What is snake's biting mechanism?
There are two types of snakes-Poisonous & Non-poisonousØBoth snakes bite.ØNon-Poisonous snakes have no apparatus for biting ,so no serious harmØPoisonous snakes have poison apparatus for biting, so serious harm These poison apparatus are- a pair of poison glands poison ducts fangsPOISON GLANDSone pair of poison glandseach one is situated on either side of the upper jaw.The poison glands are actually the parotid glands.Each poison gland is sac like in appearance.They are held in position by some ligaments.With the help of anterior ligament, the gland is attached with the maxilla.The posterior ligament is present between the gland and the quadrate.In addition to these, fan-shaped ligaments are also situated between the side walls and squamoso-quadrate junction.Poison ductEach poison gland is provided with a narrow duct at its anterior portionpasses along the side of the upper jaw, loops over itself andfinally opens at the base of the fang.Fangone pair of fangs in the upper jaw.They are enlarged maxillary teethare very sharp and pointed.There is great power of regeneration (when lost for some reason).On the basis of structure and position, the fangs are of the following types :ProteroglyphousStenoglyphousOpisthoglyphousAglyphous1)Proteroglyphous type: The fangs are comparatively small and they are present in front of the maxillae. The fang has a groove all along its anterior face. Examples : Cobra, Krait, Sea snakes and Coral snakes.2)2)2)2)2)2)Stenoglyphous type: The fangs are movable and turned inside. Poison canal runs through the fang and opens at the tip. Examples: Vipers and Rattle snakes.3)3)Opisthoglyphous type. The fangs are small and lie at the back portion of maxillae. The fang has a groove along its posterior face. Examples : Some colubrid snake (African tree snakes)4)4)4)4)4)4)4)4)4) Aglyphous type: Aglyphous dentition is present in the non- poisonous snakes.Associated bones and musclesThere are some important bones and muscles which are directly or indirectly associated with the mechanism of biting. In the skull, maxillae, quadrate, pterygoid, squamosals, ectopterygoids and palatines are movably articulated. Premaxillae are very much reduced.Sqamosals are loosely attached tocranium. The joint of quadrate and lower jaws acts as fulcrum. Quadrates are also loosely articulated with the cranium, pterygoid and lower jaw. Ectopterygoid is a transverse bone.The important muscles are Digastric muscle, Anterior and Posterior temporalis muscles and Protractor-Pterygoid or Sphenopterygoid muscle. In addition to these, there are two more muscles associated with the poison glands. These are masseter muscle and Mandibular constrictor muscle.The gastric muscle is attached with the squamosal bone anteriorly and with the base of the lower jaw (articular) posteriorly.The Sphenopterygoid muscle is attached to the Sphenoidal region anteriorly and dorsal surface of the Pterygoid posteriorly. Anterior and Posterior temporalis muscles are attached to the side walls of the cranium and the lower jaw.Biting mechanism in snakeThe skulls of poisonous snake are very flexible, so they can make a considerable degree of adjustment during biting.In cobras, the fangs are erect, but in vipers the fangs are lie against the roof of mouth when closed. So biting mechanism contains two steps:1. Erection of fangs-contraction of digastric muscle lower the mandible & the mouth opens.-lower end of quadrate pushes forward. This in turns pushes forward of pterygoid. This is also aided by the contraction of sphenopterygoid muscles.- The forward pull of pterygoid leads to the upward push of ectopterygoid.-This causes maxilla bearing fangs to rotate through 90o at hinge-joint with lacrimal . As a result the fangs become erect.2. Injection of poison-Simultaneous stretching of constrictor muscles around poison gland, forces its poison through poison duct into canal or groove of fangs to be injected into the victim.-When the 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.3)By-JyotiRIE,BBSR
