Snakes are reptiles that belong to the suborder Serpentes. Despite their flexibility, they possess a complete and complex skeletal structure composed entirely of bone.
Like all other vertebrates, snakes have a spinal column, or backbone, providing the central support for their body. Their unique, limbless body is a specialized adaptation of the typical vertebrate design, allowing for their characteristic movement and feeding habits. This internal bony framework grants both the necessary rigidity for movement and the elasticity for consuming large prey.
The Backbone of Flexibility: Vertebrae and Ribs
The snake’s body is dominated by its vertebral column, which contains a number of bones far greater than most other animals. The number of vertebrae typically ranges from 200 to over 400, with some exceptional species possessing close to 600 separate segments. This immense segmentation enables the snake’s agility and capacity for complex coiling. Each vertebra is connected to its neighbor by a ball-and-socket joint, which permits a wide range of motion in multiple directions.
Further enhancing stability and movement is a set of specialized bony connections called the zygosphene and zygantrum, which fit together on the top of each vertebra. These structures act like additional locks, restricting unwanted rotation and sheer forces while maintaining the necessary flexibility for lateral bending. A pair of long, curved ribs is attached to nearly every vertebra in the trunk section of the body, offering protection to the elongated internal organs. Unlike most vertebrates, snakes lack a sternum, or breastbone, meaning the ribs are free-floating at their ventral ends. This absence allows the rib cage to dramatically expand, aiding both deep inhalation and the passage of large meals through the body.
The Specialized Cranium: Jaws Built for Swallowing
The snake skull is known as a kinetic skull, a design highly adapted for the consumption of whole prey items larger than the snake’s head itself. The lower jaw, or mandible, is not fused at the chin, lacking the mandibular symphysis found in most other animals. Instead, the two halves of the lower jaw are connected only by elastic ligaments, allowing them to spread apart and move independently.
This flexibility lets the snake “walk” its jaws over the prey, alternating the grip of the left and right sides to slowly pull the meal down the throat. A small, movable bone called the quadrate acts as a swinging hinge connecting the lower jaw to the rest of the skull. This quadrate bone can rotate outward, significantly increasing the maximum gape, or opening, of the mouth, which is necessary for swallowing large volumes. The rest of the skull bones are loosely connected by ligaments, enabling further expansion and movement during feeding.
Skeletal Structure and Locomotion
The specialized structure of the snake’s backbone and ribs directly enables its diverse repertoire of movement styles. The high number of vertebrae and their intricate articulations allow the body to form tight curves and waves necessary for forward propulsion. The most common form of movement, lateral undulation, involves the snake pushing its body’s curves against external anchor points, such as rocks or grass, to generate a propelling force.
In rectilinear locomotion, a method often used by heavy-bodied snakes, the flexibility of the free-floating ribs becomes functional. Muscles attached to the ribs and the ventral scales work to lift sections of the body and pull the snake forward in a straight line, with the ribs acting to anchor the body. For climbing or moving in confined spaces, concertina movement is used, where the snake bunches the front of its body into an S-shape to create an anchor, and then extends the rear portion forward.