Januaby, 1904.] 



KNOWLEDGE. 



19 



more oouiplicateii crowns, aud tbe s^ps on each side of 

 the oanines were larsjer. Moreover, the small first cheek- 

 tooth, or premolar, es{<>oially in the lower jaw, was ijiiite 

 riulimeutarv, and often shed in old a>;;e. There is, like- 

 wise, another point in connection with the cheek-teeth of 

 this aud the last Ljenus. lu Aiichitlifriitin imd the earlier 

 forms, the <'heek-teetli. with their ridt^ed crown- surface, 

 were adapted solelv for an uii-and-down champing,' move- 

 ment, such as occurs in the jaws of the pifjs. On the 

 other hand, the Hat millstone-like surface formed l)v the 

 cheek-teeth of the hippariou and the modern horse permits 

 of a horizontal grinding movement, much better adapted 

 to the comminution of hard substances. These three-toed 

 horses were further peculiar for the presence of a depression 

 on the sides of the face for a gland comparable to the 

 tear-gland of deer and many antelopes ; traces of the 

 depression being visible in certain modern horse-skulls, 

 aud also existing in a much more marked degree iu the 

 extinct Siwalik horse (Eqiivf! sivalfusis) of India. 



The presence of these face-glands indicates that the 

 hipparious prolxibly frequented country covered with tall 

 grass or bush, in which the scent given out liy their 

 secretion would aid the members of a troop in tracing the 

 whereabouts of their fellows. On the other hand, in the 

 open grassy plains (which by the way are probably a 

 comparatively recent feature in the history of the earth) 

 such aids are quite unnecessary, and the glands have 

 accordingly been lost in the modern horse and its relatives. 

 In height the hipparion stood about 4 feet 6 inches 

 (13'i hands) at the shoulder. In coloration it was 

 probably strij^ed after the fashion of the zebras. 



During the Pliocene period horses obtained for the first 

 time an entry from the North into South America, where 

 they developed into two generic types known as 

 Hippidiiim and Onohlppidiiim. Having large face- 

 glands, and comparatively short and simple cheek-teeth, 

 these South American horses were specially distinguished 

 by the great length of the slit on each side of the face 

 below the nose-bones. Evidently, therefore, they were off 

 the line of the modern horse, although it is believed that 

 the second, at any rate, were single-toed. If, as some 

 believe, indigenous horses existed iu South America at the 

 time of its discovery, they must have been Onohippidiums. 

 In the Lower Pliocene of India aud the Upper Pliocene 

 of Europe aud Asia appear for the first time true horses 

 of the genus Equus, characterized Ijy the total disappear- 

 ance of external lateral digits, the sole relics of which are 

 the splint-bones at the upper ends of the cannon-bones, 

 alluded to above as being the only superfluous aud appa- 

 rently useless structures noticeable in the skeleton of the 

 horse. They seem, in fact, to be structures of which these 

 animals have been unable to rid themselves ; and are 

 actually injurious, being tbe cause of the disease known 

 as splint. To the evolutionist they are, however, inde- 

 scribably valuable, as affording incontrovertible evidence 

 of the descent of the horse from the three-toed forms. In 

 all the one-toed horses the pattern on the crowns of the upper 

 cheek-teeth (Fig. 8) differs in a certain detail from that of 

 the hipparions. The Pliocene horses approximate, however, 

 in this respect more to the latter than in the case with 

 their modern descendants, as they also do in the somewhat 

 shorter crowns of the cheek-teeth. Moreover, the occur- 

 rence of a first upper piremolar (the " wolf-tooth " of the 

 vets.) was less uncommon in these Pliocene species than 

 in the horses of to-day ; and they occasionally developeii 

 the corresponding lower tooth, which is quite unknown in 

 the latter. Whether, however, the mares of the Pliocene 

 horses resembled those of the present day in the absence 

 of the canines, 1 am unable to say. 



Passing on from certainty to conjecture, it is probable 



that at least some of these Pliocene horses were striped 

 like the zebras. S]iecies, however, such as the immediate 

 ancestors of the modern /?'/»».< rnhdllus — the domesticated 

 horse of the jiresent day and its wild or semi-wild relatives 

 th(( dun-coloured ])onies of Mongolia — th(> wild asses, and, 

 in a less degree, the extinct South African quagga, which 

 took to a life iu the open plains in countries where there 

 is strong sunlight, found this type of coloration uusuited 

 to their needs and accordingly assumed a more or less 

 uniformly coloured coat, as being best adapted for 

 protective rescmldance in such situations. The above- 

 mentioned tendency to revert to stripes, es|H'cially iu tlit^ 

 case of hybrids, affords, however, proof ()f their zebra-like 

 ancestry. 



As early as the Prehistoric ]jeriod, as we infer from the 

 rude drawings of the animal by its first masters, the 

 European horse was uniformly colourcKl — probably dun 

 with dark mane, tail, and legs. It was a small heavy- 

 headed brute, with n)ugh scrubby mane and tail, and no 

 trace in the skull of the depressiim tor the face-gland. From 

 this stock are descended the cart-horses and the ordinary 

 breeds of Western Europe. The blood-horse, or thorough- 

 bred, on the other hand, is a later imi)i)rtation into 

 Europe either from Arabia, by way of Greece and Italy, 

 or, as some think, from North Africa, the homo of the 

 barb. It has been supposed that these Eastern horses are 

 the descendants of an earlier domestication of the same 

 stock. I have, however, recently shown the existence in 

 an Indian domesticate.l horse-skull, as well as iu the skull 

 of the race-horse " Ben d'Or," of a distinct trace of 

 the depression for a face-gland, and the suggestion 

 consequently presents itself that the Eastern horses 

 (inclusive of thoroughbreds) are derived fnim E<iuus 

 sivalensis, in which the face-gland may still have 

 been functional. The thoroughbred, as contrasted 

 with the cart-horse, exhibits the extreme limit of 

 specialisation of which the equine stock is capable ; 

 this being displayed not only by the gracefulness and 

 beauty of its bodily form and the relatively small 

 size of its head and ears, but likewise by the greater 

 relative length of the bones of the lower segments of the 

 limbs as compared with the upper ones, namely, the 

 humerus in the fore-limb, and the femur in the hind pair. 

 In this respect, therefore, the blood-horse departs the 

 furthest of all the tribe from its tapir-like ancestors, as 

 it does in its height at the shoulder. 



But it is not only in its skeleton that the horse exhibits 

 traces of its affinity with its predecessors. On the hinder 

 part of the foot a little above the hoof is a structure known 

 to veterinarians as the " ergot." This, which apparently 

 attains its greatest development in Grcvy's zebra of 

 Somaliland, corresponds with one of the foot-pads of the 

 tapir, anil points to a time when the ancestral horses 

 applied the under surface of the fetlock to the ground. 

 More remarkable still are the callosities, "chestnuts," or 

 " castxirs," found on the inner sides of Iwth limbs in the 

 horse (inclusive of the Mongolian wild ponies), but only on 

 the fore-legs of the other species, which are likewise rudi- 

 mentary, or vestigial structures. Although it has been 

 suggested that these also represent foot-pads (with which 

 they by no means agree in position), it is far more 

 probable that they are really remnants of glands (similar 

 to those found in somewhat the same situation in the 

 hind-limbs of many deer and the front ones of many 

 antelopes), and that their disappearance as functional 

 organs was approximately coincident with that of the loss 

 of the face-glands of the hijiparions, owing to both being 

 no longer required. Even now, it is said, these callosities, 

 when freshly cut, exude a humoui- the smell of which will 

 cause a horse to follow for almost any distance. 



