Some years ago Mr. Sidney Galvayne made public a new method of judging the age of the horse up to the latest period of the animal's life, and as his system has proved to be extremely useful when it has been applied to old horses, the date of whose birth happened to be known or could be ascertained within reasonable limits by collateral evidence, it is desirable to rely upon that system exclusively after the age of ten years.
Mr. Galvayne's discovery, as it may be called, is based on the existence of a groove in the fang of the upper corner incisors. The groove is not visible in the living animal until the age of ten years, by which time the bone of the alveolar cavity, which contains the tooth, has shrunk. The tooth meanwhile has grown, or has been pushed forward, to an extent corresponding with the wear at the surface, and the lateral groove is exposed as shown in the next figure (fig. 618).
Fig. 618. - (a) Groove at the side of Upper Corner Incisor at ten years.
Fig. 619. - (b) Groove reaching half-way down the Corner Incisor at fifteen to sixteen years.
The method of judging the age from the point indicated in the above illustration is extremely simple. It is only necessary to recollect that, as the tooth continues to grow, and is at the same time constantly being worn, that part of the groove which is shown in fig. 618 will, at a certain period, be at the bottom of the tooth, and therefore year after year more of it will be seen. Eleven years, according to Mr. Galvayne's calculation, will elapse before the bottom of the groove reaches the cutting edge of the tooth. At that time, consequently, the animal will be twenty-one years old. When it is half-way down the tooth, as shown in fig. 619, the horse will be about sixteen years old.
The appreciation of the exact value to be attached to the gradual advance of the groove year by year can only be the result of close observation, but in any case the method is more reliable than any other which has been devised. The next illustration shows the groove extending the whole length of the tooth at the age of twenty-one years (fig. 620).
From the age of twenty-one another process has to be noted, which ends with the total obliteration of the groove through the combined processes of wear and growth in the course of another nine or ten years. The drawing below shows that the groove has been half worn out from below, and the smooth, ungrooved surface of the previously concealed portion of the organ has grown downwards, which indicates the animal to be twenty-six years old (fig. 621).
In the course of another four or five years only a trace of the groove is seen at the cutting edge of the tooth, the structure up to the place where the gum encircles it being perfectly smooth. This condition is shown in the next drawing and indicates that the animal is thirty years old (fig. 622).
It cannot, of course, be suggested that any great importance has to be attached to the means of judging a horse's age from twelve, when the animal would be called aged up to thirty, when he would usually be worn out; but the horseman will find some interest in comparing the drawings which have been given with the mark in the corner tooth in any cases which may come under his notice of horses whose ages are accurately known.
Fig. 620. - (c) Groove extending the whole length of the Corner Incisor at twenty-one years.
Fig. 621. - (d) Groove grown down from the gum, leaving the upper part of the tooth smooth at twenty-six years.
Fig. 622. - (e) Groove nearly worn out, upper part of incisor round and smooth, at thirty years.
* * * The illustrations in this section are reproduced by permission of the Council of the Royal Agricultural Society of England from the pamphlet by Professor Sir George T. Brown, C.B., entitled "Dentition as Indicative of the Age of the Animals of the Farm".
PLATE LXV1I. DENTITION OF THE HORSE AT VARIOUS AGES - V.
A. Six-year-old New Forest Pony (female) - all the teeth are permanent and show effects of wear.
B. Very aged New Forest Pony - the fangs of the teeth have become forked, and the crowns are thin as the result of wear.