interesting, however, in affording a suggestion as to the possible steps by which the toothbills, as regards the armature of their jaws, may have passed into modern toothless birds.
The Stonesfield slates have yielded up an almost entire skeleton of a wonderful extinct form, unique as yet, described under the name of Compsognathus, which possesses a singularly long neck supporting a head whose structure is light, and, except in the possession of teeth, birdlike. Its anterior limbs are small, while the leg-bone of its very long hind-limb exhibits the prominent crest of which we have so often spoken, a ridge on its outer side for the fibula, and the pulley-shaped articular surface of its lower end identical in conformation with that seen in the bird. This skeleton diverges from the bird type, however, in the absence of a "merry-thought," and in having the single hock-bone of the bird replaced by three distinct bones, fitting immovably together, of which the trifid extremity of a fowl's, for example, indicates the coalescence. The haunch-bone, moreover, indicates relationship with the reptiles, in its form and in the manner in which it unites below with its fellow of the opposite side—a feature in which it agrees with the arrangement of the corresponding bone in the crocodiles and in the rheas. This strange creature, bird or reptile, "must, without doubt," Prof. Huxley remarks, "have hopped or walked on its hind limbs after the manner of a bird, to which its long neck, slight head, and small anterior limbs, must have given it an extraordinary resemblance." There is reason for believing that it was possessed of a long tail, which must have greatly helped to support it in the erect position.
The extinct group to which this singular Stonesfield fossil has been assigned contains some of the largest known terrestrial animals, such as the carnivorous giant-lizard (Megalosaurus), thirty feet in length, whose structure in many points resembles that of the bird, especially in the form of its hip-girdle and hind-limbs, on which, in the late Prof. Phillips's opinion, it moved with free steps, sometimes, if not habitually, claiming a curious analogy, if not some degree of affinity, with the ostrich. Another example is the still more gigantic herb-eating iguanodon, from beds in Sussex, taller than an elephant and vaster in size, wherein, also, are mingled avian and reptilian characters. In the form of its vertebra, which, except in the neck, are double-cup-shaped, it is reptilian—in the absence of collar-bones it is non-avian; but in the formation of its three-toed hind limbs, which are larger than the fore, as well as of the supporting haunch-bone, it is distinctly birdlike. Again, it is unbirdlike in regard to its teeth, whose general form and crenated edges are somewhat like the iguanas', which now frequent the tropical woods of America and of the West Indies; but they differ from them in having a flat surface on the crown of the tooth, worn down evidently by the process of mastication, whereas the herbivorous reptiles of the present day clip and gnaw off, but do not chew, the vegetable productions on which they feed.
