Boa Constrictor: name for live-bearing constrictor snakes, found mostly in the Americas. This family, which also comprises the egg-laying pythons of the Old World includes the largest of all snakes as well as many smaller ones. Boa Constrictors have two functional lungs instead of one, as is found in other snakes, and vestiges of hind limbs; these primitive characteristics are indicative of their relationship to lizards.
