Page:Popular Science Monthly Volume 20.djvu/329

Rh  skeleton would imply that it was a fœtus; but it may possibly have been the young of the same species, or an allied form, that had been swallowed. No similar instance is known among the Dinosaurs.

A point of resemblance of some importance between birds and Dinosaurs is the clavicle. All birds have those bones, but they have been considered wanting in Dinosaurs. Two specimens of Iguanodon, in the British Museum, however, show that these elements of the pectoral arch were present in that genus, and in a diagram before you one of these bones is represented. Some other Dinosauria possess clavicles, but in several families of this sub-class, as I regard it, they appear to be wanting.

The nearest approach to birds now known would seem to be in the very small Dinosaurs from the American Jurassic. In some of these, the separate bones of the skeleton can not be distinguished with certainty from those of Jurassic birds, if the skull is wanting, and even in this part the resemblance is striking. Some of these diminutive Dinosaurs were perhaps arboreal in habit, and the difference between them and the birds that lived with them may have been at first mainly one of feathers, as I have shown in my memoir on the Odontornithes, published during the past year.

It is an interesting fact that all the Jurassic birds known, both from Europe and America, are land-birds, while all from the Cretaceous are aquatic forms. The four oldest known birds, moreover, differ more widely from each other than do any two recent birds. These facts show that we may hope for most important discoveries in the future, especially from the Triassic, which has as yet furnished no authentic trace of birds. For the primitive forms of this class we must evidently look to the Palæozoic.

 

HE theory of a fourth dimension of space has lately been brought forward somewhat prominently, under the imposing title of "Transcendental Physics," by Mr. John Charles Frederick Zöllner, Professor of Physical Astronomy in the University of Leipsic, although the learned professor, it should be said, imputes the suggestion of the theory primarily to Kant, and secondarily to Gauss, the celebrated mathematician of Göttingen, both of whom, he says, struck out the thought. In this, it is possible, the professor does himself less than justice.

Gauss had large expectations from the geometry of position, but its development, as contemplated by him, does not appear to have