Page:Popular Science Monthly Volume 16.djvu/272

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258
THE POPULAR SCIENCE MONTHLY.

MANY-TOED HORSES.

WHEN Professor Huxley gave his lectures in New York, three years ago, on the evidences of evolution, he brought forward the genealogy of the horse as made out by recent fossil discoveries, and claimed that it was decisive in establishing the principle of descent, derivation, and development through the geological periods. There was a good deal of wise shaking of heads and shrugging of shoulders, at his presentation of the case, on the part of many who attended the lectures; and all who were perfectly ignorant of comparative anatomy and could not comprehend the course and force of the argument, were certain that the great biologist had for once made a total failure. No doubt if these critics had been questioned they would have readily pronounced the case closed for ever against evolution; but knowledge grows and evidence accumulates, and so it will be worth while to recall the subject, that we may appreciate some of the further points of illustration that have been made out since.

Professor Marsh, of Yale College, who has had this inquiry especially in hand, has made a short communication to "Silliman's Journal," on "Polydactyle (many-toed) Horses, Recent and Extinct," the substance of which we here reproduce.

It is stated that America is the original home of the horse, and that during the whole of Tertiary time, which the geologists divide into three periods—the Eocene, Miocene, and Pliocene—early, middle, and later—this continent was occupied with horse-like mammals of many and various forms. These all became extinct before the discovery of the country, but their abundant remains furnish the materials for marking out the genealogy of the horse in an almost unbroken succession of forms.

The study of fossils has shown that the oldest representatives of the horse on this continent all had many toes, and were of small size. In the course of development there was a gradual increase in size and a diminution in the number of toes, until the present type of horse was produced. The line of genealogy has been made out through seven successive stages, and the fossil proofs of its validity and completeness are all to be seen in the Yale Museum of Natural History. In vol. x. of "The Popular Science Monthly," page 295, the figures are given that illustrate the whole subject; we here simplify the representation by indicating the succession of changes that have taken place in the structure of the fore-foot of this series of quadrupeds (Fig. 1). All the facts go to show that the horse tribe is derived from an original ancestor having five toes on each foot, but this parent of the race has not yet been discovered. The oldest member of the group that has become known is the Eohippus, which had four well-developed toes and the rudiment of another on each fore-foot, and three toes behind.