Initiative in Evolution

5. A curving flexure surrounding the thenar eminence, extending from the centre of the wrist along the palm and terminating at the radial border.

6. Variable longitudinal and oblique flexures not specified, which I have called secondary.

Meaning.

Whatever be the meaning and origin of these flexures they are not mere folds such as one makes in a garment and leaves it so. Action, function and fitting of the structures of the hand and foot are involved in their history. They may loosely be termed “ergographs” without any reference to the exact measurement of work done. No proper idea can be formed of them if the original function and evolution of the walking-pads of earlier mammals be omitted. If one goes back and back until one reaches some lowly marsupial as a vulpine phalanger, or insectivore such as a common hedgehog, one may even metaphorically see these animals being fitted by a shoemaker with rude shoes or walking-pads for the better locomo­tion on or under ground, or in the branches of trees. These pads are projecting masses of hard fat with fibrous tissue interspersed and they early become fitted or adapted to or by the use to which they are put. It is impossible to suppose that certain rudimentary pads are devised by selective processes prior to the altered habits of walking of the animal that acquires them. From the shoemaking point of view the fashion is rough and generalised, and the changing habits of the animal adapt the shoe by degrees to the function employed, much as many a private soldier knows to his cost that he has had to adapt slowly and painfully his army boot to his particular foot. This process in an early pedestrian mammal involves the breaking up and limiting of the rudimentary pads by sulci in the dense skin, and the process of struggle and adjustment between the pads and their bordering furrows issues in the characteristic flexure of each mammal. From experiences in the human body one knows how easily fibrous adhesions between the skin and deeper parts, notably in cases of Dupuytren’s contrac­tion of the palmar fascia, are formed by close apposi­tion of the two layers. Such adhesion is precluded when much movement of the part occurs, but ex-hypothesi the rudimentary flexures are distinguished by absence of movement, and the conditions for fixing down the deeper layers of the skin to the bones beneath are clearly present. That these are not indifferent structures is evident from what Macalister says, and though they be small or even trivial may be held to have acquired at some time or other selective value. Their early stages would necessarily be too tentative, varied and slight to acquire such value.

Fig. 73 represents the clumsy, thick walking-pads of a marsupial the vulpine phalanger, trichosurus vulpecula.

Reviewing these examples one observes an evolutional decay of a minor but necessary piece of mechanism of the Primate hand and foot. The general similarity, mutatis mutandis, of the flexures of the palm and sole in Primates is very noticeable, and is associated with the strong prehensile power of the foot of all the forms below man. In the cases of the two apes shown in this series, the resemblance is still well marked, more so even in the chimpanzee than the gibbon, so that the disappearance from the sole of man’s foot of any important flexure is very significant of his loss of prehensile and gain of locomotive perfec­tion, and I find it impossible to conceive any process of evolutionary change where a loss of the flexures of a prehensile foot could come under the power of selection, on its own merits. On the other hand this remarkable instance of disuse of a formerly useful structure is adequately accounted for by the evolution of an organ like the human foot which in course of long periods of time became an organ of one function. Weismann might score a point over Spencer from his laboured explanations of man’s dwindling little toe, but here, I submit, he would have had to take refuge in silence, and pass to characters of a higher and more debateable kind.

CHAPTER XX.
THE EVOLUTION OF A BURSA.

A bursa exercises a function in the animal body which is the direct opposite of that shown to belong to the flexures of the hand and foot. Whereas the latter are adapted to the preven­tion of slipping in the act of prehension, bursæ are delicate contrivances for producing the maximum effect of sliding, within certain limits, between two opposed surfaces, either between the skin and a hard surface beneath it, between two muscles, or a tendon as it moves over a bone. As they are very variable and most of them are inherited and congenital, while some are produced only in the lifetime of the individual, they are useful for considera­tion in regard to the questions of transmission of modifications and of the origin of initial variations. Their degree of utility ranges, for example, in man, from that of the prepatellar bursa without which no useful movement of the knee-joint is imaginable, to the insignificant bursa which may or may not be found on the dorsal surface of a phalangeal joint of the foot. The principle laid down by Lyell, to which allusion has been made elsewhere, that is, of “explaining changes in the surface of the earth by reference to causes now in action,” is applicable in this small department of the evolution of a minor structure of the animal body. As man furnishes the largest of all collections of these lubricating organs, his skeleton and skeletal muscles will form the main subject of this chapter, and I venture, if one may say so, to “Lyell” them. None of the sections of this book except that on the mammalian hair affords so simple and easy a field for watching in operation certain mechanical forces. We may here go down to the potter’s house and watch him moulding his clay, or the cobbler his leather. So much are bursæ in the human body under the power of extraneous forces that I venture to say that if some young surgeon of an inquiring mind were to choose a place and time when the Honourable and Vigilant Stephen Coleridge was out of the way, and were to produce in a young chimpanzee under an anæsthetic a “greenstick fracture” of his radius and ulna, immobilising it at a right angle for a month, the animal would exhibit at his death some years later a highly developed bursa over the bony protuberance nearly as good as the olecranon bursa on the uninjured side, and better than that of the injured limb. As I have reason to know the meticulous vigilance of this professional and expert humanitarian I hasten here to say in advance that I do not recommend this experiment, not because it would not be entirely justifiable, but because nature herself in the highest Primate has produced many undesigned experiments of nearly equal value, as I hope to show.

Bursæ Described.

Broadly considered a bursa is a sac lined by synovial membrane, and an extreme example of the simplest form in which it is found may be said to be that of the condition found in a domestic dog. Under its skin, except on such regions as the snout, the tail and the feet, there is hardly a place where a bursal surface does not exist. Here and there trabeculæ may divide the great sac imperfectly, but from the protective and selective point of view this mechanism under a dog’s skin may be compared to the oil with which an Indian criminal lubricates his naked body so as to elude capture. To us who are too familiar with dog-fights (to which the Hon. Bertrand Russell likened the recent Great War, as we all remember) and who know how much noise and ferocious attempts are made by the warriors to bite one another, and how little success they achieve, the beautiful adapta­tion of nature in the dog far surpasses that of the Indian criminal. Indeed the latter may well have been suggested by the former.

Between such a simple and undifferentiated bursal surface as this and another such as the small but essential bursa under the tendo achillis there are endless variations adapted to particular uses and regions.

The descrip­tion of bursæ given by Macalister is too clear and good not to be given in his own words.67

“Synovial membranes are found either as the lining of joints, or as Bursæ, which are closed sacs (a) between contiguous soft parts, or (b) beneath soft parts which glide tensely over a bone. Bursæ are formed around and beneath tendons in the neighbourhood of joints; and the hard part on which the tendon plays is often invested with a layer of cartilage over which the synovial membrane does not extend. When they completely surround tendons, as in the finger and toes they are called thecæ or sheaths, and the tendons are connected to the sheaths by synovial reflections. Sometimes bursæ lie between exposed areas of skin and projecting bony points, such as the patella, olecranon, ankles, etc.

“Their (synovial) membrane differs from the synovial membrane of joints in not having so continuous or definite an endothelial lining; indeed, while some bursæ, such as that beneath the ligamentum patellæ, have a more or less regular lining of regular endothelium, others have only elongated connective cells forming an imperfect lamella, and there are all possible gradations met with between the regular saccular bursa, and a loose meshwork of areolar tissue of which the bursa is only a specialisa­tion. Bursæ may be (1) subcutaneous, (2) subfascial, (3) between two tendons, or (4) between tendons and subjacent ligaments or bone. Of these, some communicate with the neighbouring joints always, some occasionally, and some never. Bursæ underlying parts which have an extensive range of motion are unilocular, with a single cavity. Bursæ spread over an extensive surface, and whose walls move but little on each other, are often divided by imperfect fibrous septa, and are called multilocular. Almost all the lesser bursæ are unilocular, most of the subcutaneous bursæ are multilocular.”

Now if one were not engaged upon such a problem as that of initiative in evolution and in trying to give examples of it there would be no Gordian knot to cut, and the condensed statement of Macalister might be simply taken as an accepted account of the manner in which reading between the lines a bursa is formed in the animal body. But, when an hypothesis such as the present is in question, one may not cut the Gordian knot in this way, and must produce briefly certain observations of the process, not only those known in man by anatomists and surgeons but also some found in lower Primates.

Human Bursæ Enumerated.

The following is a list of bursæ in man of which some are normal or always present, and others which are both occasional in their appearance and often imperfectly developed.

Front of Neck.

Pharynx. A small central pit constituting a single bursa the bursa pharyngea.

Behind the angle of the lower jaw. One.

On the symphysis of the chin. One.

On the Acromion process. One.

Beneath the deltoid and the acromion process, one large bursa often opening into the shoulder-joint.

Elbow.

Wrist.

Hand.

Region of hip.

Thigh.

Knee-joint. The prepatellar bursæ.

In the Ham.

Tibia.

Ankle.

Foot.

I calculate that there are at least fifty-two separate bursæ (about one hundred on the two sides of the body) in the normal or fully developed state, though of these many will be found either absent or with very little of the full structure of a bursa. One small but significant point may be referred to here. We are all familiar with the prominence of the knuckles of the hand and the very efficient bursæ which cover them, but most persons do not recognise that the foot has no such knuckles (or prominent metatarso-phalangeal joints) and no bursæ over these joints, except that of the great toe which happens to be very much more exposed to friction and has a much greater range of action than the other four metatarso-phalangeal joints. This might be called by some persons a beautiful bit of adapta­tion for locomo­tion and by others an equally admirable bit of adapta­tion produced by locomo­tion.

Examination of Two Still-born Children.

Some further light may be thrown upon the human bursæ by an examina­tion of two still-born children I dissected in 1908 in Lewisham infirmary, and give here the results as to the more important subcutaneous bursæ.

Male Child: full term.

This example of a still-born, but otherwise normal infant illustrates well the previous statement that certain bursæ are congenital and others of less functional importance are formed after birth. Whereas the olecranon, wrist, patellar, ankle and tendo achillis bursæ are fully formed, those under the acromion processes, one of those of the condyles of the femur, and the digits of the hand, those over the superior anterior spines of the ilium and those of the foot are little if at all developed in this case.

Another still-born child at seven months was also dissected and this had well-formed prepatellar bursæ, scanty ones over the olecranon processes, also over the small joints of the hand and foot where they were difficult to isolate and over the malleoli they were only slightly developed.

A fœtus in spirit I examined and found no commencement of a prepatellar bursa.

Examination of Living Primates.

Anthropoid Apes.

Eight of these I examined during life at the London Zoological Society’s gardens in 1908, four chimpanzees, two orangs and two gibbons. These afforded the opportunity of ascertaining by means of touch the presence, and in a minor degree the size and efficiency of the main subcutaneous bursa, just as one can do this in a human subject. The chimpanzees were A, aged thirteen; B, aged seven; C, aged three; and D, aged two-and-a-half years; the orangs E, aged thirteen; F, aged three years; the gibbons G and H both two to three years.

These eight specimens possessed good examples of the leading subcutaneous bursæ over the olecranon process, the styloid process of the ulna, the patella and both malleoli.

The smaller and less definite bursæ gave the following results.

Chimpanzees.

Orangs.

Gibbons.

Dead Specimens.

I also examined the hands and feet after death of certain lower Primates in 1909:—

Hapalemur Griseus H. Hands. No bursæ on styloid processes of radius and ulna, and no localised bursæ on any metacarpo-phalangeal or phalangeal joints.

Hapale Jacchus I.

Cercopithecus Callitrichus J.

Cercopithecus Mona K.

Macacus Rhoesus L.

Further Undesigned Experiments.

The preceding facts as to the natural history of bursæ in man and some lower Primates, even if they stood alone, are enough to produce convic­tion as to the manner in which bursæ of all degrees of perfec­tion are formed by function, and point to the origin of the initial stages of these structures. But they do not stand alone, for in man there have been carried out certain undesigned experiments in a similar direction, comparable to those described in the sections on direction of hair and arrangement of papillary ridges. These demonstrate the fact that frequent friction of skin over a hard surface has the power of producing adventitious bursæ in regions where they are not found in the normal state.

These adventitious bursæ are the following:—

In the first place certain normal bursæ in important situations are frequently so much enlarged by the constant irrita­tion of pressure and friction that they become considerably enlarged. This enlargement may go on to definite pathological changes and thus come under the care of surgeons.

These may be called “occupa­tion-bursæ” and may be classed with three other well-known adventitious bursæ which are formed on the shoulder in “deal runners,” on the scalp in “fish porters” and in the back of the neck in Covent Garden porters, known as a “hummy.” Entirely new bursæ are formed also over the cuboid bone in talipes equino-varus, over the internal condyles of the femur in bad cases of knock-knee from friction of one joint against the other, over the prominent vertebrae in a humpback. A structure closely resembling a bursa and arising from similar causes to those producing adventitious bursæ is found in unreduced dislocations or ununited fractures.

A small example of an adventitious bursa came under my notice. A woman, E. L., aged 49, had remarkable enlargement of the metatarso-phalangeal joint of her great toe of the left foot, and over this joint was formed a well-marked bursa on the dorsal surface. The right foot showed a much less prominent joint and only a very slight development of the corresponding bursa.

This instance of a bursa-like structure being produced in unreduced dislocations and ununited fractures suggests the concep­tion which I here propose, but do not attempt to verify that all joints in all animal forms from the lowest up to man have been evolved in a manner to which this pathological experiment may give a clue.

A remarkable case reported by Sir William MacEwen in the Royal Society’s Phil. Transactions, Series B, Vol. 199, pp. 253, 279, is worth referring to in this connec­tion. It was a case of a growth of bone in muscle connected with an old injury to the thigh of a man 38 years old, and healthy. At the operation performed by the author of the paper the tumour was found to be movable, partly attached to the fascia lata of the thigh, and the upper part of the tumour moved on the lower. It was found that the tumour consisted of two parts, the upper three-and-a-half and the lower seven inches long, altogether a mass about ten inches in length. Muscular bundles of the vastus externus were included in this ossific formation, one passed through a tunnel in the bone through which it worked, and the sides of it were polished. At the point where the newly formed bone came in contact the surfaces fitted each other and were polished as if they were covered with cartilage, and were here surrounded by a capsule. (Italics not in original.) This fibrous covering when opened was seen to contain a thin serum, which, though not of the consistence of synovial fluid, still aided in lubricating the polished surfaces as they played over one another.

A similar case was reported also by Dr. C. Paterson, surgeon to the Glasgow Royal Infirmary.

A very interesting address by the Hunterian Professor, Mr. Jonathan Hutchinson, was given in February, 1917, on Dupuytren’s work, especially in the discovery of the cause and treatment of the contrac­tion of palmar fascia known by his name. Professor Hutchinson described his method of curing this by the removal of the head of the first phalanx, and showed excellent results and evidence of the formation of a perfect new joint to take the place of the old distorted one, and the fingers were as efficient as in the normal state in the exercise of flexion. He gives photographs of the hand some months after the operation showing it to be capable of easy and full extension as well as of flexion. This again agrees well with the cases of Sir W. MacEwen and Dr. Paterson of the formation of a functional joint by use and habit.

Another distinguished Hunterian Professor A. Keith, also gave two lectures in January, 1918, on the “Introduc­tion of the Modern Practice of Bone-grafting,” which, in its modern form, he assigns to the credit of Sir William MacEwen. He lays great stress on the important work performed in such cases by the osteoblasts without whose living and formative action these results could not be obtained. He explains how necessary it is that these living elements should be stimulated into action by work. They thrive only so long as they have work to do. Another surgeon, Ollier, “wondered why the fragments of bone which he had succeeded in raising from slips of periosteum planted beneath the scalp or amongst muscles ceased to grow and tended to disappear. These bony grafts withered because they were not subjected to the strains and stresses which rouse the activity of osteoblasts.” MacEwen, “by a fortunate chance, planted his tibial grafts in a situation where they soon became subjected to muscular strains and stresses. In a short time bony fragments gathered from the legs of six boys became intrinsic parts of the humerus of a seventh; from the moment of primary union the bone cells of the graft were brought under the stimulating impulses of the biceps and triceps. Osteoblasts are the obedient slaves of muscles; muscular dominance is their breath of life.” (Italics not in the original.)

“Wolff was the first to devote thirty years of constant work and observa­tion to prove that the shape and structure of growing bones and adult bones depend on the stresses and strains to which they are subjected. By altering the lines of stress the shape of a bone can be changed.”

Wolff’s law is simply this: “Osteoblasts at all times build and unbuild, according to the stresses to which they are subjected.”

Professor Keith says further: “We are driven, as I have pointed out in a previous lecture, to look for the primary cause, not in the bones, but in the muscles, particularly in those which are tonically and constantly in action so long as we are standing.”

A terse expression of Wolff’s law is quoted from Dr. John B. Murphy, of Chicago: “The amount of growth in a bone depends upon the need for it.”

A remarkable illustra­tion of a similar process is given in the construc­tion of sponges by the scleroblasts and it is stated: “The soft walls of this sponge are constantly exposed to the force of moving waters, and we shall see that the spicule-builders—the scleroblasts—are endowed with the same properties as osteoblasts—the powers of fashioning and depositing the elements of the skeleton so that the sponge can best resist the forces to which it is habitually exposed.”

One more important quotation from this lecture will suffice. “No one who has watched the behaviour of scleroblasts and marked the design in their workmanship can doubt that they have acquired certain characteristic qualities, chief of which is a sensitiveness to vibrations—to stresses. We see them build the same form of spicules as their ancestors, and therefore must suppose that their building quality is a gift of inheritance. We see them alter their mode of building as stresses change; we must therefore suppose that their inherited powers can be changed by the circumstances under which they work.”69

In regard to the action of the scleroblasts of sponges I have only to point out that the cautious words of Professor Keith on the treacherous ground of inheritance amount to the very same concep­tion of personal selection and inheritance as are involved in the term “educability” of Sir E. Ray Lankester. Whether or not in the case of sponges this be a complete account of the matter it at any rate is a very important piece of evidence, if valid, for selection. Whether or not further it is a piece of evidence for a Mendelian factor implicit in the primordial sponges and released by some loss of inhibiting factors, as Professor Bateson would probably claim, is another and far more imaginative concep­tion. The mere neo-Lamarckian with the aid of personal selection fails to see any difficulty in realising the wonderful process described by Professor Keith.

An apology must be offered here to the patient reader for the introduc­tion under the heading of the “Evolution of a Bursa” of the apparently alien subjects of bone-grafts, artificial new joints and sponge-spicules, but I have hazarded the guess that all joints in all animals have been fashioned—“forged by the incident of use,” to employ a fine phrase of Professor Macdonald’s in another connec­tion—in slow but intelligible ways by use, and that in them, as elsewhere, function has preceded structure. This arose so simply out of the story of the bursæ that I ventured to digress as aforesaid rather than make it the subject of a separate section.

The Significance of the Proceeding.

The foregoing slender contribu­tion to the comparative anatomy and physiology of bursæ is sufficient to show that at certain important and “critical” points in the mammalian anatomy, efficient bursæ are always present. One cannot indeed conceive the function of the parts involved being carried on at all without these ingenious contrivances, and no doubt can exist that in certain of the leading bursæ selection guides and guards, while use and habit maintain them. Over such as these “dominance” or the appearance of mutations might perhaps be supposed to preside, and possibly some useful statistical results might arise from their study from these points of view. But, between these major bursæ in man and lower Primates and the undifferentiated sacs which hardly deserve the name of bursæ, there is a perfect little host of insignificant structures, which at the first attempt at dominion over them on the part of Mendel or de Vries would hoist the standard of revolt. These would even refuse allegiance to Personal Selection under the persuasive banner, “Educability,” which however valuable elsewhere, must stand aside in this little province of Nature. I have thus attempted to “Lyell” this body of facts. Basing the statement on an analysis of a considerable mass of small facts which no one disputes I claim that the modifications drawn from normal anatomy on the one hand and on the other adventitious structures, produced by acknowledged mechanical forces, are examples of the transmission of modifications, and illustrate the mode of formation of certain initial variations. In other regions where Plasto-diēthēsis, as I conceive it, is at work in producing adapted organisms, there may be included in the hyphenated area certain factors of heredity, Mendelian, mutational and others, but not in this group. This is merely an assertion of an opinion though I submit that there is good evidence for it. Not even the hardest hearted Weismannian, Mendelian or mutationist, and not even the biometrician can refuse to this poor little province the required time and mechanical forces, and, unless an opponent can offer some explana­tion more consistent with the facts than that here offered, the proof of causation is as sound as that shown in the larger one of the direction of hair.

CHAPTER XXI.
THE PLANTAR ARCH.

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-diēthēsis 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