though formerly ascribed to other viscera. This ancient CLASS IV. ment of the intellectual powers, and the source of the sensific and motory. Though, from the close connexion and synchronous action of various other organs with the brain, and especially the thoracic and abdominal viscera, such diversities were often referred to several of the latter in earlier ages, and before anatomy had traced them satisfactorily to the brain as their fountain-head. And of so high an antiquity is this erroneous hypothesis, that it has not only spread itself through every climate on the globe, but still keeps a hold on the colloquial language of every error still tinctures people; and hence the heart, the liver, the spleen, the popular language. reins, and the bowels, generally, are, among all nations, regarded either literally or figuratively, as so many seats of mental faculties or moral feeling. We trace this common and popular creed among the Hebrews and Arabians, the Egyptians and Persians, the Greeks and Romans; among every savage, as well as every civilized tribe; nor is there a dialect of the present day that is free from it: and we have hence an incontrovertible proof, that it existed as a doctrine of general belief at a time when mankind, few in number, formed a common family, and were regulated by common notions. Corrected by the study of anatomy. The study of anatomy, however, has corrected the loose and confused ideas of mankind upon this subject; and while it distinctly shows us, that many of the organs, popularly referred to as the seat of sensation, do and must, from the peculiarity of their nervous connexion with the brain, necessarily participate in the feelings and faculties thus generally ascribed to them, it also demonstrates, that the primary source of these attributes, the quarter in which they originate, or which chiefly influences them, is the brain itself. We are speaking, however, of man and the higher classes of animals alone; for, as the scale in animal life descends, the organ of a brain is perpetually diminishing in its bulk, till at length it totally disappears, and its sentient surfaces, or contractile parts of the animal. In the star-fish, a radiated animal, the central organ consists of a ring of white nervous matter, which surrounds the orifice of the stomach, and gives off opposite to the centre of each ray nerves for its supply."-Sec Mayo's Outlines of Physiology, p. 252, 2d edit. 1828.-ED. place is supplied by other fabrications, as we shall have CLASS IV. occasion to observe in the sequel of this introduction: which will lead us to take a brief notice of the following subjects: I. THE GENERAL NATURE OF THE BRAIN, ITS RAMIFI CATIONS AND SUBSTITUTES. II. THE PRINCIPLE OF SENSATION AND MOTION. division of of the brain, I. In man, and those animals, whose encephalon ap- Natural proaches the nearest to his in form, the brain is of an oval figure and figure, surrounded by various membranes of different firm- the brain. ness and density, and consists of three principal divisions; I. Nature the cerebrum or brain, properly so called, the cerebel or its ramifica little brain, and the oblongated marrow. The first forms tions and the largest and uppermost part; the second lies below substitutes. and behind; the third lies level with the second and in front of it; it appears to issue equally out of the two other parts, and in turn to give birth to the spinal marrow; which may hence be regarded as a continuation of the brain communicating with its different parts by the aid of numerous commissures, the querbänder of the German writers, and extended through the whole chain of the backbone. They are similarly accompanied with a cineritious, or ash-coloured substance, which forms the exterior of the three first divisions, but the interior of the spinal marrow, and appears to derive its hue from the great number of minute vessels that appertain to it. examination with the According to Mr. Bauer's very delicate microscopic ex- Substance periments, when the substance of the brain is made a sub- of the brain according ject of examination immediately after death, "abundance to Bauer's of fibres," to adopt the words of Sir Everard Home in lating these experiments, "are met with in every part of microscope ; it; indeed it appears, that the whole mass is a tissue of fibres, which seem to consist entirely of an accumulation of globules, whose union is of so delicate a nature that the slightest touch, even the mere immersion in water, deranges and reduces them to that mass of globules, of and the which the brain appears to be composed, when examined previous with less accuracy or under less favourable circumstances." Prochaska, Mr. Bauer found, that the globules of the brain, as well Wenzels. as those of pus, are exactly of the same size as those of and the I. Nature of the brain, CLASS IV. the blood when deprived of their colouring matter *. And hence the doctrine of Prochaska+, and the Wenzels, reits ramifica- specting the globular form of the ultimate particles of the brain, seems sufficiently confirmed §. tions and substitutes. Two sub the brain. [When we cut into the interior of the brain, we find it stances of to be composed of two substances, which differ in their colour and consistence, and are named the cortical or cineritious, and the medullary. The cortical, as its name imports, is on the outside, and is of a reddish-brown colour; it is softer than the medullary, and considerably more vascular. The medullary matter, as Dr. Bostock has remarked, is, both from its aspect and relative position, generally considered as constituting the nervous substance in its most perfect state; and Gall and Spurzheim conjecture, that the use of the cineritious is to form or secrete the medullary part. The particular facts, says Dr. Bostock, from which they derive their hypothesis, are, that the nerves appear to be enlarged when they pass through a mass of cineritious matter, and that masses of this substance are deposited on all the parts of the spinal chord, where it sends out nerves. In opposition to the above opinion, however, Professor Tiedemann states, that, in the fœtus, the medulla is formed before the cortex, and he limits the use of the latter to the conveyance of the arterial blood, necessary to support the energy of the perfect nervous matter¶.] Muscular fibres what: and how Sir Everard Home, from the above-mentioned microscopic disclosures, endeavours to show, that muscular fibres produced. are minute chains, formed by an attachment of one gobule See Sir Everard Home's Croonian Lecture, Phil. Trans. for 1818. + Op. Min. tom. i. p. 342. De Structurâ Cerebri, p. 24. § According to Prochaska, the nervous pulp consists of flocculi, which are composed of globules, about eight times less than the red particles of the blood*; and this account, in its essential parts, has been confirmed by the more recent and elaborate investigations of the Wenzelst. Bauer, whose researches confirm the existence of globules, found them larger and in greater proportion in the medullary, than in the cortical substance. See Phil. Trans. for 1818 and 1821; also Bostock's Physiology, vol. i. p. 234.-ED. Recherches sur le Systeme Nerveux, § 2. ¶ See Anatomie du Cerveau, traduite par Jourdan, p. 128; Bostock's Elem. System of Physiology, vol. i. p. 223; Magendie, Physiologie, tom, i. p. 162, &c. Op. Min. p. 342. + De Structurâ Cerebri, p. 24, et seq. I. Nature of the brain, of blood to another: and that vaseularity in coagula or CLASS IV. extravasated blood, or in granulations produced by pus, effected by the escape of minute bubbles of carbonic acid its ramifica gas from the living fluid; which hereby opens a path to a certain extent into the tenacious blood or pus that is extravasated or secreted. tions and substitutes. with nerves From the lower part of the brain, or, according to the Origin of latest researches, rather from the medulla oblongata, and nerves. also from the spinal chord, arises a certain number of long, whitish, pulpy, strings, or bundles of fibres, capable of being divided and subdivided into minuter bundles of filaments or still smaller fibres, as far as the power of glasses can carry the eye. These strings are denominated nerves; they are enclosed in sheaths of membrane; and, by their various ramifications, convey different kinds or modifications of living power to different parts of the body, keep up a perpetual communication with its remotest organs, and give motivity to the muscles. [The nerves are most Organs copiously distributed to the organs of sense and voluntary supplied motion; the viscera are much more sparingly supplied in various with them; the glands have still fewer nerves; and some proportions. of the membranous parts are sometimes conjectured to be quite destitute of them. Generally speaking, the nerves, which supply the organs of sense, proceed immediately from the base of the brain, or rather from the medulla oblongata; while most of the muscles (but not all) receive their nerves from the spinal chord. As Dr. Bostock has observed, there is much more irregularity with respect to the course of the nerves, which go to the viscera; they generally derive their immediate origin from some of the ganglia and plexuses forming part of the great sympathetic nerve, and they are connected with each other in a great variety of ways. The nervous system, viewed as a whole, General however, and comprising the brain, spinal chord, and all symmetry their ramifications, is in general so symmetrical, that if the body were longitudinally divided into two equal halves, the arrangement of the brain and nerves in each half, would, with the exception of a few deviations from this rule, caused by the situations of particular viscera, precisely correspond *. See Bostock's Elementary System of Physiology, vol. i. p. 228. of the nervous system. CLASS IV. the brain, tions and substitutes. Plexus. In various examples, the fibrils of which adjacent nerves I. Nature of are composed, are reciprocally thrown across from one to its ramifica- the other, forming what is termed a plexus. As Mr. Mayo has explained, the nerves which proceed from the further side of a plexus may be more numerous, or fewer, than those which enter it; but the essential result is, that nervous fibrils from different sources are brought together Ganglion. to form new trunks. A ganglion is a small nodule, usually 'flattened, of an oval or circular shape, and of a reddishgray colour, which is found either on the trunk of a single nerve, or where two or more branches coalesce. Mr. C. Bell's opinion respecting the ganglions will be presently noticed. Scarpa supposes, that a ganglion is but a bed of gelatinous membrane, in which the smallest fibrils of the nerves are arranged in new combinations. Others believe, that nervous filaments originate in the gray matter of ganglions*.] Reason of the division compartments not clearly known. As the brain consists of three general divisions, it might, of the brain at first sight, be supposed that each of these is allotted to into distinct some distinct purpose; as, for example, that of forming the seat of intellect or thinking; the seat of the local senses of sight, sound, taste, and smell, and the seat of general feeling or motivity. The investigations and experiments of Mr. C. Bell, and M. Magendie, to which we shall presently advert, pave the way to some important doctrines in respect to a few of these points, but leave us quite in the dark in respect to various others; and particularly as to the source of intellect; while it is difficult to reconcile even the doctrines, which have thus been fairly deduced, with the motific, and even with the sentient powers that must exist in numerous cases of an extensive disorganization of the brain and in acephalous animals. The first and second nerves and the portio mollis of the seventh sufficiently attest their exclusive uses as nerves of the special senses; while the distribution of the greater part of the third, of the fourth, and of the sixth nerves to voluntary muscles, which receive filaments from * Mayo's Outlines of Physiology, p. 324, 2d edit. It is a remark, made by Mr. C. Bell, that the principles and facts unfolded in his views of the nervous system, lead us to understand the "use of all the intricate nerves of the body, with the exception of the sixth. The sixth nerve stands |