chapter (iv) snakes · •nevertheless, most snakes employ chemical senses rather than vision or...

CHAPTER (IV)SNAKES

Objective:

• 1.Describe the general morphology and habit of snakes.

• 2.Distinguish the poisonous snakes with their specific poisonous chracters .

• 3. Explain the effect of venoms.

• Snakes are limbless and usually lack both pectoral and pelvic girdles (the lateral persists as a vestige in pythons and boas.

• The numerous vertebrae of snakes, shorter and wider than those of most tetrapod , permit quick lateral undulation through grass and over rough terrain.

• Ribs increase rigidity of the vertebral column, providing more resistance to lateral stresses.

• Elevation of the neural spine gives the numerous muscles more leverage.

• In addition to the highly kinetic skull that enables snakes to swallow prey several times their own diameter, snakes differ from lizards in having no movable eyelids

• (snakes ’ eye are permanently covered with upper and lower transparent eyelids fused together) and no external ear.

• Most snakes have relatively poor vision, but arboreal snakes posses excellent binocular vision, useful for tracking prey through branches where scent tails would be difficult to follow.

• Snakes internal ear are mainly sensitive to sounds in a limited range of low frequency.

• However ,snakes are quite sensitive to vibration conducted through the ground.

• Nevertheless, most snakes employ chemical senses rather than vision or vibration detection to hunt their prey.

• In addition to the useful olfactory areas in the nose ,which are not well developed ,snakes have a pair of pit like Jacobson’s organs in the roof of the mouth.

• These organs are lined with an olfactory epithelium and are richly innervated.

• The forked tongue, flicked through the air picks up scent molecules; the tongue is than drawn past Jacobson’son organ.

• Information is transmitted from Jacoson’s organ to the brain, where scents are identified.

• Most snakes capture their prey by grabbing it with their mouth and swallowing it when it is alive.

• Swallowing struggling, kicking, biting animal is dangerous, so most snakes that swallow prey alive specialize on small prey, such as worm, insects, fish, frogs, and less frequently, small mammals.

• Snakes that first kill their prey by constriction often specialize on larger, often mammalian, prey.

• The largest constrictors are able to kill and swallow prey as larger as deer, leopards, and crocodilians.

• However, the muscle rearrangement that permit constricting reduce the speed at which constrictors can travel.

• As a result, most constrictors tend to ambush prey.

• Other snakes kill their prey before swallowing by injecting it with venom.

• Venomous snakes are usually divided into five families, based in part on type of fangs.

Family; Viperidae

• Vipers have large, movable, tubular fangs at the front of their mouth.

• This family includes American pit viper, and Old World true vipers, which lack facial heat-sensing pits.

Viper

Family -Elapidae

• Venomous snakes have short, permanently erect fangs in the front of the mouth.

• Includes cobra, mambas, coral snakes, and kraits.

KraitCobra

Coral snake

Family; Hydrophiidae

• Small groups include the highly venomous sea snake.

Family; Atractaspididae

• The poorly known fossorial mole vipers.

Family; Colubridae

• Which contains most familier (and non venomous)snakes, does include a few venomous species, including the rear-fanged African boom slang and the twig snake, both of which are responsible for some human fatalities.

African boom slang Twig snake

Subfamily; CrotalinaeFamily ; Viperidae

• are called pit viper because they posses special heat pit organ on their heads, located between their nostrils and eyes.

• All of the best known North American venomous snakes are pit vipers,

• such as rattlesnakes, water moccasins and copperheads

• The pits are supplied with a dense packing of free nerve ending from the fifth cranial nerve.

• They are exceedingly sensitive to radiant energy (long- wave infrared ) and

• can distinguish temperature differences smaller than 0.003 C from a radiating surface.

• Pit vipers use their pits to track worm-blooded prey and to aim strikes,

• which they can make as effectively in total darkness as in daylight.

Reproduction in snakes

• Oviparous

• Ovoviviparous

• Viviparous

Oviparous

• Most snakes are oviparous species that lay their shelled, elliptical eggs beneath rotten logs, under rocks, or in holes dug the ground.

Ovoviviparous

• Including all American pit vipers( except the tropical bushmaster)

• giving birth to well formed young.

Viviparous

• very few snakes

• a primitive placenta forms

• permitting the exchange of materials between the embryonic and maternal bloodstreams.

Characters of Poisonous snakes

1. Sea snake Hydrophis

2. Viper Vipera russelli3. Green snake Trimerisurus4. Cobra Naja naja

King cobra Naja hannah5. Krait Bungarus fasciatus6. Coral snake Callophis macclellandi

•

NON-POISONOUS AND POISONOUS SNAKES

Cylindrical tail flat tail

LAND SNAKES POISONOUS SEA SNAKES

Full belly scalesPOISONOUS OR NON-POISONOUS

small belly scalesNON-POISONOUS

narrow belly scales

NON-POISONOUS

Supra-occipital

shield

POISONOUS ORNON-POISONOUS

POISONOUS

Pit viper

POISONOUS

Viper

POISONOUSPOISONOUSPOISONOUSKraitCobra

Third supra-

labial scaleNostril

Eye

VertebralsMental groove

Fourth infra-labial scales

KEY FOR IDENTIFYING POISONOUS AND NON- POISONOUS SNAKES

Venom Neurotoxic

1. Sea snakes Hydrophis2. Cobra Naja naja

King cobra Naja hannah3. Krait Bungarus fasciatus4. Coral snake Collaphis macclellandi

Venom haemorrhaegic

1. Viper Vipera russelli2. Green snake Trimerisurus

Sea snake Hydrophis

2. Head small

1. Marine3.Tail flat and

compress

2. Head small

3. Tail flat and compressed.

Sea snake Hydrophis

4. Yellow, grey or blue with dark

cross bands

5. Belly scales small and pale coloured.

• 6. Venom neurotoxic and cause paralysis and renal failure.

Sea snake Hydrophis

Sea snake Hydrophis

Viper Vipera russelli

1. Terrestrial

2. May grow to 5 feet.

3. Head is triangular like an arrow head.

6. Small scales on head.

5. Body has 3 chains of brown patches.

4. Tail is round and short.

7.Mental groove present

8. Belly scales full and white with black specks

9. Sensory pit absent.

10. Venom haemorrhaegic

Green snake Trimerisurus , Pit viper

1. Terrestrial

2.Tail round, slender and brown at the tip.

3.Body colour green with a white lineon either side.

4. Ventral scales full and yellowish in colour.

• 5.Mental groove present.

• 6.Small scales on the head.

• 7.Heat sensitive pit present between nostril and eye.

• 8.Venom haemorrhagic.

5

6

7

Cobra Naja naja , King Cobra Naja hannah

2. Tail cylindrical

1.Terrestrial

3. Shield on the head

4. Belly scales full.

5. Mental groove present.

6. Vertebrals not enlarged.

7. Third supra-labial shield touches the eye and nose shields.

123third supra-labial scale

eyenostril

8. Neck with hood and markings.

Occipital scales absent – cobra N. naja

Occipital scales present – king cobra N. hannah

Shield scales

Occipital

scales

10.Venom neurotoxic

1 2

3 4

5 6 7

8 9

10 11

ocales

Head (dorsal)

Occipital scales

Shield scales

Krait Bungarus fasciatus

1. Terrestrial

2. Tail cylindrical and blunt at the tip.

3. Body is triangular with bands andhalf-rings across the back.

4. Belly scales full

6. Shields on the head

7. Vertebral scales large and hexagonal

fourth infra-labial scales

9.Venom neurotoxic

8.Fourth infra-labial scale is largest

Coral snake Callophis macclellandi

1. Tail round

2.Terrestrial

3. Ventrals broad.

4. Mental groove present.

5. Shields on the head

6. Third supra-labial shield touches the eye and nose shields.

123third supra-labial scale

eyenostril

7. Neck without hood.

8. Coral spots on the belly

9. Venom neurotoxic

GOOD LUCK

Snake Venoms and

their Symptoms

• Poisonous snake have two grooved or tubular fangs or poison teeth communicating by means of a duct to modified salivary glands situated below and behind the eyes.

These glands contains- secrete venom- Which contains several enzymes-that destroy the tissues of man and animals.

Mouth parts of snake

SALIVARY GLANDS

VENOM

(8 TO 9 ENZYMES)

Destroy the Man & Animals

- half of them destroy proteins- other half destroy fat base compounds.

Snake venom

Haemorrhagic Neurotoxic

Haemorrhagic venom

- Larger proportion of protein destroying- enzymes- Vipers and Pit vipers- Destroy protein structure

(muscles, connective tissues & blood vessels)

- Due to the damage blood vessels, blood is oozing out at the site of the bite and within the tissue around the vessel.

Neurotoxic venom

- Larger proportion of enzymes - destroy fat base tissue- Cobra, king cobra, krait and coral snake- They break down the fatty myelin of nerves

and destroy the nervous tissues.

General symptoms of Snakebite

Vision

- Blurriness

Heart and vessels-Rapid pulse-low blood pressure- severe shock

Muscular-convulsions-loss of coordination-weakness

Gastric-Nausea -Vomiting

Intestinal-Diarrhea

Other skin sites

-Bleeding spots-Numbness-Tingling-Sweating

Wound site-Bleeding-Fang marks-Discoloration-Burning sensation-Swelling

Respiratory-Breathing difficulty

Systemic-Fever-Severe pain

Central-Dizziness-Fainting-Increasing thirst-Headache

Cytolysis of red blood cells

Cytolysis of red blood cells

Symptoms of the haemorrhagic venomof vipers and pit vipers

1. Intense burning pain at the site of bite.2. Bleeding from the fang wounds.3. Black bruises at the site of bite due to

cytolysis of red blood cells. 4. Marked swelling at the site of bite due to

accumulation of fluids. 5. The pulse is small and thready and the

blood pressure is low. 6. Collapse with pupils dilated and insensitive

to light.

7. Spontaneous and submucous

haemorrhages are common.

8. Death as a rule is due to circulatory

failure.

Symptoms of neurotoxic venom of cobra and krait

• 1.Pain at the site of bite which radiated along the limb.

• 2.Drowsiness, nausea, and vomiting.

• 3. Numbness and weakness of muscles followed by partial paralysis.

• 4.Speech is blurred at this stage.

• Symptoms resembles those of drunkenness.

• 5.Followed by dropping of eyelids, dribbling of saliva and difficulty in swallowing.

• 6. Dropping of the head due to paralysis of the neck muscle.

• 7.Collapse with difficulty in breathing and cyanosis.

• 8. Krait poisoning is characterized by intense pain in the abdomen due to intestinal haemorrhage in addition to the above symptoms.

GOOD LUCK