Snakes, properly so called, have the tympanic bone, or pedicle of the lower jaw, movable, and nearly always suspended to another bone, analogous to the mastoid bone, which is attached to the cranium by muscles and ligaments, a conformation which gives to these animals the vast power of distension they possess. Their trachea is long, their hearts placed far back, and the greater number have one very long lung and vestiges of a second. They are divided into non-Venemous and Venemous; and the latter are subdivided into Venemous with maxillary teeth, and Venemous with isolated fangs. The Snakes prey almost exclusively on animals of their own killing; the more typical species attacking such as are frequently larger than themselves: and the maxillary apparatus is, as we have seen, modified so as to permit of the requisite distension. According to Professor Owen's clear and intelligible description, the two superior maxillary bones have their anterior extremities joined by an elastic and yielding fibrous tissue with the small and single intermaxillary bone; the lower maxillary rami are similarly connected. The opposite extremity of each ramus is articulated to a long and movable vertical pedicle formed by the tympanic bone, which is itself attached to the extremity of a horizontal pedicle formed by the mastoid bone, so connected as to allow of a certain yielding movement upon the cranium. The other bones have similar loose movable articulations, which concur in yielding to the pressure of large bodies with which the teeth have grappled. The class of Reptiles is divided into three orders:--the OPHIDIANS, comprehending the Snakes; the SAURIANS, the Lizards and Crocodiles; and the CHELONIANS, the Turtles and Tortoises. OPHIDIANS.