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Snakes have greatly modified their skeletal system from their lizard-like ancestry. Growth is rapid in the first few years and is dependent upon the frequency of feeding and activity.
Head
The skull of a snake is more delicate than that of other reptiles and is characterised by its kinetic nature. The braincase is a solid structure designed to allow insertion of muscles associated with the palatomaxillary arch and mandibles. These are loosely attached and act independently. Each quadrate articulates with the caudal parts of both the palatomaxillary arch and mandible. The hinges between these bones are elastic ligaments which connect the mandibles (unique in the animal kingdom) and allow the snake to eat prey that is larger than its own head (see snake feeding and snake diet). Unlike lizards and turtles, the eyeball does not have a sclerotic ring. There is no temporal arch or interorbital septum and a middle ear cavity is lacking. A middle ear ossicle is present and fused to the quadrate. There is only one occipital condyle.
Limbs
Snakes do not have thoracic limbs, a sternum or pectoral girdle but a pelvic girdle may be present. In these species there may be external spurs which may be important during courtship, particularly in the pythons.
- For more information on reproduction, see Snake Reproductive System.
Vertebrae and ribs
The number of dorsal vertebrae may number from 80 to over 400. Each of these (except the first two) has a pair of ribs that form a tube to protect the internal organs. The vertebrae have more articulating facets than in mammals and this results in great mobility. The ribs extend to the ventral scales to which they are attached by muscles. Caudal autotomy may occur in some species of colubrids.
- For more information, see Snake Locomotion.