Snakes

Snakes are limbless reptiles of the squamate suborder Serpentes. Closely related to lizards and the tuatara, snakes are ectothermic, amniote, air-breathing vertebrates with an elongated rope-like body covered by overlapping scales, and they move around using undulatory, rectilinear, concertina, sidewinding or slide-pushing locomotion, with some arboreal species even capable of short-ranged gliding flight by flaring out the ribs to flatten and widen the body for aerodynamic lift. Snakes have skulls with significantly fewer sutures and more hypermobile articulations (i.e. cranial kinesis) than their lizard relatives, enabling them to greatly widen the mouth and swallow prey much larger than their heads. To accommodate their narrow bodies, snakes' paired organs (such as kidneys) appear one in front of the other instead of side by side, and most only have one functional lung. Despite being tetrapods from a cladistic prospective, snakes lack limbs completely, although pythons and boids retain a vestigial pelvic girdle.