34 



NATURE 



\May II, 1876 



abundant remains of horses are found, which horses 

 resembled altogether our own species , or perhaps are still 

 more nearly allied to the wild ass. The same is the case 

 in America, where the species was very abundant in the 

 Quaternary epoch — a curious fact, as, when first disco- 

 vered by Europeans, there was not a horse from one end 

 of the vast continent to the other. 



In the Pliocene and older Miocene, both of Europe and 

 America, are found a number of horse-like animals, 

 resembling the existing horse in the pattern and number 

 of the teeth, but differing in other particulars, especially 

 the structure of the limbs. They belong to the genera 

 Protohippus, Hipparion, &c., and are the immediate pre- 

 decessors of the Quaternary horses. 



In these animals the bones of the fore-arm are essen- 

 tially like those of the horse, but the ulna is stouter and 

 larger, can be traced from one end to the other, and, 

 although firmly tmited to the radius, was not ankylosed 

 with it. The same is true, though to a less marked extent, 

 of the fibula. 



But the most curious change is to be found in the toes. 

 The third toe though still by far the largest, is proportion- 

 ally smaller than in the horse, and each of the splint 

 bones bears its own proper number of phalanges; a pair of 

 " dew-claws," like those of the reindeer, being thus formed, 

 one on either side of the great central toe. These acces- 

 sory toes, however, by no means reached the ground, and 

 could have been of no possible use, except in progression 

 through marshes. 



The teeth are quite like those of the existing horse, as 

 to pattern, number, presence of cement, &c. ; the orbit also 

 is complete, but there is a curious depression on the face- 

 bones, just beneath the orbit, a rudiment of which is, how- 

 ever, found in some of the older horses. 



On passing to the older Miocene, we find an animal, 

 known as Anchitherium, which bears, in many respects, 

 a close resemblance to Hipparion, but is shorter-legged, 

 stouter-bodied, and altogether more awkward in appear- 

 ance. Its skull exhibits the depression mentioned as 

 existing in Hipparion, but the orbit is incomplete behind, 

 thus deviating from the specialised structure found in the 

 horse, and approaching nearer to an ordinary typical 

 mammal. The same is the case with the teeth, which are 

 short and formed roots at an early period ; their pattern 

 also is simpUfied, although all the essential features are 

 still retained. The valleys between the various ridges 

 are not filled up with cement, and the little anterior 

 premolar of the horse has become as large as the other 

 grinders, so that the whole forty-four teeth of the typical 

 mammalian dentition are well developed. The diastema 

 is still present between the canines and the anterior 

 grinding teeth — a curious fact in relation to the theory 

 that the corresponding space in the horse was specially 

 constructed for the insertion of the bit ; for, if the Miocene 

 men were in the habit of riding the Anchitherium, they 

 were probably able to hold on so well with their hind legs 

 as to be in no need of a bit. 



The fibula is a complete bone, though still ankylosed 

 below to the tibia ; the ulna also is far stouter and more 

 distinct than in Hipparion. In both fore and hind foot 

 the middle toe is smaller, in relation to the size of the 

 animal, than in either the horse or the Hipparion, and the 

 second and fourth toes, though still smaller than the third, 

 are so large that they must have reached the ground in 

 walking. Thus, it is only necessary for the second and 

 fourth toes, and the ulna and fibula to get smaller and 

 smaller for the limb of Anchitherium to be converted into 

 that of Hipparion, and this again into that of the horse. 



Up to the year 1870 this was all the evidence we had 

 about the matter, except for the fact that a species of 

 PalcBotherium from the older Eocene was, in many re- 

 spects, so horse-like, having, however, well-developed ulna 

 and fibula, and the second and fourth toes larger even 

 than in Anchitherium, that it had every appearance of 



being the original stock of the horse. But within the last 

 six years some remarkable discoveries in central and 

 western North America, have brought to light forms 

 which are, probably, nearer the direct line of descent than 

 any we have hitherto known. 



In the Eocene rocks of these localities, a horse-like 

 animal has been found, with three toes, like those of 

 Anchitherium, but having, in addition, a little style of 

 bone on the outer side of the fore foot, evidently repre- 

 senting the fifth digit. This is the little Orohippus, the 

 lowest member of the Equine series. 



This evidence is conclusive as far as the fact of evolu- 

 tion is concerned, for it is preposterous to assume that 

 each member of this perfect series of forms has been 

 specially created ; and if it can be proved — as the facts 

 adduced above certainly do prove — that a complicated 

 animal like the horse may have arisen by gradual modifi- 

 cation of a lower and less specialised form, there is surely 

 no reason to think that other animals have arisen in a 

 different way. 



This case, moreover, is not isolated. Every new inves- 

 tigation into the Tertiary mammalian fauna brings fresh 

 evidence, tending to show how the rhinoceros, the pigs, 

 the ruminants, have come about. Similar light is being 

 thrown on the origin of the carnivora, and also, in a less 

 degree, on that of all the other groups of mammals. 



It may well be asked why such clear evidence should 

 be obtainable as to the origin of mammals, while in the 

 case of many other groups — fish, for instance — ^all the evi- 

 dence seems to point the other way. This question can- 

 not be satisfactorily answered at present, but the fact is 

 probably connected with the great uniformity of con- 

 ditions to which the lower animals are exposed, for it is 

 invariably the case that the higher the position of any 

 given animal in the scale of being, the more complex are 

 the conditions acting on it. 



It is not, however, to be expected that there should be, 

 as yet, an answer to every difficulty, for we are only just 

 beginning the study of biological facts from the evolu- 

 tionary point of view. Still, when we look back twenty 

 years to the publication of the " Origin of Species," we 

 are filled with astonishment at the progress of our know- 

 ledge, and especially at the immense strides it has made 

 in the region of palseontological research. The accurate 

 information obtained in this department of science has 

 put the fact of evolution beyond a doubt; formerly, 

 the great reproach to the theory was, that no support was 

 lent to it by the geological history of living things ; now, 

 whatever happens, the fact remains that the hypothesis 

 is founded on the firm basis of palseontological evidence. 



THE LOAN COLLECTION CONFERENCES 



CONSIDERABLE progress has been made in the 

 arrangements for holding conferences in connection 

 with the approaching Loan Collection of Scientific Ap- 

 paratus at South Kensington. 



In the Section of Mechanics, which includes Pure and 

 Applied Mathematics and Measurement, the conferences 

 will be held on May 17, 22, and 25, and the following 

 gentlemen have promised to give addresses or to take 

 part : — 



Dr. Siemens, F.R.S., general address with special 

 reference to Measurement. 



Mr. F. J. Bramwell, F.R.S., on Prime Movers. 



Mr. Barnaby, Director of Naval Construction to the 

 Admiralty. — Naval Architecture. 



Mr. W. Froude, M.A., F.R.S.— Fluid Resistance. 



M. Tresca, Sous-Directeur du Conservatoire des Arts 

 et Metiers, Paris. — Flow of Solids. 



M. le General Morin, Directeur du Conservatoire des 

 Arts et Metiers, Paris. — Ventilation of Public Buildings. 



Sir Joseph Whitworth, Bart., F.R.S.— Linear Measure- 

 ment. 



