[L. serpens, creeping.] An animal that creeps or winds about on the ground. They are divided into two classes - poisonous, as vipers and rattlesnakes ; and snakes that are not poisonous, as boas, pythons, and many others. Serpents are vertebrate animals, without limbs, but some have rudiments of hind limbs. (See Reptile, Snake.) They are mostly long and slender, and move partly by bending the body into folds, and partly by clinging with their scales to rough surfaces. Many glide, others burrow, and some live in trees.