(b) Similar impressions which reach the brain but not in sufficient degree to arouse consciousness.

With the object of concentrating attention on the vital importance of grasping the causal nexus between these sense-impressions of movement and the actual subsequent motion, Bastian coined the term 'kinæsthesis,' meaning thereby sense of movement, i.e. the sum of all the sensory impressions just referred to, and, further, he, in addition, postulated the view that such kinesthesis, or sense of movement, strain, effort, &c., must naturally find its seat or localisation in the so-called motor or Rolandic region of the brain, since undoubtedly voluntary impulses issue therefrom. It is this postulate which embodies the great importance of kinesthesis or the so-called muscular sense to psychology and neurology, and it is this relationship which it is hoped may be considered to be demonstrated by the facts now to be related. Before plunging at once into the examination of our physical evidence, it is not saying too much, in comparing the two views just contrasted, that the weight of opinion among neurologists is practically entirely on Bastian's side, and further that as long ago as 1872 the question was virtually decided by the experiments of Bernhardt, and later of Ferrier and Brunton, which were founded on the following basis. Supposing Bain's view to be correct, it followed that if we caused the muscles of a man to raise different weights without any volitional effort on his part, he would not be able to differentiate between the heaviness of the various substances. This crucial experiment was performed by the simple expedient of electrically exciting the muscles of the arm and so causing them to raise the weights quite independently of the person's volition, with the result that he was perfectly conscious of a difference of weight amounting to an increment or decrement of one-seventeenth over previous essays. In other words, the muscular sense, impressions of weight, tension, &c. remained in full activity, and in this manner afforded the absolute negation of Bain's position.

There remains yet one more point upon which something should be said, viz. as to the sense in which the term volitionary or purposive movement is employed in these pages.

Probably no psychologist at the present day feels anxious to define a voluntary act or exhibit the line which is supposed by some to differentiate the volitional from the simple reflex act, or, what would be yet more interesting, to determine the period at which a child's acts become voluntary.' Where psychologists fail nothing more is necessary than to say with Bastian that a movement may, for the sake of harmonising modern with old ideas, be called voluntary' if the

movement by the joints themselves. Goldscheider also deals at length with the points treated by Munsterberg (see Mind, Oct. 1890, and also Beiträge, 1888), Aubert (Pflüger's Archiv), and others, viz. the differentiation of the elements of muscular control.

outgoing impulse is preceded in mental time by a conscious idea or conception of the movement to be performed. Thus we already return to kinæsthesis, the sense by means of which such ideas of motion are built up.

After this slight review of the position we are ready to consider the more recently discovered physical facts which bear on this subject. The physical, cerebral substratum of a voluntary or purposive act must be crudely imagined to have the following structural arrangement. In the first place, a sensory nerve-ending which transmits such stimulation as it receives along nerve-fibres to sensory centres in the spinal cord, and also directly to the medulla oblongata. From both of these stations the excitatory disturbance reaches, by means of other fibres, that region of the cortex, i.e. surface, of the brain which constitutes the first part of the physical basis of ideation, being the seat of perception of the stimulus. The earliest enunciation of the doctrine that cortical centres of sensory perception must exist we owe also, though not commonly recognised, to Bastian's neurological and psychological insight, while for the epoch-making discovery of them as actual facts we have to thank Ferrier's experiments on animals.

5

With the present task of reviewing the schema of a voluntary act thus made easy by the establishment of the sensory perceptive centre as the acme of the sensory nerve path, we meet, of course, with invincible difficulty when we further seek to pass from this standpoint to the so-called 'motor' centre in which, as we have before suggested, the idea of the movement to be performed is distinctly and strongly defined. The difficulty is simply due to the fact that we are compelled to enter the field of conscious intelligence equally obscure to the neurologist and psychologist. Fortunately for my present purpose, such transcendental knowledge is not requisite. For if we attempt to fit the scheme of a central apparatus just described to the hard facts of anatomical structure and physiological function of the brain as we know it at the present day, we experience no great difficulty, although we may enter fully on what is yet regarded as debateable ground, which it is hoped this paper may in some part clear.

In speaking just now of the sensory perception which forms the starting-point of the voluntary act, we must not forget that, although the sensory impressions composing the 'muscular sense' are principally those of touch, pressure, tension, &c., coming as they do from the moving joints, muscles, &c. of limbs and trunk, there are nevertheless, inextricably woven with such tactile impressions, others of sight too, and that the most striking clinical picture of loss of

The Brain as an Organ of Mind, p. 526.

* See Demeaux's case, quoted fully in Ferrier's Functions of the Brain, p. 180, 1st. edit.

muscular sensation is that in which the unfortunate patient cannot perform a voluntary movement unless the eyes are attentively directed on the limb.7

It is of course only a matter of common knowledge and experience that the cerebral accomplishment of a complex and delicate movement is the result of muscular practice principally aided by sight. But for the present purpose it is justifiable to neglect the influence of sight, and for the sake of simplicity it will be best to consider the question as it affects only one part of the body, such, for instance, as the arm, which is frequently moved in a purposive, or at least complex, manner without the assistance of visual impressions. Beginning, therefore, to analyse a voluntary movement of the upper limb, by following the order of the constitution just given of its physical substratum or basis, the first question to be answered would be, in what part of the cortex is the perceptive centre of tactile impressions coming from the upper limb localised? Ferrier was the first to attempt this determination experimentally since no evidence was forthcoming from either mental analysis or clinical records.

of

He found that the seat of the tactile sense (including the sense pressure, tension, &c.) was on the median and under surface of each half of the brain, viz. in the hippocampal convolution (see fig. 1). Much later Schäfer and myself found that, in addition, part of the rest of the limbic lobe, as Broca originally termed the continuous sweep of the calloso-marginal and hippocampal convolutions, was also the seat of the tactile sense.

These experiments were made on monkeys.

A number of investigators, Schiff, Hitzig (who speaks of the loss of 'muscle consciousness' consequent upon lesions of the so-called motor region), H. Munk (who termed the motor region' the Fühlspäre), Exner (who collected cases of lesions in man), Luciani, Herzen and others, had previously made observations on the carnivora, and had come to the conclusion that the tactile sense in these animals was represented or localised in that region of the outer surface of the brain which is commonly called the motor' region, viz. the sigmoid convolution, and not in a separate cortical area, as appeared to be the case in the monkey. My own observations on the carnivora are in harmony with these results. This seeming difference between the carnivora and apes was accentuated by the observations of Ferrier, Schäfer and myself, according to which no sensory disturbance could be definitely determined when in monkeys the so-called motor region

7 This has been particularly insisted upon by all writers, among others by Stricker, Studien über die Bewegungsvorstellungen, 1882, pp. 24, 25, et seq., in which he emphasises the fact that memory of movement aroused by sight of movements executed gives subjective sensations of precisely the same movement referred by the observer to his corresponding limbs. We shall see presently that this is probably due to an associational excitation (through the sight-perceptive centre) of the kinesthetic centres for the limbs in question.

on the outer surface was injured and the limbic lobe on the median surface left intact.

Luciani, however, stated that in the monkey it was possible to demonstrate that lesions of the so-called motor region did cause a slight loss of muscular and tactile sense, and I have little doubt that his correction represents the true position.

Space forbids, however, our entering further on this interesting subject, and I have only introduced the opposition of statements on this point in order that it should be clearly understood that it is not accepted by all neurologists that the tactile sense in monkeys and in man is represented both in the limbic lobe and in the so-called motor region, as will now be shown to be in all probability the

case.

We must now turn to the so-called motor region of the brain,

C. Ca

FIG. 1.-MEDIAN OR INNER ASPECT OF THE LEFT HALF OF THE BRAIN OF A BONNET MONKEY.

In this drawing the left hemisphere is shown as when separated from the right hemisphere by division of the internuncial fibres forming the corpus callosum, C.CA., and of the fibres connecting it with the little brain or cerebellum, and with the spinal cord, C.R. The whole surface which is shown dotted is the limbic lobe, and while its upper part is termed the callosomarginal convolution, C.M.C., the lower part is called the hippocampal convolution, HI.C.

the debateable ground in the present question, and the unquestioned source of voluntary' impulses.

The convolutions about the fissure of Rolando (see figs. 1, 2) were suspected by Hughlings Jackson, after a close analysis of forms of epilepsy, to be concerned with and the seat of 'sensori-motor centres,' each especially subserving the movement of a definite part of the body; but it was not until the wonderful experiments of Hitzig and Fritsch on animals, followed by those of Ferrier, that his speculations were established in truth as physical facts. The results of two decades' work have proved incontestably that certain regions of the cortex or surface of the brain are concerned in the voluntary' movement of certain groups of muscles. The movements of the upper limb, for instance, which was just now

selected as an example of representation, were found by Hitzig, and more perfectly by Ferrier, to be seated about the middle of the fissure of Rolando, which part of the brain consequently received the unfortunate name of 'the motor region.' Four years ago Dr. Beevor and myself began a minute investigation of these areas, and this resulted in our finding that they could be subdivided for each segment or part of a limb.

These experiments are conducted as follows. The animal being thoroughly anaesthetised with ether, a portion of the skull and membranes covering the brain is removed, and a very weak electric current applied by means of fine platinum wires to various spots of the Rolandic region of the surface of the brain. It is then found that the momentary application of the current to certain points in one half of the brain is regularly followed by contraction of one or more muscles of the opposite side of the body, and that consequently the cortex or surface of the brain may, in this region, be regarded as a series of compartments or sub-offices for the representation of the movements of the various parts and joints.

Hence, as shown in the following figures 2 and 39 of the bonnet monkey's and orang's brains respectively, the area for the purposive movements of the upper limb is, as it were, made up of horizontal or obliquely arranged compartments or foci, in which respectively are principally represented from below upwards the movements of the thumb, index-finger, all fingers, wrist, elbow, and shoulder.

The finding that such a minute localisation of movement existed enabled more accurate diagnoses and examination of small lesions of the brain in cases of disease among human beings to be made out, and clinical data are, therefore, now available for the determination of the difficult question of kinesthesis (i.e. 'muscular-sense' impressions) and its relation to 'voluntary move

ment.'

We will now examine this clinical evidence, and shall see how it shows that the sensory impressions referred to are localised in the so-called motor region as well as in the limbic lobe.

I have had the opportunity of observing cases in which a lesion was restricted to the upper limb area of the so-called motor cortex, and in which it did not involve the limbic lobe. The fact of the lesion being restricted as stated is indubitable, as in each case it was freely exposed to view by an operation undertaken for the relief of the patient. As none of the patients died, it is only a matter of inference, of course, that neither the limbic lobe nor the fibres coming to or from it were also the seat of disease. That such an inference is warranted is evident, since not only, as just stated, was the topographical situation of the lesion and wound perfectly ascertained,

These figures, constructed by Dr. Beevor and myself, are taken from the Philosophical Transactions of the Royal Society, B 52 and B 55-18.0.