[Illustration: FIG. 21.--Dog's motor centres, right hemisphere, according to Paneth.--The points of the motor region are correlated as follows with muscles: the _loops_ with the _orbicularis palpebrarum_; the _plain crosses_ with the _flexor_, the _crosses inscribed in circles_ with the _extensor, digitorum communis_ of the fore-paw; the _plain circles_ with the _abductor pollicis longus_; the _double crosses_ with the _extensor communis_ of the hind-limb.] I am speaking now of localizations breadthwise over the brain-surface. It is conceivable that there might be also localizations depthwise through the cortex. The more superficial cells are smaller, the deepest layer of them is large; and it has been suggested that the superficial cells are sensorial, the deeper ones motor;[61] or that the superficial ones in the motor region are correlated with the extremities of the organs to be moved (fingers, etc.), the deeper ones with the more central segments (wrist, elbow, etc.).[62] It need hardly be said that all such theories are as yet but guesses. We thus see that the postulate of Meynert and Jackson which we started with on p. 30 is on the whole most satisfactorily corroborated by subsequent objective research. _The highest centres do probably contain nothing but arrangements for representing impressions and movements, and other arrangements for coupling the activity Of these arrangements together._[63] Currents pouring in from the sense-organs first excite some arrangements, which in turn excite others, until at last a motor discharge downwards of some sort occurs. When this is once clearly grasped there remains little ground for keeping up that old controversy about the motor zone, as to whether it is in reality motor or sensitive. The whole cortex, inasmuch as currents run through it, is both. All the currents probably have feelings going with them, and sooner or later bring movements about. In one aspect, then, every centre is afferent, in another efferent, even the motor cells of the spinal cord having these two aspects inseparably conjoined. Marique,[64] and Exner and Paneth[65] have shown that by cutting _round_ a 'motor' centre and so separating it from the influence of the rest of the cortex, the same disorders are produced as by cutting it out, so that really it is only the mouth of the funnel, as it were, through which the stream of innervation, starting from elsewhere, pours;[66] consciousness accompanying the stream, and being mainly of things seen if the stream is strongest occipitally, of things heard if it is strongest temporally, of things felt, etc., if the stream occupies most intensely the 'motor zone.' It seems to me that some broad and vague formulation like this is as much as we can safely venture on in the present state of science; and in subsequent chapters I expect to give confirmatory reasons for my view. MAN'S CONSCIOUSNESS LIMITED TO THE HEMISPHERES.