We propose to give a brief account of a wonderful group of Dinosaurs, first introduced to the scientific world through Dr. Mantell's labours. The first of these monsters is the Iguanodon, the earliest known individual of the "bird-footed" division (Ornithopoda). The history of the gradual reconstruction of its skeleton is an instructive instance of the results that may be obtained by a careful and patient study of fragmentary remains. Through the labours of Dr. Mantell, in the first half of this century, a considerable knowledge was acquired of the greater part of the skeleton, but certain portions remained a puzzle; these, however, were eventually explained by Professor Huxley and Mr. Hulke, and a few years ago a series of complete skeletons were most fortunately obtained in Belgium, so that now every part of the huge framework of this monster is known to the palæontologist. Its history, as a fossil, is a most interesting one, and furnishes one more example of the marvellous insight into the nature of extinct animals displayed by the illustrious Baron Cuvier. Let us begin with the teeth, since they were the first part of the monster brought to light. It is, perhaps, hardly necessary to remark that, to one thoroughly acquainted with the structures of living animals, a tooth, or a series of teeth, will furnish material from which important conclusions with regard to the structure and habits of an extinct animal may be drawn. So, also, with regard to some other parts, such as limb-bones, but more especially the bones of which the backbone is composed (known as vertebræ). These are very important. The veteran anatomist, Professor Owen, has said, "If I were restricted to a single specimen on which to deduce the nature of an extinct animal, I should choose a vertebra to work out a reptile, and a tooth in the case of a mammal." Seven or eight different "characters," he says, may be deduced from a reptilian vertebra. It is, of course, impossible for any one to reconstruct an entire animal from a single bone or a few teeth, yet such fragments indicate in a general way the nature of a lost creation and its position in the animal kingdom. [Illustration: Fig. 20.--Tooth of Iguanodon, with the apex slightly worn. (From the Wealden Beds of Tilgate Forest. Natural size.) 1. Front aspect, showing the longitudinal ridges and serrated margins of the crown. 2. View of the back, or inner surface of the tooth. _a._ Serrated margins. _b._ Apex of the crown worn by use.]