Skeletal conditions in snakes
Snakes have evolved to have a very muscular structure so they move very efficiently along the ground and up into trees without the use of legs. Most snakes have no legs at all, however some snakes have vestigial (remnants) of back legs around the vent area.
Movement is facilitated by contractions of muscles and rippling the body in an s-shape. The body of the snake is protected by ribs and these are present all the way down to the level of the vent.
Reproduced with permission from Siuna Ann Reid: Reptiles are Cool, Understanding my Snake © 2013