Man : a history of the human body

Front matter

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Preface

This little book treats of the history of the human body rather than of its structure and mechanism. It reflects the opinions current among the more progressive anatomists of the present time. The author has relied to a large extent on the well-known works cited in the bibliography at the end, but it is only fair to the reader to mention the fact that many of the statements are founded on unpublished researches made by the author. The last chapter sums up the story of man's origin, and the reader, especially if unfamiliar with the geological divisions of time, may find it profitable to refer to this chapter when the first two or three have been read.

A. Keith.

Hoyal College of Surgeons of England^ London, W»C,

Contents

CHAPTER PAOm

I How THE Human Body is Studied , 9

II The Human Brain 21

Chapter II

We propose to visit the dissecting room again, this time with the definite purpose of seeing the human brain — that wonderful organ which has hfted mankind to so high an estate. We shall see a structure which, to all outward appearance, might have been that of a great man — one of those who have written our plays, our novels, our philosophies, or who have conquered the world by force, by invention or by sweet persuasion. Here, on the threshold of the medical school, a confession must be made of our ignorance : no one, however skilled he may be, can tell, from merely surveying the brain, whether its owner was a clever man or a foolish one. The day may come when an examination of the brain will reveal its capacities, but we have not yet reached that position. Having made this confession we make our way to a small anatomical theatre in the school, and take a seat with the students on the benches which rise tier on tier, almost to the roof. Before us stands a white-coated anatomist ; he is to

22 THE HTOIAN BODY

give a demonstration on the brain, showing it to us in its natural position within the body. The scalp, in the subject of demonstration, is folded back, and the cap of the skull removed. Before the brain can be seen, a thick membrane (dura mater), which lines the interior of the skull or cranial cavity, has also to be turned aside, but this is easily done, for the brain is merely in contact with it. The chief part of the brain is thus exposed — the part known as the cerebrum. We note that it occupies that region of the skull which lies above the ear-holes, and that it extends forwards to occupy the forehead above the orbits and backwards to fill the projecting occiput above the root of the neck. The brain is wrapped in a semi-transparent membrane through which we see a rich supply of blood vessels on its folded or convoluted surface. Between the folds and convolutions there are depressions and fissures.

The cerebrum is divided into two hemispheres, right and left, a fact which we could not have guessed from our inner consciousness, for we seem to think as if with one organ. The anatomist presses the right and left halves slightly apart and shows a wide white bridge of nerve fibres (the corpus callosum) joining them. He further informs us of another mystery — the right hemisphere presides over the left half of the body while the left hemisphere is connected with the

THE HUIMAN BRAIN 23

right side. He narrates a case, to illustrate the crossed relationship of brain and body, which he had seen some days previously. The case was that of a workingman, the subject of fits, in each of which he fell down with the fingers of the right hand moving convulsively. The surgeon marked out a small area on the left side of the patient's head, and operating there found a small tumour pressing on the underlying part of the brain. Its removal effected a cure. We see then why the surgeon operated on the left hemisphere when it was the right hand which was affected, but to realize how he was guided to the exact spot for operation we must look at the surface of the brain exposed before us. The surface is thrown into convolutions separated from each other by depressions. The longer and deeper depressions are known as fissures. We notice that the main one — the fissure of Sj^lvius — begins on that part of the brain which lies just behind the eye and beneath the temple and passes backwards and upwards to end some distance above the position of the tip of the ear (Fig. 1). The fissure of Sylvius separates the frontal and parietal lobes of the brain, situated above the fissure, from the temporal lobe, which is situated below it. Towards the posterior end of the brain the temporal and parietal lobes join with another important lobe — ^the occipital. Crossing the surface of the hemisphere from above downwards and separating the frontal from the parietal lobe is a fissure of the utmost importance to us. It is

FISSURE or ROLANDO

\ f>OST-CENTRAL. COHWJiJJTIOf*

^gpCeNrWAL eONVOL:

h^ FfTONTAL QONVOLl

Fio. 1. — ^The main divisions of the Brain, showing some of the functional centres.

the fissure of Rolando or central fissure (Fig. 1). On the convolution in front of the central fissure— the precentral convolution — is situated the area which regulates the movement of the arm. It was the knowledge of this fact which guided the surgeon. The central fissure is also seen on the brains of monkeys ; in the man-like apes or anthropoids the fissure is very human-like. Some forty years ago it was discovered that when the cortex or surface layer of the convolution in front of the central fissure was stimulated electrically, the unconscious ape performed certain definite movements. If the upper part of the precentral convolution was thus called into action certain movements of the opposite lower limb resulted ; if the middle part, motions in the opposite upper limb ; if of the lower part, movements of the opposite side of the face, lips and tongue could be called forth. Further, it was discovered that the parts of the convolution behind the central fissure were connected with sensations arisinor in corresponding parts of the body. There are two inferences which we draw from these facts ; (i) that the human brain must be formed on the same type or plan as that of the ape, for the medical man is able to apply, in diagnosing diseases of the brain, the knowledge he has obtained by experiments on the ape ; (ii) that each part of the brain has its own peculiar function. Only the convolutions immediately in front of the central fissure give rise to movements ; w^hen other parts are stimulated there is no muscular response. Thus it is, that at the present time there are large parts of the brain whose function is unknown — parts which we beheve serve for memory, judgment and imagination.

We must, however, keep our eyes on the demonstrator and watch him as he proceeds to show us how the cerebral hemispheres are connected with the body. When they are raised from the floor or base of the skull we see a great stem — the brain stem — issuing from them ; in size it is about the thickness of a baby's wrist. When this is cut through the cerebrum can be lifted away, and we note the remarkable fact that only one pair of nerves end directly in the hemispheres, namely, the olfactory or nerves of smell. The optic nerves from the eye are now visible ; they encircle and seem to end on the back of the brain stem. Impressions arising in the eye — -the sensations caused by light-^pass first to the brain-stem, but from their termination other nerve paths are provided which can be traced into the cerebral hemisphere towards the posterior or occipital lobes. The occipital cortex in which the paths end are known to subserve the functions of sight ; blindness is produced when they are destroyed by disease. When the cerebral hemispheres are removed from the head it is seen that their posterior parts did not rest on the base of the skull as the frontal and temporal lobes did, but on a fibrous partition. When the anatomist removes the partition we see beneath it a minor compartment which contains the cerebellum and

THE HinVIAN BRAIN 27

the continuation of the stem of the brain. The cerebellum is implanted on the upper or posterior aspect of the stem, and we note that it is only about a ninth part of the cerebrum in point of size, and that its substance is not convoluted, but is thrown into leaflets. Until a few years ago the wildest guesses were made regarding the function of the cerebellum. Phrenologists place the centre for amativeness on that part of the head which overlies it. Its exact function is not known, but we are certain it is not the seat of our consciousness, nor of our higher faculties ; there is evidence now to show that it is an automatic mechanism for regulating and co-ordinating our muscles when they are in action.

Before the cerel3ellum and the stem of the brain can be lifted out and shown to us, the anatomist finds it necessary to divide the continuation of the latter as it escapes from the skull to enter the canal of the backbone, where it changes its name and is known as the spinal cord. Even if we did not see the stem of the brain and the spinal cord in their natural position in the body we could tell where the one ended and the other began. In the spinal cord the nerves (31 pairs of them) arise from its sides by two roots, one posterior, the other anterior in position. In the stem of the brain they arise irregularlj^ some of them corresponding to the line of origin of the posterior roots of the spinal nerves, some to the anterior roots, while others arise in an intermediate line. In 1811, exactly a century ago, a young Scotsman of the name of Charles Bell made a very great discovery relating to the manner in which the nerves arise. While waiting in London for patients, he opened a private school in Soho for teaching medical students the anatomy of the body. He wished to explain to them why the brain was divided into cerebrum, cerebellum, and stem, and why the nerves arose in one manner from the stem and in another manner from the spinal cord. His difficulty was due to the fact that in his day anatomists supposed the brain to be the seat of mind, will, and consciousness. The brain they thought worked as a whole and could despatch or receive a message by any nerve. Bell came to the conclusion that this supposition must be wrong ; there must be an explanation for the division of the brain into parts and for the complex manner in which nerves arose.

Two reflections put him on the track of his great discovery. Bell did not know what we have seen, that stimulation of part of the brain gave rise to muscular movements, but he did know that there was a nerve track which descended from the cerebrum to the spinal cord through the brain-stem. He guessed it was by this nerve path that the will exercised its dominion over muscles, and he noted that it descended in the front part of the cord — the part from which the anterior roots arise. He concluded that the anterior roots must also be for carrying messages to muscles. He stimulated the anterior root in a living animal and found the muscles supplied from it were thrown into action. He therefore supposed the anterior part of the spinal cord and stem of the brain must be for producing movements and all the nerves which arise from their anterior parts must be motor nerves. We have already seen that the nerves of sight ended on the posterior part of the stem of the brain. Bell inferred from this fact that the posterior parts of the stem and of the spinal cord must be connected with sensation, for the optic nerve is purely for conveying impressions from the eye to the brain. He inferred that the posterior roots of the spinal nerves which end in the posterior part of the cord must be for conveying impressions from the body to the brain. They are the sensory roots. He stimulated them in living animals, no movements in the muscles were produced. Bell thus made the discovery not only that the roots of a spinal nerve were different in function, but the more important one that the anterior part of the great nerve stem was for motion and that the posterior parts were connected with sensation. We have seen that some nerves arise from the brain-stem neither in line with the posterior nor with the anterior roots but from an intermediate line. Bell inferred they must be so TPIE HUMAN BODY

peculiar in function because they were peculiar in their origin. Time has proved that in this he was also right ; seventy years later Dr. Gaskell, of Cambridge, found that these nerves (ninth, tenth and eleventh pairs of cranial nerves) are difierent in nature. They supply the heart, lungs and other viscera. They are visceral nerves ; over these the will has no control.

Having thus shown us the chief parts of man's nervous system — the cerebrum, cerebellum, brain-stem, spinal cord and nerves, our friend the anatomist returns to the part he commenced with — the cerebral hemisphere — ^in order that we may see some of the peculiar features of the human brain. We wish especially to see that part of the brain which is connected with speech, for of all man's gifts that of language is the most remarkable. A clever parrot or a mynah bird may have a voice and a power of imitation, but they cannot be said to have the power to receive and convey thought ; only a human brain has that power. We have already been shown that the convolution of the brain which controls the movements of the lips and tongue is situated in front of the lower end of the central fissure (Fig. 1, p. 24). We might have guessed that the convolution which serves in speech — the inferior frontal convolution — would be close by. It is a little way further forwards. Its exact position in the head is indicated when a finger is placed on the left temple, about an inch behind the upper margin of the orbit. The inferior frontal convolution is situated on the anterior margin of the deepest depression or fissure of the human brain — the Sylvian fissure, named after Sylvius, who taught anatomy in Paris during the seventeenth century. It was Broca, working in Paris in the latter half of the nineteenth century, who discovered that the inferior frontal convolution of the left side was connected with speech. The deep fissure of Sylvius, as we have seen, passes backwards and upwards on the side of the cerebral hemisphere; below it is the temporal lobe of the brain in the upper part of which the centre for hearing is situated (Fig. 1). There is a connexion or pathway between the hearing and speech centres, for if we are deaf we must necessarily be dumb ; the child listens as it imitates its mother's voice.

The chief features of the human nervous system having been thus demonstrated to us, we take our leave of the students and of the anatomical theatre, but before making our exit from the medical school we may turn aside for a minute to examine some specimens in its museum. In an out-of-the-way corner we come across the cast of a cleanly shaven head, mapped out into sixty little plots, according to the instructions of Dr. Gall, Avho founded the study of phrenology at the beginning of the nineteenth century. We notice that he has placed the organ of hope on that part of the head which Hes over the convolution connected with the movements of the body ; the organ of amativeness is situated on the region of the cerebellum, while that of constructiveness is placed over the inferior frontal convolution. We see that there is no correspondence between Gall's doctrine of phrenology and our modern knowledge of the brain. Yet to this extent Gall was right ; the various parts of the brain have their own particular function. The day may come when by looking at the brain or even at the skull which encloses it, we shall be able to tell the capabilities of a child or man, but we have not yet reached that point. Even should that day come it is improbable that the phrenologist will be able to tell character as well as the ordinary man who merely observes the expression of the face, the tone of the words, the actions and the deeds of the person under observation. It is true that a wide and high forehead, indicating great development of the frontal lobes of the brain does incline us to anticipate capacity in a man, yet we are often mistaken ; we have known men of unquestioned ability with low and narrow foreheads. Even the size of the brain is not a safe indication. In most cases one can form a fairly accurate opinion of the size of the brain from the dimensions of the head. In the average man the skull and the

THE HUIVIAN BRAIN 33

soft parts covering it do not vary in thickness so much as to upset our calculations as to its size or volume. It is true that the chambers or ventricles ^vithin the brain may be dilated and thus give the brain a false size, but that is not a common condition. The size of the brain depends to a certain extent on the bulk of the body ; tall men on the average have larger brains than small men, just as a Newfoundland dog has a bigger brain than a fox-terrier. The increase of brain which is directly due to increase in size of body gives no increase of brain power ; hence tall and bulky men are not necessarily more able than small and short men. Thus, although we cannot argue that because a man has a big brain he is a man of great capacity, yet the fact remains that many of the world's most famous men had large heads and big brains. In the average Englishman the brain weighs 1,360 grammes ^ (forty-eight ounces) ; in Cromwell it is said to have been 2,231 grammes and in Byron 2,238 grammes. In Gambetta, the French statesman, it weighed only 1,294 grammes. Still, if size of brain is not a certain index of capacity, it must be taken into account ; Broca found when he compared the brains of a group of eminent men with those of men of ordinary ability that the average eminent man had a brain eighty grammes above the ordinary. When the sexes are compared it 1 An ounce is equal to 28*3 grammes, C is found that the brain in man is 130 grammes more than in woman on the average. Woman's smaller brain is due chiefly to her smaller body, for we have seen that size of body has a direct influence on the size of brain. Whatever view may be held as to the equality of the sexes, woman cannot be disqualified on account of the size of her brain. Therefore we must admit that size is not a valuable index of capacity, and the same must be admitted as regards shape. Certain American Indian tribes distort their heads and brains by the application of bandages in infancy and yet their mental capacity does not seem to be in any way affected. We see, too, that the human head varies much in shape ; in some it is narrow and long ; in others broad and short ; in others short and high or long and low. The long and narrow head is common in England ; the broad and short head in Germany and France, and yet, as far as we know, the brain which is within the short and wide skull has no advantage over the one within the narrow and long head. Thus all attempts to read character and mental capacity by examining the outward form of the head or of the brain have so far been in vain.

Before leaving the museum of the medical school there is another group of specimens we ought to examine, namely, those which show how the brain and spinal cord are formed during the early stages in the development of the human body. The early stages of the human embryo are represented by accurate models in which the various parts are greatly magnified. During the early part of the third week of development the brain and spinal cord are seen as part of the covering or epidermis on the upper surface of the embryo ; the area of epidermis which forms the future nerve system is oblong in shape. In a model showing a slightly older stage the oblong area has become depressed to form a trough ; presently the edges of the trough come together, the margins of the embryonic skin closing over the nerve trough, which now forms a tube enclosed in the back or dorsal side of the embryo. The front or head part of the tube forms the brain ; the hinder part forms the spinal cord. By the third month two outgrowths are evolved from the brain part of the tube ; one of these forms the cerebrum ; the other the cerebellum. To one who is unfamiliar with the facts of embryology it must seem a preposterous thing to suppose that our brains can have been evolved from a modification of an area of skin. Still these are the facts of development ; how otherwise can they be explained except by supposing our brains are areas of the bodycovering which have been modified ? Children are frequently born, as may be seen from specimens in medical museums, where the nerve plate has never been folded in but remains spread out on the surface and merging at its edges into the skin of the back and of the head. In such cases we see in the human body a hark-back to a condition that must have been represented in very low forms of animal life at an early stage of the world's history. That marvellous structure, the human brain, is the product of millions of years ; its history begins with life itself, millions upon millions of years ago.

When the reader leaves that strange place, a medical school, to which we have tried to introduce him, and emerges on the street to see men busy and energetic in all the affairs of life he will find it difficult to believe that there is aught in common between man's brain and that of any other animal created. As he walks along, however, he will notice how men differ ; a man here and there has a brain weight of 2,000 grammes, and perhaps a corresponding ability ; another has perhaps only 1000 grammes ; in seeking for man's allies it is not the highest but the lowest human types we must use as a starting-point. Amongst Australian aborigines it is not uncommon to find a woman with a brain weight of 1000 grammes or even less. When it is added that the gorilla, the chimpanzee, the orang, have brain weights that vary from 300 to 500 grammes he will conclude that there is a vast difference in even weight between man and the great anthropoids. There is a great gulf, but it is not a fixed one. A fossil form of man.

Pithecanthropus it is named, had a brain which in point of size is intermediate between that of modern man and the gorilla's. There is an equally great gap between the great anthropoids— ^the gorilla, chimpanzee and orang — and the small anthropoids — the gibbons. If instead of comparing grown up men and anthropoids we compare them both at birth the difference is less. At birth the human brain weighs about 800 grammes, about one-fifth of the weight it ultimately reaches ; the brains of the anthropoids are only slightly less, 200 to 300 grammes. Thus, while man's brain is only about one-fifth of its adult weight at birth, that of the anthropoid is already two-thirds. Man has to be sheltered and educated ; the anthropoid baby has ta face the realities of life soon after birth. When we survey man and the anthropoids at birth, the brain difference does not seem an insuperable barrier between them. Indeed, in all mammals the brain grows much more rapidly than the rest of the body ; this is especially the case in man. By the end of the second year the human brain has reached two-thirds of its adult size, it has then reached the same relative degree of development that the anthropoid has reached at birth. There is another peculiar fact about the growth of the human brain ; it has reached its maximum size by the twentieth year. After the twentieth year, or even a little before, it begins to lose in weight and goes on losing until old age, when the decrease becomes more rapid. As Professor Karl Pearson has said, man's prime is not a period, it is merely a point of time.

Chapter III

man's place amongst animals

Most men are not aware of the toil and trouble zoologists have taken to name and number the animals of the earth and to arrange them in groups according to the manner in which their bodies are made. We know the commoner animals as they come before us, but do not trouble about the relationship of one beast to another. As regards man, he seems to us so very different to all the common animal forms that we cannot believe him to be related to them at all, but prefer to regard him as standing isolated and alone, as a being of a peculiar order. When, however, we begin to study his body and compare it, organ by organ, with that of other animals, we see that his isolation disappears, and that it is the thick veil of civilization in which he has so completely hidden himself that misleads us regarding his true position in the animal kingdom. The reader will see that I am preparing his mind for the kind of evidence to be produced in this chapter — evidence as to " Man's place in Nature," as Huxley happily named it in his celebrated book published in 1863. We propose to visit an institution in which Huxley loved to work and to lecture, namely, the Museum of the Royal College of Surgeons of England, situated right in the heart of London on the south side of Lincoln's Inn Fields. The museum has a history ; its foundation was laid in the latter half of the eighteenth century by the great surgeon, John Hunter, one of the very greatest men this country has ever produced. He was centuries ahead of his time, and hence he is not yet properly appreciated. The hours he could steal from work and sleep he devoted to the study of all forms of life ; but instead of describing on paper what he saw and discovered, he left the actual specimens themselves — all duly preserved, to tell their own stories to future generations. Since his day men like Sir Richard Owen and Sir William Flower have added to and tended Hunter's priceless collection, so that here we can study the evidence afforded by man's body better than anywhere else in the world. Hunter's invariable method was to commence with the simplest and lowest forms of life and work gradually through the more complex which led on to the highest — man himself. As we enter the museum it soon becomes evident that it will answer our present purpose best to reverse Hunter's order, and in each instance commence with the human form.

MAN'S PLACE AMONGST ANBIALS 41

As we pass through the first and second rooms of the museum we see the skulls and skeletons of all races of mankind, European, Asiatic, American, African and Australian, in case after case, but only the practised eye picks out the peculiar features of each race ; as far as the evidence of the skeleton goes mankind appears to be a very uniform species. It is in the third room that the first real break is encountered, where the human series ends and the anthropoid skeletons begin. The skeleton of the gorilla is not at all human in appearance, the great crests on the skull, the massive jaws and face, the long stout arms, the short lower limbs with a thumb-like great toe, seem to assure us that even the most man-like of apes is a long way off from man himself. Yet when we look more closely we see that every bone of man's body is present in the gorilla, they occupy exactly the same place in the skeleton ; each bone shows the same leading features ; the differences relate merely to proportion, size and detail. When we look at the skull of the young gorilla, before the massive, brute-like crests have appeared, the human resemblance is more marked. In the skulls of the adult chimpanzee, these cranial ridges, which are developed to give attachment to the great muscles of mastication, are much smaller than in the gorilla. In the orang they are intermediate in size. They are much larger in the male than in the female anthropoids. The gorilla and chimpanzee are from Africa ; the orang from Borneo and Sumatra, It is thus in the forests of the tropical parts of the earth that we find the animals which most nearly resemble man in structure. There are various races of gorillas, chimpanzees and orangs, just as there are various races of mankind, each race being a native of its own peculiar district or country.