Biting mechanism of snake

A short note on Biting mechanism of snake:-

The skull and jaw bones of poisonous snakes are very flexible. They are loosely articulated thus allowing a considerable degree of adjustment during the act of swallowing or striking. In cobras, the fangs are permanently erect. But in vipers the large fangs lie against the roof of mouth when closed. Thus the mechanism of biting serves two main purposes-
a. Erection of fangs and
b. Injection of poison into victim’s body
During a strike a series of movements occur in chain. Contraction of diagastric muscles lowers the mandibles so that mouth opens and lower end of quadrate thrusts forward. This in turn pushes the pterygoid forward. The forward pull of pterygoid in turn pushes the ectopterygoid upwards. This causes the maxilla bearing fangs to rotate through 900. As a result fangs become vertically erect and in the most effective position to strike. A simultaneous stretching of constrictor muscles around the poison gland forces its poison through poison duct into the canal of fang to be injected into the victim. When mouth is closed by the contraction of temporal muscles, the above movements are reversed. The fangs embed in the prey which is drawn in the mouth. At the same time the vertical fangs rotate to become horizontal.

Detailed note:- 

The skull and jaw bones in poisonous snakes are loosely and movably 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 frontals behind and prefrontals 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 mechanism of biting is a complicated process and it can be described in the following four steps:

(i) Opening of the Mouth:

By the contraction of digastric muscles the mouth is opened (lower jaw moves down).

(ii) Rotation of Maxilla:

As the mouth opens the lower jaw moves down and the lower end of quadrate moves forward. Quadrate and squamosal are very movable. The pterygoid is movably attached to the palatine. Quadrate pushes the pterygoid forward and the pterygo-palatine joint bent.

This forward movement of the pterygoid is conveyed by the transpalatine bone to the maxilla and causes it to rotate through about 90° upon its prefrontal articulation in such a way that the surface to which the fang is attached is carried forwards and ventralwards, and the fang is erected, i.e., is made to project downwards at the front end of the mouth. The contraction of sphenopterygoid muscles also helps in the movement of pterygoid forward.

(iii) Closing of Mouth:

The closing of the mouth is brought about by the contraction of the temporalis and sphenopterygoid muscles. The point of fang is directed backward while the mouth is closed. It takes longer time to open the mouth than to close it.

(iv) Transference of Venom:

During the contraction of the digastric muscle the posterior ligament is relaxed and during the rotation of the squamosal bone the fan-shaped ligaments are stretched to squeeze the wall of the poison gland. This makes the poison to come out of the poison gland through the poison duct and the fang.