HORSES. 



491 



shown at C, which represents the jaw of a six-year-old horse, in which the third 

 incisor is partly worn, although still retaining a large mark. Up to five years 

 the age of a horse can consequently be determined with accuracy, and also approxi- 

 mately for some years longer. As a rule, the mark disappears in the first, 

 incisor of the lower jaw at six years, in the second at seven, and in the third at 

 eight, while in the corresponding upper teeth it persists about two years longer. 

 I) shows the upper jaw of a horse about eight years of age, when the mark has 

 nearly disappeared in the first incisor. After the mark has been lost in all the 

 incisors no indications of age are afforded. In old horses, as in E, a kind of spurious 

 mark is, however, produced, owing to the tooth having become so much worn down 

 that the pulp-cavity of its basal portion is exposed. Such spurious marks have, 

 however, no ring of enamel, and cannot be made to counterfeit the true mark, 

 although attempts to make them pass for this were, and perhaps still are, made by 

 unscrupulous dealers. When the spurious mark makes its appearance, the section 

 of each incisor forms a wide triangle, the broad and flattened crown having been 

 completely worn away ; and in extreme old age, when the teeth are ground down 

 to their very roots, as at F, they become very narrow. 



The Horse (Equus caballus). 



The horse differs from the other members of the genus in having the tail 

 thickly covered with long hairs from the root to the extremity, and also by the 

 mane being longer and more flowing. It has also a bare callosity on the inner 

 side of the hind-limb a little below the heel-joint, or hock, so that such callosities 

 are present in all the four limbs. Moreover, the head is smaller, the ears are 

 shorter, the limbs proportionately more elongated, and the hoofs broader than in 

 any of the other species. In colour, domesticated horses vary greatly, but they 

 seldom show any definite markings beyond a more or less distinct dappling. The 

 wild horses of the Asiatic steppes are, however, of a dun colour ; and since domesti- 

 cated dun-coloured individuals — especially in India and Argentina — frequently show 

 a dark streak down the middle of the back, and sometimes two or even three 

 transverse shoulder-stripes, and likewise dark bands on the limbs, it has been 

 inferred that originally the horse was a dun-coloured animal, more or less marked 

 witli dark stripes. The height among the domesticated breeds is no less varied than 

 the coloration. Thus, while cart-horses frequently attain the height of 17 or 18 

 hands (5 feet 8 inches or 6 feet) at the withers, the Shetland pony seldom 

 exceeds 11 hands (3 feet 8 inches), and is occasionally as low as 8| hands (2 

 feet 10 inches). The Asiatic wild horses are of medium stature. 



From what is known of the present wild or half-wild races, it is probable that 



the horse was originally an inhabitant of open steppes, where it dwelt in large 



droves headed by an old stallion. And from the habit displayed by domestic horses 



of clearing away the snow from their pasture in winter by scraping with the front 



hoof, Darwin was of opinion that the original habitat of the species was in 



regions where the ground is covered during a portion of the year with snow. 



So far as we know at present, the true horse in its original wild 



Distribution. * i.-ti >j. j 1 



state was mainly confined to Europe and Asia, although it extended 



