Snakes, with their limbless, undulating forms, possess a spine. As vertebrates, they have an internal skeleton that includes a highly specialized spinal column. This structure is shared with humans and many other animals.
The Snake’s Unique Spinal Column
A spine is a series of interlocking bones called vertebrae that form the central axis of a vertebrate’s skeleton. In snakes, this vertebral column is exceptionally elongated and contains a remarkable number of vertebrae, ranging from around 100 to over 400 in most species, with some pythons potentially having up to 600. Each of these numerous vertebrae, except for a few near the head and those in the tail, connects to a pair of ribs.
This intricate arrangement of bones creates a highly flexible yet strong structure. Unlike human spines, which have about 33 vertebrae, the snake’s spine features many more individual segments, each capable of independent movement. The connections between snake vertebrae involve a ball-and-socket joint at the centrum, along with additional points of articulation called zygapophyses and unique zygosphenes and zygantra, which enhance stability while allowing extensive flexibility. This specialized design allows the snake’s body to bend and twist in multiple directions, providing both support and a wide range of motion.
How the Spine Enables Movement
The snake’s highly flexible spinal column, coupled with its numerous ribs and powerful muscles, is fundamental to its diverse modes of movement. Muscles attached to the vertebrae and ribs allow the snake to precisely control each segment of its body. This enables various forms of locomotion, such as lateral undulation (the common S-shaped slithering), rectilinear movement (moving in a straight line), concertina movement (bunching and extending), and sidewinding.
In lateral undulation, the snake creates waves of muscular contractions that push against irregularities in the surface, propelling it forward. For rectilinear movement, particularly used by heavier snakes, sections of the belly scales lift and pull forward, with the ribs playing a role in anchoring the body. The coordinated action of the spine, ribs, and the extensive musculature also facilitates climbing, constricting prey, and striking with speed and precision. The flexibility derived from the multitude of vertebral joints allows the snake to adapt its body shape to different terrains and situations, making its limbless locomotion remarkably effective.