For instance,

the different channels of communication. the ganglia which receives the fibres of the optic nerve may become inoperative, from the effect of disease, while those of hearing and general sensation may remain sound, and, vice versâ, those of hearing and feeling may become disordered and that of sight remain sound; whereas, if the nerves of all these channels of communication were to centre in one ganglion, a disorder of this one would at once close up all means of communication with the world outside.

These ganglia, however, are not supposed to be the terminal points of the nerve-fibres, which reach them from all parts; on the contrary, the fibres appear to pass through or around them, and are found emerging from them toward the nerve-cells we have already described as largely composing the grey matter of the cortex of the brain. This view of Luys has been regarded by some anatomists of the brain as somewhat fanciful and has not yet been fully confirmed; of its general accuracy, however, there can be little doubt. Dr. W. Bevan Lewis,* while appearing to be somewhat guarded in his statement, says that "radiative fibres in coarse fasciculi are seen passing from the whole extent of the upper margin of the thalamus, either directly outward toward the parietal lobe or arching upward toward the occipital region. These fasciculi consequently form the outer wall of the lateral ventricle in their course toward the parietal lobe. If the scalpel divide across parallel to the direction of the stria cornea, the blade passes directly into the internal capsule, and it becomes evident that the outer obliquely-placed surface of the thalamus rests upon the internal capsule as upon a couch, and gives off from the

"Text-Book on Mental Diseases," pp. 43, 45.

whole of its outer aspect medullated fibres, which enter into the constitution of this capsule, and then spread as coronal radiations to the various districts of the cortex of the parietal and temporo-sphenoidal lobes. * The

zonular layer of the thalamic capsule receives fibres from almost every region of the brain-the frontal, parietal, temporo-sphenoidal, and occipital lobes, and the mesial aspect, or gyrus fornicatus, as well as the retina."

In like manner fibres radiate from other bodies of grey matter; the caudate nucleus, the lenticular nucleus, and from the olfactory bulb.

But there are others

The corpus striatum has already been referred to in connection with the optic thalamus and, indeed, forms a sort of complement to it. It is situated a little laterally and anteriorly to the thalamus, and consists of a reddish, dark, ovoid body, with its largest portion to the front, and receives the converging nerve-fibres which come to it from the various regions of the cortex of the brain. It is supposed that these fibres terminate in this body, or at least they have not yet been traced, as passing through it. emerging from the under-side of it, which pass down and out to the various portions of the body in some such manner as do those which pass from the thalamic ganglia to the various regions of the cortex. If these views shall be verified by further researches of anatomists, this body may be supposed to serve as a sort of station or halting place for all impressions which have been received and transmitted through the sensory nerves to the optic thalami, and to other ganglia of grey matter in its vicinage, thence up to the nerve-cells of the cortex of the brain, and again down to this and other bodies of grey matter. Here they are supposed to be reinforced, and again become materialized by being converted into motor action; that is, they are sent

out in the form of speech, movement, or action in some direction.

The nerve-cells which are found in these ganglia, and, indeed, in all other parts in which fibres and grey substance are endowed with special functions (according to van der Kolk), have a character peculiar to themselves in their form, size, and structure, as also in their relations and connections with other cells. Nerve-cells also differ very materially in size according to the ganglia and the regions of the cortex in which they are found, and the character and importance

FIG. 12.

FIGURE SHOWING THE RELATION OF THE NUCLEUS CAUDATUS TO THE

CORTEX.

of the functions over which they preside, and possibly the length of time they have existed.

It has already been noticed that the nerve-cells which are found in the different layers of the cortex vary very considerably in size, the larger portion of those found in the second and fourth layers being much smaller than those which are found in the third layer. As the layer containing the larger cells lies between the others, this difference in size cannot arise from their location, or upon advantages secured through nutrition; and as they are arranged

upon a system which is found to invariably obtain in the human brain, it is reasonable to look for the explanation in the degree or quality of function. The arrangement of the cortex in more or less definitely bounded layers, would also indicate diversity of function; indeed, it is difficult to conceive of any other cause for such diversity in the anatomical arrangement of the cortex except this, as nature always proceeds upon the simplest plan which is adequate to the discharge of function.

The fact, therefore, that the cortex cerebri presents in its constitution such complexity of arrangements and such diversity in its elements, points to diversity of function, in quality, if not in quantity. Dr. W. Bevan Lewis calls attention to the probability that the larger nerve-cells in the motor region of the cortex are, by their medullated fibres, connected with and preside over the ganglia of the spinal cord which govern the movements of the lower extremities. The fact that this influence has to pass over such a long distance, as compared with that which passes to the ganglia located at the cervical portion of the cord, would indicate the requisition of a larger amount of function. This will also vary in size to some extent, according to the height and physical constitution of the individual. Larger muscles also require for their functional activities more of nerve energy than small ones.

A similar view was suggested some years ago by Dr. Hughlings Jackson.* This is as follows: "I have suggested that the size and shape of cells, as well as their nearness to the tumor or other source of irritation, will have to do with their becoming unstable; other things being equal, the same quantity of matter in many small cells will

*"On Temporary Paralysis after Epileptiform and Epileptic Seizures."

present a vastly greater surface to the contact of nutrient material than the same quantity in one large cell. I have also suggested that small muscles, or, more properly, movements, which require little energy for the displacements they have to effect (those of the face and hands in touch, for example) are represented by small cells. Such movements are rapidly changing during many of the operations they serve-in writing, for example-and require repetitions of short liberations of energy and necessitate quick recuperations of the cells. Movements of the upper arm are, in comparison, little changing, and require persistent, steady liberations of energy."

Before referring further to the peculiar manner in which these cells act in connection with the nerve-fibres connected with them, it may be necessary to refer somewhat in detail to the structure and arrangement of the nerves themselves. There exist two kinds of nerves, first, the excito-motor, or nerves of sensation; these all convey impressions from the periphery of the body to the spinal cord, and thence up to the aggregations of ganglia which have been already referred to. Second, the motor nerves, which emerge from the various centres of the cortex and pass down through the corpora striata and other basal ganglia; or according to some authorities, directly through the internal caspule and the pyramidal tracts of the pons and medulla, and in their turn are distributed through the cord and convey sensations, after they have become materialized, back to the periphery of the body, eventuating in speech or motion. All medullated nerve-fibres have axes which are covered with two or more envelopes or coats, which appear to serve the purpose of isolating them from the parts which lie adjacent. They arise in connection with the cells of the grey matter, and extend to all portions of the body. They compose largely