The series of permanent teeth in the Horse consists of three incisors, one canine, three premolars, and three molars in each jaw, or 40 in all; and is of great interest. The grinders (or molars and premolars) are remarkable for their length, the complexity of their pattern, and for the thick coating of cement which fills up the interspaces of the folds of enamel. The incisors present a peculiar pattern, which is of great importance in deciding the age of a Horse. Each is covered with a layer of enamel, which is folded inwards at the top, after the manner of the finger of a glove, the top of which has been pulled inwards, as is seen in the accompanying figure of a vertical section of an incisor tooth. This hollow is filled with cement, and its state of wear enables the age of the Horse to be ascertained, constituting “the mark.”
VERTICAL SECTION OF INCISOR OF HORSE.
(After Owen.)
e, enamel; c, cement; a a′, inverted fold of enamel, &c. (“the mark”).
A Colt when born has usually the first and second molars forced through the gum, and at seven or eight days old the two central incisor teeth appear; five or six weeks later, the next two incisors. At three months, they are equal to the central ones, and both pairs have nearly reached their natural level. A third grinder has then appeared; and about the eighth month, the third incisor above and below on each side. The Colt has now his full complement of incisor teeth—viz., six in each jaw. At six months the obliteration is apparent in the four central incisors; and at a year and a half the mark will be very faint in the central incisors, and diminished in the other two. A fourth molar appears at twelve months, and a fifth at two years. These are all milk or temporary teeth. At about three years old, the central pair of incisors, or nippers, both in the upper and lower jaws, are pushed upwards and removed by two permanent teeth, which take their place, and which are distinguishable from the milk teeth by their increased size; a three-year-old Colt, therefore, is easily recognised by the possession of these two new and enlarged incisors. At three years and a half the second incisors will have given place to permanent ones; and at four and a half the remaining incisors will have followed suit. Thus at four years old the central nippers will be fully grown; the next pair will not have attained their full size, and the corner temporary incisors will be worn small, and the mark nearly obliterated. At five years old the mark from the central teeth begins to be effaced, the next pair fully grown, and the corner pair only partially grown. Between the fourth and fifth year the canines begin to appear in the male, two in each jaw; in the female they do not appear until old age. At six years old the mark on the central nippers is much diminished, or obliterated. The other incisors will also be worn, and the canines fully developed. At seven the mark on the next pair of incisors is nearly gone, and the canines rounded at the point and edges. At eight the mark disappears from all the incisor teeth, and the canines are much rounder and blunter. From this time the age of a Horse is difficult to decide, and the teeth of the upper jaw seem to be the best guides. In the accompanying figure (B) the incisors of a Horse aged sixteen years are represented, in which it will be observed that the oval island of enamel, or “mark,” has been obliterated, and its place is indicated by a round, dark, island (A), composed of osteo-dentine, which has been formed within the pulp-cavity of the tooth. The absence of the fine white crystalline enamel from the centre of the tooth at once points out the aged Horse from that “in mark,” and renders all attempts to produce by artificial means the same pattern impossible, though this trick is by no means unknown or unattempted in horse-dealing.
INCISORS AND CANINES OF HORSE (B)
AND MARE (A).
BONES OF FORE (1) AND HIND (2) LIMBS OF HORSE.
A, Carpus (knee); A1, Tarsus (hock); B, Cannon bone; B1, Splint bone; C, Greater Posterior; D, Coronet; E, Coffin bone; F, Navicular.