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of Smell (olfactory nerve, 1st pair); the nerve of Sight (optic nerve, 2nd pair); the nerve of sensation of the Tongue and Face generally (5th pair)-(this nerve contains also a motor portion distributed to the muscles of mastication); the nerve of Hearing (auditory nerve, part of the 7th pair). These nerves, therefore, are engaged in transmitting influence from the surfaces of special sense, the nose, eyes, ears, tongue, and face, towards the cerebral mass. Five nerves are enumerated as purely motor or outcarrying:-the nerve supplying three of the four recti (or rectangularly arranged) and one of the oblique muscles of the eye, and sustaining its ordinary movements (motor communis oculorum, 3rd pair); the nerve supplying the superior oblique muscle of the eye (trochlearis, 4th pair); the nerve distributed to the external rectus muscle of the eye, and serving to abduct the two eyes by an independent stimulus requisite in adjusting the eyes to different distances (abducent, 6th pair); the trunk nerve for setting on the movements of the face and features (2nd part of 7th pair); the nerve for moving the tongue (9th- pair). The pair reckoned the 8th has three divisions: (1) the glossopharyngeal or sensory nerve of the tongue and throat; (2) the vagus or pneumo-gastric, the sensory nerve concerned in respiration, circulation, deglutition, and digestion; (3) the spinal accessory or motor nerve for regulating the movements of the parts supplied by the vagus-as the throat, larynx, and lungs.

If any one of the four sensitive nerves issuing from the cranium be cut through, sensation in the connected organ is lost; disease will produce the same effect. Injury in the optic nerve causes blindness, in the auditory nerve deafness. If any one of them is irritated by pricking, corrosion, or electricity, a sensation is produced of the kind proper to the nerve; if the olfactory nerve, there is a smell; the optic, a flash of light; the auditory, a sound; but no movement is generated. If any one of the five motor pairs is cut, the corresponding muscles cease to act; they are said to be paralyzed, an effect also produced by nervous disease. If the

FUNCTIONS OF THE SPINAL CORD.

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third pair were cut, the motion of the eyeballs would cease, there would no longer be any power of directing the gaze at pleasure; the most brilliant spectacle would fail to command the sweeping glances of the eye. If the moving portion of the 7th pair were cut on one side, all the muscles of the face on that side would lose their tension, and the equipoise of the two sides being thus destroyed, the face would be set awry, by the action of the unparalyzed muscles.

By experiments of this nature, the functions of the several cerebral nerves have been successively ascertained. In like manner, the discovery of the compound nature of the spinal nerves has been fully confirmed. It has been shown beyond the possibility of doubt, that the nerve fibres are of two distinct classes, with different functions, and that the same fibre never serves both functions.

Functions of the Spinal Cord and Medulla Oblongata.

14. With regard to the Spinal Cord, we find, in the first place, that it is necessary to sensation and to voluntary movement (movement from feeling) throughout the entire trunk and extremities of the body. If the cord is cut across at any part, all feeling is lost, and all power of movement by the will, everywhere below that place, or in every portion of the body where the nerves arising beyond the cut are distributed. If the division is made far down in the back, the lower limbs are the parts principally paralyzed; from them feeling comes no more, nor is it possible to move them by any mental effort. If the cut is in the neck, the paralysis overtakes the arms, trunk, and legs. It becomes evident, that the continuity of the cord with the brain is necessary in order to connect the mental system with the bodily members. The cord by itself will not give the power either of sensation or of voluntary movement. We must regard this portion of the cerebro-spinal axis as a main channel of nervous conveyance for sensation and for voluntary action, between the brain, and the trunk and the extremities of the body. The nerve ramifi

cations are here, as it were, gathered together into one rope or bundle, for convenient transmission to and from the masses of the encephalon. To this extent the cord is the assemblage of the general mass of ramifying or communicating fibres; we may look upon it as the trunk of the tree, the final stream of the river system.*

If now we make experiments upon the cord when dissevered from the brain, we discover that a power of producing movements, though not voluntary, still remains. On irritating any portion of the substance, movements of the limbs are observed. This effect might, no doubt, arise from the continuity of the part with some of the motor nerves; for we have seen that movements in a limb are caused by pinching one of the nerves that supply the limb. But there is a mode of trying the experiment so as to prove decidedly that the spinal cord is itself a source of movement; that is, to prick the skin of the toes. When this is done, a convulsive stimulus instantly returns upon the limb and throws it into action. Hence we infer that an impression arising on the surface of the body and conveyed to the spinal cord, but not to the brain, causes the cord to send forth a motor stimulus to the moveable organs; a phenomenon, moreover, that ceases on the destruction of the cord.

'In most instances where the spinal cord has been divided, whether by design or accident, it has been found that al

Dr. Brown-Séquard has determined by decisive experiments that the transmission of sensitive impressions, in the spinal cord, takes place chiefly through the grey matter, and partly through the anterior columns; the impressions being conveyed to the grey matter by fibres passing obliquely across the posterior columns. The novel part of this doctrine is the attributing of a conducting function to the grey matter; although the grey substance of the cord contains white fibres, these are comparatively few in number, and the conclusion seems inevitable that a line of nervous communication is maintained by the corpuscles of the cord and their connecting fibres. The communication with the brain is maintained after cutting through the white columns, provided the grey substance remains intact; or if, although cut into at different places, it is nowhere completely severed. In the point of special function, there is much uncertainty as between tl anterior and the posterior columns.

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though the will cannot move the paralyzed parts, movements do occur in them of which the individual is unconscious, and which he is wholly unable to prevent. These take place sometimes as if spontaneously, at other times as the effect of the application of a stimulus to some surface supplied by The apparently spontaneous movements spinal nerves. frequently resemble voluntary actions so closely, that it is almost impossible to distinguish them.'

The following experiments serve to illustrate these actions:

'If a frog be pithed by dividing the spinal cord between the occipital hole and the first vertebra, an universal convulsion takes place while the knife is passing through the nervous centre. This, however, quickly subsides; and, if the animal be placed on the table, he will assume his ordinary position of rest. In some exceptional cases, however, frequent combined movements of the lower extremities will take place for a longer or shorter time after the operation; when all such disturbance has ceased, the animal remains perfectly quiet, and as if in repose, nor does there appear to be the slightest expression of pain or suffering. He is quite unable to move by any voluntary effort. However one may try to frighten him, he remains in the same place and posture. If now a toe be pinched, instantly the limb is drawn up, or he seems to push away the irritating agent, and then draws up the leg again into its old position. Sometimes a stimulus of this kind causes both limbs to be moved violently backwards. If the A similar movement follows stimulation of the anus. skin be pinched at any part, some neighbouring muscle or muscles will be thrown into action. Irritation of the anterior extremities will occasion movements in them: but it is worthy of note that these movements are seldom so energetic as those of the lower extremities.'-TODD and BOWMAN, I., 308-9.

These and other experiments prove, that to the cord belongs a power of originating movements, at the instance of stimulation applied to the surface or extremities of the body.

This function must be attributed to the grey matter, or to the mass of corpuscles enclosed in its substance. It is by the corpuscles that a stimulation can be reflected, diverted, or radiated into new channels. The movements prompted through the cord, by itself, may even be complex and rhythmical, as standing and walking, and locomotion generally; all which are possible to a certain extent, in many animals, after loss of communication with the brain.

The independent action of the spinal cord, in man, is shown in occasional acts of the reflex kind (to be afterwards fully enumerated). When the foot of any one asleep, or under chloroform, is tickled, the limb is withdrawn. In rupture of the spinal cord, irritation of the legs will induce movements, the patient being insensible to the effect.

There is one instance of muscular action by most physiologists ascribed to the spinal cord, and believed to have a peculiar interest in this point of view; that is, the tension, tone, or tonicity of the muscles. By this is meant the fact that a muscle is never wholly relaxed while the animal is alive. Even in the perfect repose of sleep, there is yet a certain vigour of contraction inhering in all the muscles of the body. The force of contraction is increased at the moment of wakening, and still more when an effort is to be made; but at no time is the relaxation total; the limbs never dangle like a loosely constructed doll, until after the animal is dead.

The experiments relied upon for showing that the permanent tension of the muscle is in part due to spinal influence, are very striking and not easily explained away. I quote from Dr. Carpenter: 'It has been proved by Dr. Marshall Hall that the muscular Tension is not dependent on the influence of the Brain but upon that of the Spinal Cord, as the following experiments demonstrate: Two Rabbits were taken from one the head was removed; from the other also the head was removed, and the spinal marrow was cautiously destroyed with a sharp instrument: the limbs of the former retained a certain degree of firmness and elasticity; those of

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