How does a snake walk without feet?

When a snake walks on land, it moves forward in an "S" shape mainly by bending left and right, and crawls forward by the scale activity of its abdomen. The two closely cooperate and coordinate freely.

The surface of snakes is covered with tiny scales, and the ventral surface of snakes of terrestrial and arboreal species has a row of extremely huge scales, which are called ventral scales from one ventral side to the other. Abdominal scales are covered with tiles and can move back and forth, which is the main tool for snakes of terrestrial and arboreal species to crawl. But terrestrial or arboreal snakes can't crawl with large belly scales. More importantly, it relies on the special structure of the skeletal system and muscle system in the snake and the control of the central nervous system to make all parts coordinate their activities and achieve the purpose of crawling. The spine of a snake is very long, usually consisting of more than 300 vertebrae, some as many as 400. At both ends of each vertebra, in addition to the anterior and posterior joints like all vertebrates, snakes also have 1 pair of accessory articular processes. The front end of the spinal nerve solitary tract is called kyphosis, which is a wedge-shaped protrusion; The back end is called the central concave, which is concave. In this way, the accessory joints between the anterior and posterior vertebrae are convex and concave, and they are embedded with each other. Therefore, every vertebra of a snake has a special double joint. Therefore, the whole spine of the snake not only does not dislocate, but also increases its flexibility and flexibility. In this way, when it crawls forward, its body can do left and right "S" bending movements.

In addition to the double joints in the spine, the snake has 65,438+0 pairs of slender and curved ribs in each vertebra except the first vertebra in front and several vertebrae at the end. They are connected by movable joints, so all the ribs can move back and forth regularly due to muscle contraction. At the end of the ribs, there are extremely developed subcutaneous muscles connected with the abdominal scales. So when the ribs move back and forth, you can also move the abdominal scales back and forth. When the abdominal scales move forward, because the scales are arranged in tiles, it does not affect physical activities; However, when the abdominal scales move backward, the free rear edge of the scales contacts with the rough ground to form a fixed point. When the abdominal scales continue to rotate backward, they will generate a reaction force and push the body forward. This effect will complete the crawling action together with the left and right movement of the body.

As for arboreal snakes, they can crawl on vertical tree trunks, because their belly scales are particularly flat and bent inward, their free edges are similar to "V" shapes, and they have many small protrusions. There are sharp edges on the surface of abdominal scales. Therefore, when they climb trees, they should not only crawl on the vertical trunk with the edge of the scale with mucro, but also support the whole body with the sharp edge of the scale, so that they can crawl on the trunk effectively. Also adapted to its arboreal habits, the body is generally light and thin, and the tail is particularly long, which can wrap around branches to help crawl.