inIt appeared from facts already stated (p. 167 & 306), that such voluntary efforts as continue to be made by an animal in which the medulla oblongata only remains in the cranium, are still effectual in exciting muscular contraction; but that all indications of those more complex acts of thought,-which precede and cause most of the voluntary efforts by which the muscles are moved,-disappear, at least in the higher animals, after the removal of the higher parts of the nervous system, and especially of the hemispheres of the brain. Hence it may naturally be inferred, that, in most cases of voluntary actions, where the volitions exciting them are consequent on recollections and trains of thought (however short), some physical change is transmitted downwards, from the upper portions of the brain or cerebellum, to the medulla oblongata, and excites the peculiar action there, by which the voluntary muscles are excited; and it is reasonable to suppose that any such physical change, which these higher portions of the brain or cerebellum thus transmit downwards to the medulla oblongata, may be imitated by a mechanical injury.

Those considerations enable us to understand how it should happen, as many experiments by MAGENDIE and others have shown, that in consequence of sections of different parts of the nervous system within the head, superior to the medulla oblongata, certain definite and combined actions of voluntary muscles are excited; such as apparently indicate, not that the muscles are moved involuntarily, as by irritation of

their own nerves,-but that the will of the animal is constrained so to act, as to excite certain movements only. Phenomena exactly similar are occasionally observed in the course of various diseases of the nervous system.

The most uniform effects of this kind, observed in experiments on animals, have been a movement forwards, when the bands of medullary matter passing forwards through the Corpora Striata, from the crura cerebri into the hemispheres, have been cut through; a movement backwards, when the Cerebellum has been wounded or cut off; and a movement of rotation, to either side, when the bands of medullary matter passing through the Crura Cerebelli, to form great part of the Tuber Annulare, have been divided on that side. And these facts seem to lead to the conclusion, that those acts of thought which prompt the volition to move in these different ways, act on the Medulla Oblongata for that purpose, through these different parts respectively. It is a fact ascertained by FLOURENS, and which must at present be regarded as anomalous, that section of the branches of the seventh nerve contained in the semicircular canals, in birds, produces movements of the head, horizontal or vertical, according to the parts injured, similar to those now mentioned in the trunk and limbs; which abate when the animal is at rest, but constantly recur when it attempts any other motion *.

*The loss of the Cerebellum in animals, particularly

* See Ann. des Sciences Naturelles, t. xv.

warm-blooded animals, appears from the experiments of ROLANDO, FLOURENS, and others, to be generally attended by a peculiar effect on voluntary motion. The animals, after this mutilation, provided that compression of the parts of the nervous system which are left is avoided, not only appear capable of sensation, but give all the usual indications of intelligence, and evidently exert volitions which throw many voluntary muscles into action; but they are unable so to regulate the contractions of their muscles, as to perform any definite voluntary action, excepting only those which are the most strictly instinctive, and the most closely linked with some of their sensations, such as biting and deglutition. All the voluntary movements of the body and limbs are performed in this state, in so irregular a manner, that they are generally ineffective for the purposes which are evidently in⚫tended; and most of the usual complex movements cannot be performed.

This may be supposed to be, either because the injury produces certain permanent uneasy feelings, such as vertigo, which interfere with and confuse the sensations, by which the voluntary movements are regulated; or because the recollection of muscular sensations, which are the guide to all definite voluntary movements, depends upon the cerebellum, and is lost when it is destroyed, in like manner as the recollection of other sensations and mental acts appears to be lost when the hemispheres of the brain are destroyed*.

* See GIROU de BUZAREINGUES, in Annales des Sciences Naturelles, t. xv. p. 52.

This last opinion may be thought to be supported by the fact, that in Man, where a greater number and variety of complex voluntary movements are learned by experience, and are associated in trains by means of the muscular sensations accompanying them, than in any other animals, the lobes of the cerebellum are more developed than in any other; and again, that, in those animals which have, immediately after birth, the power of regulating their voluntary movements for definite objects, with the most precision, the cerebellum is very generally found, at the time of birth, the most developed.

This is all that can be stated, at present, as to the parts of the nervous system which furnish the condi❤ tions necessary for the excitation, first, of the volitions by which the actions of the voluntary muscles are caused; and secondly, of the muscular sensations, by which they are guided. When the volitions take place, it appears from facts already stated, that it is by changes which they effect in the medulla oblongata, spinal cord, and nerves, that they produce the contractions of muscles.

THERE is reason to think, not only that all mental acts are attended by some physical changes in the nervous matter itself, but that different mental acts, and particularly any strong efforts of voluntary atten tion, produce effects in the state of the circulation through the nervous system. But all the well marked effects upon other organs, which can be ascribed to mental causes, may be referred to the heads of Volitions and Instinctive propensities, already considered, of Emotions, and Sensations. The effects of these last involuntary acts of mind, on the body, deserve more attention than they have received from most physiologists. They constitute one important element, which must be taken into account in considering va rious questions in pathology and therapeutics; and they may serve to give precision to our inquiries, into the physiological uses of those parts of the nervous system, which we have reason to suppose to be concerned in producing them.

The effects which can be distinctly ascribed to mental Emotions, are the following.

I. When acting in full force, they excite strictly involuntary motions of the voluntary muscles; of