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why this riv, brings down a volume of water, which raises | ternal corering termed dura mater, from its being of a it fár above the Ganges and Irawaddy, and claims for it the firmer texture than the other two membranes, encloses the first place among the rivers of S. Asia. (Rennell ; Francis brain with all its appendages, and lines the whole internal Hamilton ; Klaproth's Mémoires ; Nefville and Wilcox in surface of the bones of the cranium. It is of a fibrous texAsiatic Researches ; Ritter, Asien; Maps of Klaproth, Ber- ture, the component fibres interlacing each other in every ghaus, and Wilcox)
possible direction, and forming by their firmness and densiir BRAHMEGUPTA. [VIGA GANITA.]
the thickest and strongest membrane of the whole body. BRAIDWOOD, THOMAS, is known as one of the By its external surface the dura mater adheres every where earliest teachers of the deaf and dumb in this island. to the inner surface of the cranium, just as the periosteum He began this useful career at Edinburgh in 1760. No adheres to other bones. When torn from the cranium this authentic record of the methods which he pursued has surface appears somewhat rough and irregularly spotted been made known, unless a work published by the late with bloody points, which are the lacerated orifices of vessels Dr. Watson, formerly the head master of the London In- that pass between the membrane and the surrounding stitution for the Deaf and Dumb, may be so considered. bones. These vessels are much more numerous in tlie Dr. Watson, as an assistant to Mr. Braidwood, acquired young than in the adult, and are most abundant at the his mode of tuition, and says, speaking of Braidwood, His sutures or junctions of the bones that compose the skull, method was founded upon the same principles; and his The inner surface of the dura mater, which is shining and indefatigable industry and great success would claim from smooth, is lubricated and kept in a state of muisture by a me respectful notice, even if I could forget the ties of blood tluid secreted by its own vessels. This membrane performs and of friendship' (Instruction of the Deaf and Dumb, a twofold office; it supplies the place of the periosteum to Introduction, p. xxiii. London, 1809). A work entitled Vox the inner surface of the bones of the cranium, sustaining Oculis Subjecta, published at London in 1783, the produc- their nutrient vessels; and it serves as a defence to the tion of an American gentleman, whose son was educated by brain, and a support to the different masses into which it is Braidwood, professes to give 'a particular account of the divided. academy of Messrs. Braidwood, of Edinburgh,' but it throws The dura mater gives off several elongations or producno light upon the system of instruction pursued by those tions called processes, which descend between certain porgentlemen. It is chiefly valuable for its copious extracts tions of the brain; the most remarkable of which is termed from the writings of Bulwer, Holder, Amman, Wallis, and the superior longitudinal process, which extends from the Lord Monboddo, who had all considered the subject of fore to the back part of the skull, between the lateral halves speech with philosophical attention, and in relation to those of the cerebrum. Narrow in front, it becomes gradually persons who are born deaf, or who become so at an early broader as it passes backwards, bearing, as has been conage, and who consequently labour under the deprivation of ceived, some resemblance in shape to a sickle or scythe, speech. There was doubtless much merit in the mechanical whence the common name of it, falx cerebri. methods used by Braidwood and his son to produce in their Where the falx cerebri terminates behind, there proceeds pupils an artificial articulation, and in the persevering ap- a large lateral expansion of the same membrane, extending plication of principles which had been previously ascertained. across the back part of the skull beneath the posterior parts Braidwood succeeded in attracting the notice of many emi- of the cerebrum, and forming a complete floor or ranlt over nent persons. He is spoken of with praise by Arnot (Hist. the cerebellum. This membranous expansion is called lenof Edinburgh), Dr. Johnson (Tour to the Hebrides), Lord torium, the obvious use of which is to prevent the cerebrum Nonbocido (Origin and Progress of Language), Pennant from pressing upon the cerebellum; while from the middle (Tour through Scotland), and John Herries (Elements of of the tentorium proceeds another membranous expansion, Sperch). In addition to these, Lord Morton, president of which descends between the lobes of the cerebellum and the Royal Society, Lord Hailes, Dr. Robertson, Sir John terminates insensibly at the edge of the foramen magnum, Pringle, Dr. Franklin, Dr. Hunter, and others attended the performing for the cerebellum the same office as the falx public examinations of his pupils, and attested their pro- performs for the cerebrum : hence it is called falr cerebelli. gress. After having resided some years at Edinburgh, Moreover, the component fibres of the dura mater, in cerBrailwood removed his establishment to Hackney, near tain parts of its course, separate into layers, which are so London, where he continued to instruet the deaf and dumb, disposerl as to leave spaces between them, for the most part and to relieve impediments in the speech, till his death in of a triangular form. These triangular spaces, which are 1806.
commonly termed sinuses, are lined by a smooth membrane BRAIN, a soft and pulpy organ, which in man occupies perfectly analogous to that which lines ihe veins in the other the cavity of the cranium, and forms one of the central parts of the body, and these sinuses perform the office of masses of the nervous system [NERVOUS SYSTEM). In veins, returning the blood from all the parts of the brain to man and all the higher animals the nervous system consists the neck. Nothing analogous to this structure occurs in any of four distinct parts--the white threads called nerves; other part of the venous system. In almost every other part knots or masses of nervous matter situated along the course of the body the pressure of surrounding parts is a most imof the nerves called ganglions; a long cord of nervous portant aid to these vessels in enabling them to carry on the matter filling the cavity of the vertebral or spinal column, circulation of the blood ; but in the brain, the venous Tubes called the spinal cord; and a large inass of nervous matter are guarded from' pressure, the dense dura mater being for now generally considered as a continuation and expansion this purpose stretched so tensely over them that the weight of the spinal cord, called the brain. The spinal cord and of the surrounding parts is completely taken off' them. brain constitute the two central masses of the nervous One of the conditions essential to the performance of the system, that is, the immediate seat of the functions pecu- functions of the brain is, that it be free from pressure. The liar to this system.
brain is a soft substance, enclosed in a hard unyielding ease. The general mass of nervous matter designated under A preternatural accumulation of blood in its vessels would the common term brain, together with its membranes, produce pressure upon its substance, because that substance vessels, and nerves, completely fills the cavity of the skull. cannot expand with any additional quantity of fluid that This mass is divided into three parts, the cerebrum or may be poured into it; consequently, such additional quanbrain proper, which occupies the whole of the superior part tity of fluid would inevitably occasion a disturbance of funcof the cavity of the cranium; the cerebellum, much smaller tion, if not organic injury. than the cerebrum, whence its name, little brain, which The smooth surface of the brain which is exposed on the occupies the lower and back part of the cavity of the cra- reflection of the dura mater, is formed by its second investnium; and the medulla oblongata, by much the smallest ing membrane, which is named the tunica arachnoidea, portion of the mass, situated at the basis of the cavity, be- from the extreme tenderness and delicacy of its tissue, neath the cerebrum and cerebellum. The medulla ob- which give it a resemblance to a spider's web. This thin longata passes out of the cavity of the cranium into that of colourless and transparent membrane is spread uniformly the vertebral canal by the foramen magnum of the occipital over the surface of the brain, covering all the eminence's bone, being continuous with and forming the commence- termed convolutions (fig. 1. 2, 2), but not insinuating itself ment of the spinal cord.
between any of the depressions between the convolutions This general nervous mass is closely enveloped in three (fiy. 1v. 7). On account of its extreme tenuity and its close distinct membranous coverings, two of which have been adhesion to the membrane beneath it, it cannot be easily called matres, from the fanciful notion that they give separated from the latter ; but there are situations at the rije to all the other membranes of the body, The ex- basis where the arachnoid membrane, as it passes between
opposite parts of the brain, can be seen distinct from the subjacent tunic.
The third investing membrane, the pia mater, derives its name, like the former, from the tenderness and delicacy of its tissue ; but unlike the tunica arachnoidea, in which not a single blood vessel has hitherto been discovered, the pia mater is exceedingly vascular. The blood vessels with which every part of this delicate membrane is covered are the nutrient arteries of the brain ; before they penetrate the brain these vessels divide, subdivide, and ramify to an extreme degree of minuteness upon the external surface of this inembrane, so that the blood does not enter the tender cerebral substance with too great force. When a portion of the pia mater is gently raised from the brain, these blood vessels appear as exceedingly fine delicate threads, which on account of the elasticity with which they are endowed are capable of elongation as they are drawn out of the cerebral substance. As the pia mater contains and supports the nutrient vessels of the brain, this membrane is not only spread as a general envelop over its entire surface, but it penetrates between all its convolutions and lines every cavity which is formed in it.
It has been stated that the large portion of the cerebral mass, termed the cerebrum, occupies the whole of the upper part of the cavity of the cranium. The cerebrum is divided
(Base of the brain.] 1, anterior lobes of the cerebrum; 2, middle lobes of the cerebrum; 3. posterior lobes of the cerebrum ; 4, fissure separating the anterior from the middle lobes, named the fissura sylvii; 5, situation of the supe ficial excavation forming the boundary between the iniddle and the posterior lobes; 6, the two hemispheres of ihe cerebellum composed of flattened laminæ or layers; 7, the medulla oblongata, which in this position of the brain rests upon and covers the vermiform process; .8, corpora pyramidalia ; 9, corpora Olivaria ; 10. lv. ber aunulare, or puns varolii; 11, decussation of the corpora pyramidalia ; a, b, c, d, cerebral nerves.
The whole of the external convex surface of the hemispheres is divided into numerous eminences termed convo. lutions, which run in different directions, and are of different sizes and lengths, in different parts of the hemisphere (fig. 1. 2). The depressions or fissures between the convolutions termed clefts, or sulci, generally penetrate the consistence of the brain to the depth of about an inch or an inch and a half (fig. 1v. 7). The greater number of these pursue a zigzay course, but some run longitudinally, others obliquely; some communicate with each other, while others terminate separately in the substance of the brain (fig. iv. 7).
The nervous matter constituting the cerebrum is composed of two distinct substances, which differ from each other materially both in their colour and consistence (fig. iv. 7). The outer substance is sometimes termed cineritious, from
its being of a greyish brown colour; at other times cortical, (Upper surface of the brain.]
from its surrounding the inner part of the brain, as the bark 1. cut edge of the bones of the cranium ; 2, superior convex surface of the two the inner parts of the tree; by some it is also called glanhemispheres of the cerebrum with their convolutions ; 3, separation between dular, and by others secretory, from the supposition that its the two hemispheres of the cerebrum occupied by the falx cerebri.
nature is that of a gland, and that it secretes a peculiar into two equal lateral halves termed hemispheres (fig. 1. 2), Huid. It is of a softer consistence than the inner part, and which have an ovoid figure somewhat resembling an egg leaves by desiccation a smaller quantity of solid residuum. cut longitudinally into two equal parts. The hemispheres It is composed almost entirely of blood vessels connected are separated from each other by the membrane already and sustained by exceedingly fine cellular membrane. Its described, the falx cerebri (fig. 1. 3); and their inner sides, structure is uniform throughout, presenting no appearance in apposition with the falx, are flattened, while their upper whatever of a fibrous texture. It gives to the entire surface and outer surfaces are convex, being accurately adapted of the cerebrum an external covering, generally about the to the concavity formed by the inner surface of the bones of tenth of an inch in thickness (fig. iv. 7). the cranium.
The inner substance, termed white or medullary(fig. iv.7), Each hemisphere is subdivided into an anterior, a middle, is firmer in consistence and larger in quantity than the grey and a posterior lobe, but it is only on the under surface of matter; and when an incision is made into it, its surface is the brain that these lobes are accurately defined (fig. 11. 1, spotted with red points, the cut orifices of its vessels, which 2, 3). The anterior and middle lobes are separated from vary in number and size according as they may be more or each other by a deep fissure, named the fissura sylvia less distended with blood. It is now universally agreed that (fig. 11. 4), which extends obliquely backwards from the this part of the brain is composed of fibres. When examined basis to a considerable depth between the convolutions; but in its recent and most perfect state, especially after it has been the middle is distinguished from the posterior lobe, not by artificially hardened and condensed by the action of heat or a fissure but by a superficial excavation on the under surface certain chemical substances, if it be carefully scraped with a of the posterior lobe (fig. 11. 5). The anterior lobes rest blunt instrument, these fibres become perfectly distinct and upon the orbitar plates of the frontal bone ; the middle lobes are of considerable magnitude, with furrows between them, are lodged in the temporal fossa formed by the sphenoid which for the most part are placed in such a direction as to and temporal bones, while the posterior lobes are supported converge towards the base of the brain (fig. iv. 6, 5, 4). The upon the tentorium.
fibres do not merely unite, forming what are called commis
sures, but they actually cross each other and pass into the strata, presents an arborescent appearance commonly deno opposite sides of the body. This decussation of the medullary ninated the arbor vitæ (fig. 11. 3). These strata diverge fibres has been demonstrated in the most satisfactory manner towards the circumference of the cerebellum, and are covered by Drs. Gall and Spurzheim.
externally by grey substance (fig. in. 3). It is now very generally admitted that the medullary In front of the cerebellum is placed a large mass of substance of the brain is the true and proper nervous nervous matter, forming a very considerable eminence, cum. matter, or the nervous substance in its most perfect state; monly termed the tuber annulare, or the pons varolii that the grey matter is entirely subservient to it, and is (fig. 11. 10). The external surface of this body is convex, indispensable, if not to its generation, at least to its nutri- and it is divided into two lateral halves by a middle groove ment and support. Drs. Gall and Spurzheim indeed main-(fig. 11. 10). It is joined to the cerebrum by two thick tain that the sole use of the grey is to form or secrete the white cords named the crura cerebri, and to the cerebellum medullary matter; and this opinion they ground, first, on by two similar cords named the crura cerebelli. The the fact, that whenever the medullary matter is obviously to crura cerebri are continued (from the tuber) outwards and be increased, it is invariably surrounded by a mass of grey forwards to the under and middle part of each hemisphere of matter, which incloses it as in a bed or nucleus; and, se the cerebrum, in which they are lost. In like manner the condly, on this further fact, that in the course of the spinal crura cerebelli are continued outwards and backwards into cord, wherever it sends off nerves, masses of grey matter the hemispheres of the cerebellum, in which they terminate. are always accumulated. Professor Tiedemann, who dis The medulla oblongata is that portion of the cerebral putes the correctness of the opinion of these physiologists, niass which intervenes between the tuber annulare and the on the ground that in the fætus the medullary is formed foramen magnum (fig. 11. 7): beyond the foramen magnum before that grey substance, thinks nevertheless that the it takes the name of spinal cord. On the anterior surface use of the grey substance is to convey the arterial blood of the medulla oblongata there are four eminences contiwhich may be necessary to support the energy of the perfect guous to each other (fig. 11. 7). The two internal are nervous matter.
named corpora pyramidalia, or the pyramids (fig. 11.8); and It is not intended, in this article, to pursue further the the two internal the corpora olivaria (fig. 11. 9), or the olivary dissection of the cerebrum in the mode usually adopted by bodies. anatomists, both because the description could not be fol. If the membranes which invest the medulla oblongata lowed unless the object were before the eye, while that are carefully removed, and its middle groove be gently drawn description, if needed, can be easily obtained in the common asunder, there will be discovered four or five bands of white anatomical books; and because however convenient such a substance ascending obliquely from one side of the medulla mode of examining the organ may be for the purpose of to the other (fig. 11. 11). These bands on each side decussate, ascertaining its healthy or diseased conditions, it affords no some of them passing above and others below those of the insight into its real structure.
other side, so that they are interwoven like plaited straw The cerebellum is situated at the basis of the cerebrum, to- (fig. 11. 11). These bands are named the decussating bands wards its posterior part (fig. 11. 6,6). Its form is elliptical, its of the corpora pyramidalia, and their decussation is conlargest diameter extending transversely from one side to ceived to explain the phenomenon familiar to the physician the other (fig. 11. 6). Like the cerebrum, it is divided into and surgeon, that when injury is done to one side of the two lateral halves or hemispheres (fig. 11. 6), which are brain, the consequent disturbance of function is manifested separated by the falx cerebelli. In the centre of its upper on the opposite side of the body. surface there is a distinct prominence termed the ver Taken as a whole, the nervous mass constituting the miform process (fig. 11. 7), which may be considered as brain is strictly symmetrical, that is, the different parts of the fundamental part of the organ, because in the lower which it is composed are so arranged, that if the organ be animals, whatever other parts of the cerebellum are absent, supposed to be divided into two lateral balves by a plane this is invariably present, affording thus the nucleus or pissing perpendicularly through its centre, the parts placed rudiment of the organ, from which, by the addition of other on each side of this plane have a perfect correspondence parts, as the hemispheres or lateral lobes, &c., the more with each other, and form in fact reduplications of each other perfect organ of the higher animal is built up.
(fig. 11). The principal parts of the cerebral mass are thus The external surface of the cerebellum is divided into double, but they are all united on the median line with flattened strata or layers (fig. 11. 6), separated by fissures their fellows of the opposite side. This union is effected by which correspond to the clefts or sulci between the con- medullary bands of various sizes, and figures which pass volutions. The pia mater, bearing the nutrient arteries from one to the other, called commissures. Thus the of the cerebellum, passes between every one of these fis-double parts of the cerebellum are united by means of the sures; while the arachnoid membrane is simply extended large mass of cerebral matter already spoken of under the over them. If a vertical section be made through either he name of tuber annulare or pons varolii (fy. 11. 10). The
hemispheres of the cerebrum are united chiefly by a broad expansion of medullary matter, which extends transversely across from the bottom of one hemisphere to that of the opposite side, called the corpus callosum, or the great commissure of the brain (fig. 111. 6, 6). There are other connecting bands of smaller size, by which minor portions of the cerebral mass are placed in communication, into a description of which it is not necessary to enter here.
The cerebral parts are separated from one another at certain places, and the intervals form cavities which are termed ventricles. Of these ventricles there are commonly enumerated four, all of which are in communication with each other. By far the largest of these are the two great cavities called the lateral ventricles, which are situated in the interior of the hemispheres of the cerebrum. Commencing in the fore part of the anterior lobes, these cavities proceed backwards in a direction parallel to each other
through the middle into the posterior lobes. Their figure FIG. III.
is winding and exceedingly irregular, and they are separated (Vertical section of the brain.]
from each other by a tender mass of medullary matter 1, bundles of medullary fibres in the central part of the nervous apparatus ; termed the septum lucidum (fig. 11. 5). They are lined um; 3, vertical section of the cerebellum, showing the urborescent arrange throughout by a fine transparent membrane, which secretes ment of its component laminæ, and forming the appearance callerl arbor a fluid that keeps them moist, gives them a bright polished vitæ ; 4. situation of the third ventricle: 5, tibres of white matter, forming appearance, and prevents them from uniting. This memventricles from each other; 6, fibres of white matier, furining the corpns culo brane is the pia mater, which is continued from the exterior Josim, immediately beneath which are situated the lateral ventricles; 7, con surface of the brain into these interior cavities, and some volations of the cerebrum.
anatomists describe the arachnoid membrane as accompanymisphere of the cerebellum, a thick mass of white substance ing the pia mater in all its course through the ventricles. is seen in the centre, which, as it divides into the several The middle or third ventricle is a vertical fissure between
the two large convex eminences called the thalami optici that one-fifth of all the blood sent out of the left ventricle (fig. 111. 4), situated in the middle and back part of the of the heart is carried to the head, yet the weight of the lateral ventricles. The fourth ventricle, called also ventricle brain in the human subject is not more than one-fortieth of of the cerebellum, is a cavity of considerable extent, situated that of the whole body. Even if this estimate, which is between the cerebrum, the tuber annulare, and the medulla generally thought too large, be reduced to one-tenth, accordoblongata.
ing to the idea of Monro, it will still leave a very great It is not necessary to enter into a more minute description over-proportion. There is no part of the structure of the of the several parts of the cerebral mass; but it is indis- brain more curious than the various contrivances connected pensable to a clear conception of the organization of the with the circulation through the head, which have for their brain that something should be understood of the course of object the prevention of this prodigious quantity of blood the fibres that constitute the main part of the medullary from producing any injurious effects upon the tender cere. substance. For a detailed account of the course of these bral substance, whether by its pressure, or by its unequal fibres, the reader is referred to the admirable work of distribution, in consequence of its stagnating in the vessels, Drs. Gall and Spurzheim, entitled Recherches sur le Sys- or of its being too violently propelled against them. Many tème Nerveux en général, et sur celui du Cerveau en par- conjectures have been formed respecting the object of furticulier in which the direction of the cerebral fibres is not nishing this organ with such an extraordinary quantity of only minutely and exactly described, but illustrated by blood, but nothing is really known of the use to which it is excellent drawings as large as the objects. Some idea applied, through it may be admitted to give a degree of
plausibility to the opinion that the brain has some analogy to a secreting organ. Without doubt, one use both of the ventricles and the convolutions is to afford a more extended surface by which the blood vessels may enter thic cerebral substance at a greater number of points, and consequently in small quantity at any one point, while at the same time they are more firmly supported in their passage by the greater quantity of investing membrane with which they are supplied.
The cerebral substance, when examined by a powerful microscope, is found to be composed of a pulp containing a number of small particles or rounded globules. The pulp itself appears to consist of flocculi, likewise formed of globules, connected together by fine cellular substance, the ultimate globules being of a tolerably firm consistence and about eight times less than the red particles of the blood. These observations, which were first made by Prochaska, have been confirmed in the essential points by the still more recent and elaborate examination of the Wenzels, who by
using higher magnifiers detected more clearly the constituFIG. IV.
tion of the brain as composed of a series of these small [Course of the fibres of the brain.)
globules, which were apparently of a cellular texture, and 1, entrance of the anterior pyramids into 2, the tuber annulare, or pons va- which constituted the whole solid mass of the organ. Bauer annulare; 4, 5, continued increase in the fibres of the pyramids as they ad states that the globules are disposed in lines so as to give vance onwards towards the convolutions ; 6. divergence of the fibres of the the brain its fibrous appearance ; that the diameter of the pyramids ; 7. convolutions of the cerebrum, showing their depth, their grey globules varies from stod to duo of an inch, the general size matter, and the sulci between them; 8, cerebellum. may be formed of the course of the fibres from fig. iv., taken portion in the medullary than in the cineritious substance,
being abo; that they are both larger and in greater profrom a smaller work by Dr. Spurzheim. Let us follow the and that they are connecied together by a peculiar gelatinous course of some of these fibres; those, for example, that com- matter. pose the pyramids (fig. 11. 8, and fig. iv. I), and trace them Chemical analysis shows that the medullary matter confrom the medulla oblongata to the convolutions of the cere- sists of a peculiar chemical compound, unlike any other of brum (fig. iv.7). Immediately before their entrance into the constituents of the body. In some respects this comthe tuber annulare, the pyramids are a little contracted (fig. pound resembles a saponaceous substance, being miscible 11. 8). As soon as they enter this mass, the pyramids are with water, and forming with it an emulsion which remains divided into innumerable bundles of fibres (fig. iv. 2), which for a long time without being decomposed. Vauquelin has are covered by a thick layer of transverse fibres (fig. iv.2) found in it two species of adipose or adiposerous matter, that come from the cerebellum ( fig. iv. 8). These fibres of soluble in alcohol; also the peculiar animal principle called the pyramids, thus increased in number, ascend and receive osmazome, together with a quantity of albumen, a small at every point of their course fresh accessions, until at their quantity of phosphorus, and some saline matter, consisting exit (from the tuber) forward and outward, they form at least principally of the phosphates of lime, soda, and ammonia. two-thirds of the crura cerebri, as is seen at fig. iv. 3. Fol Such is a brief outline of the nature and relation of the lowed in their course forwards from fig. iv. 3, they are ma- principal parts that enter into the composition of the brain. nifestly increased at every point by the accession of infinite The functions of this organ will be considered in counexion numbers of fibres (fig. iv. 4). At the point (fig. iv. 5) the with those of the spinal cord, and of the nerve. [NERVOUS fibres, now exceedingly numerous, manifestly assume a di- System.] verging course, proceeding in every direction forwards, up. *BRAIN OF ANIMALS, its peculiarities and diseases. wards, laterally, and backwards (fig. iv. 5, 6, 7). At length The most obvious distinction between the brain of man and the radiating fibres, crossing and interlacing each other in that of the other mammalia is its diminished size in most all directions, form an expansion or tissue, which being folded of the latter. The moment the skull-cap is raised, the difin various ways and covered with grey matter constitute the ference between the full rounded appearance of the former convolutions (fig. iv. 5, 6, 7, 7). Thus the pyramids pro- and the compressed flattened shape of the latter cannot fail gressively increased and developed form a large portion of to be observed. The convexity of the middle lobes is strangely the anterior and middle lobes of the cerebrum. If the cor- lessened, and the posterior lobe is in a manner lost in quapora olivara (fig. 11. 9) were traced in like manner, they drupeds. If the brain is now removed from the cranial cavrould be found to form the posterior lobes of the cerebrum ; vity, the difference in bulk between that of man and the and the origin and course of the fibres constituting the main inferior animals is strikingly displayed. The brain of the ox bulk of the cerebellum can be demonstrated with the same scarcely weighs a pound: the average weight of the brain of clearness and exactness.
the human being is more than 2 lbs. From the preceding account of the structure of the brain, In man the brain is supposed to constitute about 1-35th which shows it to be an exceedingly complex organ, it might part of the weight of his body. In the dog, averaging the have been inferred from analogy that it would receive a different breeds, it is 1-120th part; in the horse it is only the large supply of blood ; but the quantity actually sent to it is far greater than any analogy could have led us to sup; on the Brain, it is necessary to remark that these articles contain the sun
As the reader may perceive some discrepancies between the two articles pose. Haller made a calculation, from which he concluded | spective views or opinions of two different writers
450th part, in the sheep the 750th part, and in the ox the redbreast, it approaches to the proportionate size of that 800th part. Does there appear already a connexion between of the human being, it is, as in the smaller quadruped, on the relative bulk of brain and the quantity of mind ? The account of the quantity of medullary matter required for the bulk of the brain has alone been spoken of, but, in point of origins of the nerves; and the cineritious matter forms only fact, these animals have just been ranged in the order of a very small part of the brain. The brain of the bird has no their intelligence and docility.
convolutions on its surface; no corpora striata in the venThe prominences and depressions which mark the surface tricles; no pons varolii between the brain and the spinal of the brain in man, and which are supposed by phrenolo- cord; and the origins of the optic nerves are separate from gists to indicate certain peculiarities of mind and disposition, the brain, and lie behind and below it. are tame and inexpressive in the quadruped. They are not In fishes the brain is yet more diminished in proporfound in the hare, or the rabbit, or in the rodentia generally. tionate size. In some species it does not constitute a twoThey are not so bold or so deep in the ox as in the horse; thousandth part of the bulk of the fish. It scarcely balf nor so much so in the horse as in the dog.
fills the cranial cavity, but is surrounded by a cellular tissue The brain is composed of two substances essentially dis- containing a transparent semifluid mass. It singularly tinct from each other, the medullary deep in the base of the varies in different species. It consists of at least four or organ, and the cortical or cineritious without : the one con more rounded eminences, placed in pairs opposite to each nected with the animal, and the other with the intellectual other, and forming two parallel lines; and there is often principle: the one the medium through which the impres. only a very slight connexion between these lines, or the Bion made by surrounding objects is conveyed, and the other eminences of which either of them is composed. The two the substance to which that impression is referred, and principal hemispheres of the brain and the optic thalami where it is received, registered, and compared : the one are always present. The olfactory nerves often form a third the agent by means of which the voluntary motions of the pair of tubercles anterior to these and the cerebellum, and frame are effected, and the other directing and controlling is always found posteriorly on the mesian line. The optic the working of the machine.
nerves usually cross each other without any intermingling As an illustration of the greater size and development of of medullary matter. The cineritious substance is found in the nerves of sense in animals, the olfactory one may be an exceedingly small proportion in the brain of fishes. selected. In man, who has other means of judging of the As for insects and worms, little needs to be said here. qualities of his food, and of surrounding objects, than by the In the worm the brain or upper ganglion of the nervous sense of smell, the olfactory nerve is not one-fourth of the system is placed near 10, or may be said to be perforated by, size of that of the horse; in the ox, that is not so much the superior portion of the esophagus, and thence proceed domesticated as the horse, and oftener sent into the field to little white threads or cords, which run along the course of shift for liimself, it is considerably larger ; it is larger still the digestive canal. In insects, the upper ganglion usually in the swine, who has to search for a portion of his food surrounds the esophagus, and a ganglionic system of nerves buried in the earth, or deeply immersed in refuse or filth; can generally be traced proceeding from it. In the larvæ and it is largest of all in the dog, whose acuteness of scent of insects the brain is inclosed in a horny cavity. The ren'lers him so useful a servint to man.
spinal cord proceeding from it, pursues its course through The diflerent development of the medulla oblongata in the whole of the abdomen, presenting evident ganglia at different animals may be adduced as another proof of the different points, from which nerves are distributed: while admira-le aslaptation of each to the situation which he oc- from the intermediate spaces are given out other nerves cupies and the functions which he discharges. The medulla without ganglia; presenting a rude but satisfactory sketch oblongata is the prolongation and condensation of the me of the combined systems of sensitive and motor nerves disdullary matter of the brain, and it is the origin of that covered by modern physiologists. portion of the spinal cord which is devoted to organic life. A sketch of the diseases of the brain in different animals In the human being the breadth of it is only a seventh part can, in this place, scarcely extend beyond those that have of that of the brain; in the horse and the ox it is nearly a been domesticated by man. The preponderance of the third ; and in the dog it is more than a half.
medullary matter explains the cause of the unfrequency of In every part of the brain of the quadruped the medullary any affection of the brain that can be called insanity in portion preponderates, and the cineritious is deficient. In animals. If there is so small a portion of cineritious matter, his wild state the brute has no idea beyond his food and the if the intellectual principle is so slightly developed, aberreproduction of his species: in his domesticated state, he is ration of the mind is scarcely to be expected. In certain the servant of man. The acuteness of his senses and the states of cerebral excitation, delirium is occasionally obpreponderance of animal power qualify him for this service; served. It is one of the concomitants and characteristic but were proportionate intellectual capacity added, he would symptoms of rabies. Pure mental alienation unaccomspeedily burst his bonds. It is, however, only in the pro panied by inflammatory or other disease is however, alportions of the two substances that the brain of the biped though very rarely, seen in the quadruped. The eagerand of the quadruped differs : the cineritious and the me ness with which the female, the sow, the bitch, the rabbit, dullary parts are found in each. It was necessary that in or the cat, will search out and pursue their own offspring in the servant of man some degree of intelligence should be order to destroy them, and the evident delight with which acided to animal power; that he should possess the faculties they devour them, is not this insanity ? The fury which of attention, neinory, and judgment, and that to these some animals, gentle in every other respect, show at the should be added not only the gerin, but, often, the pleasing sight of one object, and one alone, is not this true monoderelopment of courage, fidelity, gratitude, disinterested- mania? A mare that had not the slightest fear of any ness, and a consciousness of right and wrong.
other object, was always roused to uncontrollable fury by In the smaller quadrupeds the comparative size of the the sight or rustling of paper; another mare would endeaa brain approaches nearer to that of the human being. In vour to tly upon and tear io pieces every light grey horse the mouse it is a forty-third part of the weight of the animal. that came within her view; and a third would rush furiBut of what is it composert? Of the medullary matter ously against every white object, animate or inanimate ;which is necessary to form the origin of the nerves of pure were not these cases of monomania ? sensation, and of those of the spinal cord, which are as The brain of the quadruped is proportionally much numerous as in a larger animal. This must necessarily smaller than that of man. Comparing bulk with bulk, the occupy a considerable bulk ; but there is little of the cineri- brain of the horse is not a twelfth, and that of the ox tius inatter, or that which is connected with the mind. is not a twentieth part so large as that of the human being.
For several minor points of difference between the brain In a state of health, a much greater quantity of blood is of the biped and the quarruped, the reader is referred to determined to the brain than to any other part, in order to Coulson's edition of Blumenbach's Comparative Anatomy,' | enable it to discharge its important functions. From some and to Dr. Grant's Outlines of Comparative Anatomy.'
sudden disturbance in the circulation, a still greater quan. Tie brain of the larger birds agrees with that of the tity of blood is sometimes determined to the brain of the hu. inammalia in the stallness of its bulk, compared with the man being. What is the consequence ? All the vessels of development of the same organ in the human being. The that organ are overloaded - the origins of the nerves are brain of the engle is not more than a two-hundred-and-pressed upon-no cerebral functions can be discharged sixtieth part of the weight of the bird. The brain of the ihe man is seized with a fit of apoplexy, and unless the curgose is not more than a three-laundred-and-sixtieth part. rent is speedily diverted, and the overcharged vessels to a If in some of the lesser birds, as in the chaffinch and the certain extent drained of their contents, he must inevitably