Biting and Swallowing Mechanism of Snake

Biting and Swallowing Mechanism of Snake

The truly poisonous snakes are provided with a pair of poison glands which are specialized salivary glands that manufacture poison. The glands are situated one on either side of the upper jaw. Each gland is sac-like and continues anteriorly into a narrow duct, the poison duct, which opens at the base of the fang. The poison gland is kept in position by means of two ligaments. The anterior end of the poison gland is attached to the maxilla by an anterior ligament, while a posterior ligament passes between the gland and quadrate bone of the skull. Between the lateral sides and junction of squamosal and quadrate are present fan-shaped ligaments. The paired fangs are sharply pointed and grooved and are actually enlarged maxillary teeth. They act as syringe and inject poison into the victim. The fangs are regenerated when lost or destroyed. The fangs may be of open type or closed type. When the poison groove is open it is called open type (as in cobra) and in closed type the groove runs like a tunnel through the length of the fang (viper) having two apertures, one at each end.

The fangs of Snake are of three types:

1. When the fangs are situated at the posterior end of the maxillae, they are known as opisthoglyphous. Snakes having such fangs are slightly poisonous.

2. When the fangs are situated at the anterior end of the elongated maxillae, they are called proteroglyphous. Highly poisonous snakes like king cobra, kraits, sea snakes, etc. have such type of fangs.

3. When the maxillae are short and have only the poison fangs with narrow grooves then the fangs are called solenoglyphous. Such fangs are long and when not in use, they remain folded under the roof of the mouth, as in vipers and pit vipers.

The biting habit has brought about structural modifications in the skull bones and jaw which together constitute the biting apparatus. The concerned bones are - the maxilla, squamosal, quadrate, pterygoid, palatine and ectopterygoid or transverse. The maxilla is usually reduced and freely movable. It can rotate on its lachrymal joint clockwise and the connected fangs can be erected into a vertical position. The maxilla is also attached to pterygoid by ectopterygoid. The squamosal is horizontal and is attached to the cranium on the one hand, and on the other to the quadrate. The quadrate suspends the lower jaw and their junction acts as fulcrum for the rotational movement. Teeth may be present on the palatine, pterygoid and upper and lower jaws. The biting mechanism is a rather complicated process and may be discussed under the following four heads. 

1. Opening of the Mouth: In resting condition the mouth remains closed and the fangs lie incurved within the mouth. At this time the posterior end of quadrate lies ahead of the posterior end of pterygoid. When the snake is ready to strike, the mouth opens by the contraction of digastrics muscles as a result of which the lower jaw is depressed.

2. Rotation of Maxilla: As the mandible is lowered the distal end of the quadrate is thrust forward, consequently pushing forward the pterygoid and ectopterygoid bones also. This action is aided by the contraction of sphenopterygoid muscles. The forward and upward movement of the ectopterygoid brings about the rotation of the maxilla and the fangs become erected into a vertical position.

3. Closure of the Mouth: This is brought about by the contraction of the temporalis muscles pulling up the lower jaw. As the mouth closes the fangs are inserted into the body of the prey.

4. Injection of Venom: As the fangs are pierced, the masseter muscles contract and squeeze the poison gland forcing the poison through the fang. The fan-shaped ligaments also come into play at this time and help in squeezing the poison.

The biting apparatus is so constructed that all the actions take place automatically. With the raising of lower jaw all the related bones are brought to their normal position. The time taken in opening the mouth is longer than the time taken in closing it.

Snakes are capable of swallowing very large animals through their mouth gape which can be widened enormously. This is possible because of the peculiar structure of the skull. In snakes the skull is kinetic, that is, the two maxillae are able to move in relation to the rest of the cranium. The upper jaw is loosely attached to the skull and freely movable. The quadrate which suspends the jaws (streptostyly) is loosely attached to pterygoids and lower jaw. Muscles known as the levator and protractor pterygoidei raise the pterygoids and pull them forwards and inwards, so that the prey is held between them. The two rami of the lower jaw are separate anteriorly, but are connected by an elastic ligament which allows much expansion of lower jaw. Thus the lowering of the lower jaws and forward movement of reduced upper jaws bring about great expansion of mouth gape enabling snakes to swallow large animals. The brain case is protected underneath by large parasphenoid bone, so that the brain cannot be injured by the struggling prey. The contraction of the pharyngeal muscles present in the region of the throat propels the prey backwards. The skin of the throat is greatly distensible and a prey much wider than snake`s head can be swallowed. The absence of pectoral girdle and sternum also facilitates the process of swallowing.

Reference

1. Britannica Reference Encyclopaedia 

2. Knowledge Encyclopedia Animal!: The Animal Kingdom as you've Never Seen it Before

3. Images are taken from Zoo-Que and Google.

4. In Defense of Plants: An Exploration Into the Wonder of Plants

5. A Naturalist’s Guide to the Birds of India

6. Earth: A Sustainable Planet

Also See

• Migration & Navigation of Birds

• Archaeopteryx – The First Bird`s Fossil

• Parrots 

• Bats

• Bears

• Woodpecker 

• Birds

• Flightless Birds 

• Corals, Jellyfish and Sea Anemones

• Butterflies, Bees and Ants 

• Starfish and member of Echinoderm 

• Jawless Fish

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