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• Most of the Indian snakes are non-poisonous and
• Of 330 Indian species only 69 are poisonous comprising
29 species of sea snakes and 40 species of land snakes.
• In which only 4 are deadliest- cobra, kraits, viper & sea
• Poisonous snake have a poison apparatus in head and a
pair of larger teeth or fangs in upper jaw.
• When they bite, there may be two large circular
punctures made by the fangs on the skin of the victim.
• But non-poisonous snakes have neither poison
apparatus nor fangs. When they bite, they leave many
small pricks only.
• Poison apparatus of snakes consist toxic substance
which is considered as poison or venom.
• The poison and venom both substances are toxic in
nature but the difference are;
Poison- its origin may be plant or animal. If the plants
and animals produce toxic reaction after eating them
than the plants and animals supposed to be
Venom- it has animal origin. there should be
presence of some poison apparatus and hypodermal
needle. When substance injected into the body of
enemy or victim by those animals having poisonous
apparatus it is called venomous.
• All the poisonous snakes have poison apparatus in
their heads, which is not found in non-poisonous
snakes. This apparatus includes:
(i) a pair of poison glands
(ii) poison ducts
• Two sac-like poison glands are situated one on
either inner side of the upper jaw, below the eyes
and somewhat behind them.
• Poison glands are modified superior labial or
parotid gland (modified salivary gland).
• Size and shape of poison glands is varied
depending upon species, these are small and oval
in sea snakes and large and tubular in vipers.
• Poison gland is held in position with the help of
ligaments. Anterior ligament attaches anterior
end of the gland with maxilla and the posterior
ligament attaches the gland to the quadrate.
• Each gland is thickly encapsulated with fibrous
connective tissue and mostly covered by a fan-
shaped constrictor muscle also called as temporal
or masseter muscle.
• Stretching of muscles during biting squeezes
poison from gland into its duct.
• A narrow poison duct leads anteriorly from
each poison gland to the base of a poison fang
to enter its groove or canal.
• Fangs are certain specialized teeth attached to
• They are long, curved, sharp and pointed.
• They serve as hypodermic needles for injecting
poison into the body of victim.
• When a functional fang is lost or damaged, it is
replaced by one of the reserved fang.
• On the basis of structure and position 3 types of
fangs occur in poisonous snakes:
• A hollow poison canal, lined with enamel runs
through the fang opening at the tip (solen, pipe +
• In vipers and rattle snakes, this single large
functional fang occurs on the front of each
• Its base is covered on all sides by a sheath
containing a few reserve and developing fangs.
• The fangs are movable and turned inside to lie
close to the roof of mouth when it is closed.
• Proteroglyphous fang: in cobras, kraits coral
snakes and sea snake, fangs are small, at the front
of maxillae and permanently erect.
• Each fang is grooved all along its anterior face
• Opisthoglyphous fang: in some poisonous
snakes, in family colubridae, fangs are small, lie at
the back of maxillae and each grooved along its
posterior border (opistho, behind)
• There are 4 muscles involved in the biting
1. Digestric muscles- its contraction, open the
2. Sphenopterygoid muscles- contraction result in
forward movement of
pterygoid and up-pushing of the ectopterygoid
3. Constrictor muscles- its stretching cause
squeezing the poison gland.
4. Temporal muscles- its contraction, mouth closed
• The skull and jaw bones of poisonous snakes are very
• They are loosely or movably articulated thus allowing
a considerable degree of adjustment during the act
of swallowing or striking.
• In cobras, the fangs are permanently erect.
• But in vipers, the large fangs lie against the roof of
mouth when closed. Therefore, mechanism for biting
serves two main purposes-
(1) erection of fangs and
(2) injection of poison into the victim’s body.
• The mechanism of biting is a complicated process and
the sequences of biting may be discussed in these
1. When a viper wants to strike, a series of movements
occur in a chain. Contraction of digastric muscles lower
the mandible so that mouth open.
2. As mouth opens and lower end of quadrate thrusts
forward. This in turn, pushes forward the pterygoid. Now
the sphenopterygoid muscles contract. This contraction
results in the forward movement of pterygoid and up-
pushing of the ectopterygoid.
3. The upward movement of the ectopterygoid brings about a
rotation of the maxilla on its own axis round the lacrimal and
as the end result the fang is raised and comes to its striking
4. A simultaneous stretching of constrictor muscles around
the poison gland, forces its poison through poison duct into
the canal or groove of fang to be injected into the victim.
5. When mouth is closed by the contraction of temporal
muscles, the above movements are reversed. The fangs
embed in the prey which is drawn into the mouth. At the
same time the vertical fangs rotate to become horizontal.
Venom and Antivenom
• Venom is a clear sticky liquid of faint yellow or
• It is tasteless and odourless and acidic in reaction.
• It is a complex mixture of enzymes and specific
toxins and is a good digestive juice.
• It is fatal only when mixed with blood.
• It can be swallowed and if there is no scratch in
mouth or alimentary tract, it will pass out with
faeces without doing any harm.
• In laboratory it can be precipitated in reagent
such as silver nitrate and potassium permagnate.
• It can also be dried and kept indefinitely,
retaining its poisonous properties.
• Dried poison or crystals of poison can be
dissolved in water, salt solution or glycerine, it
will be equally poisonous.
• Snake venom is secreted by poison gland, found
in the head of snake. And injected in victim or
bitten prey body by fangs, serving as hypodermic
• Venom has evolved in snakes as an aid to
capturing and subduing prey.
• Snake biting is certainly in most of the cases, is
just an accident.
• Snake venom is of 2 type- neurotoxin and
• Most snake venom consist both, but one of them
may be predominant.
• The venom of different snakes has its own
• Degree of virulence differs not only in different
snakes but in the same snake under different
• The bitten person may die or recover depending
upon the amount injected and its virulence.
• The venom of viper is Haemotoxic, it contains an
endotheliotoxin (haemorrhagin) which damages the
capillary endothelium and produces haemorrhages in
• Endotheliotoxin also produce some toxin which leads
to failure of peripheral circulation with marked fall in
blood pressure by paralysing the neuromuscular
junction of vasoconstractor muscles.
• Viper venom also contain a thromboidnase which
causes intravascular clotting, if it happens to
enter directly into the vein during the bite.
• It also contains an enzyme an enzyme which help
in formation of lysocythin which cause extensive
• A cardiotoxin is also found in viper’s venom,
which cause damage to heart.
• Proteases cause local inflammation, necrosis and
damage to vascular epithelium.
• In general the venom of vipers act principally on
the vascular system.
• A class of enzymes Hyabronidases help in rapid
absorption of venom.
• Venom of cobra, krait and sea snakes is
• They cause death by paralysis of respiratory
muscles and asphyxiation.
• Neurotoxin (venom) attack CNS, the nerve
centers and causing paralysis of muscles,
especially those of respiratory muscles.
• Due to neurotoxin coagulation of blood is
reduced causing excessive bleeding.
• Death occurs due to asphyxia as respiratory
centers of brain are destroyed.
• The best cure for snake bite is an antivenom serum or
antivenin, which is injected into the body of the victim
to counteract snake venom.
• Different antivenins are required against different
snakes due to differences in the qualities of their
• An antivenin is prepared by injecting a horse with
gradually increasing dose of a snake venom until the
horse becomes fully immunized to any amount of
• Now blood serum of horse is collected and preserved.
• This is antivenom serum or antivenin which has
developed sufficient antibodies to neutralize the effect
of that particular snake venom.