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النشر الإلكتروني

CHAPTER V.

I EMISPHERICAL GANGLIA; CORTICAL CELLS OF TAE CEREBRAL HEVISPHERES; IDEATIONAL NERVOUS CENTRES;* PRIMARY NERVOUS CENTRES'; INTELLECTORIUM COMMUNE.

THAT

MHAT the nerve-cells which exist in countless numbers in the

grey cortical layers of the hemispheres are the nervous centres of ideas, is fully admitted by all those who have most studied the physiology of the brain, and are best entitled to speak on the matter. The cerebral hemispheres represent, in reality, two large ganglia that lie above the sensory centres, and are superadded in man and the higher animals for the further fashioning of impressions, or of sensory perceptions, into ideas or conceptions. This important step in the evolution of the human mind consists in the abstraction of the essential from the particular and its re-embodiment in idea; it is strictly an idcalization of the sensory impressions, and represents, so to speak, an epigenetic development of nature: what the true artist does in his art nature does continually in the development of the human mind. Looking not at the individual man and his work as the end, l'ut looking at liim as a small anil subordinate part of the vast and hariuonious whole, as a means to a far-off en l, it is sufficiently evident that the history of mankind is the liistory of the latest and highest organic development that in the evolution of the human mind nature is undergoing its consummate development through m.in. And the law manifest in this highest display of organic d velopment, is still that law of progressive

"We hare not a name fue that complex notion which embraces, .-- one whole, all the different phenomen to which the term “Jilca' relates As 1. say.Sen. mlion,' we might also say "Ideation ;' it would be a very useful worl; and there is no ol.;. ction to it, excej ihe pedantic habit of decrying a new tor..."-JANES Mili, Inalyste of the lion in Vinil, p. 12.

specialization and increasing complexity which has been traceable through the long chain of organic beings. So exquisitely delicate, however, are the organic processes of mental development which take place in the minute cells of the cortical layers, that they are certainly, so far as our present means of investigation reach, quite impenetrable to the senses; the mysteries of their secret operations cannot be unravelled; they are like nebulæ which no telescope can yet resolve.

The cerebral hemispheres are not alone the nerve centres of ideas, but they are also the centres of emotion and volition. In animals that are deprived of their hemispheres, all trace of spontaneity or will in their movements disappears; this effect being, as might be expected, much more evident in experiments on the higher than on the lower Vertebrata. In Fishes, as for example in the carp, scarcely any difference is observed in its swimming after its hemispheres have been removed ; but if its movements be watched more carefully, and compared with those of a carp which has not been mutilated, a certain change will be recognised. According to Vulpian, it moves forward in a straight line, never turning to one side or the other except when it meets with an obstacle, and not stopping until it is completely fatigued ; it seems impelled to move by some necessity, a necessity occasioned probably by the stimulus of the water on its body. The more marked effects pro luced in the higher Vertebrata by the removal of the hemispheres have already been described.

The anatomists believe that they liave now demonstrated that the nerve-fibres which ascend froin the spinal cord through the inedulla oblongata do not pass directly to the surface of the hemispheres, lut end in the ganglionic cells of the corpora striata and optic thalami; new fibres starting from these cells, and ralliating to the cortical cells, to establish the communication between the primary and secondary nervous centres. There is, then, a sufficient anatomical rason for an inference previously made on other grounds, which is, that an idea, or an impulse of

Vulpian, however, belieres that sone fibres from the cerebral peduncles pass directly to the cerebral hemispheres of tho corresponding side, either through the corpus striatum or beneath it; foundi... his opinion on some cases in which he has seen lesion of the hemispheres, 1": affecting the corpus siriatum, followed lis. a descending atroplıy of nerve fibres analogous to that which follows lesion of the corpus striatum.

the will, cannot act directly upon the motor nerve-fibres of the body, but can only act through the medium of the proper subordinate centres. There is an explanation also of the fact that irritation of the white substance of the brain does not occasion either movements or signs of pain. At is extremely probable, again, that different convolutions of the brain do discharge different functions in our mental life; but the precise mapping out of the cerebral surface, and the classification of the mental faculties, which the phrenologists have rashly made, will not bear scientific examinations That the broad, high, and prominent forehead indicates great intellectual power was believed in Greece, and is commonly accepted as true now; the examination of the brains of animals and idiots, and the comparison of the brain of the lowest savage with the brain of the civilized European, certainly tend to strengthen the belief. Narrow and pointed hemispheres assuredly do mark an approach to the character of the monkey's brain. There is some reason to believe also, that the upper part of the brain and the posterior lobes have more to do with feeling than with the understanding. Huschke has found these parts to be proportionably more developed in women than in men; and Schroeder van der Kolk thought that his pathological researches had afforded him the most convincing proofs that the anterior lobes of the brain were the seat of the higher intellectual faculties, while the upper and posterior lobes ministered rather to the emotional life. Recently some observations have been made with the view of establishing a theory, that a portion of the anterior lobe, the third frontal convolution of the left hemisphere, was the seat of language; but the observations reporteil are unsatisfactory, directly coni radictory observations are overlooked or ignored, and it is contrary to the first principles of p-ychology to suppose that languaye, complex and organic as it is in its intellectual character as the sign or symbol of the idea, can have so limited and defined a seat in the brain. On the whole, it must be conf-sed that, so far, we have not any certain and definite knowledy of the functions of the different part of the cerebral convoluti ng The anatomists cannot even agree on any convolution as puliar to inan; all that they can surely say is, that his convolutions are more complex and less symmetrical than those of the monkey. “If man was made in

the image of God, he was also made in the image of an

ape."

The cortical cells of the hemispheres, like the ganglionic cells of the sensory centres and of the spinal cord, may certainly act as nervous centres of independent reaction. Without any volition, or even in direct defiance of volitional effort, an idea which has become active may pass outwards, and produce movement, or some other effect upon the body. The suddenly excited idea of the ludicrous, for example, causes involuntary laughter; the idea of an insult, a quick movement of retaliation; the idea of a beautiful woman, a glow of amatorial passion; the idea of a great impending danger, or of a sudden terrible affliction, serious or even fatal disturbance of the organic life; the idea of an object, sometimes an actual hallucination. Most of the earlier actions of children are prompted by ideas and feelings which are excited by suggestions from without, and which immediately react outwards. In the phenomena of electro-biology or hypnotism, the mind of the patient is possessed with the ideas which the operator suggests, so that his body becomes an automatic machine, set in motion by them. Every one's experience will recall to him occasions on which an idea excited in his mind could not be dismissed therefrom by the will, and perhaps would not let him rest until he had realized it in action, even though such realization appeared to his judgment inadvisable. Those who have attended carefully to the course of their own thoughts, and reflected upon their actions, will readily acknowledge that an idea sometimes arises and procluces a movement without there having been any active consciousness of it, the effect being that which first arouses consciousness, if it be aroused at all. How many of the daily actions of life, thus accomplished, are we never conscious of unless we set ourselves deliberately to reflect. It is most certain that there may be a reaction outwards of an ideational nerve-cell, independently of volition, and even without consciousness.

As it is with the faculties of the spinal and the sensory centres, so is it with the faculties of the ideational centres : they are not innate, but are developed by education. The notion of in mite idea, in the exact meaning of the word, as con

• Hallam, Introduction lo llistory of Europe.

natural or contemporary with birth, is not less untenable and absurd than an innate pregnancy. (') But if by innate is only meant that, by the necessity of his nature, a well-constituted individual placed in certain circumstances will acquire certain ideas, then all the phenomena of a man's life, bodily or mental, are just as innate or natural. It is necessary here to distinguish between what is predetermined by the nature of things, and what is preformed. The formation of an idea is an organic evolution in the appropriate nervous centres, a development which is gradually completed in consequence of successive experiences of a like kind. The impressions of the different properties or qualities of an object received through the different senses, are combined in the compound idea of it which is gradually matured in the mind; there is a consilience of sensory perceptions in the production of the idea ; and henceforth we can make assertions concerning the object when it is not present to sense. The cells of the cerebral ganglia do, in reality, idealize the sensory perceptions : grasping that which is essential in them, and suppressing or rejecting the unessential, they mould them by their plastic faculty into the organic unity of an idca, in accordance with fundamental laws. Every iilea is thus an intuition, and implicitly comprises far more than it explicitly displays. It is not the idea of any particular object or event, but the idea of every object and event of a particular kinil. Herein the process of ideation only follows the law of orgauic development as manifest everywhere, and as previously illustrated in the development of nerve element itself. Whosoever, biassed by the metaphysical conception of mind, finds it difficult to realize this process of the organic growth of idea, let him reflect upon the manner of organic growth which conte-sedly takes place in the language in which our ideas get embodiment. Language was not innate in mankind; it lias under one a slow developinent thagh the ages, in conformity with the development of thoug!: ; and by using the study of linguage as an instruinent of rlie analysis of ideas, we may make use of the science of what is seen to indicate the nature of processes that at present a unseun. Ahose "sho are metaphysically minded lave done with idea as they have done with sensation : they have converted a complex

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