The Foot as a whole.
The details I have given of the structure and uses of each separate part of the foot will, I hope, be sufficient to enable us to understand the form and action of the organ as a whole.
No one part of the foot is of greater importance than another, each is dependent for its highest development and soundest condition upon the integrity of neighbouring parts.
A weak wall allows of the flattening and spreading of the sole, whilst a weak sole permits contraction of the wall. Overgrown heels cause wasting of the frog, but low weak heels are usually accompanied by excessive development of frog.
The special function of the foot is to sustain the weight of the animal whilst standing or moving. The horse standing squarely on all four feet rests his weight chiefly on the lower circumference of the wall. On level ground the sole, on account of its arched form, takes no direct bearing, but if sole and wall be sound a proportion of all pressure applied to the wall is transmitted to the sole. So also must all weight imposed on the arch of the sole be transmitted, through its abutments or union with the wall, to the wall. If the sole be so thin that it yields to pressure then its proper action is destroyed, and instead of acting like an arch and supporting weight imposed on it, it yields and injury results. The arched form of the sole indicates that it was not intended to take a direct bearing on hard ground. On a soft surface the edge of the wall sinks and the whole under surface of the foot takes a direct bearing. Pressure of the sole on the soft surface does no harm because it is diffused evenly over the whole of the sole. We take advantage of this when the wall is diseased or injured, and we desire to throw on the sole a larger share of weight. We turn such animals out into a soft field or stable them on sand or saw-dust. Any system of shoeing founded upon the true form and action of the foot must recognise the arch, and not endeavour to force the sole to take a bearing for which it is not adapted. There is only one part of the sole which should act as a bearing surface, viz., that outer border which is firmly joined to the wall. This part—the abutment of the arch—is destined by nature to take a bearing and through it the whole of the sole supports its share of weight.
The frog takes a bearing on the ground but it has a weight sustaining function quite secondary to the harder and firmer parts of the hoof. It is formed of a softer horn, and it has above it only soft tissues which permit yielding. The frog then, when weight is placed upon it by the standing horse, recedes from pressure, and leaves the heels (wall and bars) to sustain the primary weight. Wall, sole, and frog, each take their share in supporting weight, but this function is distributed over them in different degrees, and it is fulfilled by each in a varying manner. During progression the foot is repeatedly raised from and replaced on the ground. It has not only to support weight but to sustain the effects of contact with the ground at each step, and the effects of being the point of resistance when the body is carried forward and the foot is again raised from the ground.
What part of the foot comes first to the ground? Many different answers have been given to this question. It has been said by some that the toe first touches the ground, by others that the foot is laid flat down, and by a few that the heel is the first part to come in contact with the ground. Fortunately it is not now necessary to argue this question on a purely theoretical basis. Instantaneous photography has shown that on level ground, at all paces, the horse touches the ground first with the heel. This fact gives significance to the structural differences we find between the front and back portions of the foot. At the back part of the foot we have the wall thinner than elsewhere, we have the moveable and elastic frog, the lateral cartilages, and the frog-pad. We have in fact a whole series of soft and elastic structures so arranged as to provide a mechanism best adapted to meet shock and to avoid concussion. Whilst drawing heavy loads, or ascending or descending hills, the horse may vary his action to suit the circumstances, and then we have the exception which proves the rule—then we have sometimes the heel, sometimes the toe brought first to the ground.
At the time when the foot first touches the ground, the leg is extended forward and the pastern is in the same oblique position to the shank as when a horse is standing. This obliquity of the pastern is another safeguard against concussion, and it renders impossible the first contact with the ground at any point other than at the heel. As the leg becomes straightened, the weight of the body is imposed upon the foot, but the greatest strain arrives just before the toe leaves the ground, for then there is not only weight to sustain, but the friction to be borne which results from the toe being the fulcrum upon which falls the whole effect of the muscular effort necessary to raise and carry forward the body of the animal. The front part of the foot is structurally well adapted for its use. It presents the thickest and strongest part of the horny covering, and, as an inside basis, it has the unyielding coffin bone. Thus we have at the toe strength and rigidity—at the heels strength and elasticity.
Another important point in the action of the foot is implied by the question—does it expand when weight is thrown on it? The principles of horse-shoeing require that this question should be answered. There are those who say that the foot does not alternately expand and retract as weight is placed upon or removed from it. There are others who assert that the expansion of the foot is an important natural function that must be provided for in any system of shoeing. It is agreed by most observers that at the upper border of the hoof, more particularly at the heels, expansion does occur. It is when we come to the lower border of the foot that the statements are most conflicting. Ordinary measurements taken at this part with calipers or by tracings on paper of the foot when raised from the ground and when resting upon it, show no variations in the width of the foot. These methods of measurement are not sufficiently delicate to be trustworthy. Experimentalists in Germany and in this country have recently used an apparatus by which the slightest variations are detected by electrical contact, and the results are very interesting. These experiments show that in a well-formed, healthy foot the hoof throughout its posterior two-thirds does expand to pressure, and perhaps that the arch of the sole is slightly flattened. This expansion is, however, comparatively slight—about equal to the thickness of a sheet of writing paper—and may practically be disregarded in considering the best methods of shoeing sound feet.
One result of these experiments is to show what an important part the frog plays in the foot, and also how the action of one part depends upon the conditions of others. When the frog rests firmly on the ground and weight is placed upon the foot expansion occurs, especially at the upper or coronary border of the hoof. When the frog does not touch the ground and weight is imposed upon the foot, contraction occurs. The explanation of this difference seems to be as follows. When weight is placed upon a foot, the coronet bone is depressed upon the soft mass of the frog-pad. With a sound frog taking a bearing upon the ground, the frog-pad cannot descend, and the compression to which it is therefore submitted causes it to bulge laterally and so expand the back of the foot. When the frog does not reach the ground and weight is placed upon the frog-pad, there is nothing to prevent it yielding downwards, and in so doing the fibrous bands connecting together the two lateral cartilages of the foot are depressed and the cartilages drawn together—hence the contraction of the foot. No better illustration could be given of the unity of all parts of the foot, and how one or many parts may suffer if the structure or function of one be defective.
There is one more movement of the hoof which is possible and which must be referred to, as it has been made the basis of a grave error in shoeing. I have said the back part of the foot is elastic and yielding. If you examine a shoe, so applied to a foot that an inch or more of its extremity has no contact with the hoof, you will find that when weight is rested on that foot the horn yields downwards and comes in contact with the shoe. This simply demonstrates that when there is nothing to support it the horn at the heels may be forced downwards. It is not a normal action, and in an unshod foot cannot occur on a level surface. The effect of this downward movement of the heels is to put a strain on the horn of the quarters. A shoe so fitted as to permit this evil is in common use, and no fault is more serious than thus forcing an unnatural action upon the hoof at every step. With unintentional irony this piece of bad work has been called "easing the heels."
In concluding this chapter, I would just repeat that the natural bearing surface of the horse's foot is the lower edge of the wall and that portion of the sole immediately in union with it; that the arch of the sole should not be in contact with the ground; that the frog ought to have a bearing on the ground, but ought not to be so prominent as to unduly share in sustaining weight. This natural bearing surface is what we want to utilize in shoeing. We put on a shoe merely to prevent excessive wear of the hoof. If we can protect the wall the frog can take care of itself, and we have only so to apply our shoe that we do not damage any useful structure or interfere with any natural function.
Note.—No person is expected to learn the structure of a foot entirely from this description. He must obtain two feet cut off at the fetlock joint. One he should soak in water till the hoof can be pulled off. The sensitive foot is then visible and the inside of the hoof; with these before him, the drawings and descriptions in this chapter will be of great assistance. The second foot he should have sawn vertically down the middle through the point of the toe, and again across the quarters, so as to show the inside of the foot from two different points of view; this will afford a view of the relation of parts.
[CHAPTER III.]
Preparation of the Foot.
The cheap wisdom of the amateur is often expressed in the remark "the shoe should be fitted to the foot, not the foot to the shoe." Like many other dogmatic statements this is only the unqualified assertion of half a truth. Foot and shoe have to be fitted to each other. There are very few horses whose feet do not require considerable alteration before a shoe can be properly fitted to them. As a rule, when a horse arrives at the forge, the feet are overgrown and quite out of proportion. In a few cases—as when a shoe has been lost on a journey—the foot is worn or broken and irregularly deficient in horn. In either instance the farrier has to make alterations in the hoof to obtain the best bearing surface before he fits a new shoe. The claim often made for some novel inventions in horse shoes, "that they may be fitted and applied in the stable by a groom or stableman" is evidence of a sad misunderstanding of the art of horse-shoeing. If shod feet always remained of the same shape replacement of shoes would be a very easy matter—but they never do. The living foot is constantly changing, and therefore the man entrusted with fitting shoes to it, must know what its proper form should be. When he finds it disproportionately overgrown he must know how much horn to remove—where to take away and where to leave alone. He must not carry in his head a theoretical standard of a perfect foot and attempt to reduce all feet to that shape. He must make allowance for varieties of feet, and for many little differences of form that present themselves in practice. He has, in fact, to prepare the foot for a shoe, and it is just as important to do this properly as it is to prepare a shoe for the foot. To fit a shoe to a foot which has not been properly prepared may be even more injurious to the horse than "to fit the foot to the shoe."
The general principle to be followed is—to remove superfluous horn, to obtain a good bearing surface for a shoe, to bring all parts of the hoof equally into proportion. A good foot so prepared, when the horse is standing on level ground should show, when looked at from the front, both sides of the wall of equal height; the transverse line of the coronet should be parallel with the line of the lower border of the hoof, and
the perpendicular line of the leg should cut those lines at right angles. ([Fig. 17]). When looked at from the side the height of the heels and the toe should be proportionate. When looked at from behind the frog should be seen touching the ground. On lifting the foot a level bearing surface wider than the wall should be presented, extending from heel to toe all round the circumference of the hoof; within this level border, the sole should be concave, strong, and rough.
Fig. 17.
In [Fig. 17] is shown the foot on its ground surface and from the side. The parallel lines are quite arbitrary, but assist in explaining how the proportion of the foot is to be attained. Both sides of the foot are of the same height. The bearing surface just meets the middle line. All the lines at coronet, heel, and toe, are at right angles to the perpendicular line. The side view shows the proportionate height of heel and toe, and the slope of the wall in front. Compared with [Figs. 22] and [23] deviations from proportion are seen.
These conditions are not attainable with all feet, but the prudent farrier does the best he can under the circumstances. It is easy to make the frog touch the ground by over-lowering the heels, but this is only introducing one evil in attempting to avoid another. Some feet have naturally a long toe with an excessive slope of the front part of the wall. To hide this defect a farrier may "stump up" the toe and leave the heels too high, but he does so at the expense of the horse's foot. Each foot requires treating with full knowledge of the form best adapted to its natural formation, and most capable of carrying a shoe.
The Instruments used to prepare a foot for shoeing are a rasp, a drawing knife, and a toeing knife.
The rasp is the most indispensable. It should be sixteen inches long, proportionately broad, and one part of it should be a file-surface. The shorter, narrow rasps do not afford all the advantages a farrier should possess to enable him to do the best work. To strike an even all-round level bearing surface on a hoof a farrier requires a large rasp, just as a joiner must have a large plane to produce a level surface on wood. Harm may be done by the careless use of a rasp, and a bearing-surface spoiled by the over-reduction of horn at one place. This fault may be aggravated by attempts to mend it, if such attempt take the form of further reduction of the whole hoof on a foot where horn is deficient.
The drawing knife is a comparatively modern instrument which replaced a tool called the buttress. A drawing knife is formed with great skill for the purpose of paring out the concave sole of the hoof, and has done infinite harm. In the days which have now almost passed away, when it was thought the proper thing to make the hoof look clean, smooth, and pretty, the drawing knife was the chief instrument in the preparation of the foot. Now, when nearly all men know that the stronger the sole and frog of the foot can be preserved the better for the horse, this knife is less used—and the less the better. The doorman, preparing a foot for the fireman to fit a shoe to, should not use a knife at all. The man who fits the shoe requires a knife to remove occasional little prominences of horn which are liable to cause uneven pressures or which are in the way of a properly fitted shoe—as, for instance, the edge of the wall to make way for a clip, or the angle of sole at the heel to prevent uneven pressure by the shoe.
The toeing knife usually consists of about a foot of an old sword-blade. This knife is held and guided by one hand of the farrier, whilst with the other it is driven through overgrown horn by the hammer. Skilfully used it is unobjectionable, and for the large strong hoof of heavy draught horses it saves a great deal of time and labour. For the lighter class of horses it is unnecessary, and for weak feet with a thin horn covering it is dangerous.
The toeing knife cannot leave a finished level bearing surface, and its work has to be completed by a few strokes of the rasp. A farrier should, therefore, never attempt to remove all the superfluous horn with the knife, he should leave some for the rasp so that in producing the final level surface no encroachment upon the necessary thickness of covering horn need be made.
Fig. 18.
The overgrown foot such as we find on a healthy horse that has retained a set of shoes for some weeks, or that has been without shoes on a surface not hard enough to cause sufficient wear, is quite unfitted to receive a shoe. It must be reduced to proportions. In [Fig. 18], I have attempted to show diagrammatically a side view of an overgrown hoof. The dotted lines at the base show two effects of lowering one part more than another, although both attain a level surface. In [Fig. 21] we see the result of over-lowering the heels, and in [Fig. 20] of leaving them too high. It may also be noticed that these conditions affect other parts of the foot; in fact not only other parts but the whole foot, and even the relative position of the foot to the leg. If we compare the proportionate foot, [Fig. 19], with the diagram [Fig. 21], it will be seen that by over-lowering the heels the slope of the front of the foot is increased, that the bearing surface from heel to toe is slightly increased in length, and that if the dotted perpendicular line be accepted as showing the direction through which the weight of the body passes, lowering the heels tends to put an increased proportion of weight on the back parts of the foot. If we compare [Fig. 19] with [Fig. 20] we see the effect of leaving the heels too high. The bearing surface from heel to toe is shortened, the slope of the wall at the toe is made less, and more weight is thrown upon the front parts of the foot.
Fig. 19.—A proportionate hoof.
Fig. 20.—A disproportionate hoof—heels too high.
Fig. 21.—A disproportionate hoof—heels too low.
Now these alterations in both cases affect not only the form of the foot but its relative position to the leg, and as the bones of the limb above are a series of levers connected by muscles and ligaments so placed as to be most efficient for movement, it is evident that alterations of the foot must affect the action of the limb. (Compare [Figs. 19], [20] and [21]) In the unshod horse roaming about there is a natural automatic return to proper relative position whenever it has been temporarily upset. A long toe is worn down and high heels are reduced to their proper level by friction. Not so a foot protected by an iron shoe. Wear is stopped, and a disproportionate hoof becomes more and more disproportionate. Temporary alterations of the position of the foot do little harm because they are permitted, within a margin, by the movement of joints and by the elasticity of muscles. When, however, an alteration of position is continued for many weeks it tends to become permanently fixed and may thus do a great deal of harm, which is not traced to its real cause because the effect is slow and gradual. It is important, therefore, to remember that the proportion of the hoof is to be maintained not only because it is necessary to the well-being of the foot; but because it affects the action of the whole limb. Too long a toe may cause a horse to stumble, and it must always increase the strain on the back tendons during progression. Heels too high prevent the frog from taking its proper bearing on the ground, and thus cause a loss of function in the back parts of the foot. An excessively high heel has a tendency to throw the knee forward and to straighten the pastern.
Fig. 22.—Heels high—under surface and side view.
Fig. 23.—Heels low—toe long.
It is impossible to lay down any hard and fast rule to guide a farrier in maintaining the proportions of heel and toe when reducing an overgrown hoof to proper form. Feet differ much in their natural formation, some are high-heeled and some low, some are straight in front some very much sloped, some are narrow and upright, others round and spreading. In [Fig. 22] the heels are too high, and the bearing surface does not reach the transverse line at the heels. The side view shows the excessive height of heels and the slope of the wall in front too upright. Great assistance is afforded the farrier in judging whether he should remove more horn from heel or toe by the appearance of the under surface of the foot. When the heels are much above the level of the frog there is an indication for their lowering. When the wall and bars are about flush with the angle of sole between them, there is, as a rule, no more horn to spare at that part. The length of the toe may be usefully gauged by the condition of the junction between wall and sole. When the sole is sound and strong all the wall above its level—wall unsupported by sole and showing on its inner aspect marks of the horny laminæ—may be rasped down so that a firm bearing surface is obtained consisting of wall and sole.
In [Fig. 23] the bearing surface at the heels is below the line marking a proportionate foot. The toe is too long and projects beyond the transverse toe line. The side view shows the low heel and the corresponding excess in the slope of the wall in front. The lower transverse line in each figure does not represent the ground, but is added to make clear the height of heels and length of toe.
Important as it is to maintain the relative proportions between the front and back parts of the foot, it is perhaps even more important to preserve the balance between the two sides of a foot. Both sides must be left of equal height. If one side be higher than the other a disproportionate amount of weight is thrown on the lower side, and more or less strain is put upon the ligaments of the joint above. In the [Figs. 24] one limb is shown with both sides of the hoof even, and the straight line of the limb cuts squarely across the transverse line of the bearing surface of the foot. In the the other limb one side of the hoof is too high, and in the preparation for shoeing only that side will require attention.
Fig. 24.
Through constant neglect of this point some feet become more or less permanently twisted—and the twist occurs at the coronet. The ground surface of a foot or a shoe always tends to remain at right angles to the direction of the limb, and when the sides of a hoof are allowed to remain of unequal height, the higher side presses the soft tissues of the coronet upwards. As the hoof grows from the coronet the side thus increased in height is not so noticeably uneven at the lower border of the wall as at its upper, and it cannot be restored to its proper form, except by months of careful attention and slight over-lowering at each shoeing. The diagrams ([Figs. 25] and [26]) represent vertical sections through a foot from side to side. One shows the wall uneven at the base, the other shows it uneven at the coronet.
Fig. 25.—Uneven at ground surface.
Fig. 26.—Uneven at coronet.
Peculiarities in the formation of a limb sometimes cause an apparent error in the relative position of the foot. Thus we have horses that turn their toes in, and those that turn their toes out. The cause of this twist takes place at the upper part of the limb, and it will be found that when the toes turn out the elbow turns in and vice versâ. The farrier can do no good to this formation, and attempts to alter it or disguise it by devices in shoeing are only injurious to the foot,—little deceptions worthy of a horse-coper.
A good bearing surface is the primary object aimed at in preparing the foot for a shoe. The relative position of the limb to the foot and the proper proportions of every part of the foot are matters to be borne in mind whilst the farrier is directly forming the bearing surface for a shoe. A good bearing surface must be even, level, on sound horn, and as wide as can be obtained to give stability to the shoe. It should not be limited to the wall. If, without over-reduction, the use of the rasp leaves a firm portion of the sole as a level surface continuous with the lower edge of the wall, the best of bearing surfaces is obtained. ([Fig. 27]). The bearing surface should be level from heel to toe, and no part of it can be singled out either as unfit to bear weight or as specially capable of enduring undue pressure. No broken or diseased horn should be used as bearing surface for a shoe. The broken horn should be removed and the diseased horn must, if not entirely removed, have so much of its border cut or rasped off as will prevent contact with a shoe.
Fig. 27.
After forming a level bearing surface with the rasp the sharp outer border of the wall is lightly removed with the file, so as to prevent splitting of the horn. The outer surface of the wall should not be rasped for it affords protection to the deeper layer of horn. The harder the outer layer of horn is kept the tougher and firmer is the whole thickness.
The Sole and Frog require very little attention. No sensible farrier now puts himself to the unnecessary trouble of cutting away horn that is wanted for protection. It was not the practical farrier that introduced the stupid "paring and cutting" that ruined horses' feet for nearly a century. It was the theorists, who taught expansion of the wall and descent of the sole as primary necessities in the function of a foot, who must be credited with all the evils resulting from robbing the sole and frog of horn. When a horse is shod with an iron shoe the wall cannot wear, and therefore it has to be artificially reduced at each shoeing. But the shoe does not interfere with the wear of a frog, and the farrier may safely leave that organ entirely to take care of itself. To some extent the shoe does interfere with the natural wear of the sole, and, therefore, any flakes of horn which have been prevented by the shoe from detaching themselves from the sole may be removed. The best way to remove these is with the buffer. The sole should not be pared out. I mean not only that the horn should be left strong, it should not be pared with a drawing knife, even if only a harmless surface layer be removed. The effect of leaving the sole of a shod foot with a smooth, level, pared surface is to stop its natural method of throwing off more or less broken flakes, and to cause it to retain that which is half loose until it is removed in one great cake.
A portion of the sole that requires a little special care in preparing for shoeing is the angle between the wall and the bars—the well-known seat of "corn." This must not be left so as to come in contact with the shoe. It is not to be "scooped" out, but it should be reduced distinctly below the level of the wall so that when the shoe has been in position for a week or two there is still no contact between the horn of the soles and the iron at that point.
Level or adjusted surface? The bearing surface of a hoof must, of course, be exactly adapted to the surface of shoe intended to be applied. Presuming that the best surface for a shoe is one level from toe to heel, I have insisted upon the necessity of a level bearing surface on the foot. There are, however, exceptional cases in which a level shoe is not used, and then we must alter the foot accordingly. Horses that wear the toe of a shoe out of all proportion to the rest of the iron may be beneficially shod with a shoe turned up at the toe. To fit such a shoe the hoof surface must not be made level, it must be rasped away at the toe and rounded off to follow the line of the shoe. In the three diagrams ([Fig. 28]) is shown—(a) side view of a foot prepared to suit the turned-up shoe at the toe, (b) a level line to fit a level shoe and, (c) a form often adopted on the Continent to suit a shoe fitted with a slight curve throughout. This adjusted shoe is designed to imitate the shape of the worn surface of an old shoe or to some extent the worn surface of an unshod foot. Every farrier knows how many horses go better after a level shoe has been worn a few days than when first applied, and it is argued, with reason, that the greater ease is due to the shoe being worn to the form offering least resistance to the movement of the foot in locomotion. I have nothing to say against this form of shoe and the necessary form of foot surface for it, except that it is more difficult to make than the ordinary level one. When adopted the curve of the foot should not be obtained by over-lowering the toe and heels but by leaving the quarters higher.
Fig. 28.—Three forms of bearing-surface.