The principle of Lyell cannot be applied to this section of my subject for it is unique in the animal world. There is here a simple compila­tion of facts such as the medical schoolboy is supposed to know, and only requires for its setting forth the valuable expert knowledge of our predecessors in anatomy. It is indeed a pedestrian chapter.

Man alone possesses this mark of a high lineage, and it adds point to Shakespeare’s descrip­tion of man as “paragon of animals,” and Huxley’s “a superb animal, head of the sentient world.” For winning this integral part of a perfect walking-foot man must stoop to conquer; he must descend from the trees in order that he may have life and liberty; whether he bears the ancient surname of Tarsius or the more honoured one of Pithecus matters not. Names had not in those early times usurped that tyranny over man’s mind which they have done among his modern descendants. He came into that terrestrial kingdom which was to be his own with many a limita­tion, but with the promise and potency of an unexampled evolution, when he assumed more fully the erect posture and saw that his inheritance was very good. Neither then nor since has he ever reached the fleetness of foot of the Thibetan wild ass, the astonishing sense of smell of the dog or horse, the keen sight of the hawk, or the climbing power of that simian family upon whom he turned his back as on a poor relation. He became par excellence the walking biped of earth, as, even with greater value to his mastery of the world he learned to talk in articulate language. A walking animal and a talking animal, with vast stretches of time for training these new powers of his, he became modified into the variegated human stocks, black, yellow and white, that now inhabit the earth.

A Crumbling Arch.

A digression, I hope, will be pardoned here before the value and beauty of the plantar arch and its mode of forging are described, and it is possible the latter may add some force to the former. Scientific (or, must I say?) semi-scientific writings are not concerned with the snobbishness of much of the pride of birth which still survives among us. But I would indeed think myself to be doing “my bit” if I could induce the present genera­tion of young women and men to think highly of their plantar arches, nobler evidence of a “good” family than soft fair skin, taper fingers, Grecian nose, slender waist or that hair of which the decaying line of the long-haired kings of old France were too proud. For one reason or another, probably analogous to those for which he has lost so much the vigour of his hair of the scalp, or his dwindling wisdom-teeth and shrinking little toes, in other words, racial degenera­tion, modern man seems to be losing his plantar arch. For about three years I have made careful but saddening study of the ankles and feet of young women, and have embodied it in a variety of journals. This study has included about two thousand examples in young women of incipient or advanced flat-footedness as revealed, nay, flaunted before us in our towns and villages. This revela­tion has been offered by women’s shortened skirt, so that one can now note for oneself the ugly and disabling ankles and feet in the streets of any town, without the complicated business of a surgical examina­tion. Such an examina­tion, as it happens, and as it is usually undertaken, serves only to show a moderately advanced degree of this deformity, indeed, just so much as induces a patient to go to a doctor for relief of pain or obvious deformity. This is wholly insufficient for the study of a defect which in the various degrees of its development affects nearly 90 per cent. of all youngish women so far observed and noted. The doctors may—or may not—cure this evil, but they are not likely to find time even to discover during their strenuous lives, the great spread of this physical defect. But the merciful ukases of fashion, from Paris or elsewhere, and the obvious benefits, for once, of a fashion, are so powerful that the short skirt has remained with us for several years past and does not seem likely to go. I can only hope it will last until women who lead their sex in these days become ashamed of the feet of their sisters and their own, and make a forcible attack upon the Health Minister or Minister of Education, or both, so that systematic foot-drill in all elementary schools may be established. No other means than this, added to improved general health, can be conceived as able to correct so widely spread a deformity. I do not desire to be considered as making an attack on the bodily charms of women, for whose multifarious attractions I yield to none in sincere regard. But here is the revela­tion, here are the cases walking unashamed before us, and if the skirts should lengthen again and cruelly hide up the evil, no one will be induced again to take up the unpopular attitude of saying that nearly all young women have feet that are deformed and ugly and, therefore, more or less inefficient. There is, alas! only too much reason to know that the evil is great among the better class, even of boys, for in 1919 Captain Coote said publicly at a Schoolmasters’ Conference that fully 30 per cent. of the new boys entering leading public schools had flat-foot, and Captain Coote, the highest exponent of physical training in the Navy, knows a flat-foot when he sees it. The measures here suggested in connec­tion with the feet of women have the great merit that from them boys and girls will alike benefit.

Non-Arboreal Man.

Many problems faced non-arboreal man as he descended from the trees to claim his suzerainty and place of toil. Not least among them was the question of methods of protec­tion against the terrible creatures among which he was to live. Their produc­tion must needs be slow, and for him to meet by “direct action” with weapons invented ad hoc the fierce large carnivora and clumsy but dangerous dinosaurs would have proved highly dangerous. Too long had they been in possession of his Canaan, and he could not cross his Jordan, walk seven times round their Jericho, blowing with trumpets of rams’ horns, and on the seventh day march in and “consolidate his position.” He had first to do what his descendants have always been bound to do; he had to learn to walk terrestrially long before he could think and live imperially. Sufficient for him was the evil of his day, and, as an old arboreal denizen he had much to learn and not a little to unlearn; and we know from the prehistoric pictures of his own doings and trophies, that he did in course of ages learn to walk, run and jump with variety of step and efficiency unknown in any other Primate group. We can ask, and we can but supply speculative answers as to the details of how he did it, but somewhere and at some time he learned first to become as good a walking animal as later he became a talking one, and some at any rate of the steps of the process are plain for all to read to-day.

How the Arch was Built.

Did I not know something of the severity of the judges in such a Court of Appeal as we are facing in this case and of the opposing counsel—of the jury I have less fear—I should be disposed to settle on a half-sheet of note-paper the problem that non-arboreal man settled ages ago for himself on the ground, by a familiar saying. It really meets the non-scientific mind which is not weighed down by what Captain Marryat used to call “top-hamper,” to answer Solvitur Ambulando. But I hear judges and counsel both saying “This will never do,” and must address myself to opening up the case.

If an adventurous gorilla and his mate, whom we may call gorilla Columbi, had long ago made a bid for a life completely terrestrial rather than partly arboreal, it is difficult to imagine how the feet of this pair could have failed to adjust themselves and their separate tarsal elements to a better if rudimentary form like that of man, and that their progeny would not have followed or improved upon this. Professor Keith,70 in his work referred to, and Professor Wood Jones in Arboreal Man, have much to say on the evolution of man’s foot and arch, and I mention this ab initio so as to be free from any supposed claim to originality which is apt in the present extended range of scientific progress to be as damaging to a man as for him to proclaim his honesty or a woman her virtue. And I also formally grant to the Mendelians and Mutationists, without offence and with some possible relief to their minds, a period of leave from this poor trench-warfare—Plasto-diethesis will not be obliged to call in at the place of its hyphen any reinforcements from these of the higher command.

The assumed precursor of our human walker was probably more highly evolved in his own special line than the real ancestor, but we have so little yet of discoveries of whole skeletons of earliest man that the bodily structure of gorilla C. may fairly be taken as a starting point, indeed he is for this purpose a valuable lay-figure, almost artistic for once, on which may be draped the following story of the making of an arch. The ultimate verdict, which word I use in the old English sense of a “true saying” rather than the most recent declara­tion of those who “ride on white asses and sit in judgment,” does not therefore invalidate the verisimilitude of this picture. One may go farther and affirm that, given certain anatomical and physiological facts in an earlier Primate stock, which marvellously resemble those of modern man, and it must follow as the night the day that his more primitive physical basis employed in a new mode of progression, that is of terrestrial walking on two feet, will be converted by use and habit into the construc­tion of such new formations as will best agree with the new style—in other words, in this instance, a plantar arch.

An Unique Phenomenon.

That a plantar arch is peculiar to man is a matter of fact, and Lydekker in the Royal Natural History, Vol.I., p.41, says of the gorilla’s foot incidentally “there is no sort of resemblance to the human instep in the whole foot,” and Professor Keith in the work referred to “the arch is a human character.” One may see this for oneself in living apes and monkeys and in the wonderful series of drawings of apes in all kinds of postures in the Royal Natural History, and indeed in the feet of dead apes and monkeys. All Primates other than man walk on a flat sole.

Equipment.

Our adventurer starts with the following equipment of tools for making his arch as he learns to walk entirely on the ground which it must be remembered he can only do by unlearning pari passu his highly cultivated power of grasping with his foot. The old and the new cannot flourish together. The evolving foot of man is an example of a slow change in the function of an organ and consequent modifica­tion of certain structures in it. He walks with his feet turning in, or in the axis of the leg; his great toe is not in this axis but may even lie at a right angle to the foot; he rests weight on his heel and even more on the outer border of his sole, and thus the sole of one foot turns more or less towards the other; and he puts a good deal of weight on his toes which are frequently doubled over; and his gait, though erect, is never completely so, and is clumsy in appearance.

Bones: his heel-bone is relatively long and pointed and slightly arched below; the bones of his great toe are short and thick, and the other four toes relatively long and slender. You can see at once it is not primarily a walking foot. Any active boy of twelve could give him points and a beating in a race for life in the open. Further, his foot shows a much larger propor­tion of the whole foot in front of the end of the great toe than is ever seen in man. The ligaments which bind the joints of his foot together, while the muscles play upon them, are little different from those he will require for the girders of his arch, except for such a throwing out of slips, and shifting under the stresses and strains of such walking as his new gait involves.

The muscles of his leg and foot are the most important by far of his original equipment with which to set about making his arch: he could no more do this out of his present muscles than a Hebrew could make bricks without clay. It is these variable and plastic structures which are most readily adapted by use in a fresh direction or increased degree. He has the great flexors of the ankle and foot in his poorly-shaped calf (this feature might be adduced as a human character and studied in this manner if it were not of so elusive a nature) and the long flexors of his four outer toes, the special long flexor of the great toe, which in his case does not of course act in the axis of the other metatarsal bones. He is lacking here in the special detached portion of the flexor accessorius, which eventually becomes of use in maintaining the arch, between the heel-bone and the tendons of certain digits. He has, in a measure, the oblique adductor muscle of the great toe and the transverse adductor muscle, more for future use perhaps than of much present value. Like all apes and monkeys he has a peroneus longus with its tendon passing across the sole from the outer border to the base of the great toe and a peroneus brevis, both of them for everting the foot and supinating it. But here again he is lacking, for he has no little peroneus tertius, which Professor Keith speaks of as a muscle “peculiar to man” and “a special evertor of the foot”—a muscle passing from the tendons of the extensors of the toes and inserted into the little toe. He has also the tibialis anticus and tibialis posticus, the latter which flexes the ankle on the leg, and the former which also flexes it and everts the foot; he has also the special extensors of the toes.

This enumera­tion of the bony, ligamentous, and muscular possessions of gorilla C. is enough to show that, though he has little of new tools to make, he has to modify greatly those he has learnt to use so well, so that one can almost hear him echo the words of David to Saul as to his new armour.

The problem of an arch remains to be solved by eversion instead of inversion of the foot, growth in all directions of the heel-bone, and the enlargement and straightening of the great toe, and the “setting” of the foot in a certain degree of pronation and over-extension.

Description of the Arch.

The plantar arch is double, but the longitudinal one must be chiefly considered here. It lies under the concave roof of the tarsal bones, seven in number, and the metatarsal bones, and rests in a well-formed foot in front on the heads of the latter, and behind on the inferior surface of the heel-bone. The astragalus alone of these bones in contact with those of the leg, acts like a washer to the ankle joint, and has no muscles attached to it. Three more of the tarsal bones need reference: these are the three wedge-shaped bones which have their bases on the dorsal and their apices directed towards the plantar surface. With such a set of bony tools as this, all the requisites for an arch are at hand. Let the half-tree, half-ground walker become a complete ground-walker, and in the first place the manifest increase of the action of the flexors of the leg will pull to an unusual extent on the tendo achillis and heel-bone, leading, in accordance with a well-known law, to steady enlargement of the parts near to which it is attached. The greater amount of weight thrown henceforth on the heel tends in just the same direction, indeed, to general enlargement of the whole bone. The astragalus being in No Man’s Land, so to speak, takes less part in the change than any other tarsal bone. The wedge-shaped bones are exactly so constructed as to retreat a little in a dorsal direction as the modified walking increases under the action of certain muscles which will later be mentioned. This, in conjunc­tion with the projec­tion backwards of the heel and the general growth of the bone, permits, as far as the bony parts go, a gradual hollowing out of the originally flat plantar surface, and the increasing eversion of the foot places more weight on the front pier of the arch, that is, the heads of the metatarsal bones. The squeezing-up process of the smaller tarsal bones contributes also to the formation of the transverse arch.

The ligaments need no new invention on his part but only a more human degree of development, and in particular the calcaneo-navicular ligament and internal lateral of the ankle undergo in the human foot great development, and the long plantar ligament, originally part of the tendon of the gastrocnemius, comes in to the aid of the arch and goes to bind it together, so that these humbler structures follow in the wake of the changing and enlarging bones.

The plantar fascia, though a powerful protective armour for the deeper parts of the sole, cannot be held to enter into the formation of the arch. The initiative in this process lies with the muscles, and, even if neither gorilla C. himself, nor his descendants, had altered the muscles of his foot and just given up climbing for walking, there were muscles strong enough and appropriate for modifying very profoundly his simian foot, though he might not have arrived at an arch. He or they might have become long-distance walkers, but never sprinters.

If the sole of the dissected foot is observed it is seen that the plantar arch lies approximately over a triangle of which the base is formed by the transverse adductor muscle of the great toe, across the heads of the metatarsal bones, and the two sides by the oblique adductor of the great toe and the short flexor of the little toe. It extends, of course, somewhat further back under the heel-bone, but this is its highest part.

In the changing foot the tibialis posticus, which was originally a flexor of the metatarsal bones, obtains a secondary attachment to the scaphoid bone, and the tibialis anticus becomes inserted anew into the internal wedge-shaped and metatarsal bones. “Both of these muscles, thus modified, help to maintain the arch of the foot. So does the tarsal part of the tendon of the tibialis posticus.” (Keith).

The three peronei muscles, especially the new peroneus tertius, attached to the little toe, are called in by increased walking to redress the balance of forces in the foot and produce that eversion, with some supina­tion, which is essential to the arch. No arch was possible till these muscles came into some preponderance of action over the flexors, so beloved of gorilla C. The short flexor of the digits becomes modified so that its attachment to the tendons of the long flexors in the sole has its origin completely transferred to the heel-bone in man (Keith). “It can thus act more powerfully in maintaining the arch,” and finally the flexor accessorius, a muscle which cannot fail to surprise the dissector when he first penetrates into the deep layer of muscles of the sole, and which is a detached piece of the long flexor of the great-toe, becomes especially well-developed and helps to maintain the arch.

The order of events then is: first, increased and altered muscular function; second, growth of bones and adjustment; third, binding together of these by new or modified ligaments. If it were possible to separate in this way the age-long formation of such a living tool as the human foot, this is the order in which alone, I submit, the sequence of events can be placed. It is a convenient, because simple and plain example of initiative in evolution, and I cannot say how much I owe to Professor Keith’s teaching on the subject.71