ZOOLOGY.] HOUSE 175 toe (in.) greatly elongated, and with its unguul phalanx and hoof expanded, and the stability of the forearm and leg in creased by the complete subordination of the ulna and iibula to the larger bones, the radius and tibia, which alone are concerned in the formation of the wrist and ankle joint. Fossil remains of true horses, differing but very slightly from the smaller and inferior breeds of those now existing, are found abundantly in deposits of the most recent geo logical age, in almost every part of America, from Escholz Bay in the north to Patagonia in the south. In that con tinent, however, they became quite extinct, and no horses, either wild or domesticated, existed there at the time of the Spanish conquest, which is the more remarkable as, when introduced from Europe, the horses that ran wild proved by their rapid multiplication in the plains of South America and Texas that the climate, food, and other circumstances were highly favourable for their existence. The former great abundance of Equidte in America, their complete extinction, and their perfect acclimatization when reintro- duced by man, form curious but as yet unsolved problems in geographical distribution. The existing species of the genus Equus are the follow ing : (1.) The Horse, Equus caballus, Linn., is distinguished from the others by the long hairs of the tail being more abundant and growing quite from the base as well as the end and sides, and also by possessing a small bare callosity on the inner side of the hind leg, just below the "hock" or heel joint, in addition to the one on the inner side of the forearm above the carpus, common to all the genus. The mane is also longer and more flowing, and the ears shorter, the limbs longer, and the head smaller. Though the existing horses are usually not marked in any definite manner, or only irregularly dappled, or spotted with light surrounded by a darker ring, many examples are met with showing a dark median dorsal streak like that found in all the other members of the genus, and even with dark stripes on the shoulders and legs indicating " the pro bability of the descent of all the existing races from a single dun-coloured, more or less striped, primitive stock, to which our horses still occasionally revert." : In Europe wild horses were extremely abundant in the Neolithic or polished-stone period. Judging from the quan tity of their remains found associated with those of the men of that time, the chase of these animals must have been among his chief occupations, and they must have furnished him with one of his most important food supplies. The characters of the bones preserved, and certain rude but graphic representations carved on bones or reindeers antlers, enable us to know that they were rather small in size, and heavy iu build, with large heads and rough shaggy manes and tails, much like, in fact, the present wild horses of the steppes of the south of Russia. These horses were domesticated by the inhabitants of Europe before the dawn of history, but it is doubtful whether the majority of the animals now existing on the Continent are derived directly from them, as it is more probable that they are descendants from horses imported though Greece and Italy from Asia, derived from a still earlier domestication, followed by gradual improvement through long-continued attention bestowed on their breeding and training. Horses are now diffused by the agency of man throughout almost the whole of the inhabited parts of the globe, and the great modifications they have undergone in consequence of domestication and selective breeding are well exemplified by comparing such extreme forms as the Shetland pony, dwarfed by uncongenial climate, the thoroughbred racer, and the London dray-horse. In Australia, as in America, 1 Darwin, Variation of Animals and Plants under Domestication, 1868, vol. i., chap. ii. horses imported by the European settlers have escaped into the unreclaimed lands, and multiplied to a prodigious extent, roaming in vast herds over the plains where no hoofed animal ever trod before. (2.) E<iuus asinus, Linn. The Domestic Ass is nearly as widely diffused and useful to man as the horse. It was known in Egypt long before the horse, and is probably of African origin, indeed its close resemblance to the existing wild ass of Abyssinia, E. tvenlopus, Heuglin, leaves little doubt as to its identity with that species. (3.) The Asiatic Wild Asses, which roam in small herds in the open plains of Syria, of many parts of Persia, of the north-west of India, and the highlands of Tartary and Tibet from the shores of the Caspian to the frontiers of China, differ from the last in being of a more rufous or isabelline colour, instead of pure grey, in wanting the dark streak across the shoulder, and having smaller ears. They have all a dark-coloured median dorsal stripe. 1 hough it is considered probable by many zoologists that they form but a single species (E. hemionus, Pallas), they present such marked variations in size and form that they have commonly been divided into three the Syrian Wild Ass (E. hemippus, Geoff.), the Onager (E. onagtr, Pall.) from Persia, the Punjab, Scinde and the desert of Cutch, and the Kiang or Dzeggetai (E. hemionus, Pallas) of the high table-lands of Tibet, where it is usually mei with at an elevation of 15,000 feet and upwards above the sea-level. The last is considerably larger than either of the others, and differs from them in external appearance, having more the aspect of the horse. They are all remarkably swift, having been known to outstrip the fleetest horse in speed. Lastly, there are three striped species, all inhabitants of Soutli Africa. These constitute the genus Hippotiyris of Hamilton Smith, but they are not separable except by their coloration from the true asses, and one of them (4), the Quagga (E. ^uagga, Gmel.), may be considered as inter mediate. This animal has the dark stripes limited to the head, neck, and shoulders, upon a brown ground. In (5) the Dauw or Burchell s Zebra (E. burckellii, Gray), the ground colour is white, and the stripes cover the body and upper part of the limbs. This is the commonest species in the great plains of South Africa, where it roams in large herds, often in company with the quagga and numerous species of antelope. It ranges from the Orange River to the confines of Abyssinia. In (6) the Mountain Zebra (E. zebra, Linn.) the contrast between the clear white of the ground and the black of the stripes is most marked, and the latter extend quite down to the hoofs. This is, conse quently, the most beautiful species of the group as regards colour, if the horse may bear the palm in elegance of form. It frequents mountainous districts rather than the open plains which are the dwelling-places of the other two species, and as it appears to be limited to the southern portion of the continent, within the confines of the Cape Colony, its numbers are rapidly diminishing under the encroachments of European civilization. There are thus at least six modifications of the horse type at present existing, sufficiently distinct to be reckoned as species by all zoologists, and easily recognized by their external characters. They are, however, all so closely allied that each will, at least in a state of domestication or captivity, breed with perfect freedom with any of the others. Cases of fertile union are recorded between the horse and the quagga, the horse and the dauw or Burchell s zebra, the horse and the hemionus or Asiatic wild ass, the com mon ass and the zebra, the common ass and the dauw, the common ass and the hemionus, the hemionus and the zebra, and the hemionus and the dauw. The two species which are perhaps the farthest removed in general structure, the
horse and the ass, produce, as is well known, hybrids or
