Biting Mechanism of Poisonous snake
Snakes, belonging to
the order Ophidia, constitute a specialized group of limbless reptiles. With
approximately 3,000 species inhabiting tropical and subtropical regions
globally, around 300 of these species are venomous. Poisonous snakes possess a
specialized poison apparatus in their heads, characterized by highly flexible
skull and jaw bones that facilitate swallowing or biting adjustments. The
positioning of fangs varies among species; for instance, cobras exhibit erect
fangs, while vipers have fangs lying against the roof of the mouth when closed.
Biting Mechanism:
The biting mechanism serves two primary functions:
fang erection and venom injection into the victim's body.
Biting
Apparatus:
The components involved in the biting mechanism
include the poison gland, poison duct, fangs, and associated bones and muscles.
Poison Apparatus of Snakes:
1. Poison Gland:
Situated on each side of the upper jaw, the poison gland resembles a sac-like
structure held in place by anterior and posterior ligaments. The anterior
ligaments connect the gland to the maxilla, while the posterior ligaments link
it to the quadrate. Additionally, a fan-shaped ligament exists between the side
walls and squamoso-quadrate.
2. Poison Ducts: These
run alongside the upper jaw and open at the base of the fangs.
3. Fangs: Enlarged
maxillary teeth, typically sharp and pointed, exist as one pair in the upper
jaw. Fangs possess a remarkable capacity for regeneration when lost and exhibit
different types based on structure and position, such as proteroglyphous,
opisthoglyphous, and aglyphous.
Associated
Bones and Muscles:
Various bones and
muscles are directly or indirectly associated with the biting mechanism,
including the skull, maxillae, quadrate, pterygoid, squamosals, ectopterygoids,
and palatines. Notable muscles include the digastric, anterior and posterior
temporalis, protractor-pterygoid (or sphenopterygoid), masseter, and mandibular
constrictor muscles.
Biting
Process:
1. Opening of the Mouth: Digastric muscle contraction facilitates
mouth opening as the lower jaw moves downward.
2. Rotation of Maxilla: Simultaneously, as the mouth opens, the lower
jaw moves down, and the quadrate's lower end shifts forward. This forward movement,
transmitted through various bones and joints, causes the maxilla to rotate,
erecting the fang.
3. Closing of Mouth: Mouth closure results from the contraction of
temporalis and sphenopterygoid muscles, directing the fang backward.
4. Transference of Venom: Contraction of the digastric muscle relaxes the posterior ligament, while rotation of the squamosal bone stretches the fan-shaped ligaments, facilitating venom expulsion from the poison gland through the poison duct and fang.
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