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true interpretation of the phenomenon, we obtain from it a striking confirmation of the doctrine (to be afterwards adverted to) of internal or self-originated movements, as contrasted with the movements from outward stimulation.

17. The cerebral ganglion named the Corpora Quadrigemina is associated with the power of sight. Its destruction produces blindness, and also a permanent dilatation and immobility of the pupil of the eye. The destruction of one side causes loss of vision on the opposite side; but the irritation of one side will produce contraction of both pupils. The partial removal of the ganglion is attended with partial and temporary blindness, debility of the muscles on the opposite side of the body, and sometimes giddiness and slight rotatory movements. The anatomical connexions with the optic nerve also point to the conclusion, that the principal track of visual impressions to the brain is by the corpora quadrigemina.

18. Notwithstanding its name, the large ganglion called Optic Thalami has but little relationship to the sense of vision. Being in immediate connexion with the hemispheres, it is the final organ of multiplication or diffusion of fibres coming from below; and is supposed to consist chiefly of the sensory tracts. Like the other ganglia, it is inferred to contain fibres reflected downwards, as well as those diffused into the hemispheres. Experiments appear to show that it contributes to the function of co-ordinating movements, such as those of locomotion and emotional expression. Section on one side causes rotatory movements, usually towards the opposite side.

19. The other great ganglionic mass at the entrance to the hemispheres, the Corpora Striata, is believed to contain principally the motor fibres. We are to presume that the large amount of grey matter is chiefly concerned in multiplying the fibres entering into the hemispheres, but partly also in reflecting them downwards, so as to constitute circuits of reflex movements. The collective reflected fibres of all the ganglia at the base of the brain, together with the cerebellum,

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are considered as making up a department or region, which is the seat of reflex acts, and of a large number of grouped or associated movements, involved alike in voluntary action and in emotional expression. It is not unlikely that consciousness accompanies the reflected, as well as the transmitted, currents of this whole region.

Functions of the Cerebral Hemispheres.

20. The Convoluted Hemispheres of the brain, in man and in the higher animals, are by far the largest mass of nervous substance, white and grey, and may be considered as associated with the most complicated of the mental functions, namely, those related to Intelligence.

Cutting or pricking the hemispheres is not attended with either sensation or movement. Pressure from above downwards, or concussion, produces stupor. When the hemispheres are removed, the following results are observed :— First, the two higher senses, Sight and Hearing, are lost. Secondly, Memory, and all the powers characteristic of intellect or thought, are abolished. Thirdly, Volition, in the shape of purpose and forethought, is extinguished.* This is involved in the loss of intelligence. An animal cannot proceed in the search for food, without ideas of what it wants, and a recollection of the means or instrumentality of procedure. Fourthly, there is still a power of accomplishing mary connected movements. An animal may walk, swim, or fly, but there is no tendency to begin these actions. Fifthly,

* A lower kind of volition is possible in the absence of the hemispheres, as is shown by the experiments of Pfliiger and others. A beheaded frog, whose hind foot is touched with an acid, makes efforts with the other hind foot to wipe away the acid. If a drop is placed on the back, on one side, the animal uses the leg on that side to relieve itself of the sting; but, if by cutting the nerve that leg is rendered powerless, the other leg is stimulated to remove the acid. These actions have the essential character of voluntary actions, and yet they proceed from no higher a centre than the spinal cord. They represent volition in one of its initial or undeveloped forms, the putting forth of action, to alleviate a present pain. The appearances would betoken that the pain is felt, or that the animal is conscious.

there remains an inferior form of the sensibility of the three lower senses-Touch, Taste, and Smell. By stimuli applied to these senses, reflex movements may be excited.

Thus, the hemispheres are not the exclusive seat of consciousness, but they are doubtless the seat both of Intelligence and of nearly all the innumerable shades and varieties of Sensation and Emotion.

The attempt to localize the mental functions in special portions of the cerebral mass, has been thwarted by observations of a remarkable kind. The phrenologists noticed cases where the destruction or disease of one hemisphere was unaccompanied with the entire loss of any function; the inference being that the hemispheres were duplicate bodies performing the same office, like the two eyes, or the two halves of the nostrils. But cases have been recorded of disease of large portions of the brain in both hemispheres at once, without apparent loss of function; which would require us to extend still farther the supposition of a plurality of nervous tracks for a single mental aptitude.

Functions of the Cerebellum.

21. The experiments made upon the Cerebellum, and the inferences founded upon its comparative size in different animals, have led some physiologists to assign to it the function of harmonizing and co-ordinating the locomotive and other movements.

'Flourens removed the cerebellum from pigeons by successive slices. During the removal of the superficial layers there appeared only a slight feebleness and want of harmony in the movements, without any expression of pain. On reaching the middle layers, an almost universal agitation was manifested, without any sign of convulsion; the animal performed rapid and ill-regulated movements; it could hear and see. After the removal of the deepest layers, the animal lost completely the power of standing, walking, leaping, or flying. The power had been injured by the previous mutila

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tions, but now it was completely gone. When placed upon bis back, he was unable to rise. He did not, however, remain quiet and motionless, as pigeons deprived of the cerebral hemispheres do; but evinced an incessant restlessness, and an inability to accomplish any regular or definite movement. He could see the instrument raised to threaten him with a blow, and would make a thousand contortions to avoid it, but did not escape. Volition and sensation remained-the power of executing movements remained; but that of co-ordinating these movements into regular and combined actions was lost.

'Animals deprived of the cerebellum are in a condition very similar to that of a drunken man, so far as relates to their power of locomotion. They are unable to produce that combination of action in different sets of muscles which is necessary to enable them to assume or maintain any attitudes. They cannot stand still for a moment, and in attempting to walk, their gait is unsteady, they totter from side to side, and their progress is interrupted by frequent falls. The fruitless attempts which they make to stand or walk are sufficient proof that a certain degree of intelligence remains, and that voluntary power continues to be enjoyed.' (TODD and BOWMAN, 1., p. 359.)

When the cerebellum is cut away at the top, the ammal moves backward. When one side is cut away, the animal rolls over to the other side; the eye of the sound side is turned outwards and downwards, the other eye inwards and upwards. Sometimes a vertiginous action ensues, as if the body were revolved on a spit.

The inference drawn from these experiments-that the cere bellum is the exclusive seat of combined movements-is denied by Dr. Brown-Séquard. He says 'I have ascertained that it is by the irritation they produce on the various parts of the base of the brain that the diseases of the cerebellum, or its extirpation in animals, cause the disorder of movements which has been considered as depending upon the absence of a guiding power. In fact, the least irritation of several parts of the brain with only the

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point of a needle, may genciate very nearly the same disorder movement that follows the extirpation of the cerebellum. have thus been led to conclude that, after this extirpation, or after the destruction by disease of a large or small part of this nervous centre, it is not its absence, but some irritative influence upon the parts of the encephalon that remain unaltered which causes the irregularity of movements (Lectures, p. 79).

This line of criticism has the defect of proving too much; it would lead to the conclusion that the cerebellum has no function. The views of Flourens have been recently supported by M. Vulpian; who, after comparing numerous facts, has shown that, although disease or deficiency of the cerebellum is not uniformly attended with utter incapability of locomotion, yet there is a want of steadiness, and a great liability to stumble, in such instances. The safest inference at present seems to be, that the cerebellum is not the sole organ concerned in rhythmical or combined movements, but concurs with some of the other ganglia in upholding this function. The remark above made, regarding the plurality of nervous tracks for the higher cerebral aptitudes, may be extended to the inferior department of the combined or associated movements.

Of the Nerve Force, and the course of Power in the Brain.

22. The structure of the nervous substance, and the experiments made upon the nerves and nerve centres, establish beyond doubt certain peculiarities as belonging to the force that is exercised by the brain. This force is of a current nature; that is to say, a power generated at one part of the structure is conveyed along an intervening substance, and discharged at some other part. The different forms of Electricity and Magnetism have made us familiar with this sort of action. In a voltaic cell, energy is generated and transmitted along a wire with inconceivable rapidity to any place where the conductor reaches.

This portable, or current, character of the nerve force is what enables movements, distant from one another in the body, to be associated together under a common stimulus.