- Snakes are ectothermic reptiles belonging to the sub-order serpentes and are thought to have evolved from lizards.
- Though the different species of snakes exhibit diversities in structure and habit, they closely resemble each other.
- Many of them are poisonous. These poisonous snakes bear well-formed biting/poison apparatus that makes them a dreadful creature.
The poison apparatus includes :-
- A pair of poison glands
- Their ducts
- A pair of fangs
- Associated muscles
(1) Poison Glands
- Poison glands are modified superior labial or parotid glands.
- Poison glands are situated one on either side of the upper jaw, below the eyes or somewhat behind them.
- These are sac-like (as in sea snakes), tubular (as in vipers), or almond-shaped (as in cobras).
- The poison gland is thickly encapsulated in dense fibrous connective tissue.
- The body of the poison gland is covered by a fan-shaped constrictor muscle, also called as temporal or masseter. During biting, its stretching squeezes poison into the poison duct.
(2) Poison Duct
- A narrow duct arises from the anterior end (neck of the poison sac), passes along the side of the upper jaw, loops over itself, and opens at the base of each fang.
- The duct of poison gland opens into the fang by an intake aperture.
(3) Fangs
- Fangs are specialized maxillary teeth attached to the maxillary bone.
- They are usually larger than the ordinary teeth and are either grooved or perforated by a canal for the passage of the poison duct (duct of the poison gland).
- They are long, curved, and pointed. They are extremely hard and calcified with a superficial enamel layer.
- When a functional fang is lost or damaged, it is replaced by one of the reserved fangs.
- Fangs serve as hypodermic needles for injecting poison into the victim's body.
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| Poison Apparatus (undissected view) |
Classification of Fangs
According to the structural differences, poison fangs are of two broad categories :
(i) Closed Type
(ii) Open Type
(i) Closed type - Solenoglyphous (Solen = pipe + glyph =hollowed)
- It occurs in viperidae (vipers and rattle snakes).
- A large functional fang occurs at the front of each half of maxilla.
- Each poison fang contains a poison canal which is lined by enamel. The poison canal runs through the fang opening at the tip. These fangs serve as hypodermic syringes for injecting poison in the victim's body.
- The poison fang is capable of rotating through a considerable angle. it can be turned inside and lie in a horizontal position along the roof of the mouth embedded in the folds of mucous membrane.
(ii) Open type
(a) Proteroglyphous (protero = first)
- It occurs in cobras, kraits, sea snakes and coral snakes.
-each fang lie at the front of the maxillae and is grooved all along its anterior face.
- The fangs are small and permanently erect.
(b) Opisthoglyphous (opistho = behind)
- It occurs in some poisonous snakes of the family Colubridae e.g. Dryophis.
- Each fang lies at the back of the maxilla and is grooved along its posterior border.
- Fangs are small.
(c) Aglypghous ( A= absent)
- It occurs in non-poisonous snakes.
- Fangs are absent.
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| Solenoglyphous Fang in Longitudinal Section |
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| Transverse Section of Fangs |
(4) Associated muscles
- The poison apparatus is associated with specialized bands of three types of muscles -
- Diagastric muscles
- Sphenopterygoid/protactor-pterygoid
- Anterior and posterior temporalis.
- Diagastric muscle: It is attached to the squamosal of the skull at one end and the articular of the lower jaw.
- Sphenopterygoid: It is attached anteriorly to the sphenoidal region and posteriorly to the dorsal surface of the pterygoid.
- Temporalis muscle: They are attached to the side walls of the cranium and the lower jaw. They help in closing the lower jaw.
Feel free to ask any relevant questions.
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