The Snake Skull (Head)
The snake skull is a highly evolved complex structure which is characterised by mobility, flexibility, and a greatly reduced number of bones.
All reptiles, with the exception of turtles, have what is commonly referred to as Diapsid skulls. These skulls are easily identifiable by the two temporal fossae (openings) on either side of the skull.
The term "diapsid" is derived from the latin word "Di" meaning two, and Greek words "hapsis" or "hapsid" meaning "arch" or "loop".
These temporal openings greatly reduce the overall weight of the skull and allows greater mobility of the skull.
In addition to the reduced number of bones within the skull there are also several hinge joints located at various points that allows the movement and slight rotation of certain segments.
These kinetic joints allow for varying degrees of mobility depending on the location of the joint. The joints linking the quadrate bone to both the rear mandible and supratemporal bones allows for both vertical and lateral movement which permits a wider gape and flexibility. The joints between the nasal and frontal bones allows for a lesser degree of vertical movement. The joint between the dental and rear mandible allows for greater lateral movement allows snakes to swallow prey items several times larger than the diameter of its head.The term used to describe the movement of bones within the skull is referred to as Cranial kinesis.
Most of the bones within the snake skull are not fused, but rather loosely attached by ligaments. This allows the expansion and flexion of the skull itself necessary to engulf prey.
Another significant difference is that the two bottom jaws are not fused together as in mammals. Instead, the dental bones are connected via a ligament which once again allows greater lateral movement.
A common misconception is that snakes can dislocate their jaws.
Diagramatic bone representation of a viper skull
G Quadrate bone
H Rear manible
Diagramatic bone representation of a python skull
I Quadrate bone
Diagramatic bone representation of the upper jaw
A Quadrate bone
E Palatine teeth
G Pterygoid teeth
The evolutionary adaptation of the snake skull is directly related to their feeding habits. Without these adaptations, and the inability to chew, would restrict snakes to much smaller prey.
It is also important to note that cranial kinesis alone is not sufficient to swallow prey. Snakes also require a complex dental structure (teeth) whcih plays a vital role in ingesting prey.
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