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The Pamphlet Collection of Sir Robert Stout: Volume 29

The Teeth of the Horse

The Teeth of the Horse.

As might be expected, and as 1 have already said, the apparatus for providing this page 31 machine with the fuel which it requires is also of a very highly differentiated character. A horse has, or rather may have, 44 teeth, but it rarely happens that in our existing horses you find more than 40—for a reason which I will communicate directly—and in a mare it commonly happens that you find no more than 36, because the "tushes," or canine teeth of the mare, are rarely developed. Then there are some curious peculiarities about these teeth. As everyone who has had to do with horses know, the cutting teeth—the incisors—are six above and six below, and those incisors present what is called a "mark;" at least, that mark is usually present in horses up to a certain age. It is a sort of dark patch across the middle of the tooth. The presence of that dark patch arises from a great peculiarity in the structure of the horse's incisor tooth. It is in fact in sections shaped in this fashion (illustrating), considerably curved, and with a deep pit in the middle, and then a long fang. In the young foal this pit is very deep. As the animal feeds, this space becomes filled up with its fodder, that fodder becomes more or less carbonized, and then you have the dark mark, and the reason the dark mark serves as an indication of age is, that as the horse feeds this is more and more worn down, until at last, in an aged horse, the tooth is worn beyond the bottom of the pit, and the mark disappears. Then, as I said, the male horse generally has canine teeth. We need not notice their structure particularly. In the female, these are rarely present. Following that, you may notice a very small and rudimentary tooth, but that is very often absent. It really represents the first tooth of the grinding series. Then there are usually to be found six great teeth, with exceedingly long crowns. The crowns, in fact, are so long that the teeth take a very long time to wear down, whence arises the possibility of the great age to which horses sometimes attain. This is shown in the side diagram. Then the pattern and structure of a horse's tooth are very curious. The crown of the horse s tooth presents a very complicated pattern; that is to say, supposing this to be one of the grinders of the left side (illustrating) above, there is a kind of wall like a double crescent. Then there are two other crescents, which fall in that direction, and these are complicated by folds, and all the spaces between these crescentic ridges are filled up by a kind of bony matter which is called cement. Consequently, the surface of the tooth is composed of very uneven materials—of the hard mass of the tooth, which is called dentine, then a very much harder enamel, and a softer cement between, the practical effect of which is the same as the lamination of a millstone. In consequence of the lamination of the millstone the ridges wear less swiftly than the intermediate substance, and consequently the surface always keeps rough and exerts a crushing effect upon the grain. The same is true of the horse's tooth, and consequently the grinding of the teeth one against the other, instead of flattening the surface of the teeth tends to keep them always irregular, and that has a very great influence upon the rapid mastication of the hard grain or the hay upon which the horse subsists.

I think that will suffice as a brief indication of some of the most important peculiarities and characteristics of the horse. If the hypothesis of Evolution is true, what ought to happen when we investigate the history of this animal? We know that the mammalian type, as a whole—that mammalian animals—are characterized by the posses ion of a perfectly distinct radius and ulna, two seperate and distinct moveable bones. We know further that mammals in general possess five toes, often unequal, but still as completely developed as the five digits of my hand. We know further that the general type of mammal possesses in the leg not only a complete tibia, but a complete fibula. The small bone of the leg is almost always smaller than the tibia. The small bone of the leg is as a general rule a perfectly complete, distinct, moveable bone. Moreover, in the hind-foot we find in animals in general five distinct toes, just as we do in the fore-foot. Hence it follows that we have a differentiated animal like the horse, which has proceeded by way of evolution or gradual modification from a similar form possessing all the characteristics we find in mammals in general. If that be true, it follows that if there be anywhere preserved in the series of rocks a complete history of the horse, that is to say of the various stages through which he has passed, those stages ought gradually to lead us back to some sort of animal which possessed a radius and an ulna, and distinct complete tibia and fibula, and in page 32 which there were five toes upon the fore-limb, no less than upon the hind-limb. Moreover, in the average general mammalian type, the higher mammalian, we find as a constant rule an approximation to the number of 44 complete teeth, of which six are cutting teeth, two are canine, and the others of which are grinders. In unmodified mammals we find the incisors have no pit, and that the grinding teeth as a rule increase in size from that which lies in front toward those which lie in the middle or at the hinder part of the series. Consequently, if the theory of Evolution be correct, if that hypothesis of the origin of living things have a foundation, we ought to find in the series the forms which have preceded the horse, animals in which the mark upon the incisor gradually more and more disappears, animals in which the canine teeth are present in both sexes, and animals in which the teeth gradually lose the complications of their crowns and have a simpler and shorter crown, while at the same time they gradually increase in size from the anterior end of the series towards the posterior. Let us turn to the facts and see how they bear upon the requirements of this doctrine of Evolution.


Fore Foot. Hind Foot. Fore Arm. Leg. Upper Molar. Lower M