Popular Science Monthly/Volume 28/January 1886/The Physiology of the Feet
|THE PHYSIOLOGY OF THE FEET.|
DISREGARDING the action of those parts not affecting the feet, the act of walking may, as I think, be thus described: The foot put forward should reach the ground when nearly flat; the toes, the organs of feeling, should be the first to reach it, not the heel, which could not be without some concussion, however slight. The heads of the metatarsal bones and the toes are then pressed firmly against the surface. The great-toe, having only two phalanges, is held down in its whole length, the flexor tendon being attached to the final phalanx close to the joint between them. The little toes touch at their tips only; their flexor tendons being also attached to the final phalanx of each, traction on them causes a rising at the joint between the two proximal phalanges as the tips of the toes are drawn backward. By this arrangement, in the one case a firm, solid base is formed from which the body can be propelled onward; in the other an additional hold on the surface, by a rudimentary action or grasping, is afforded. As the body is moved onward, the extensors of the great and of the little toes, without lifting them from the ground, where they are held by the flexors, draw the leg forward, while the anterior tibial, in assisting this movement, serves another purpose. It is attached to the crown of the arch, and in action tends to prevent any sinking there as the weight of the body comes upon that structure. This purpose is much more effectually served in another way: the muscles of the calf allow the heel with firmness and precision, but withal gently, to touch the ground, and the step is completed.
The heel is then raised, but the weight of the body is not borne, as commonly stated, by the muscles acting on the heel and by them only: the deeper muscles, the posterior tibial with the long flexors and the long peroneal, acting round the inner and outer side of the ankle respectively, all of them assist in raising the body and at the same time have a most important influence in maintaining the arch. The tibialis posticus, attached by its expanded tendon to the tarsus on the under surface beyond the astragalus, the bone on which the weight of the body rests, materially assists in supporting the arch from below. The long flexors passing beneath the arch from one abutment to the other are, in relation to it, as bowstrings to a bow, or rather, as the two tendons cross each other, they may better be compared to the tie-rods of a roof.
This arrangement of the two tendons crossing each other is very curious: that going to the great-toe is lowest in passing round the ankle, in order to be, as nearly as possible, at the extremity of the arch or bow at that end, as it is at the opposite one; if, however, it passed directly across the sole from end to end there would be little if any free space beneath, but, being crossed by the flexor longus digitorum, which comes round the ankle at a higher level, it is so drawn up that a hollow beneath the arch is formed; the flexor accessorius, by drawing back the tendon of the flexor longus pollicis, compels it to cross the other nearer to the heel, and so increases this effect. Thus the flexor longus pollicis, regarded as the chord of the arc, becomes itself an arc.
The tendency to inversion which all these muscles, acting from the inner side of the ankle, might occasion is corrected by the long peroneal on the outer side; it also, acting on the base of the first metatarsal bone, a point considerably beyond the center of gravity, has a bracing action on the arch, as the weight of the body falls upon it. In this, too, no doubt the small muscles of the sole assist those of the calf, but I can not accept the converse statement that it is the "muscles of the sole assisted by the tibial muscles" which "are the active agents." The deep muscles of the calf have much the more potent influence. Thus it is that by the action of muscles the whole of the strain which the weight of the body in walking would otherwise throw on the ligaments binding the arch together is removed, and any tendency to flattening of it prevented.
This, which has been called my "bowstring theory," is the view I put forward in a little monograph, "On the Arch of the Foot," written and printed in 1877. For reasons therein given I could not accept the view that the arch is maintained by ligaments, or believe in the carriage-spring movement of those ligaments, yielding to the weight of the body, as the explanation of a springy gait. It is really due to the heel being gently lowered and firmly raised. Upon this the grace of walking depends. On the same grounds I hold that in proper walking the foot does not lengthen. Camper, whose treatise is regarded as classical, but which, as I think, contains many important errors of fact and of induction, said that his knowledge of anatomy taught him that it did so. On the contrary, I believe that as the tightening of a bow-string approximates the ends of the bow, so the bowstring action of the flexor muscles on the arch of the foot tends to shorten it. If walking were a succession of standings, flat-footed alternately on either foot, no doubt there would be lengthening, as the ligaments of the arch yielded. Such a mode of progression is, we know, possible; and, indeed, we sometimes see something like it, hardly, however, to be called walking. I would ask those who believe that the foot in walking lengthens "one tenth of its length, or about an inch" (a statement on high authority made during the past year), to consider this: What, then, would be the condition of the sole, after a long walk, from friction caused by the necessary sliding with the weight of a man borne upon it? As in every mile of the ordinary march of soldiers more than a thousand steps are taken on each foot, the result would not be pleasant even to imagine.
The position of the foot is important. To turn out the toes seems to me to be not only untrue to nature, but objectionable as well as inelegant. Camper regarded it as incontestabiy the proper position. For the following reasons I believe that the toes should be directed forward, the inner margins of the feet parallel: It is desirable that the propulsion of the body onward from, and consequent thrust backward on, the foot, and especially on the great-toe, should be in the direction of its length rather than obliquely across it, not only as giving a firmer bearing from which to propel the body onward, but as diminishing the friction on the sole and consequent tendency to foot-sore. This applies also to the smaller toes in a less degree. The long axes of all the toes continued backward seem to converge on the heel. By standing with the bare foot and springing forward it can readily be seen how much more tendency there is to slide on the sole when the foot is turned out than when it is directed forward. In the latter position, too, the arch is much more firmly braced up—a fact recognized by surgeons who advise, in cases of flat-foot, that the toes should be directed inward rather than outward. In standing, the everted position is not more stable. When a body stands on four points I know of no reason why it should stand more firmly if those points be unequally disposed. The tendency to fall forward would seem to be even increased by widening the distance between the points in front, and it is in this direction that falls most commonly occur.
Those who look on the human foot as fully partaking of the beauty of which artists in every age have regarded the human body to be the highest expression, ought not readily to admit that the boot which best conforms to its outline, reveals its features, and expresses its leading characteristics, will require an apology for want of elegance. I, at any rate, can not admit anything of the kind. The human foot is, moreover, an object of far more than the ordinary interest belonging to every part of the human structure. In the monograph already mentioned I ventured to suggest that, anatomically, there is no more marked distinction between man and the lower animals than is to be found in the special development of the foot.
However much we may regard it as in itself calling for admiration on account of its fitness for the purposes it has to fulfill and for others it may on occasion serve, the human foot is far more remarkable as an adaptation of the mammalian type, modified to suit a purpose kindred to but differing from that which the corresponding member supplies in other animals. The heel has its special form and signiticance in that man only has one adapted for crushing an offensive object beneath it. The large size and important function of the great-toe is also a specially human feature. In the mammalian typical limbs the bones of the hand and foot (or rather, to avoid confusion, in four-handed or fourfooted animals, manus and pes) are arranged on a uniform plan: to each five digits, the first having two phalanges and the others three. The first digit is generally attenuated, often suppressed, but whenever it exists it has two phalanges only.
This curious difference is nowhere, so far as I know, explained. I can not discover that any animal (below man), recent or fossil, exists or has existed from the times of the Trias formations till now in which this arrangement has appeared to be essential. It may be of some advantage in the quadrumana, and doubtless the human hand is thus better fitted for its functions, but it seems to me to be much more difficult to imagine it possible for any other arrangement to exist in the foot unless the whole scheme of it, so to speak, were changed. It is essential that the only joint in the great-toe should be drawn to the ground by the strong flexor tendon attached to the final phalanx close to it; if another joint existed it must rise up, as occurs in the other toes, and the solid bearing would be lost. Apart from this, it must be admitted that it is mainly due to the special development of the great-toe in a line with the long axis of the foot that man is enabled to exercise the attribute, in all ages regarded as a noble one, of standing erect. Yet this special feature is the one which the conventional boot does most to conceal, and in direct proportion as it is successfully concealed the wearer is supposed to be dressed in good taste. It would seem to be regarded as necessary to reduce the foot to even-sided symmetry; but there is no law of beauty which requires this. Mr. Ruskin assuredly would not say that it is in any of "the eternal canons of loveliness" decreed that an object to be beautiful must be symmetrical. An architect required to provide more space on one than on the other side of a building would not seek to conceal or even to minimize the difference; he would seek rather to accentuate it, and give the two sides of the structure distinctive features. To me it appears that it is on this principle only that a boot, to be at once useful, graceful, and appropriate, can be designed.
Moreover, the sense of symmetry, natural and reasonable where the same function has to be performed, is, or ought to be, satisfied by the exact correspondence of the two feet, which, taken jointly, may be described as the two halves of an unequally expanded dome, irregularly extended at the base, the greatest extension being in the line of the greatest expansion of the dome, through which line the division runs. The dividing-line thus makes the margin of the two feet parallel to each other. It may be that the inner margin of the great-toe, if produced backward, would fall a little distance from the inner side of the heel. A perfect adult foot, in which the great-toe is not and never has been diverted outward, and in which there has been no consequent thickening of the large joint, is not easy to find. In children the inner line is often visibly concave. It may be remarked that in rest the great-toe is everted as well as drawn upward, in which position the toes are usually packed in a tight, medium-pointed boot; it is only therefore in action as the toes are pressed against the ground that the full extent of the approximation to a straight inner line is seen.
In the boot it is of first importance that the sole (technically, the part in front of the hollow or "waist") should allow the great-toe to occupy its natural position; it must, therefore, be straight, or nearly so, on the inner margin; but it is of little use to provide the room thus given unless it be occupied; the foot must be invited to occupy it by giving plenty of room in the upper leather on this side. It is obvious that where a flexible material is fixed on both sides and left loose between, it can be drawn farthest from the surface to which it is attached, in a line midway between the fixed parts. For this reason the highest part of the foot, which is on the inner side, will, in any case, have some tendency to go to the middle line of the boot where most room can be made; this tendency is largely and needlessly aggravated by the high ridge of the last being along the middle line instead of being on the inner margin. But not only ought the room there given to be much more according as the foot projects the more upward; it ought to be proportionally more. I have insisted that the foot does not lengthen in walking, but rather shortens. This shortening, due to the powerful action of the long flexors, causes the foot to rise across the middle, the rising being almost entirely on the inner side. Here, therefore, over (not by the side of) the ball of the great-toe is special room required. The lateral thrust, too, already spoken of as consequent on turning out the toes, tends much to displace the foot and to throw it against the outside of the boot. Toe-caps also are objectionable, as giving the most room in the middle line and inviting the great-toe to occupy that position.
No useful or ornamental purpose is served by leaving space unoccupied round the outer margin of the sole opposite the little toes, as if it were necessary to make the two sides of the boot to match. No angle existing in nature, none should be represented; the outline of the sole of the boot should conform to that of the foot.
If it be true, as already stated, that grace in walking, as well as free propulsion of the body onward, and maintenance of the arch in walking, are all due to the free action of the flexor muscles, letting the heel down with gentleness and precision, and raising it with firmness and vigor, it follows that none of these can be if the boot prevent the heel from going down, a necessary antecedent to springing up. A low heel, therefore, if any, is imperative. The perfect boot should have none. Nor can the free action of the flexor muscles have full effect, so as to draw the toes to the ground, if the sole be turned up at the toes, especially if it be a stiff one. Some turning up will come from walking, however good, but there is no reason why it should be aggravated by having the boot-last so. In it the sole should be flat to the end. Objection is made that boots with a straight, or nearly straight, inside line give the feet a pigeon-toed or inverted appearance, which is unnatural. This is not altogether due to the eye being accustomed to a more conventional pattern. It is, I am sure, mainly due to a removable cause. Any conspicuous line, that of the laces or a seam, is always carried from the front of the leg to a central point on the upper surface of the foot. The eye, falling on this line, in imagination continues or produces it, and so divides the front part diagonally into two very unequal portions, the larger on the inner side. I have found that if the line of the laces or seam be kept parallel throughout to the line of the long extensor tendon—in other words, along the crest of the ridge, thus marking out a distinctive feature—the unpleasant effect is removed.
In proper walking, which can not be done in an improper boot, friction of the foot on the sole and of the latter on the ground is reduced to a minimum, the sole being pressed against, not rubbed along, the surface. This is shown by the very little wearing of the leather; when at last it does give way, it should be at an oval spot a little distance from the margin of the sole, under the middle joint of the great-toe. This is the last point to leave the ground in walking; here, therefore, is the greatest tendency to slide on the surface and consequent friction.
The great-toe, in any but the most perfect feet now to be found, is so easily diverted outward that socks and stockings with a straight inner line are very desirable; indeed, no others can be said to really fit the feet. When any considerable distortion exists, a separate stall for the great-toe is necessary.
For the reasons given, a last should have the inner margin nearly in a line with the inner side of the heel, and joining in front by a rounded angle a long curve on the outer margin, where no angle should be shown. The sole should be flat, touching the base-line in front. The thickest part (highest vertically) should throughout be on the inner margin, especially above the ball of the great-toe. The boots should have low heels—to be perfect, none. The line of laces or of any conspicuous seam down the front should be in a line corresponding with the inner margin of the foot along the highest part. The boot should, if possible, be left on the last for a considerable time, to overcome the tendency of the leather to recoil after the forcible stretching to which it has been subjected, and so to fix it in its proper shape.—Lancet.