Horseshoeing Part 2

A Text-Book of Horseshoeing

by A. Lungwitz and John W. Adams Copyright 1897

This is the second part in what will be a complete reprint of Lungwitz & Adams’ important ‘Textbook of Horse-Shoeing’ originally written in the 1880’s and containing some remarkably modern information. This volume goes into the greatest detail on the subject and with an intelligent clarity that belies how old it is. Coming as it did at the end of the first horse era, and well before anyone might have reasonably predicted the advent of the automobile and tractor, it is apparent how important the equine was to the whole of society. The authors, of Germany and Pennsylvania, compiled what was, at the time, to be the ultimate word on the subject. As with all of the reprints we have offered over forty years time, we trust that readers will be triggered by these words to complete their education with diligence and introspection. Just because something is old doesn’t always make it right, and of course just because something is new doesn’t make it the true culmination either. LRM

CHAPTER II

THE FOOT IN ITS RELATION TO THE ENTIRE LIMB

As there are well-formed and badly formed bodies, so there are well-formed and badly formed limbs and hoofs. The form of the hoof depends upon the position of the limb. A straight limb of normal direction possesses, as a rule, a regular hoof, while an oblique or crooked limb is accompanied by an irregular or oblique hoof. Hence, it is necessary, before discussing the various forms of the hoof, to consider briefly the various positions that may be assumed by the limbs. In this discussion we shall deal with the living horse.

A. Standing Positions of the Limbs

The position of a limb depends upon the varying lengths of its component bones and the angles at which they meet one another. To judge the standing position of a fore-limb one must stand in front of the horse; to judge a hind limb, stand behind the horse; the backward or forward deviations of both front and hind limbs are judged by standing at the side. But a horse does not always move as his standing position would lead one to suspect; standing and moving are different. Therefore, in order to arrive at a proper judgement, one must observe the limbs both at rest and in motion.

(a) The position of a limb viewed from in front is normal or straight (Fig. 44) when it stands vertical or perpendicular. A plum-line dropped from the point of the shoulder (middle of the scapulo-humeral articulation) should pass down the middle line of the limb, dividing it into inner and outer halves of equal width, and meeting the ground at the middle of the toe.

In the base-wide standing position (Fig. 45) the plumbline falls to the inner side of the limb; the limb extends obliquely downward and outward. To this class belong also the knee-narrow (knock-kneed) position, in which the knees are too close together, while the feet stand wide apart, and the toe-wide position (splay-footed, Fig. 46) in which the toes point obliquely forward and outward. In base-wide positions either the entire limb extends downward and outward or the foot alone is turned outward.

The base narrow position is frequently observed in horses with very wide breasts. The limbs run downward and inward, a plumb-line dropped from the point of the shoulder falling to the outer side of the leg and foot. A special form of the base narrow position is the toe-narrow or pigeon-toed position (Fig. 47). In some instances the legs are straight and perpendicular down to the fetlock, while from there to the ground the phalanges incline obliquely inward. Another form is the knee-wide or bandy-legged position, in which the knees are placed too far apart, while the cannons and phalanges incline downward and inward.

The position of a fore-limb viewed in profile is regular or normal (Fig. 48) when a perpendicular line dropped from the tuberosity of the acromian spine (point of union of the upper and middle thirds of the scapula or shoulder blade) divides the leg from the elbow to the fetlock into anterior and posterior halves of equal width, and touches the ground immediately back of the bulbs of the heel. A perpendicular line dropped from the point of union of the middle and lower thirds of the scapula (shoulder blade) will cut the humerus into halves, and meet the ground between the toe and the heel.*

*In station of rest, the normal position of a fore-leg, as seen from the side, is somewhat different. The station of rest is the position that is maintained with the least possible muscular effort. With gradual muscular relaxation the head and neck sink to a point somewhat below the line of the back, the top of the shoulder blade sinks a little, and the shoulder and elbow joints move forward till the centre of the elbow joint is directly above the ground-surface of the hoof. Therefore, when a horse at rest stands firmly on all four feet, the fore-leg viewed from the side, has a normal (regular) direction, when a perpendicular line dropped from the tuberosity of the aromian spine passes through the middle of the elbow joint and meets the ground near the middle of the hoof.

The foot-axis (line of direction of the three phalanges) and the wall at the toe form an angle of from forty-five to fifty degrees with the horizontal ground-surface.

From this normal or regular standing position, there are deviations forward as well as backward.

Forward Deviations. — “Standing in front” or “camped in front” (Fig. 50) is that position in which the entire leg from the body to the ground is placed too far forward. Sheep-kneed (Fig. 51) is that position in which the forward deviation is from the knee downward, the knee being placed too far under the body. “Weak-jointed,” “low-jointed,” or “acute-angled” (Fig. 52) is that position in which the limbs are perpendicular and straight down as far as the fetlock-joint, but the feet are placed too far in front.

Backward Deviations. — Standing under in front (Fig. 53) is that deviation in which the entire leg from the elbow down is placed back of the perpendicular line and, therefore, too far under the body. When this deviation affects only the cannon bone, the horse stands bent forward at the knees, – a condition known as “goat-kneed,” “buck-kneed,” “over in the knees,” or, more commonly, “knee sprung” (Fig. 54). When the backward deviation is only from the fetlock down, the animal is said to stand upright or “straight in the fetlock.”

(b) A hind leg viewed from behind is said to be regular or straight (Fig. 55) when a perpendicular line dropped from the tuberosity of the ischium (see Fig. 1, 9” in Horseshoeing Part 1A) divides the entire limb into inner and outer halves of equal width and touches the ground opposite the median lacuna of the frog. Seen from the side, this line just touches the point of the hock and, passing down at some distance from the flexor tendons, meets the ground considerably back of the heels. A perpendicular line dropped from the hip joint should pass through the foot, meeting the ground half-way between the point of the toe and the heel (Fig. 49). There are base-wide, base-narrow, toe-width, and toe-narrow deviations in the hind limbs as in the fore-limbs.

The hind limbs are base-wide when they, either as a whole, or in part, deviate outward from the normal. The “cow-hocked” position (Fig. 56) is an example of the base-wide; in this case the points of the hocks are too close and turn towards each other, while the feet are widely separated and the toes turned outward. Base-narrow is that position of the hind legs in which either the entire leg deviates to the inner side of the perpendicular (Fig. 57), or the leg is about perpendicular down as far as the hock, but below this joint runs downward and inward (Fig. 58). In this latter case the hocks may be too far apart, the leg is bend outward at the hock and the animal is termed “bandy-legged,” “bow-legged.”

Viewing a hind limb from the side, it may be observed to deviate either forward or backward from the normal. Among forward deviations is the so-called “sabre-leg” or “sickle-hock” (Fig. 59), in which the hock-joint is too much flexed, the foot placed too far forward under the body, and the fetlock too slanting. In the position known as “camped behind” (Fig. 60) the leg is behind the body and the pastern is too upright, too nearly vertical.

It is possible for each limb of the same horse to assume a different direction. It more often happens that if the forelimbs are base-wide the hind limbs are base-narrow, or vice versa. While there are some other deviations that differ somewhat from those already described, they are of less importance to the horseshoer.

B. Forms of Feet, Viewed from in Front, from Behind, and in Profile.

In all the various positions of the limbs we find the feet in one of the following three forms, or very closely approaching one of them. By means of a proper knowledge of these three forms, the judging of the form, flight of the foot in traveling, and preparation of the hoof for the shoe, as well as the choice of the length of the shoe, are regulated, facilitated, and simplified.

Whether a horse’s feet be observed from in front or from behind their form corresponds to, or at least resembles, either that of the regular position (Figs. 61 and 62), the base-wide or toe-wide position (Figs. 63 and 64), or the base-narrow or toe-narrow position (Figs. 65 and 66).

By the direction of the foot-axis — that is, an imaginary line passing through the long axis of the three phalangeal bones (Figs. 61, 65, 67, 68, and 69) — we determine whether or not the hoof and pastern stand in proper mutual relation.

In regular standing position (Figs. 61 and 62) the foot-axis runs straight downward and forward, in the base-wide position (Figs. 63 and 64) it runs obliquely downward and outward, and in the base-narrow position (Figs. 65 and 66) it runs obliquely downward and inward.

Viewing the foot from the side, we distinguish the regular (normal) position (Fig. 68), and designate all forward deviations as acute-angled (long toe and low heel, Fig. 67), and all deviations backward from the regular position as upright (short toe and high heel, Fig. 69), steep-toed, or stumpy.

When the body-weight is uniformly distributed over all four limbs, the foot-axis should be straight (Figs. 67 and 69), not “broken” (bent); the long pastern, wall at the toe, and foot-axis should have the same slant.

A peculiar form of foot is the so-called bear-foot (Fig. 70), in which the foot-axis, viewed from the side, is broken strongly forward at the coronet. The wall at the toe stands much steeper than the long pastern and is more or less convex; in other words, a low-jointed, sloping pastern is attached to an upright hoof. Such a foot is sometimes improperly called a “club-foot”.

C. Lines of Flight of Hoofs in Motion.

If we observe horses moving unrestrained over level ground, we will notice differences in the carriage of the feet. Viewed from in front, or from behind, in the regular standing position of the limbs the hoofs are carried forward in a straight direction, — that is, in a line parallel with the median line of the body (Fig. 71). The toes likewise point straight forward; the hoofs alight properly (flat) on the ground. If the horse stands base-wide, the hoof is carried in a circle; from its position, which is behind and well out from the median line, the hoof passes first forward and inward until it is close to the supporting leg, and then outward to the ground (Fig. 72), where the shock is received principally upon the outer toe. The toes point either directly forward, as in the regular standing position (Fig. 72), or forward and outward as in the toe-wide position (Fig. 73). In the toe-wide position the hoof in its flight may cross the median line.

Exactly the reverse is true of the horse that stands base-narrow; in this case the hoof is moved in a circle whose convexity is outward, — that is, the hoof from its position behind, and close to the median line, is carried forward and outward and then inward to the ground (Figs. 74 and 75).

Viewed from the side, the line of flight of the hoof is determined largely by the obliquity (slant) of the foot-axis.

1. With a straight foot axis of normal slant (45º-50º, Fig. 76, A), the hoof follows the are of a circle and reaches its highest point when directly above the supporting hoof, i.e., when half-way in the stride.

2. With a straight, but acute-angled foot-axis (less than 45º, Fig. 76, B), the hoof rises rapidly, reaches its highest point before it has completed the first half of the stride, i.e., before it has passed the supporting hoof, and descending gradually in a long curve alights easily on the ground.

3. With a straight, upright foot-axis (55º or more, Fig. 76, C), the hoof rises slowly, reaches its highest point in front of the supporting hoof, from which point it descends rapidly. The gait is “choppy,” and in the saddle horse unpleasant for the rider. The length and the height of the stride are greatest in acute-angled feet; least in upright feet. Furthermore, length and height of stride are in a measure dependent on breeding, training, condition of the legs (whether stiffened by use or disease), length of the hoof and the weight of the shoe.

Many deviations in the line of flight of hoofs and in the manner in which they are set to the ground occur; for example, horses heavily burdened or pulling heavy loads, and, therefore, not having free use of their limbs, project their limbs irregularly and meet the ground first with the toe; however, careful observation will detect the presence of one or the other of these lines of flight of the foot. Irregular carriage of the feet renders a horse unsuitable for general purposes only when it is very pronounced, in which case certain troublesome conditions, such as interfering and disease of joints, are of frequent occurrence.

D. The Influence of Weight in the Shoe or Otherwise Attached to the Hoof, in Altering the Flight of the Hoof.

There is nothing mysterious in the effect of weight upon the flight of the feet. On the contrary, the lines of flight are determined (as shown in Figs. 71-76), first, by the relation of the transverse axes of the hinge-joints of the leg and foot to the line of the progression (median line); second, by the length and obliquity of the hoof and pastern; third, by the height and length of stride which is natural to each individual.

Weight induces higher action and a longer stride. Inertia increases with the weight. A heavy shoe cannot be snatched from the ground as quickly as a light one, but when moving forward at a given velocity its greater momentum (momentum=mass (wt) x velocity: m=wt x v) carries the foot farther forward than does the lighter shoe. Thus, the heavier shoe, or weight is placed, i.e., the nearer to the toe it is placed, the greater the muscular effort required to start it and to stop it.

Height of action, though largely the result of breeding, temperament, and the exhilaration that accompanies perfect health and entire absence of muscular fatigue, is to a certain extent influenced by the inclination of the pastern and toe to the cannon. The acute-angled foot, in the folding of the leg during the first half of the stride, moves through a longer are of a circle whose centre is the fetlock joint than does the normal or the upright foot; rises more rapidly and to a higher point. (See Fig. 76, B) When the momentum of a foot moving rapidly and abruptly upward is increased by weight the result is extreme and even exaggerated flexion of all joints of the leg, and by allowing the hoof to grow long the flexion is still further increased. In the show ring, harness horses with fair natural action may be made to “climb” by shoes weighing from thirty to sixty ounces upon hoofs an inch or more longer than normal. The leverage of a heavy shoe on a long hoof is excessive, fatiguing and most injurious to ligament, tendon, and muscle. The action, while high, is labored, pounding and altogether inelegant.

In training of trotters weight is often used to increase the length of the stride, or to cause a higher folding of a front foot, in order to prevent “scalping” or “speedy-cut.” As soon as the new gait becomes a fixed habit the weight should be gradually lessened. Weight is carried with less fatigue at a trot than at a pace, or at a gallop. It therefore steadies a trotter that is inclined to pace, or “break” into a run. The increased momentum of the weighted hoof makes for rhythm or movement, and increases the difficulty of skipping, dwelling, or mixing gaits.

In the base-wide (toe-wide) and base-narrow (toe-narrow) standing positions, the flight of the hoofs, as seen from in front or behind, is not straight forward, i.e., parallel to the line of progression of the body, but in arcs of circles. (See Figs. 72-75) In these cases, increasing the weight of the hoofs, by increasing the momentum, must of necessity increase the tendency of the hoofs to move off at a tangent to the curves which they describe. In other words, weight increases the centrifugal force of a body moving in a curve. The outward swing of the hoofs of a base-narrow horse (paddling), and the inward swing of a base-wide horse (interfering), are made more pronounced by adding weight to any part of the hoof. The centrifugal force is greatest in base-wide feet when the weight is on the medial, or inner side of the hoof; in base-narrow feet when it is on the lateral or outer side.

A side weight, or side weight shoe is often of service in a crossfiring pacer. This animal usually stands base-narrow (toe-narrow) behind, and in motion his hind hoofs describe a curve at first forward and outward and then inward till contact is made with the diagonal hoof or leg. The added weight (placed on the outer side) by increasing the centrifugal force carries the hoof just enough farther from the centre around which the hoof swings to prevent contact. (See cross-firing)

Finally, it must not be forgotten that weight is always weight; that it cuts speed and devours endurance.

E. Forms of Hoofs.

A front hoof of the regular standing position (Fig. 79). The inner and outer walls differ but little in direction and thickness. The outer wall is a little thicker and somewhat more slanting than the inner (see Figs. 61 and 62, Horseshoeing Part 2A), and its outer circumference describes a larger arc of a circle, — that is, is more curved, as can be seen both at its plantar border and at the coronet. The length of the quarter in relation to the length or height of the side wall and toe is about as 1:2:3. The toe forms an angle with the ground of forty-five to fifty degrees (see Fig. 68, Horseshoeing Part 2A). The direction of the wall at the toe, viewed from the side, should be parallel with the direction of the long pastern.

A hoof of the base-wide position (Fig. 80) is always awry, because the outer wall is naturally somewhat longer and decidedly more slanting than the inner (see Figs. 63 and 64). The plantar border of the outer wall describes a large arc, whose sharpest curvature is where the side wall passes into the quarter. The plantar border of the inner wall is straighter (less curved); the outer half of the ground surface (sole) of the hoof is, therefore, wider than the inner. So long as the hoof is healthy, both branches of the frog are equally developed. The wryness of the hoof depends upon the direction of the limb, therefore, a base-wide hoof should be regarded as a normally wry hoof, to distinguish it from hoofs which are wry from disease.

A hoof of the toe-wide position (Fig. 81) is distinguished from the preceding by the bending or curvature of the plantar border of the outer toe and inner quarter being often decidedly less pronounced than on the inner toe and outer quarter; therefore, two short curves and two long curves lie opposite each other; in other words, the inner toe and outer quarter, lying opposite each other, are sharply curved, while the outer toe and inner quarter, lying opposite each other, are much less sharply bent or curved. The toes are turned out. The feet are not set down flat upon the ground, but meet it with the outer toe.

A hoof of the base-narrow position is normally wry, but never so pronounced as a hoof of the base-wide position. The inner wall is but little more oblique than the outer, the difference being most noticeable at the quarters (Figs. 65 and 66). The curve of the plantar border of the wall is similar to that of a regular hoof, except that the inner side wall and quarter are a little more sharply curved in a base-narrow hoof. Occasionally the outer quarter is somewhat drawn in under the foot.

This form of hoof is most distinctly marked in animals that stand toe-narrow or are bandy-legged.

As to the forms of the hind hoofs, what has been said concerning the influence of position of the limbs upon the shape of the front feet will apply equally well to them. The hind hoof (Fig. 82) is not round at the toe, but somewhat pointed or oval. It greatest width is between the middle and posterior thirds of the sole. It usually has a strongly concaved sole and a somewhat steeper toe than the fore-hoof; viewed from the side, the angle of the toe with the ground in the regular standing position is from fifty to fifty-five degrees.

Finally, we also distinguish wide and narrow hoofs; they are not dependent upon the position of the limbs, but upon the race and breeding of the animal.

The wide hoof (Fig. 83) is almost round upon its plantar surface. Its wall runs quite oblique to the ground. The sole is but moderately concave, and the frog is strong and well developed. The narrow hoof (Fig. 84) is rather elliptical, with steep side walls, strongly concaved sole, and small, undeveloped frog. The horn of the narrow hoof is fine and tough; of the wide hoof, usually coarse. The wide hoof may readily become flat. Narrow hoof may readily become flat. Narrow hoofs are either the result of breeding or premature shoeing.

In enumerating the preceding forms of the hoof we have by no means referred to all the forms in which the hoof may be found; on the contrary, hoofs vary in shape and quality to such an extent that among a hundred horses no two hoofs can be found which are exactly alike. In fact, the same variety exists as in the faces of people, and we know that we can recall in succession even many more faces without finding two that are exactly alike. This explains the manifold differences in horseshoes with respect to size, form and other qualities.

Suppose now a hoof is before us; it is first necessary to know whether or not it is healthy. Unfortunately, a perfectly healthy hoof is not so easy to find as one may think. We recognize a sound hoof by the following marks: Seen from in front or from the side, the course of the wall from the coronet to the ground, in the direction of the horn-tubes, is straight, — that is, bent neither in nor out. A straight edge, placed upon the wall in the direction of the horn-tubes, touches at every point. The wall must show neither longitudinal nor transverse cracks or fissures. If there be rings, their position and course are important. Rings which pass around the entire circumference of the wall parallel to the coronet indicate nothing more than disturbances of nutrition of the hoof; but the hoof cannot pass for sound when the rings have any other position and direction than the one mentioned, or if the rings upon any part of the wall are more marked than elsewhere, even though they may be parallel to the coronary band. Marked ring-building upon the hoofs of horses which have regular feeding, grooming, and work indicates a weak hoof. Viewed from the ground-surface and from behind, the bulbs of the heels should be well rounded, strongly developed, and not displaced. The concave sole should show no separation along the white line. The frog should be strong, well developed, and have symmetrical branches and a broad, shallow, dry median lacuna. The lateral lacunae of the frog should be clean and not too narrow. The bars should pass in a straight direction forward and inward towards the point of the frog. Any bending outward of the bars towards the branches of the sole indicates the beginning of a narrowing of the space occupied by the frog, — that is, contraction of the heels. The horn of the branches of the sole in the buttresses and in their proximity should show no red staining. The lateral cartilages should be elastic. No part of the foot should be weakened at the cost of other parts. By firm union of all strong parts the strength and vigor of the hoof is in no sense disturbed. If one desires to ascertain the exact form and state of health of the hoof, it must never be inspected and judged alone, but in connection with the entire limb.

F. Growth of the Hoof and Wear of the Hoof and Shoe.

All parts of the horn of the hoof grow downward and forward, the material for this growth being furnished by the remarkably large quantity of blood which flows to the pododerm. The growth of the hoof is regulated by the nerves.

As a rule, the hoof grows uniformly, — that is, one section of growth of the hoof is regulated by the nerves. A visible indication of growth is the increase in height and width of the hoof colthood to maturity.

The rapidity of growth of the wall varies, amounting in a month to from one-sixth to one-half of an inch. The average monthly growth in both shod and unshod horses of both sexes is, according to my own experiments, one-third of an inch. Hind hoofs grow faster than front hoofs, and unshod faster than shod. The hoofs of stallions grow more slowly than those of mares and geldings.

Abundant exercise, proper grooming (flexibility and moistness of the horn), regular dressing of the wall, and running barefoot from time to time favor growth; while little or no exercise, dryness, and excessive length of the hoof hinder growth.

The time required for the horn to grow from the coronet to the ground is, therefore, equally variable, and is, moreover, dependent upon the height (length of toe) of the hoof. At the toe the horn grows down in from eleven to thirteen months, at the mammae or sides in from six to eight months, and at the quarters in from three to five months. The time required for the renewal of the entire hoof we term the period of hoof renewal. If, for example, we know exactly the rapidity of the horn growth in a given case, we can estimate without difficulty the length of the “period of hoof renewal,” as well for the entire hoof as for each individual section of the wall. The duration of many diseases of the hoof (cracks, clefts, partial bendings of the wall, contractions, etc.) can be foretold with relative certainty only by knowing the period of hoof renewal.

Irregular growth sometimes takes place. The chief cause of this is usually an improper distribution of the body-weight over the hoof, — that is, an unbalanced foot. Wry hoofs of faulty positions of the limbs are often exposed to this evil; a faulty preparation of the hoof (dressing) for the shoe, as well as neglect of the colt’s hoofs, is in the majority of cases directly responsible for this condition.

If in the shortening of the wall a part is from ignorance left too long, or one-half of the hoof shortened too much in relation to the other half, the foot will be unbalanced. The horse will then touch the ground first with the section of wall which has been left too high, and will continue to do so until this long section has been reduced to its proper level (length) by increased wear which will take place at this point. In unshod hoofs this leveling process takes place rapidly; such, however, is not the case in shod hoofs, for here the shoe prevents rapid wear, and, indeed this leveling process is often rendered impossible through the welding of high steel calks to the shoe. If this fault in trimming be repeated at the next and the subsequent shoeings, and if the faulty relation of the ground surface of the hoof to the direction of the foot-axis remain during several months, the portion of wall left too high will grow more rapidly, the walls will lose their natural straight direction and become bent. If, for example, the outer wall has been left too long during a considerable period of time, a crooked hoof results (Fig. 85) in which the rings are placed closer together upon the low (concave) side than upon the high (convex) side. If for a long time the toe is excessively long, it will become bent; or if this fault affects excessively high quarters they will contract either just under the coronary band or will curl forward and inward at their lower borders. These examples are sufficient to show both the importance of the manner in which a horse places his foot to the ground and its influence upon the loading, growth, and form of the hoof.

Wear of the Shoe and of the Hoof upon the Shoe.

The wear of the shoe is caused much less by the weight of the animal’s body than by the rubbing which takes place between the shoe and the earth whenever the foot is placed to the ground and lifted.

The wear of the shoe which occurs when the foot is placed on the ground is termed “grounding wear,” and that which occurs while the foot is being lifted from the ground is termed “swinging-off wear.” When a horse travels normally, both kinds of wear are nearly alike, but are very distinct when the paces are abnormal, especially when there is faulty direction of the limbs. While in the majority of horses whose limbs have been stiffened by age and overwork both kinds of wear are most marked at the toe of the shoe, we see relatively fewer cases of the “grounding wear” at the ends of the branches (as in laminitis); on the contrary, we always notice “swinging-off wear” at the toe of the shoe. It is worthy of notice that length of stride has much to do with the wear. We observe that with shortening of the stride both kinds of wear occur at the toe of the shoe, and this is rapidly worn away, as is the case with horses which are fretful and prance under the rider, draw heavy loads, or from any other cause, as disease or infirmity, are obliged to shorten their steps. With increase of length of stride the wear of the shoe becomes more uniform.

The position and form of the shoe have a marked influence upon its wear; at the place where the shoe is too far under the hoof either as a result of shifting or of having been nailed on crooked, or where the outer branch has not the necessary width, or does not form a sufficiently large curve, the wear will be increased.

Also the relative length of side-walls, or of toe and heels, influences rapidity of wear of the shoe. If through ignorance or carelessness one side-wall be left too long, the branch beneath will meet the ground before other parts of the shoe and will wear faster (see Figs. 87, 88, 89).

The wear of the hoof upon the shoe occurs as a result of the movements of the quarters. Visible indications of this are the brightly polished, often sunken places upon the bearing-surface of the ends of the branches, showing that scouring occurs between the horn and the iron. Shoes which show brightly polished places in their anterior halves have been loose. The wear of the quarters upon the shoe is not always uniform, but is usually greater on the inner than on the outer quarter, especially in base-wide feet. The degree of this wear of the hoof may be from nothing to one-fourth of an inch or more from one shoeing to the next. Finally, we should remember that this usually invisible scouring away of the hoof gradually causes the nails at the quarters to become loose, and that this is more clearly marked in the front than in the hind hoofs.

G. Physiological Movements on the Hoof. (Mechanism of the Hoof.)

These movements comprise all those changes of position within and of the hoof which are brought about by alternately weighting and relieving the foot, and which are manifest as changes of form of the hoof. The following changes in form of the hoof are most marked at the time that the hoof bears greatest weight, — that is, simultaneous with the greatest descent of the fetlock-joint.

1. A lateral expansion over the entire region of the quarters, occurring simultaneously at the coronary and plantar borders. This expansion is small, and in general varies between one-fiftieth and one-twelfth of an inch.
2. A narrowing of the anterior half of the hoof measured at the coronary border.
3. A decrease in height of the hoof, with a slight sinking of the heels.
4. A flattening (sinking) of the sole, especially in its branches.

These changes of form are much more pronounced in the half of the hoof that bears the greater weight.

A hoof while supporting the body-weight has a different form, and the tissues enclosed within it a different position, than when not bearing weight. Since loading and unloading of the foot are continually alternating, the relations of internal pressure even in the standing animal are continuously changing, so that, strictly speaking, the hoof is never at rest.

The changes in form take place in the following order: the body-weight falls from above upon the os coronae, os pedis, and navicular bone, and at the moment that the foot is placed upon the ground is transmitted through the sensitive laminae and horny laminae to the wall. At the instant that the fetlock reaches its lowest point the os pedis bears the greatest weight. Under the body-weight the latter yields, and with the navicular bone sinks downward and backward. At the same time the upper posterior portion of the os coronae (Fig. 90, A) passes backward and downward between the lateral cartilages (a), which project above the upper border of the wall, and presses the perforans tendon down upon the plantar cushion. The plantar cushion being compressed from above, and being unable to expand downward, is correspondingly squeezed out towards the sides and crowded against the lateral cartilages, and they, yielding, press against and push before them the wall the quarters. The resistance of the earth acts upon the plantar surface of the hoof, and especially upon the frog, and it, widening, crowds the bars apart, and in this manner contributes to the expansion of the quarters, especially at their plantar border (see Fig. 90). The horny sole under the descent and pressure of the os pedis sinks a little — that is, the arch of the sole becomes somewhat flattened. All these changes are much more marked upon sound unshod hoofs, because in them the resistance of the earth upon the sole and frog is pronounced and complete. These changes in form are more marked in front feet than in hind. In defective and diseased hoofs it may happen that at the moment of greatest weight-bearing, instead of an expansion a contraction may occur at the plantar border of the quarters.

Three highly elastic organs there are which play the chief part in these movements, — namely, the lateral cartilages, the plantar cushion, and the horny frog. Besides these structures, indeed, all the remaining parts of the horn capsule, especially its coronary border, possess more or less elasticity, and contribute to the above-mentioned changes of form.

In order to maintain the elastic tissues of the foot in their proper activity, regular and abundant exercise, with protection against drying out of the hoof, are absolutely necessary, because the movements of the different structures within the foot and the changes of form that occur at each step are indispensable in preserving the health of the hoof. Long-continued rest in the stable, drying out of the hoof, and shoeing decrease or alter the physiological movements of the foot, and these lead under certain conditions to foot disease, with which the majority of horse owners are entirely unacquainted.

As an outward, visible indication of the mobility of the quarters upon the shoe we may point to the conspicuous, brightly polished, and often sunken spots, or grooves, upon the ends of the branches. They are produced partly by an in-and-out motion of the walls at the quarters, and partly by a forward and backward gliding of the quarters upon the shoe.

The benefits of these physiological movements within the hoof are manifold:

1. Through them shock is dispersed and the body protected from the evil consequences of concussion or shock.
2. These movements increase the elasticity of the entire limb and in this way contribute much to a light and elegant gait.
3. They maintain a lively circulation of blood in the vessels of the pododerm, and this insures a rapid growth of horn.

Since it is a generally accepted fact that shoeing interferes with the physiological movements of the hoof, alters them, indeed almost suppresses them, and that all these movements are spontaneous and natural only in sound unshod hoofs, we are justified in regarding as a necessary evil. However, it is indispensable if we wish to render horses serviceable upon hard artificial roads. If, in shoeing, consideration be given to the hoof-surface of the shoe, the ends of the branches being provided with a smooth, level bearing-surface, which allows free play to the elastic horn capsule, in so far as this is not hindered by the nails we need have no fear of the subsequent disease of the hoofs, provided the horse is used with reason and receives proper care.