A work of great value to the biologist has been written by one whose work has led him in the widening path of human physiology and its very title is instinct with meaning. The Integrative action of the Nervous System may not aid the systematist or the student of genetics, but for insight into formative powers, where the former can but record facts and find no interpreta­tion, such a work is of supreme importance. When the plant sealed its fate and enclosed itself in a cell-wall and abandoned a life of movement, it was foreordained that its rival would be that cell and its descendants which could adopt a free life, and that the future of the world would lie at the proud foot of that conqueror who could command and mobilize the resources of a nervous system. And, as we know, it has fallen to man to receive the rewards of this promise and potency of a higher life. If one seeks to understand the steps by which man has arrived at his primacy it can only be by the highway of nervous progress, however much the tracing of certain connecting or collateral paths may throw light on contributing causes. So that man’s place in Nature is nearly synonymous with the structural evolution of his brain, as Huxley has shown in his clear and simple manner. Even if man is to remain still an animal Melchisedec for generations to come, or to put it lower, a foundling, no future discoveries that can be imagined will disprove Huxley’s declara­tion, “Evolution is no longer an hypothesis, but an historical fact.” And yet if man has become adapted to his world, and, in it, crowned with glory and honour by the unfolding of some original complexity, or as the result of some fortunate mutations in the distant past, the human brain, with its cranial capacity of nearly three times the number of cubic centimetres to that of the gorilla, has been making false claims to a paramountcy over all factors in the wonderful initiative of fresh capacities and their mobilisa­tion for conquest. Nothing less than such a “claim” was understood by the ancients, and, though metaphysics had to supply the lack of anatomy and physiology, it has always been held that mind was lord of matter, and now scientific research has told us why. But no one, even the most hard-shelled scholastic, can refuse to the brain organ its predominant share in the making of man. This is seen even in the frigid sphere of science by the difference of interest there is shown between any great discovery bearing on the evolution of man, or on some new lower animal form. When Sir. H.H. Johnston astonished zoologists in 1901 by his discovery and proof of the existence of an archaic large mammal which had been interned for an incalculable time in the Semliki Forest, the thrill felt at that historic meeting passed off very soon when the leading British biologist had monographed the Okapi, settled its name and surname and introduced it into text-books. This is never the fate of such as Pithecanthropus or Eoanthropus dawsoni, or of the more recent genealogical theory and researches as to arboreal man. The call of these studies of man’s evolution is felt by all, and the difference in the two branches of biology may account for what must have struck many others, that is the neglect of adding the blue ribbon of science to the honours of the discoverer of the Okapi.

These few trite remarks as to the importance of the nervous system in the making of man have been introduced here, though they bear more closely on the next two chapters, because this importance comes in at every stage of the present treatment of the origin of modifications in muscle.

Anatomists’ Views of Muscles.

There is a very strict and austere custom among anatomists, which doubtless is in a measure necessary, of insisting upon following rigorously the homologies of muscles, especially in human anatomy, and in this branch of a greater subject the canons are followed to an extent that surprises the seeker after origins. A remarkable example of this is in a paper by an eminent anatomist, now Professor at King’s College, Dr. E. Barclay Smith. It is a paper on the “Morphology of the short extensor of the human fingers.”72 He says “the precise significance of this occasional extensor brevis digitorum manus is a matter of considerable interest.” He gives four possible interpretations of this unusual muscle. The last, viz., that it is derived from a new muscle-germ alone interests us here because of the remarkable caution and austerity of his remarks on this interpreta­tion. “If an ext. brevis dig. manus cannot be regarded as an atavistic anomaly, or as a derivative from any existing musculature, the only way in which its presence can be accounted for is to suppose that it is of entirely new origin—the product of a new muscle-germ. Such an explana­tion is, of course, the last resort, and all other possible derivations must be disproved before it can be accepted.” The physiologist would probably think such an interpreta­tion was the obviously first resort. The same writer discusses at length the homology of an exceedingly rare anomaly among muscles, the extensor ossis metacarpi hallucis, and his desire on the one hand to find a missing parent for Japhet, and his honesty and accuracy on the other hand lead him to say “even when it is present, it cannot be regarded as directly atavistic, since it does not represent a normal mammalian tendency.” And he adds a gentle but remote sugges­tion—“Brooks certainly describes such a muscle in menobranchus and hatteria—two rare and remote reptiles!” But, lawful and necessary though this be, there must be stages on the path of human evolution where such a method must fail and the anatomists can do no more than hold aloof from theory or specula­tion, with a certain grim enjoyment of the disputes and difficulties of the genealogists.

Initiative in Muscles.

Initiative in the evolution of muscles clearly occurs somewhere in the stem, and behind the formed expression of an altered habit is the integrating action of the nervous system. This will be by some looked at askance as a deus ex machin and reckoned as part of the argument from ignorance in a way which recalls Weismann’s scorn of Lamarckian factors in germinal selection. I submit that what he and Osborn call “the unknown factor” of use and habit, arising in response to new stimuli meets as no other proposed sugges­tion does the formation of new muscles. Given a certain fundamental architecture of skeleton and musculature, such as of primitive vertebrates, one can, without doing violence to any known facts, place the formation of new organs of movement in the following order:—

1. Neural changes and habits.

2. Muscular modifications.

3. Consequent modifications of bone. It carries the question no further to say that these are correlated, however loose may be the meaning of that word that is understood. If the prerogatives of Selection within the germ, of segrega­tion of unit-characters and dominance, and of mutations are not unlimited in the construc­tion of organisms, there still remains a sphere of action for the initiating power of the nervous system. Bones grow and change their form in response to increased or altered muscular action on them, and it is necessary to look back a stage further in the story to the neural changes however produced. There have been abundant opportunities in the long history of mammalian evolution for primitive forms to take a new course of life, and they have done so on an extensive scale. The impulses that have led them may have been started by some “needs” such as Lamarck taught, some change in their surroundings involving new stimuli, or “insults,” as Haeckel called them, but the first of the structural stages must have been in the cerebral cortex.

Cross-Roads in Evolution.

The most instructive levels of animal evolution are those where two or more great stocks have diverged from a primitive one. There may have been several factors leading to the division of the early Ungulates into the odd-toed and even-toed groups, of the Carnivora into cats, dogs and bears, the FelidÆ into the highly-specialised genera of that intense family, the early parting of gibbons from the common anthropoid stem, and then the division of this line into the three great genera with which we are familiar. Whatever may have been the unknown factors in the environment such as changes of climate and level, geographical isolation, increase of foes, profusion or lack of food, to which these diverging stocks became adapted in their organs and form, in fact whatever we do not know, we know this—that in their measure they acquired more convoluted and often larger brains, and the stimuli passing through their receptors into their consciousness increased with an everflowing tide, in volume, intensity and complexity. Many an archaic habit of their race they must unlearn, and it is doubtful if germinal selection would avail in this valuable process of economy as it is held to do in the case of the human little toe.

It may be taken as granted that increasing complexity of brain in their own lines of life did accompany these adventurers of small or large groups. It follows that muscular changes from the original stock would follow neural changes, for movement and activity is inseparable from the animal, and the integrating action of the nervous system would constantly initiate, maintain and establish fresh habits and these be expressed in new muscular structure. Whatever higher uses, as we believe them to be, man makes of his brain, as reflec­tion, reasoning, imagina­tion and associa­tion, such were not the new properties acquired by these adventurers. They were very much concerned with hunger and love, and for them “philosophy” did not sustain the structure of their world. But more varied movements of head, trunk and limbs, and greater agility and strength brought them such prizes as were within their reach. This may be only another way of expressing Sir E. Ray Lankester’s concep­tion of educability, which he maintains to be the only acquired character the organism inherits, and it may be therefore assumed to be under the iron law of selection. This must be accepted with the respect due to the high authority from which it proceeds. But such a concep­tion, while it removes a false light in certain regions, sheds no light on the pathway of animal evolution, unless modifications be transmitted, and we can now take it that man does not inherit the power to speak which for incalculable ages he has been learning, nor to write, even though in the days of the early Pyramid-builders and the Sumerians in the plains of Chaldea they possessed the power of writing, nor can a musician’s child learn to play an instrument without teaching, or indeed man perform any of his arts and crafts by second nature: so, negatively, this knowledge is valuable, and the neo-Lamarckian must proceed on his quest without anything more than educability to aid him—but it will serve. The fact is that we do not inherit habits or associations as such at all, but the neurones of the grey matter in spine and brain which subserve, direct and control them. Though a fresh neurone or two in the brain of an early ungulate deliberating, so to speak, as to the life he shall take up, whether that of oxen or horses, may be trifling in itself as to immediate value to the animal, it may be to him as much a matter of fate to acquire those microscopic cells as it was to the undifferentiated organism that paused before it sealed its fate as plant. Under the free and enlightened government of the integrating nervous system liberty to express itself to an almost unlimited extent, in accordance with progress, is thus open to the hypothetical adventurers.

When considering such an aspect of the organism as the “choice” between the career of an odd-toed or even-toed ungulate, a cat or dog, a lion or tiger, a gibbon or other of the four anthropoid genera which assuredly was presented to certain groups of primitive ungulates carnivores, felidÆ or apes, as historical beings, the vision of the process is sore let and hindered by the limiting force of certain expressions which have been sanctioned with the imprimatur of fifty years’ high thinking in the realms of high biology. I refer of course to the terms Selection and Evolution which, though they cannot be replaced by better terms, have the power and sometimes have had the effect of impressing on the story of organic existence an aspect of determinism which does not allow, for any purposive action of the individual, the working out of its own salvation, on the part of higher forms at any rate. As among nations self-expression has become of late a powerful force in their development, and indeed of individuals, so it may be argued by analogy that the total experience of an organism, may result in its co-operation in the process of its progress towards higher things. Bergson hints at such a process in organisms, but appears to allow nothing for the individual in his Élan vital, where the mass alone counts. So if the two binding terms of Selection and Evolution must be granted their enormous power over our thoughts, there must be also a loosing as well as a binding, and we, as well as certain young ecclesiastics in a hurry, may put in a plea for Life and Liberty. Thus is Lamarckism immortal, and the integrative action of the nervous system supplies the reason.

This well-worn subject is not out of place here, where I am trying to show evidence of self-expression in terms of muscular modifica­tion arising from fresh activities of the brain.

New Muscles.

If it can be said without fear of question that “the differentia­tion of muscle and nerve is the morphological result of division of labour, whereby the unit of protoplasm, in which irritability and contractility are combined, has, on the one hand, become modified into muscle, which retains the property of contractility, and on the other into nerve, which retains that of irritability,”73 and if Wolff’s Law of Bone Transforma­tion teaches that if a normal bone is used in a new way its structure and form will change to meet its new function, which Sir Charles Bell had more vaguely taught in 1834, it cannot well be denied that at certain turning-points in the history of animal organisms the sequence of changes which arise is neural change, muscular modifica­tion and finally change of bone, whether ungulates, carnivores, felidÆ, gibbons or big anthropoids or man, be the dramatis personÆ. The only question is whether selection or use and habit initiates the subtle and slow process.

Unstriped Muscles.

The simplest of the muscular acquirements of mammals is of course that great mass of little structures which constitutes the unstriped musculature. I must admit that here again I am engaged with what the professed biologist may call trifles, but these, like some others of a corresponding rank, have a provoking quality of persistence, and display, if one may personify them, an insistent desire to know whence they come and why they are here. Some of these, like the one before us, may be comprehended in the great chapter of the Evolution of the Indifferent of which they form a page. This world, at any rate in the moral sphere, would be an intolerable house of bondage if there were not many things that matter not as well as things that matter, and there is reason to believe that in the process of the making of man and a vast number of forms below him there is a large field of structures, parts and organs, where things that matter not are to be found. One strange province of this realm is the coloura­tion of animals in certain regions where no eye ever can see the colour or can take any heed of the markings, treated very fully many years ago by Mr. Beddard in Animal Coloura­tion.

Unstriped muscle arises, as the striped variety does, from the mesoblastic muscle-plate and appears in nearly all organs, blood-vessels and skin, and as trade is said to follow the flag, so a development of new unstriped muscles must speedily be found in every new structure of the regions where unstriped muscle is found. The skin is the simplest, and less complicated by the presence of other structures than vessels and organs, where it also exists, but where it trespasses too much on the territory of selection for my immediate purpose. A small band of this muscle called an arrector, or erector, pili is attached to most, if not all, of the third of a million hairs which cover the skin of man, and is inserted into that side of each hair which forms an obtuse angle with the plane of the skin. This tiny structure is endowed with the quality of contracting in response to certain stimuli falling on the skin, so that it causes the hair to which it is attached to stand erect instead of sloping, and incidentally squeezes some of the secretion out of the sebaceous gland which lies in each angle. The human skin thus possesses about a third of a million minute muscular bands and shows no sign of parting with this old gift from a lower hairy stock, and whatever value, if any, their function be to their possessor they show a remarkable readiness to perform it efficiently. It makes their existence and persistence no clearer to call them vestigial, for one only thus throws the question of their origin much farther back. Undoubtedly they come from afar and were in full development in the earliest hair-clad mammals, so an ancestry reaching back to Monotremes or Marsupials is not to be lightly set aside. The raw material was undoubtedly formed in response to stimuli conveyed to the brain, and the earliest appearance of muscles which erected the hairs must have been wholly insignificant either upon the survival or comfort of the possessors.

A Remarkable Example.

The arrectores pili exhibit very little evidence of control or interference from the action of the brain, but there is one region of one animal, like the Rosetta stone that set Champollion at work, where a very simple hieroglyph is recorded. I have been able to find no other in all the hairy mammals I have examined than that startling pattern which the back of the lion, shown in Fig.37, sometimes displays. That well-formed patch of reversed hair of roughly triangular shape which is frequently found on the back of a lion has been described and, as I interpret this strange structure, it would seem clear that neural change in some examples of this species has led to so persistent contrac­tion of the arrectores pilorum over a certain area of skin, and that these have permanently reversed the normal and primitive slope of the hair. I have never found it present in a lioness, and not in all cases of male lions. It marks its possessor with the brand of a fierce and especially savage character, and he is not able to screen it from the eye of the Zoologist as well as Milady did her brand of shame, until that fatal day when D’Artagnan disclosed it. This pattern on a lion’s back is strangely reminiscent of the ridge of bristling hair we see on the corresponding region of a fierce dog’s back when he is infuriated. In the latter it may be said to have selective value, as perhaps also is the bristling hair on the head of a gorilla when enraged, much in the same way as the Chinese warriors sought to alarm their enemies by terrifying grimaces, or those terrifying tones and expressions of face which the Tyrant man, really a coward, is said by such as Miss Wisk to exercise over the women of his circle. We may present all these to the Pan-Selectionist, but inasmuch as the short, bristling hairs on the back of a lion are on the one hand hidden by the mane from an animal in front, and on the other are so small as to be seen quite close if at all, the survival-value of the reversed pattern of hair in question is quite outside the province of selection. It is so manifestly under the control of cerebral action, that it may be compared, as an undesigned experiment, with that of man in placing harness upon a horse, as to the power of cerebral action in producing structure. Though, as far as I can learn, it stands alone, it is difficult to believe that such a thing as a unique example occurs in nature, but it is interesting and suggestive from the Lamarckian point of view, and even the opposing counsel must admit that it is among indifferent structures.

Facial Muscles of Expression.

This record in terms of hair of personal and ancestral emotions has, however, a link with certain more numerous and important striated muscles, such as the facial muscles of man and apes, modifications of the great platysma-sheet, and which are disposed in two layers, a deep and a superficial. This covers like a hood at the third month the head and neck of the embryo, and later assumes on the face its specialised form of certain bands which operate round the eyes and mouth. As they are of the striated kind these muscles can be moved at will, but their main action is much more under the government of the mental processes of their possessor. As they are fundamentally the same in apes and man very little new muscular structure arises in man, and little more than shaping or refining takes place.

The facial muscles which operate round the orbit have less mental action represented in them than those of the mouth, though the action of the special elevator of the upper eyelid is conspicuous among the expressions of a vigorous person. Both apes and man have muscles on each side which raise or lower the angles of the mouth, draw the angles upwards and outwards, and raise the upper and depress the lower lip; and, though the muscle of the mouth which corresponds to the orbicularis of the eye is not a continuous structure, but formed of interrupted bundles of fibres, it is powerful in closing the lips and active in the expressions. There are also in man scattered oblique fibres in the substance of the lower lip, well-developed and closely-set in a sucking child, and these in the adult are scattered and less conspicuous.

There is thus a remarkable set of structures in the face of a higher primate which convey mental emotion. As they also belong to animals with a high degree of convolu­tion of brain, though certain are found in lower mammals, their specialisa­tion is only to be accounted for by the long-continued involuntary expression of mental states existing in the particular form of primate. Professor Keith says in the work before referred to: “Muscles supplied by the facial nerve are the physical basis into which many mental states are reflected, and in which they are realised. Through them mental conditions are manifested. It is found that the differentia­tion of this sheet into well-marked and separate muscles proceeds pari passu with the development of the brain. The more highly convoluted the brain of any primate the more highly specialised are its facial muscles,”74 and he points out in a smaller work75 that in the gibbon, and monkeys of the Old and New Worlds the facial system becomes simpler and at the same time more robust, and he pictures the facial muscles as the “servants of the brain.”

If an ape can express a good many of the coarser emotions of an animal by the action of its facial muscles, and through kindness and training exhibit some of the finer ones, there is a wide distance between this level of attainment and the multiplied moods and unnumbered varieties of expression which give to the human face its unique charm. If we can express pleasure, pain, anger, contempt, hatred, surprise, affection, sympathy, fear, hope, reflec­tion, perplexity, gaiety, melancholy, cunning (and many another can be supplied) what a remarkable field of physiology in terms of anatomy we have in the facial muscles! There is a very obvious reason why none of these emotions have been fixed in an objective form in ape or man, as the patch of reversed hair is on the back of a lion, for moods and states of feeling in every individual man are subject to such endless variations that it would be impossible for them to stamp any individual face with a record of even one emotion which could be transmitted to descendants, to say nothing of the inconceivably great probability that heredity would at once swamp any initial modifica­tion.

Three Stages.

The stages then are but three—mental states, specialisa­tion of small muscular bundles from an existing simple sheet of muscle, and disuse of the remaining portions, and in this small but highly significant field we see structures created independently of will as servants of the brain, and without any survival-value in their earliest stages. It is more than likely no monkey, ape, or early man whose face was covered with thick hair from his eyes downwards, ever saved his life or gained a better mate by reason of the subtle modifica­tion of a tiny muscle which was proceeding pari passu with the growing complexity of his convolutions and their manifested emotions. This is not to claim that a more modern man or woman would not find sexual selection of value by reason of his or her more pleasing or commanding facial expression. That the initiative of these alluring modifications was simple and Lamarckian cannot be gainsaid, whatever the fruit of the finished process may be to-day. We know in our own experience that many a handsome person with good features and little expression is often unsuccessful in the matrimonial market, when another with defective features and a fine, delicate, attractive expression takes the prize. So the early story of the formation of muscles of expression is seen to be a page in the evolution of the indifferent.

The Fly-shaker Muscle.

The panniculus carnosus, of which the facial muscles are part, is a great system of musculature found in various animal forms, and it furnishes a field for study of the evolution of the indifferent and the initial stages of the formation of a muscle. This is a servant of the brain in a more indirect manner than the facial muscles, but it, too, arises in obedience to the integrative action of the brain. The early specialisa­tion of it need not be considered here. It may be considered unwarrantable to claim the great Fly-shaker muscle of Ungulates as an indifferent structure, but the arguments by which the Pan-Selectionist would annex it to his sceptre, as a triumph of the minute care of the organism by selection, rest only on the assump­tion that he knows how it has become an adapta­tion to the life of its possessors. This is now more than it used to be a matter of opinion since the publica­tion of Professor Bateson’s revolutionary Materials, and others beside he have reserved to themselves the liberty of doubting the accepted explanations by the tangled path of adapta­tion. The statement of Weismann, “Everything is adapted in animated nature” was necessary to his theory of germinal selection, but it admits of extensive and numerous exceptions in view of the fact that so much of adapta­tion is partial and imperfect. If he had said that every organism as a being is adapted he would have been nearer the truth, but that every tissue and part of an organism is adapted is demonstrably untrue. A large number of organisms, themselves apparently well adapted, flourish well enough and reproduce their kind in spite of faulty and rudimentary tissues and parts. If it were not so we should have seen little of progress except what come under the laws of genetics,—a distributional matter. Even the super-Geddes could not distribute what was not there, for he could not deal with raw materials and change them by a fairy wand into manufactured articles. In the great field of domesticated plants and animals man has to find not only some mutation or some dominant strain and breed it to his will, but to cultivate the domestic qualities of animals and employ cultural conditions for plants. There is doubt expressed as to the length of time or numbers of generations during which these cultural conditions can extend, but Professor Thiselton Dyer many years ago made the remarkable statement as to plants:—“While specific stability under constant conditions appears to be the rule in nature, it is widely different in cultiva­tion. When a plant is brought under cultural conditions it maintains its type for some time unaltered, then gives way and becomes practically plastic. From my experience at Kew, where I saw the process continually going on, I hazarded the generalisa­tion that any species, annually reproduced from seed, could be broken down in five years. During that period specific stability, though menaced, tends to maintain itself. Darwin was well aware of this.”76

Most biologists from time to time betray the fact that their minds can only be relieved from an intolerable burden, in accounting for the numberless adaptations in organisms, by the view that many of them originate through factors of use and stimuli from environment, and at first are entirely indifferent as regards the survival or better mating of their possessors. To which the stern opponent replies, “What is there to show that in the existing scheme of things there is any provision made which will minister relief to the burden of your little mind?” To which, “answer came there none,” except a subdued reflec­tion that everything we see of living, striving nature around us has a most provoking way of speaking to us of daily, hourly and incessant action and reaction, stimulus and response, and that those who view the process thus do seem to bring some order into what would otherwise be chaos—and yet all the while someone is being grossly deceived! This “may be magnificent but it is not proof,” some will say, and will ask if the older observers of the heavenly bodies were not wrong in their complete convic­tion that the sun went round the earth. This digression introduces the role of the fly-shaker. If I am told that this muscular sheet in a cow or horse to-day is a relic of raw material inherited from a remote ungulate stock little evolved, and that it contributes in hot weather in the time of flies to the comfort and better mental state of the cow or horse, that it shall be able to keep those enemies at bay, and that the muscle is kept well in order by two or three months’ practice in each year I can understand in a measure its presence to-day. It has an efficient ally in the sweeping tail of a cow and that of a wild horse, and both of these weapons are further aided by the mobile ears of cow and horse, and the stretching movements of its head and neck. Thus the body of a cow, for example, is like a map with four territories delimited, that of the fly-shaker, the tail, the ears and the head and neck. Between these offensive weapons a cow is better defended against flies than a European in India by his punkah, or China was by its great wall, or Britain by the wall of Vallum of Hadrian or the wall of Severus, which with forts and garrisons was designed to protect it. Speaking in allegory the evolving brain of an early ungulate occupies the position of an ancient Chinese Emperor or a Roman Proconsul in Britain in its provision against “barbarians,” either Asiatic or Celtic. The resemblance goes further, for no experienced Roman General, whatever the Celestial minds in China may have thought, would fear that the loss of a sector of his wall would imperil the army of occupa­tion in Britain or the fabric of the Roman Empire. But as, in the long run it contributes to one’s welfare to be comfortable, and even the domestic ungulate is somewhat of a hedonist, a well-developed fly-shaker is maintained, the occasional use of which in winter and frequent use in summer and the active purposeful switching of tail, twitching of ears and jerking of head have their limited value. Here there is ample room for diverse opinion and the opponent will ask with some degree of force how we know that there is no more benefit to the cow from its fly-shaker than a mild degree of comfort, and may assert that the possession and use of it may have survival-value by its defence against deadly parasites. We do not know, nor does he, but it would seem that except for the tsetse fly in Africa the plague of flies does little to an ungulate beyond irritating its brain, and if he had no fly-shaker, he would still be able to reach a considerable distance with his tail, ears and head over the irritated regions. The question of survival indeed resolves itself into the vigour and energy of his integrating brain.

To this view of the function and origin of the panniculus carnosus the busy systematist and student of genetics may refuse to listen, and pass to the order of the day, but I submit that in stating a position it is useful to put forward a crude example in which the issue is plain, and which subsumes an immense number of smaller and more subtle cases, and in a region where the most hardy rebel will not dispute altogether the sway of personal selection. It is a question here of the manner in which, speaking in metaphor, the early ungulate first set about making his eolithic or palÆolithic weapons and fashioned them into what we see to-day. “Forged by the incident of use” and habit meets the story of the fly-shaker far better than some mutation arising in far back ages or some dominant variation, or “useful variation within the germ.” At any rate Lamarck finds the raw material to hand, and there are supplied adequate noci-cipient stimuli with response, in regions where these are most active under the dominating action of the brain.

Other Muscles.

In the skeletal muscles of the primates many muscles offer themselves for considera­tion as examples of inherited structures arising under the stimuli of altered function, and only a few of these will be dealt with. It might appear sufficient to those who yield, perhaps too willingly, to authority, if I were here to try and prove my point by quoting the statements of one of the greatest anatomists of our time and country, and so pass on—but it is to be feared authority cannot carry one far in a dispute so important. Macalister says, however, “The anatomical arrangement of the muscular system is the physical exponent of habitual actions and those actions are the chief factors in moulding the bones and in regulating the position of the somato-pleural vessels and nerves”—and “the locomotory function and consequent utility of the trunk-muscles were lost when the early vertebrates became terrestrial. In higher vertebrates, and notably in man, the mobility of several regions of the vertebral column differs both in degree and kind: the outgrowing vertebrate processes show consequent variations, and the muscular system is varied accordingly.”77 Also “as both origins and insertions (of muscles) are the creatures of habit, they are both equally variable with variation of function; but, as in higher animals the kind of work to be done is more constant than its degree, so, as a rule, insertions alter less than origins.”78 Macalister, at any rate, held a very clear dynamical rather than static view of the making of the muscular system. But as the days of authority are in a certain sense gone for ever, and we live under the reign of experiment, research and questioning, every biologist, within certain limits, does what is right in his own eyes; there is no King in these days.

Skeletal muscles are structures in which, if ever, the factors of use and habit and disuse would be shown, because muscle is a tissue, with highly active metabolism, so that it has been called “an expensive tissue” for the animal to maintain.

Muscles of Primates.

This physiological fact agrees with the anatomical results of an extended study in the musculature of primates, especially of man, and Hartmann’s book on Anthropoid Apes supplies abundant evidence of the variations of the muscles of these animals, which are not at all more striking than their differing modes of life would suggest. It would be wearisome to quote all these, but a single muscle may be given as an example of a special ape’s muscle with variable distribu­tion. It is called latissimo-condyloideus and starts from the insertion of the latissimus dorsi and passes along the inner aspect of the humerus for a variable distance. In the baboon and others it goes to be inserted into the inner inter-muscular septum and the internal condyle of the humerus, in the orang to the condyle, and in the gibbon to the centre of the shaft. As to origin it proceeds from the insertion of the latissimus dorsi, but in the gorilla from the coracoid process of the scapula and from two portions of the pectoralis minor, and is finally attached to the inter-muscular septum between the brachialis anticus and the triceps; in the chimpanzee it divides into an anterior and posterior portion, the former being attached to the inner condyle, the latter to the middle and inner head of the triceps; in the orang it divides similarly, but in one particular example it had an anterior thin portion attached by a slender tendon to the coracoid process of the scapula and a posterior portion arose from the latissimus dorsi; in the white-handed gibbon it arose from the function of tendons from the latissimus dorsi and teres major and was inserted into the fascia between the tendon of the biceps and the brachialis anticus.

Such a divergence as this within the strict limits of an anthropoid muscle, concerned in the various forms of climbing action of these apes, can only suggest an origin from a divergent set of functions and small details in their respective modes of climbing.

Hand and Foot of Man.

Both the hand and foot of man supply a small muscle for considera­tion in the present connec­tion of habit with formation of new structure. If man be regarded as of simian origin there are not as many entirely new muscles in his equipment as would be expected from his departure from the habits of simian ancestors, though many muscles are found to be altered in size and shifted from the ancestral positions. But the human hand presents one suggestive example of a little muscle not found in any other animal, the special small extensor of the thumb, arising from the interosseous membrane between the radius and ulna, and from the radius, being segmented off from the extensor of the metacarpal of the thumb, and it accompanies this muscle and tendon to be inserted into the first phalanx of the thumb, and is peculiar to man. It can be easily seen at the radial border of the well-known “snuff-box” which is produced by it when it is fully extended. This is of course a muscle of small importance to the functions of the hand, and its appearance in man can only be supposed to be a subordinate detail easily derived from the greater extensor by reason of the more delicate adjustment to complicated movements of the hand under the directing power of higher cerebral development.

Peroneus Tertius.

The foot of man possesses the small peroneus tertius which was referred to as one of the evertors of the foot concerned in the construc­tion of his plantar arch. Macalister and Professor Keith both speak of it as peculiar to man, and the latter refers to it at some length,79 the whole passage being worth quoting here. “Although the evolution of the human method of progression was attended by a profound altera­tion in the form and action of every muscle and bone with lower limbs, yet this great transforma­tion was produced without the appearance of any really new element. One new muscle—the peroneus tertius—did appear, and the history of its evolution throws an interesting sidelight on the origin of new structures. It arises by the outer fibres of the common extensor muscles of the toes being separated. In all the anthropoids the feet are so articulated at the ankle-joints that the soles are directed towards each other, and only the outer edge of the foot comes to rest on the ground when the animal tries to stand. The feet have a tendency to assume a similar position in children at birth. The advantage of a muscle, such as the peroneus tertius, is apparent in the human foot, for it tends to raise the outer border of the foot, so that the sole is properly applied to the ground. If we examine the muscles which, rising from the front of the leg, cross the ankle-joint to end on the back of the foot on the toes of fifty men, we shall find every stage in the evolution of this muscle. In one man at least it will be undeveloped; in two or perhaps three it will be represented by a part of the tendon of the extensor muscle of the little toe, which in place of ending entirely on the toe sends a part to end on the metatarsal bone of the little toe. In only forty of the fifty men will the peroneus tertius be found quite isolated from the parent muscle—the extensor communis digitorum, and to have a distinct origin from the fibula in the leg, and a separate insertion to the base of the fifth metatarsal bone in the foot. In a series of fifty specimens every stage in the isolation of this new muscle will be seen. It has never been found in any anthropoid, and is more often absent or undeveloped in African than European races.”

To this excellent account I have only to add one comment. It can hardly be an accident or without significance that this special human evertor of the foot concerned in the construc­tion of the plantar arch is “often absent or undeveloped” in African races, which are well-known in some groups to have adapted themselves to a form of foot which shows no plantar arch, being normally flat-footed. In this small field of observa­tion, a mere plot of lentils like that which Shammah defended of old, there is set forth a mimic battlefield, and it is not difficult to see that the forces at work can owe allegiance to one and one only of various commanders. The problem as to the origin of the peroneus tertius would no more attract the Mendelian than did the trousseau and approaching marriage of Caddie Jellyby attract the far-away gaze of her mother, fixed upon the world of Borria-boula-gha, and, for that matter, de Vries would hardly pay it more attention—to him it would be indifferent; whereas Weismann would have as much to say about it as about the little toe of man, which furnished for him and Herbert Spencer such fruitful material for debate many years ago. This muscle resembles the results of some of Michael Angelo’s first attempts at sculpture, thrown aside perhaps in his place of work and from time to time taken up, rough-hewn again and again and finally shaped into a form far from perfect, but with the value and teaching of a failure for him who was some day to outshine all modern rivals. If the history of this muscle be not one of initiative in evolution through the factor of use and habit the Pan-Selectionist must do the best he can with an incalculable number of “trials and errors,” and must suppose that, rather than allow this small territory to the neo-Lamarckian, a long series of man’s ancestors have been making experiments for the benefit of man’s walking power under the guidance of selection with an insignificant muscle whose only function is that of aiding in the eversion of the foot, and that in the rudimentary condition described by Professor Keith it had selective value. No one who was not committed to a dominating theory could hesitate for a moment which of the two alternative views of the origin of the peroneus tertius he would choose. Dr. Barclay Smith speaks in the paper referred to above of the extensor brevis pollicis, or minor, as a muscle of extremely late appearance, and as “peculiarly human,” and says all the evidence points to its being a segmenta­tion product of the extensor ossis metacarpi pollicis, its appearance being foreshadowed in the anthropoid by an extension of that muscle on to the proximal phalanx of the thumb.

It is not without interest to the thesis before us to read the rather bewildering story of the early life of a very insignificant muscle such as the small extensor of the thumb of man.

As illustrations of the moulding and pruning of perfected muscles it may be remembered that, as Macalister says, “portions of muscles may also become detached and degenerated so as to act as ligaments,” and “the adult muscular system of man bears everywhere traces of earlier cleavings and subsequent fusions, partial disappearances and local outgrowths.”80 This passage recalls one in which Huxley says in watching certain phases of development you can almost see the hidden artist at work, and here the sculptor may be pictured in his chipping, trimming, rejecting and finally shaping, some creation of his brain; and from a biological point of view a vision of the processes of use and disuse may be obtained. Professor Keith also speaks often of the migrations of muscular attachments in a way which agrees with the passage quoted from Macalister.