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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 spinal nerves. The apparently spontaneous movements 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. A similar movement follows stimulation of the anus. If the 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

FUNCTIONS OF THE MEDULLA OBLONGATA.

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the second were perfectly lax.' Again: The limbs and tail of a decapitated turtle possessed a certain degree of firmness and tone, recoiled on being drawn from their position, and moved with energy on the application of a stimulus. On withdrawing the spinal marrow gently out of its canal, all these phenomena ceased. The limbs were no longer obedient to stimuli, and became perfectly flaccid, having lost all their resilience. The sphincter lost its circular form and contracted state, becoming lax, flaccid, and shapeless. The tail was flaccid.'-(Carpenter, p. 700.) Here we see that the disconnecting of the muscles from the brain still leaves them in a tense condition; whereas that tension gives way the instant the spinal cord is removed; whence we infer that there is an internal source of nervous energy, independent of stimulation from without, although greatly enhanced by the application of the stimulants of the senses. The importance of this fact will be afterwards seen.

15. The Medulla Oblongata, being a continuation of the spinal cord, with additional deposits of grey substance, has the same importance as respects the communication of impressions to and from the brain, but operates more widely in the way of diffusing, transferring, diverting, radiating, and reflecting nervous stimuli. Many of its corpuscles must have for their function the upward spread and ramification of fibres; while some serve for lateral communication, and others for the reflex function, which probably attains its highest development in this portion of the cerebro-spinal axis.

Most of the cerebral nerves arise from the medulla oblongata. It is the proximate centre of hearing and taste; of the sensibility of the face, the pharynx, larynx, windpipe, and bronchial tubes; and of the heart, lungs, and stomach.

Among reflex movements operated by means of it arethe contraction of the Pupil, and the closure of the Eye-lid, under the stimulus of light; the act of Deglutition; Sucking in the infant; and, lastly, the capital function of ordinary Respiration.

Functions of the lesser grey centres of the Brain.

16. These various masses lying between the medulla oblongata and the convoluted hemispheres, must be considered still as the continuation upward of the main stem of the brain, with multiplying, ramifying, and collateral communications through the aggregates of corpuscles in the grey portions of each. The paths of sensory impressions upwards, and of motor impressions downwards, must lie in these bodies, although the two lines are not always exhibited in marked local separation. There are also certain instances of the reflex function embodied in these centres.

The Pons Varolii, with the crura cerebri, is to be viewed in great part as a continuation of the spinal cord towards the brain, in which capacity it is essential to sensation and to volition. The paths of sensation are supposed to be through the fibres and grey substance of the central and posterior portions; the paths of voluntary motion, through the fibres of the anterior and under portions.

By means of the grey centres of the pons, there are manifested reflex acts of a marked and powerful kind. It shares in the regulation of the pupil of the eye. More remarkable is its mediation in the prominent movements of expression, as gesticulation and cries. It has also, in an eminent degree, the function of grouping or associating the movements; so long as it remains, the locomotive rhythm can be maintained, although, after the destruction of the hemispheres, there is no longer a spontaneous commencement of movements. While the pons, and all the centres beneath it, are intact, an animal will retain and secure the erect posture. Lastly, the removal of the parts above the pons does not take away the promptings to remedy uneasiness, and to remove irritating agents. This is the continuation of that exceptional function of the spinal cord, whereby, in the inferior animals, it can give birth to actions apparently of a voluntary character (see Note, p. 45).

It is in connexion with the pons that we have the most

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conspicuous manifestations of the curious fact of rotatory movement in animals, arising on injuries of parts of the brain. Thus, when the transverse fibres leading to the cerebellum are cut on one side, the animal revolves, as if on a spit, towards the injured side. Accompanying the rotation, there is a downward movement of the eye-ball on the injured side, and also rolling movements in the other eye. The effects are arrested by cutting the corresponding fibres leading to the other half of the cerebellum. In reality, the cerebellum may be considered the seat of the disturbance in the case now supposed; still the movements may also arise by a partial section of one of the cerebral crura or peduncles (in the heart of the pons), but they are in the opposite direction, that is, away from the injured side. A complete section of one peduncle causes the animal to fall on the opposite side, on which side the stimulus to the muscles survives.

These rotatory movements likewise follow from unilateral incisions, injuries, and diseases, in the corpora striata, thalami optici, corpora quadrigemina, cerebellum, medulla oblongata, and lastly, the auditory nerve, and the semicircular canals of the ear. The sensation of giddiness or vertigo corresponds to the same class of effects; a sensation known to be caused by whirling movements, even although voluntary, and by rapid visual movements, as well as by alcoholic stimulation and other cerebral derangements.

The hypothesis suggested by this singular manifestation is, that there exists, in permanence, a powerful nervous stimulation to the muscles of the two sides of the body, such as would cause an energetic propulsion of each. In the ordinary condition, the two sets of stimuli are balanced, and produce an equilibrium, disturbed only by the slight remissions necessary for locomotion and other voluntary exertions. The destruction of the nervous tracks or centres, on one half of the body, leaves a preponderance on the other; and the one-sided movements, that are seen in consequence, testify how energetic the persistent current must be. If this be the