INTRODUCTORY OBSERVATIONS. 
xi. 
Hippotherium. — The generic name Hippotherium, in place of the older Hipp avion, 
has been mainly adopted in conformity with the usage of the “Fauna Antiqua 
Sivalensis of which this work is to be regarded as a continuation. 
One of the equine bones from Hundes, in Tibet, noticed on page 68, is a 
cannon-bone, now in the collection of the Geological Society, and evidently belongs 
to Hippotherium. If the Hundes beds are pleistocene, it is the only known instance 
of the occurrence of the genus in that period. 
Additional species of Equus and Hippotherium. — To the list of species of Equus 
given on pages 71-2 add — 
Equus t^niopus , 1 Heuglin. Recent, North Africa. 
About the time that the third part of this volume was in the press, a new species 
of horse, said to be allied to the zebras, was described from the pleistocene of S. 
America, under the name of E. lundi, Boas. 2 Since the publication of the same part 
a new species of zebra, inhabiting Shoa and the adjacent districts of that part of 
Africa, has been described by M. A. Milne-Edwards 3 under the name of E. grevyi. 
Assuming this form to be distinct from the allied E. zebra of South Africa (not 
improbably extinct) these additions 4 make the number of species of Equus 25 (of 
which 10 are, or were recently, living), the African species 7, and the American 12. 
A new species of Hippotherium has been described by Prof. Leidy 5 from Panama, 
under the name of H. montezuma. 
Connection between Hippotherium and Equus. — It may be noticed in reference to the 
observations on page 7 9 that there is in the British Museum the metatarsus of a 
hippothere from Eppelsheim, in which, while the lateral bone is fully developed on 
one side, on the other it is extremely small, though extending along the whole length 
of the ‘ cannon-bone.’ This instance looks much like the incipient disappearance of 
the lateral digits, and indicates a transition from the hippotherian to the equine type. 
It. has been observed by Prof. Flower 6 that in many of the instances of polydactylism 
among existing ' horses, the additional digit (for there is usually but one developed) 
is due to a splitting' of the mesial digit, and cannot therefore be regarded as in any 
sense a reversion towards Hippotherium.. In many of these instances, moreover, the 
supplementary digit is on the inner side ; whereas in other perissodactyles the inner 
digits disappear before the corresponding outer ones. In a polydactyle horse from 
Bagdad, of which the right pes is figured by Mr. J. Wood-Mason, 7 the supplementary 
1 See Sclater, ‘Pro. Zool. Soc.,’ 1864, p. 374. 
2 “ Om en fossil Zebra. 1 ’— ‘ Mem. Acad. Roy. Copenhagen,’ 6th ser., Classe des Sciences, vol. I., 1881, p. 307. 
3 See 1 La Nature,’ No. 470 (3rd June, 1882) ; ‘ Pro. Zool. Soc.,’ 1882, p. 721 : Ibid, 1883, p. 175. 
4 From his own observations on their skulls the writer is disinclined to accept the views of some zoologists as to the 
specific identity of all the wild asses of Asia. See W. T. Blanford, “Eastern Persia, etc.,” London, 1876, vol. II., p. 84. 
Equus hemippus, Geoff r., St. Hil., of Syria is by some regarded as distinct from E. onager , under which its name should be 
put on page 72, instead of under E. hemionus. 
5 ‘ Pro. Ac. Philad.,’ 1882, p. 290. 
6 Lectures on the Anatomy of the Horse ; Royal College of Surgeons, 1883 _ 
7 ‘ Pro. Asiat. Soc.,’ 1871, p. 18, pi. I. 
