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1847] True Mode of Studying the Brain.
289 these details and on scrutinising the excellent figures by which they are brought before the eye, find that a knowledge of this complex organization is indispensable to the satisfactory investigation of cerebral pathology. The reason why the descriptions of the anatomist have, as regards this part of the body, become so distasteful, is because they have been unfruitful; because, in the midst of a detail which is discouraging and redundant even to professed teachers, not a glimpse of those relations upon which the actions of the brain, whether healthy or morbid, repose, is to be caught; because, in fine, the authors of France and Germany, and herein too often imitated by our own countrymen, have broken up the brain into an infinitude of fragments, insignificant in themselves and utterly obstructive to those general and connected views of structure, which can alone subserve an enlightened physiology. The account given by Mr. Solly is opposed in toto to this barren topographical school : the several parts, instead of being considered piece-meal, are invariably viewed in reference to those other structures with which they are allied as members of an active living organization : if complex bundles of fibres are to be considered, the tedium of tracing them is obviated, by making the anatomical process reveal some interesting physiological action ; or, if nodules of the vesicular matter are to be decribed, the question is not what is the precise shade of colour or the exact number of indentations, but what part does it play in the mysterious operations of conscious existence.
But we must allow the author to speak in his own language.
" According to the plan generally pursued in treating on the brain in systematic works of anatomy, the information conveyed amounts to little more than a vain catalogue of names applied to parts, without reference to their structure, their functions, or even their analogies in the nervous system of the lower orders of animals. Such a barren prospect as a list of names holds out but little to attract the most zealous among students, while the dryness of unconnected detail, and the obstacles to clear conceptions engendered by the absence of everything like arrangement, almost certainly deter him from attempting to learn more than is required to prepare him for examination for the diploma. It is unfortunate, indeed, that candidates for this honourable certificate are still very generally required to describe the appearances presented by the brain dissected, or rather destroyed, by the old method of slicing; a method most unphilosophical in its conception, and totally inadequate to impart any real information in regard to the structure of the organ. And I do not hesitate to affirm that this mode of examination has contributed essentially to retard the diffusion of sound knowledge in regard to the anatomy and pbysiology of the most important system in the body.”—Preface,
We had hoped that the mode of examination here so properly condemned, had been long since abolished: if, however, any remnants of the old and barbarous system still linger in high places, we trust the scientific works on the brain, which have lately issued from the press of this country, will speedily induce the examining bodies to place themselves on a level with the present state of knowledge.
A few extracts will serve to justify the very favourable opinion we have expressed of Mr. Solly's work; and, also, to illustrate what we conceive to be the true method of pursuing the anatomy of the nervous centres. The question respecting that somewhat unpromising subject--the fissures and subdivisions of the spinal cord, is thus discussed :
“ Line of demarcation between the tracts of sensation and motion.-Although the different offices performed by the anterior and posterior roots of the spinal nerves have been, I think, clearly ascertained, and as it is also evident that the spinal cord consists of tracts of neurine whose office is the same as the nerves which are connected with them, and therefore that there are portions of the cord which perform functions as distinct from each other as the arteries and veins, still anatomists are not yet agreed as to the line of demarcation between them. Sir Charles Bell, for instance, in a paper published in the 135th vol. of the Philosophical Transactions, states that he regards the lateral portion of the anterolateral columns as a part of the tract for sensation, and I have no doubt of its correctness. The circumstance of there being no decided anatomical line of division between the two columns is not of itself an argument against the correctness of this view; for it is quite possible that perfect distinctness of parts, as regards their function, without any visible line of separation between them, may exist. We must always bear in mind that the neurine which composes the cord is supported and clothed by a perfect though delicate membrane, which, pervading its substance in every direction, is undoubtedly as capable of separating masses of neurine endowed with distinct powers, and ordained by nature to execute distinct offices from each other, as any fissure however wide, or membrane however thick. The presence of such gross and palpable partitions, it is true, would save us some trouble in discovering the line of demarcation, but would not necessarily make it in any way more efficient. They are not the less distinct organs because of our ignorance of their respective limits, any more than a nerve of motion is one of sensation because we are incapable of unraveling the fibres of each from their common investing membrane.
“ That the boundary line between the two organs of sensation and voluntary motion comprised within the spinal cord cannot be formed by the posterior peak of grey matter, is very decidedly proved by the fact that a portion of the fifth pair of nerves, which we know to be a nerve of sensation from the beautiful experiments of Mayo and Sir Charles Bell, is not connected with the posterior, but with the lateral columns.”—L. c. p. 223.
This is as it should be; the physiologist refusing to be bound by the apparent evidence of anatomy, when that evidence is over-ruled by superior considerations; but availing himself of a significant structural arrangement, to explain a difficult point of function. We are reminded by this quotation, that, as far as our memory serves us, the merit of seizing upon the precise attachment of the portio major of the fifth pair, as an indisputable indication of the extent of the sensory column, in this and other parts of the work, is due to the author.
There is no point of greater interest to the practitioner, than to have a clear conception of the mode in which the cerebellum and the cerebrum are respectively brought into connexion with the motor and sentient organs of the animal frame; for without this knowledge no satisfactory investigation can be made into a single case of paralysis, apoplexy, or convulsion. There is one fundamental truth which is the sole clue in all these cases ; and which, although it may appear to be sometimes contravened by pecu. liar and inexplicable symptoms, is nevertheless recognisable on a careful scrutiny as a real principle in cerebral pathology : it is this——that the more bid effects, as evidenced by disturbance of the organs of sense and motion, are to be understood by following the tracts of fibrous matter proceeding from the spinal cord to the cerebrum and cerebellum. In this point of view, the physiological character of the fibres composing respectively the corpus restiforme going to the cerebellum and the crus cerebri running to 1847)
Relations of the Cerebellum and Spinal Cord.
the cerebrum is a point of primary importance. The credit of explaining the true constitution of the former of these cords belongs exclusively to Mr. Solly; for although some preceding writers, and especially Rolando, were in part acquainted with the fact that some fibres of the anterior cords of the medulla spinalis passed towards the cerebellum, the author was the first anatomist who discovered that the corpus restiforme receives fibres from the anterior or motor column of the spinal cord. He remarks, with justice, that " the fibres just described as connecting the antero-lateral columns of the cord with the cerebellum are peculiarly interesting when viewed in relation to the functions of the cerebellum. For although it is true that its functions have not yet been clearly ascertained, the experiments of Flourens, Bouillaud, Magendie, and others, and the numerous cases on record in which disease of the cerebellum has been followed by paralysis, all tend to prove that the cerebellum is in some way or other connected with the regulation of muscular action, most probably, as before hinted at, that it has the power of combining the action of individual muscles so as to effect an harmonious result, such as is necessary to enable us to stand, walk, &c.”-L. c. 231.
Our readers will agree in the truth of these observations, when they recollect that some most distinguished authorities, being ignorant of this connexion between the lesser brain and the motor tract of the cord, and equally uninformed as to the true formation of the crus cerebri, have not hesitated to enunciate theories, which, if received, would involve the whole pathology of the encephalon in hopeless confusion. Thus, at no very distant period Foville, assuming that the posterior columns of the spinal medulla are alone prolonged into the cerebellum, and the anterior or motor as exclusively into the cerebrum, inferred that the former is more especially the organ presiding over the sentient phenomena, and the latter, or cerebrum, as exclusively the agent predominating over voluntary motion ; an hypothesis which, notwithstanding it was opposed to all the evidences of physiology and pathology, received a considerable portion of assent, and was even admitted as a probable opinion by that eminent writer Dr. Pritchard.
As in addition to the motorial fibres, the corpus restiforme is well known to receive threads from the posterior aspect of the spinal cord, or the sentient tract; and as moreover there is evidence to show that the restiforme fibres form a part of the decussating apparatus of the medulla oblongata, all the anatomical relations required to explain the phenomena of disease are realised. The subject thus elucidated, there is no longer any difficulty in comprehending how irritation of the cerebellum may disturb the muscular actions ; how effusion of blood into its substance may cause a paralysis both of motion and sensation; and, lastly, as so many cases, especially those recorded by Andral prove, how extravasation or ramollisement of one of the hemispheres will, as in the case of the cerebrum, induce hemiplegia on the opposite side of the body. A reference first of all to the graphic illustrations of Mr. Solly (especially to figs. 88, 89 and 90), and then to the sections on the pathology of the cerebellum, will remove all obscurity on this very interesting and difficult subject.
The true anatomical structure of the crus cerebri is a point of equal importance with that of the restiforme body; as this, however, is so well known, we will only call attention to the circumstance of there being, altogether distinct from the decussation of the pyramidal bodies, a distinct decussation of the fibres forming the sensory tract of the cerebrum. This interesting disposition takes place where these sensory tracts form the floor of the iter a tertio ad quartum ventriculum ; and, as many anatomists have overlooked its existence, the following account of the mode of exposing this structure may not be unacceptable :
“ The best mode of demonstrating this interlacement is first to separate the medulla oblongata, with the pops Varolii, crura cerebri, and optic thalami, from the rest of the brain. Secondly, divide the pons Varolii anteriorly, in a longitudinal direction, through the centre to the depth of half an inch; divide the pyramidal decussation; then take the two lateral halves of the cord and split them upwards, tearing through the floor of the fourth ventricle. When the rent passes the roots of the auditory nerve, fibres, the size of ordinary ligature silk, may be seen running obliquely across the mesial fissure, from one side to the other, decussating with their fellows. This decussation may also be demonstrated anteriorly, though it requires more care and some dissection.” P. 243.
We need hardly observe that this intercrossing of the sentient fibres, regarded in connexion with the decussation of the motor tracts or corpora pyramidalia, offers a perfectly satisfactory explanation, why, in cases of effusion into one hemisphere, sensation as well as motion, is lost on the opposite side of the body.
As it is one principal object with us to lay before our readers, with the assistance of the work before us, some of the fundamental facts connected with the organization of the nervous centres, we would now call their attention to two points, which, although they are perhaps of greater importance than any others relating to cerebral anatomy, have been either denied or doubted by some late writers, and especially by Foville. The first of these questions concerns the ultimate destination of the motor and sentient fibres of the crus cerebri. That these fibres, after traversing the corpus striatum and optic thalamus, continue their course and run finally into the very substance of the cerebral convolutions, is one of the most fertile truths for which anatomical science is indebted to Gall and Spurzheim, but especially to the former. Mr. Solly has always contended for the correctness of this view of the subject; and, as it affords a satisfactory explanation of some of the most common cases of cerebral disease, we cannot do better than follow the example of our author, who has quoted the following familiar but truthful description from the great founder of modern physiology, Sir Charles Bell.
“ The thalamus forms a nucleus round which the corpus striatum bends, and when their respective layers of striæ make their exit beyond these bodies to form the great fan, or solar-like expansion into the hemisphere of the cerebrum, their rays mingle together. A rude representation of these two parts of the cerebrum as we have traced them may be made with the hands. If I place my wrists together, parallel, and closing one hand embrace it with the other, I represent the two portions of one crus. The closed fist is the thalamus, and the other is the corpus striatum. If I then extend my fingers, interlacing their points, I represent the final distribution of the portions of the nervous matter which are dedicated to sensation and volition." P. 244.
A sccond point, which has also been placed in some degree of doubt, is
the real formation of the corpus callosum. If we are to adopt the hypothesis of Foville, this vast organ, the largest of the encephalon, is nothing else than a connecting medium between the crura cerebri, instead of being, what is shown equally by careful dissection and comparative anatomy, the great commissure of the hemispheres of the brain. The author, herein concurring with the best English anatomists, contends for the truth of the latter account ;—" the great transverse commissure, or corpus callosum, is a body consisting of fibres of medullary neurine, the extremities of which are everywhere in contact with the internal or central surface of the cineritious layer which forms the convolutions of the hemispheres,—the hemispherical ganglia. These fibres consequently establish a communication between the cineritious neurine of the whole convoluted surface of both sides of the cerebrum."-(L. c., p. 250.) This account is illustrated by an admirable and most correct figure of the fibrous expansion above described.
Condemning, as we totally do, the cumbrous descriptions still persisted in by so many writers and teachers; and confidently anticipating that, at no distant period, the whole of these will be replaced by an intelligible and simple anatomy of the brain, we have much pleasure in extracting the following judicious observations, with which the author concludes his philosophic account of that organ:
“ In conclusion, let me express the hope that these views or analyses, if I may be allowed so to call them, of the component parts of the encephalon will really simplify the whole of its anatomy, and materially assist the student in acquiring a knowledge of its true character. I wish that custom did not require the student to burthen his memory with fanciful and unmeaning names, and that, instead of learning a long catalogue of the contents of the lateral ventricles as they are erroneously designated, and puzzling himself with the absurd titles of hippocampus major and minor, pes hippocampi, tænia hippocampi, cornu Ammonis, &c., he should be required simply to observe how the spinal columns appear to terminate superiorly in two large tubercles, the corpora striata and thalami, from the sides and under parts of which the hemispheres spring out, being afterwards reflected so as completely to envelope this bulbous extremity of the spinal cord. In the same way the third ventricle should be described as a fissure separating the two balves of the brain, his particular attention being directed to the commissures which pass across it to connect the different cerebral ganglia with one another. The description of the relative position of these ganglia, the commissures connecting them, and their relation to the ganglia and columns of the spinal cord, comprehend all the information which is either interesting or useful to the student.”
L. C. p. 283. We regret that our limits compel us to pass by the section treating on the central attachments of the so-called cerebral nerves, and especially that relating to the development of the nervous system.
In the tenth chapter the author gives a brief resumé of his physiological views, in many of which we fully coincide; but from others we must withhold our assent. The following are regarded, and justly, as “fundamental principles.”
“ 1. That vesicular neurine is the source of power. “ 2. That medullary neurine is the conductor of it.
“ 3. That medullary neurine is also the conductor of those impressions which call forth the power of the vesicular neurine.
“ 4. That the vesicular neurine is collected in masses of variable form and size-the ganglia.