The Horse's Mouth, Showing the age by the teeth

by Edward Mayhew

However, while the milk tooth is retained in the mouth the neck is not particularly well shown, because the gum encircling the crown in a great measure conceals that part. But the form of the outer surface of the crown can hardly be mistaken. In the foal’s tooth it more or less approaches to a semi-circle, from which the permanent teeth greatly differ, as will be seen by comparing the representations of the two as given in the plates. The outer surface likewise is characterized by peculiar indentations: a number of small channels run along it, taking a course from the neck towards the margin of the table, and giving an irregular fluted appearance to the enamel. There will be seen, on the crown of Figure 2, lines intended to convey an idea of the situation and direction of these little grooves. The table is always oblong, but the infundibula are generally absent after the second year, and when they are present, the cavities are narrow, and obviously of little depth. These numerous signs enable the milk tooth to be recognized with facility, at a single glance, for it is seldom that one of the various indications is absent; and after all have been impressed by observation, the milk tooth can hardly be mistaken.

26. The permanent incisors are indicated by their greater size, a circumstance which the foregoing wood-cut does not exaggerate. The gum is much further retracted, and this gives to these organs an irregular oblong figure, which is very different from the semi-circular shape of the milk teeth. The incisors, however, are not of equal length in all horses, and in some the gum may be so prominent as to give the permanent somewhat the appearance of a temporary incisor; other indications, however, even then, enable the different nature of each to be with certainty distinguished. The enamel is only partially exposed in the horse tooth; the shaded portion of Figure 1, in the preceding wood-cut, denotes the extent to which it is generally covered during the period of dentition; and when the teeth first appear, the enamel is wholly concealed by a covering of crusta petrosa. That covering is never entirely removed—a small portion of it, even in the oldest mouths, is seen near to the gums. It looks like an accumulation of tartar, and is most conspicuous in the tooth that has been newly cut. The presence or absence of this substance, therefore, should be noted, and moreover, the enamel surface should be further inspected. The numerous channels that give so peculiar a fluted appearance to the milk tooth, are not to be seen upon that of a permanent description; but in the stead are to be detected only one or two broad grooves, which extend the entire length of the crown. Figure 1, at page 48, indicates the shape and direction of the grooves upon the surface of the permanent tooth, though probably a better idea of them is to be derived from an inspection of the coloured engravings, in which they are more prominently exhibited. By means of such guides, the opinion is rendered positive, and the inspection of the table is hardly needed to confirm it; but the table affords corroborative evidence, which may be of service. The table is broader, and the infundibulum is deeper. In this latter cavity, food accumulates in the permanent, but rarely in the temporary incisor. The gum may so contract as to give to the tooth some appearance of possessing a neck, but in reality no such part is developed in the horse incisors, as will be seen by referring to the previous cut, which may, with profit, be compared with the coloured engravings, which depict these members as they are exhibited in the mouth of the living animal.

27. The temporary cannot be well distinguished from the permanent molars, while the horse is alive. It is true that the table of the first is somewhat narrower than, though of equal length, with that of the last; but the difference is not so marked as to justify an opinion being pronounced upon the imperfect inspection which, under the most favourable circumstances, can be made of these organs. The number of the molars may, however, be counted, and from this the age of the animal deduced with correctness. The operation can be at all times performed, and the fact ascertained. When, however, removed from the jaw, the character of the molar is easily recognized, for the difference in the length and shape of the fang renders it then impossible to confound the temporary with the permanent tooth.

28. The various points which denote youth must now be noticed. The remarks on this subject, however, must be confined to the mouth, to which this treatise is devoted. In the foal, the membrane of the mouth is of a delicate pink colour, suggestive of its high vascularity. The gums are prominent, for as the permanent are cut posteriorly to the milk incisors, and the germs of the horse teeth are developed even at the time of birth, the anterior part of the jaw is pushed forward to make room for their growth. This gives the little animal somewhat the appearance of being parrot-mouthed, as will be observed by referring to the coloured plate of nine months. Then the palate is low in its position, and the bars appear almost on a level with the tables of the upper teeth, and may even descend beyond them. The lower jaw, also, if felt, will be found to be quite round; and the face, if observed at that part under which the molar teeth are situated, will seem full, or the cheek will look a little blown out. These last signs, more or less, remain till the process of dentition is completed.

29. The indications of age are no less deserving of notice. The edges of the lower jaw become sharp, and ultimately retracted; the cheeks grow flat; the membrane of the mouth loses its vascularity, and puts on a dull yellowish colour; the gums look hard, and the front of the jaw becomes narrower, while at the same time it inclines more backward, causing the teeth to project horizontally. The inclination which age gives to the teeth, will be easily perceived by comparing the coloured engravings with each other; and the peculiarity of the upper and lower incisors not being perceptible at the same time in the mouth of a thirty-years old, entirely springs from the acuteness of the angle which they form at that period. The bars, as years accumulate, also change their positions, being drawn upwards. From the space between the corner incisors and the first molars, the tongue on either side protrudes, as if the narrowed cavity left not sufficient room for the organ to repose in. The extent to which the tongue will project may be conjectured, by regarding the representation of it given in the coloured plate of the thirty-year old mouth. At that age, the protrusion is too strongly marked to escape the observation of any one whose attention has once been directed to the circumstance. Accompanying the inability to retain the tongue within the jaws, is a constant flow of saliva, which continually falls from the mouth of the old horse when the lips be held apart. The latter fact, the author, when he made the drawings for the present work, had ample experience of, as in some instances it occasioned serious delay.

30. The incisor teeth, in old age, have their characteristic signs. Mostly they appear unnaturally long, though in rare instances they are worn down almost to the gums. When long, they will generally show interstices dividing them, such interstices, however, not being free, but occupied by a compact mass of foreign matter, derived from the food, and having a black colour. The reader will, by turning to the coloured plates of twenty and thirty years, see these accumulations indicated. When the incisors are very short, they are arranged in a different order to those of the young animal. The tables of the teeth of the young horse, form almost a semi-circle; in the adult animal, they gradually assume a crescentic order, and as age progresses, they ultimately range, more or less, in a straight line. The teeth also look narrower as the fangs descend with the wear of the organs, and in colour they slightly change. The enamel loses much of its semi-opaque and characteristic appearance, assuming a more dull aspect, and a yellowish tint. The crusta petrosa is to be seen only near to the gums, and within the grooves, which often are deep and very well defined, and within which the remains of the once-investing membrane becomes almost black. Then again, the tables themselves change their shape as the years increase. At first, these surfaces are of an oblong and somewhat oval figure; by degrees, however, they become angular, and ultimately more or less square. The continental authors have been very minute, and not a little profuse upon the changes of form which the tables undergo, and attribute the alteration to the gradual wear of the teeth. The correctness of this view they endeavour to establish by sawing a tooth through at various places, and attempting to show, that the forms of the surfaces exposed by this process correspond to the shapes assumed by the table during the progress of age. Their deductions can, in the study, be made to appear true, but in the stable will not bear the absolute application to which these writers would put them. By means of this test, Pessina asserted he would tell the age of a horse, accurately, up to the twenty-second year. The Girards acknowledge the tables will not guide them so far, but nevertheless are willing to apply them during the first seventeen years of the animal’s life. I leave the reader to form his own opinion of the value of such speculations—for while I confess they are of some worth as guides to the primary study, and helps to the proper understanding of the cause of those changes of figure to be anticipated—I am not satisfied that any rule drawn from them can be depended upon. For that reason I shall hereafter present the reader with figures of the tables taken from authenticated mouths, rather than amuse him with speculations, which, however imposing they may seem to the ignorant, practice soon discovers to be no more than remote and plausible possibilities.

31. Some judges depend upon the tushes as indicative of the age, and taken in conjunction with the other parts they afford corroborative evidence; singly, however, they should not be relied upon, nor should too much weight at any time be placed upon their appearance. In the first place, the tushes are cut irregularly; they may appear in the mouth between the second and third, and they may not pierce the gums so late even as the eighth year; the periods named being of course the extremes. As a general rule, however, they come up between the fourth and fifth year. The custom, however, which Nature so frequently disregards, can afford no positive guide to the judgment, and the wear which may begin thus early or late, should not be too particularly insisted upon. The tushes when they first show are shaped somewhat like a spear head, smooth and rounded on their external surfaces, but grooved on the side which touches the tongue, pointed at their extremities, and sharp at their edges. The inclination of the young tush is oblique, standing forward, and the situation is comparatively near to the incisors. As the animal’s age advances, the tushes retract, the grooves on the inner surfaces wear out, and the space which separates them from the incisors increases: all observations, however, concerning the tushes, must be accepted with much allowance, for these teeth are very irregular. As a general rule, the lower tush becomes blunt, or rounded at its point and edges, and also of considerable length, while the upper is often so diminished as to be worn almost to the level of the gum. In stallions, kept only for service, the lower tush, however, frequently attains a great length, presenting the appearance depicted in the coloured engravings of the mouths at twelve and sixteen years. In those plates, the reader will observe the tushes no longer point in a forward direction, but have a decided inclination outward, and somewhat backward also. Another indication of extreme age is also worthy of notice, although, if too absolutely relied upon, it may occasionally mislead. Tartar, not generally found in any quantity upon the other teeth in the horse, accumulates around the tush, and in very old animals almost conceals it. This excessive deposit I have rarely observed in horses of moderate age.

32. The wolf’s teeth or eye teeth aid us in judging of the age; though we are bound to state of these that they can be received only as presumptive evidence. The wolf’s teeth have not been before alluded to, because they are not concerned in mastication, and are no more than the representatives of those organs which form the continuous chain in the mouths of some other animals. These teeth appear to be of no use to the horse. They are little nodules of tooth-like structure, having minute fangs, which are inserted immediately anterior to the first molars of the upper, being rarely seen in the lower jaw, and when present there, always being even yet more diminutive. These wolf’s teeth are generally shed with the first temporary molars, and therefore if they can be seen, it may be assumed that the permanent molars have not begun to appear. The assumption, however, must not be converted into an assertion; for in some instances the wolf’s teeth are retained, and, in a few heads, will remain after the horse has reached an age far beyond that of colthood: their presence, therefore, rather leads our expectations than confirms our judgment.

33. The mode in which the horse cuts his teeth remains to be pointed out. It is generally said, that the tooth, originally growing in its circumscribed cavity, pushes its way through the parts which oppose its entrance into the mouth. So mechanical an idea is characterized by a small amount of physiological knowledge, and it is time the notions which attributed development to mere force were discarded. The tooth is first a pulpy mass, very soft and highly vascular; the superior part, or that part which primarily shows itself above the gum, is the first to become consolidated. Enamel and ivory are there simultaneously deposited, and gradually these extend towards the fang. When a portion of the fang is completed, and the time has arrived for the tooth to be cut, those structures which oppose the egress of the tooth are absorbed; the absorption taking place, not only on the internal surface, against which the young tooth has been supposed to exert its force, but also upon the external parts, upon which it could have no effect. By absorption the barrier is removed and the tooth then comes forward. The process is very beautiful, and no less worthy of admiration is the manner in which the milk teeth are shed. The incisors lose their fangs, and just when the permanent teeth appear, the crown of the temporary ones is removed from the mouth. The removal of the fangs of the milk incisors is the result also of absorption, and the same process effects the removal of the temporary molars, only its operation is not precisely similar; for in these last, not only the fang but the greater portion of the crown is taken away, and little more than the table is cast off when the remnant of what once was a tooth is at length shed. The process of cutting the molar teeth will be more clearly comprehended by referring to the annexed wood-cut, in which the darkened spots indicated by the line running from a denotes the permanent tooth already through the gum and in the mouth, though still covered and partially concealed by the retained table of the temporary grinder c. The appearance of the table of the temporary molar when cast off is shown in the figure immediately underneath, to which the letter c is also affixed, and the projecting portions ascending from its edges exhibit the last remnants of what originally was the fang: b b are molars, well up and worn to a level.