rocks, possibly of Wealden age, in Western America, and described by Cope and by Marsh, indicate that even _Ceteosaurus_ had not attained to the maximum of Dinosaurian dimensions. These new animals have vertebræ twenty inches in length and from twelve inches to thirteen inches in the diameter of their bodies, while their lateral processes stretched three and a half feet. The shoulder-blade of one species is five feet in length, and its thigh-bone is six feet long. From these measurements Cope concludes that, unlike most other Dinosaurs, it had the fore-feet larger in proportion than the hind-feet, so as to have somewhat the appearance of a large giraffe. The bones of the back have a remarkable cavernous structure, which Cope interprets as indicating air cavities, to give lightness, as in the case of the bones of birds; but Owen suggests that the cavities were filled with cartilage, and that the animals were aquatic in their habits. Evidently in point of size the Dinosaurs had a better claim than even Behemoth to be called the “chief of the ways of God.” Some of them, however, were of small size, and probably active and bird-like in their movements. One of these is the animal represented in Fig. 154, a species from the lithographic limestone of Solenhofen.[68] [Illustration: FIG. 153.—Tooth of _Megalosaurus_. Natural size. _a_, Cross section. _b_, Crenellation of edges. Enlarged.] Nothing in the life of the Mesozoic has so seized on the imagination of evolutionists as the links of connection between birds and reptiles, which has even been introduced by Huxley into the classification of animals, by his grouping these heretofore very distinct classes in one gigantic and comprehensive class of _Sauropsida_. It is necessary, therefore, to glance at these connections, and if possible to arrive at some conception of their true value. The links which connect the reptiles and the birds are twofold. First, that between the Dinosaurs and the ostrich tribe,[69] and, secondly, that between the Pterodactyls and their allies, and the peculiar Mesozoic birds, such as _Archæopteryx_. The first would serve to account for the few exceptional Struthious birds of the modern world. The second would account for the Passerine and other more ordinary birds; and thus, according to evolution, the now somewhat homogeneous class of birds would have a double, or more probably multiple, origin from several lines of reptilian ancestors. This, no doubt, greatly complicates the links of connection, whether these be supposed to indicate derivation or not. [Illustration: FIG. 154.—_Compsognathus._ One of the smaller Dinosaurs.—After Wagner.]