The teeth of the modern horse are, perhaps, the most perfect grinding battery that could be devised. There is an external layer of enamel, and a second inner ring of enamel around the pit of the tooth, and these grinding one upon and across the other, as the horse chews, make a most effective crusher and masticator of his food.
The incisor teeth of the horse have all the great peculiarity, not found in the teeth of any other mammal, and only in the Equidæ of comparatively recent geological periods, of an involution of the external surface of the tooth, by which what should properly be the apex, is carried deeply into the interior of the crown, forming a pit, the bottom of which becomes partially filled up with cement. As the tooth wears, the surface, besides the external enamel layer as in an ordinary, simple tooth, shows in addition a second inner ring of the same hard substance surrounding the pit, which, of course, adds greatly to the efficiency of the tooth as an organ for biting tough, fibrous substances. This pit, generally filled with particles of food, is conspicuous from its dark color, and constitutes the "mark" by which the age of the horse is judged, as, in consequence of its only extending to a certain depth in the crown, it becomes obliterated as the crown wears away, and then the tooth assumes the character of that of an ordinary incisor, consisting only of a core of dentine, surrounded by the external enamel layer. It is not quite so deep in the lower as in the upper teeth.
Between the canines and premolars is a space called the "bars" of a horse's mouth. It is here that the bit is placed, and not a few horsemen believe that this space in the horse's mouth has been gradually worn away by the use of bits until now it has become a regular bit-socket produced by the constant use of the horse by man. This is only one of the many absurd beliefs of the equinely wise in their generation. This space is no doubt the result of the lengthening of the jaw and head of the horse to reach his food. As his legs grew longer, placing him farther and farther above the ground, his neck grew longer and his jaw lengthened, and lengthened at a place where the grinding muscles would not interfere. The incisor teeth, three below and three above, developed more and more into effective nippers, and the premolars and molars into grinders of the most delicately complicated and complete kind.
It must not be supposed that this outline of the evolution of the horse is part patchwork and part surmise. On the contrary, the history of the evolution of the horse is the best-known illustration—and has been worked out with greater detail and success than any other example—of the doctrine of evolution by natural selection and adaptation to environment. "The skull of a man and the skull of a horse are composed of exactly the same number of bones, having the same general arrangement and relation to each other. Not only the individual bones, but every ridge and surface for the attachment of muscles and every hole for the passage of artery or nerve seen in one, can be traced in the other." The difference is mainly in this: in man the brain-case is very large and the face relatively of very small proportions; while in the horse the brain is very much reduced, and the face, especially the mouth, of great size. One can readily recall types of both animals where these differences sink to insignificance.
Even the man who is least interested in the ancestry of the horse cannot fail to see that the horse of to-day is the result of thousands of years of adaptation to his environment. His legs grew longer that he might go faster; his feet grew harder and encased themselves in a hoof; his head and neck grew longer that he might the more easily get his natural food; his teeth adapted themselves to the nipping, grinding, and mastication of that food; his bones, muscles, intestines, lungs, stomach, and general conformation inside and out, developed along the lines that have brought him to the point where he is far and away man's most useful sidepartner amongst all animals.
These matters are worth keeping in mind when you look over a horse with a view to his purchase. So far as your purse permits, you want the horse best adapted to your requirements. As you look him over, you have at least an intelligent notion of what you may expect from his past history and the points of the animal which indicate that he will bear out those expectations.
Let us suppose you want a harness horse for all-round work, one that will go single, double, or in a makeshift four. It is not required that he trot in 2.10, nor that he be able to be one of four to pull a loaded coach ten miles an hour.
First of all, he must see. Next he must have legs and feet to go on. Then he must have room for a furnace inside of him, to furnish the propelling force for those legs; and the more intelligence he has, and the more good-natured he appears, the better. Later, some of the more prominent good points and bad points of the horse will be noticed in detail, but it is as well to say at the start that the horse-dealer, or your most horsy friend, or the veterinary, avail little to find you the perfect horse.
All that reading, study, and experience can do is to avoid the worst faults, to keep in mind the salient good points, and then to make the very most of your purchase by care and training after he is your property. You may learn the good and bad points of a horse by heart and be as a babe in the hands of a clever horse-seller, whether he be professional or amateur. He knows the weaknesses, and also the good points, of what he has to sell, and you do not; and there are very few Launcelots in the horse business. We have all bought horses of a shrewd dealer and sold them again for five times what we paid; we have also bought horses and gladly disposed of them for one-fifth of the purchase price.
The main trouble in the whole matter is that buying and selling horses is looked upon by many people as either necromancy or thievery. It is neither. Study, intelligence, and experience are as necessary and as valuable in choosing a horse as in any other department of life, and in the end are just as valuable. Art critics have been fooled; book-worms have been deceived; lovers have been disappointed; financiers have gone into bankruptcy; educated men have been failures; but study, intelligence, and experience still rank high, none the less. It is possible that in this matter of choosing a horse the aleatory instinct in man comes to the fore and he is apt to think luck plays too great a part, but, aside from that, much the same qualities succeed here as elsewhere.