A family of poisonous Old World snakes, the true vipers, composed of about 50 species and characterized by two relatively long caniculated fangs at the front of the upper jaw which are attached to movable bones, allowing them to be erect during the bite when the mouth is open, and folded into a palate skin fold when the jaws are shut. [L. vipera, viper]
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Vi·per·i·dae vī-'per-ə-.dē n pl a widely distributed family comprising heavy-bodied venomous snakes that include Old World snakes (subfamily Viperinae) and the pit vipers (subfamily Crotalinae) and that are characterized by large tubular venom-conducting fangs erected by rotation of the movable premaxillae compare CROTALIDAE
vi·per·id 'vī-pə-.rid adj
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Vi·per·i·dae (vi-perґĭ-de) a family of venomous snakes, the true or Old World vipers, characterized by front, movable, hollow fangs. It includes the genera Bitis, Cerastes, Echis, and Vipera. Cf. Crotalidae. See table at snake.Medical dictionary. 2011.