth are slender and backwardly directed or curved to hold the prey while swallowingPoisonous snakes have a pair of large teeth, the fangs on the maxilla of upper jaw The fangs are grooved or tubular to inject venom into the prey Tongue is slender and forked ,it serves in bringing odours of water,food or mates to the Jacobsons organ

Asymmetrical Disposition Of Organs In SnakesSnakes are bilaterally symmetrical vertebrates In relation to the creeping ,burrowing mode of life the body is elongated.Most of the paired visceral organs have become ASYMMETRICAL ie . Reduced on one side or lying at different levelsDIGESTIVE SYSTEM : The entire alimentary canal lies at the LEFT side of the body cavity.The first part of the intestine is coiled and the posterior end is straight.As an adaptation to feeding habit the glottis is shifted forwards on the floor of the buccal cavity so that respiration proceeds even when the food is being swallowed.Liver is formed of two unequal lobes.The right lobe is larger than the left lobe RESPIRATORY SYSTEM

The tracheal tube leads into a solitary RIGHT lungs. The left lung is reduced or rudimentary.The right lung is very long and extends upto the cloaca.The right lung has an anterior vascular spongy respiratory part and posterior saccular reticular part , acting as hydrostatic organ for balancing. Circulatory system is modified due to compressed body, absence of limbs and presence of only right lungBlood vessels to the limbs are aborted due o absence of limbsElongation of neck is associated with asymmetrical arrangement of carotid vesselsThe right carotid is thin and the entire blood supply to the head is by the large LEFT carotidCIRCULATORY SYSTEMUrinary system consists of a narrow strip-like RIGHT kidneyA delicate ureter runs down into the cloacaUrinary bladder is absentSome snakes also have a small left kidney situated at a fairly low levelURINARY SYSTEMTestis in male and ovary in females are elongated structures.The PAIRED structures are placed at different levels in relation to the position of the kidneysREPRODUCTIVE SYSTEMCredits :

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