Snakes belong to limbless group (ophidia) of class- Reptilia (Phylum–chordata). Most of the snakes are non poisonous and there are four poisonous genera of snakes, In India every year 30,000 persons die of the Snake bite. Snakes do not chew their food but swallow its whole food. They are different from lizards because most of the snakes have ability to swallow its animals larger than own body.
Snakes in particular are hated by all because these slippery, creeping creatures, dispatch man to his heavenly abode within seconds. It is true that bite of poisonous snakes is sometimes fatal, but most of them are harmless and even beneficial to man.
Feeding Mechanism of Snakes
The feeding mechanism of snakes is the dominant characteristics of snakes, during swallowing, their sharp teeth curve inward that prevent pray from slipping forward from mouth. By moving the two sides of jaws alternately, the snakes gradually pushes the prey (animals) down into its oesophagus (food pipe) through which it passes by peristaltic movements into stomach of snakes.
Poisonous Apparatus of snakes
All the poisonous snakes have poison apparatus in their heads, which is not found in non–poisonous snakes. Poison apparatus of snakes consist toxic substance which is considered as poison and venom. The poison and venom both substances are toxic in nature but the difference are; if the plants and animals produce toxic reaction after eating htem than the plants and animals supposed to be poisonous. When substance injected into the body of enemy or organism by those animals having poisonous apparatus it is called venomous.
Poisonous apparatus of snakes include the following parts;
- A pair of posion glands
- Poison ducts
- Fangs
- Muscles
A pair of poison glands
A paired sac-like poison glands are situated on the entire sides of the upper jaw. The poison gland is modified into salivary gland, from the anterior part of the gland a thin poison duct comes out, which comes ahead through the lateral part of the upper jaw and from a loop above the fangs.
The glands may be small and oval (sea snakes) or large and tubular (vipers) depending on species. Ligaments help in the position of poison gland. Anterior ligament attaches anterior end of the gland with maxilla and the posterior ligament runs between the gland and quad-rate.
Poison Ducts of Snakes
A narrow poison duct come anterior from each poison gland to the base of a poison fang to enter its groove or canal.
Fangs
The fangs of snakes evolved to inject venom into the pray of various snakes that possess them. the term fangs refers to a grooved or tubular tooth that is used to inject venom. It has pared pointed and hook like teeth, which are the modified form of maxillary teeth. They are long, curved, sharp and pointed.
Fangs are divided into three types on the basis of structure and position which are given bellow;
(a) Proteroglyphous (protero, first)
Proteroglyphous types of fangs are small, grooved and articulated and permanently erect at the anterior end of maxillae. Such fang is found in cobras, kraits, coral snakes and sea snakes,
(b) Opisthoglyphous (opistho, behind)
Opisthoglyphous fangs are also small, grooved but remain associated with the posterior end of maxillae.
(c) Solenoglyphous (solen, pipe + glyph, hollowed)
Solenoglyphous fangs in vipers and rattle snakes, a large functional fang occurs on the front of each maxilla.This contain a narrow hollow poison canal with enamel,which opens at the anterior end of the fang. The fangs are movable and turned inside to lie in the roof of mouth when it is closed.
Muscles of Snakes
The muscles of snakes are as the skull and jaw bones of poisonous snakes are very flexible. In cobras, the fangs are permanently erect. But in vipers, the large fangs found against the roof of mouth when closed.
Mechanism for biting give two main reasons;
A. erection of fangs and B. injection of poison into the victim’s body.
The following muscles remain associated with the biting apparatus of a snakes.
Digastric Muscles
Digastric muscles are attached with the squamosal bone and articular of the lower fang.
Sphenopterygoid Muscles
Sphenopterygoid Muscles anteriorly remain attached with a sphenoid area and posterior with dorsal surface of the pterygoid bone.
Temporal Muscles
The temporal muscles remains divided into two parts, the interior part attached with the cranium and the posterior part remains associated with the lower jaw.
Masseter Muscles
Masseter muscles are associated with the poison gland and contract to press it when needed.
Biting Mechanism of Snakes
The skull and jaw bones in poisonous snakes are loosely and movable articulated, thus,
allowing an enormous gape and swallowing whole of large prey. In cobras fangs are
small and remain permanently erect, but in vipers the fangs are large and curved and lie
against the root of mouth cavity when closed. Premaxilla, usually toothless and the
bones of the upper jaw are loosely attached to rest of the skull. Quadrate jointed to the
squamosal.
There are movable joints between the frontal behind and prefrontal and nasals in front
and also between several other bones of brain case, palate and jaws. These joints have
loose ligaments and allow movement in several directions and so permit a huge gap.
The two halves of the lower jaw are connected together by elastic ligamentous tissue.
So they are capable of being widely separated from one another.
The biting mechanism of snakes is a complicated process so it can be discussed under the following headings;
Opening of The Mouth
The fangs remain curved include in closed mouth during resting conditions.
Rotation of Maxillae
Rotation of maxillae is the contraction of sphenopterigoid cause the forward movement of pterygoid and ectopterigoid bones.
Closure of Mouth
The contraction of temperalsis muscle pull lower jaw upward which result in closure of mouth and insertion of fangs into the body of the prey.
Retraction of the fangs / insertion of venom:
At the time of insertion of venom actually accompanying discharge of venom, the muscles contract after the piercing of the fangs. The contraction of the muscle causes the squeezing the poison gland into the groove or channel of the fangs.
Snake Venom
The snake venom is a clear sticky liquid of faint yellow or greenish colour. It is tasteless and odourless and acidic in reaction. An acidic solution which becomes crystalline after drying up. It contains proteolytic enzymes, which causes severe damage to muscle endothelium.
The phosphatidaes causes haemolysis, which is present in the venom of pit vipers, proteases, erepsin, cholinesterase, Hybronidases, Ribonucleases, ophio, oxidases etc. also remain present in the venom.
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