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which is in many parts ciliated, and which rests on a layer name of tænia hippocampi, forms the free border of the of neuroglia. This lining is continuous through the fora- hippocampus major. If the body of the fornix be now men of Monro with that of the third ventricle, which divided by a transverse incision, its anterior part throwu again is continuous with the lining of the fourth ventricle forwards, and its posterior part backwards, the great trangthrough the aqueduct of Sylvius. A little fluid is con verse fissure of the cerebrum is opened into, and the velum tained in the cerebral ventricles, which, under some patho- interpositum lying in that fissure is exposed. logical conditions, may increase greatly in quantity, so The velum interpositum is an expanded fold of pia mater, as to occasion considerable dilatation of the ventricular which passes into the interior of the hemispheres through cavities.
the great transverse fissure. It is triangular in shape; its If the corpus callosum be now divided about its middle base is in a line with the posterior end of the corpus callosum,
where it is continuous with the external pia mater; its lateral margins are fringed by the choroid plexuses, which are seen in the bodies and descending cornua of the lateral ventricles, where they are invested by the endothelial lining of those cavities. Its apex, where the two choroid plexuses blend with each other, lies just behind the anterior pillars of the fornix. The interval between the apex and these pillars is the aperture of communication between the two lateral ventricles and the third, already referred to as the foramen of Monro. The choroid plexuses contain the small choroidal arteries, which supply the corpora striata, optic thalami, and corpora quadrigemina; and the blood from these bodies is returned by small veins, which join to form the veins of Galen (Fig. 75). These veins pass along the centre of the velum, and, as is shown in Fig. 63, open into the straight sinus. If the velum interpositum be now carefully raised from before backwards, the optic thalami, third ventricle, pineal gland, and corpora quadrigemina are exposed.
The optic thalamus is a large, somewhat ovoid body situated behind the corpus striatum, and above the crus cerebri. Its upper surface is partly seen in the floor of the body of the lateral ventricle, but is for the most part covered by the fornix and velum interpositum. Its posteroinferior surface forms the roof of the descending cornu of the ventricle, whilst its inner surface forms the side wall
of the third ventricle. At its outer and posterior part are positum. a, under surface of corpus callosum, turned back; 0, b, posterior
two slight elevations, placed one on each side of the optic pillars of the fornix, turned back; C, C, anterior pillars of the fornix; d, velum
named respectively corpus geniculatum internum interpositum and veins of Galen; e, Afth ventricle; J, J, corpus striatum; f, g, tænia semicircularis; h, h, optic thalamus; k, choroid plexus; I, tænia
and externum. hippocamp:; m, hippocampus major in descending cornu; n, hippocampus The third ventricle is a cavity situated in the mesial minor; o, eminentia collateralis.
plane between the two optic thalami. Its roof is formed oy a transverse incision, and the posterior half of this by the velum interpositum and body of fornix; its floor, structure be turned back, the body of the fornix on which by the pons Tarini, corpora albicantia, tuber cinereum, the corpus callosum rests is exposed. If the anterior half infundibulum, and optic commissure ; its anterior boundof the corpus callosum be now turned forward, the grey ary, by the anterior pillars of the fornix, anterior commispartition, or septum lucidum, between the two lateral ventri sure, and lamina cinerea ; its posterior boundary, by the cles is exposed. This septum fits into the interval between corpora quadrigemina and posterior commissure. The the under surface of the corpus callosum and the upper cavity of this ventricle is of small size in the living head, surface of the anterior part of the fornis. It consists of for the inner surfaces of the two thalami are connected two layers of grey matter, between which is a narrow ver- together by intermediate grey matter, named the middle tical mesial space, the fifth ventricle. If the septum be or soft commissure; but in taking the brain out of the
moved, the anterior part of the fornix is brought cranial cavity this commissure is usually more or less torn into view.
through, and the cavity is consequently enlarged. ImmeThe fornix or arch is an arch-shaped band of nerve fibres diately in front of the corpora quadrigemina, the white extending in the antero-posterior direction. Its ante fibres of the posterior commissure pass across between the rior end forms the anterior piers or pillars of the arch, its two optic thalami. If the anterior pillars of the fornix be posterior end the posterior piers or pillars, whilst the inter- separated from each other, the white fibres of the anterior mediate body of the fornix forms the summit or crown of commissure may be seen entering the two corpora striata. the arch. It consists of two lateral halves, one belonging The pineal body is a reddish cone-shaped body, enveloped to each hemisphere. At the summit of the arch the two by the velum interpositum, and situated upon the more lateral halves are conjoined to form the body; but in front anterior pair of the corpora quadrigemina. From its broad of the body the two halves separate from each other, and anterior end two white bands, the peduncles of the pineal form two anterior pillars, which descend in front of the body, pass forwards, one on the inner side of each optio third ventricle to the base of the cerebrum, where they thalamus. Each peduncle joins, along with the tænis form the corpora albicantia, and then enter the substance semicircularis, the anterior pillar of the fornix of its own of the optic thalamus. Behind the body the two halves side. In its structure this body consists of a vascular diverge much more from each other, and form the posterior stroma of connective tissue, in the meshes of which pillars; each of which curves downwards and outwards lymphoid cells are contained. Branched corpuscles are into the descending cornu of the ventricle, and, under the also found not unlike nerve cells. Amylaceous and gritty
calcareous particles, constituting the brain sand, are also considerable numbers, and that the greater number of the found in it. Usually it is hollowed out into two or more cells of the occipital lobe are small and nearly uniform in small cavities. The function of the pineal body is not size, there is no difficulty in recognising in the occipital understood, but both it and the pituitary body, which lobe a small proportion of cells, quite equal in magnitude possess a certain structural correspondence, are usually to the largest cells of the frontal lobe, interspersed amongst referred to the type of the ductless glands.
the smaller pyramidal cells. The nerve fibres which ascend The corpora quadrigemina or optic lobes are situated into the grey matter from the white core of the convolution behind and between the two optic thalami, and rest upon radiate into its several layers, and are apparently continuous the posterior surface of the crura cerebri. The division with the basal axis-cylinder processes of the nerve cells. into two lateral halves is marked by a shallow longitu- According to Cleland, the elongated apices of the cells, dinal fissure, and the subdivision of each half into an an which are directed to the surface of the convolution, are terior and a posterior eminence, by a shallow transverse continuous with the nerve fibres situated in the superficial fissure. The anterior pair of eminences are called nates; layer of horizontal fibres. Immediately subjacent to the the posterior, testes. From each testis a strong white large pyramidal cells numerous small, irregularly shaped band, the superior peduncle of the cerebellum, passes back nerve corpuscles, like those of the internal granule layer of wards to the cerebellum, and stretching between the pair the retina, form the so-called granule layer of the grey matter. of peduncles is the valve of Vieussens or anterior medullary Fusiform cells, which give off lateral processes, are found velum. The corpora quadrigemina are tunnelled in the in the deepest layer of the grey matter, and form the antero-posterior direction by the aqueduct of Sylvius, which claustral layer of Meynert. Gerlach has described here, opens anteriorly into the third ventricle immediately below as in the spinal cord, a network of extremely minute nerve the posterior commissure, and posteriorly into the fourth fibres, with which the branched lateral processes of the ventricle under cover of the valve of Vieussens. It is nerve cells are apparently continuous. The neuroglia conlined by a cylindrical ciliated endothelium.
tains multitudes of small rounded corpuscles. In it also INTERNAL STRUCTURE OF THE CEREBRUM.—The cere are found small stellate cells, provided with minute branched brum is composed both of grey and white matter, the processes, which cells, as Meynert states, are so pellucid, general relations of these two forms of nerve matter to that in the healthy brain they seem to be only free nuclei; each other may be seen by making sections through the it is difficult to say whether these cells belong to the cerebrum. The determination, however, of their minute neuroglia, or are nerve cell elements. The grey cortex of structure, and of the relations and connections of the the cerebrum is much more vascular than the white matter. nerve fibres to the nerve cells is, owing to the delicacy The arteries derived from the pia mater pass vertically into of the organ, one of the most difficult departments of ana- it, and end in a close polygonal network of capillaries; but tomical study. Several anatomists have endeavoured to it is also traversed by the arteries, which terminate in the trace out the course of the nerve fibres in the organ, and capillary network of supply for the white matter. though our knowledge is by no means complete, yet many In the grey matter of the cortex of the occipital lobe important facts have undoubtedly been ascertained. These eight layers have been described by Clarke and Meynert. facts have been summarised, and numerous valuable addi- | The increase in number is due to the intercalation of two tions made to them by Meynert in a recent elaborate additional granule layers, which coalesce and form a dismemoir, which has been frequently consulted and made use tinct white band in the grey matter, owing, as Meynert of in writing the following description.
states, to the absence of pigment in the cells of the granule The Grey Matter of the cerebrum is disposed in three layers. great groups : a, The grey matter of the cortex of the hemi
The grey matter of the cortex of the island of Reil and spheres; b, the grey matter of the great ganglia of the base of the convolutions bounding the Sylvian fissure contains a of the cerebrum ; c, the central grey matter which forms very large proportion of fusiform cells. They form the chief the wall of the cerebral end of the cerebro-spinal tube. constituent of the grey claustrum, situated deeper than the
a, The grey matter of the cortex of the hemisphere forms grey matter of the island, and separated from the outer part the superficial part of the convolutions, and is known as of the corpus striatum by a thin layer of white matter. the great hemispherical ganglion, but in some localities, as Fusiform cells also occur abundantly in the nucleus amygat the loci perforati antici and the septum lucidum, it has dalæ, a grey mass situated below the corpus striatum, received distinctive names. When a convolution is divided which in some sections seems as if isolated, but in reality vertically the grey matter is seen to be confined to the is continuous with the grey matter of the inferior temporosurface and to enclose a white core. The grey matter sphenoidal convolution. presents a laminated appearance, and as a rule consists of The grey matter of the cortex of the gyrus hippocampi five or six layers, which are composed of the characteristic and of the hippocampus major is apparently destitute of pyrannidal nerve cells of the cortex of the cerebrum, of nerve both the granule and claustral layers of cells. Its superfibres, of matrix or neuroglia, and of blood-vessels. The ficial layer has been named the nuclear lamina, and contains most superficial layer consists of neuroglia, in which nerve small and scattered nerve corpuscles. Next this lamina fibres extend parallel to the surface of the convolutions. lies the striatum reticulare, in which the apices of the In the deeper layers are found the pyramidal nerve cells, numerous pyramidal cells of the third layer branch and which lie with their long axes vertical to the surface of again unite to form a delicate network. Deeper than the the convolutions, and which contain angular nuclei. From pyramidal cells is a thick layer of so-called "granules," the observations of Lockhart Clarke, Arndt, Cleland, and which A. B. Stirling recognised some years ago as like Meynert, there can be no doubt that the pyramidal nerve the granules of the rust coloured layer of the cerebellum ; cells vary in relative size and in numbers in the different like them they consist of a well-defined nucleus invested layers of the grey cortex, and that the largest sized pyra- by delicate branched protoplasm. The grey matter of the midal cells lie in the third and fourth layers. L. Clarke two layers of the septum lucidum, though included bestated that the cells of all the layers of the posterior or tween the corpus callosum and fornix, is yet in the same occipital lobe were small and of nearly uniform size, whilst plane as the grey matter of the cortex of the inner surface in the convolutions anterior to it numerous cells of a much of the hemispheres, but is cut off from it by the developlarger kind were found; but though it is undoubtedly true ment of the transverse fibres of the corpus callosum, that large pyramidal cells are found in the frontal lobe in | The grey matter of the locus perforatus anticus contains
clusters of minute granules and a compact arrangement of thalami fibres radiate into the convolutions of the lobes of small nerve cells.
the hemisphere and form the corona radiata. To some b, The great ganglia of the base of the cerebrum are the extent the fibres of the corona are directly continuous with corpora striata, the optic thalami, the corpora geniculata, those of the cerebral peduncles, but there can be no doubt the corpora quadrigemina, and the locus niger in each crus that a large portion of the peduncular fibres terminate in cerebri.
the grey matter of the ganglia of the base of the cerebrum, The corpus striatum cerebri consists of two masses of and that a still larger number arise from their nerve cells grey inatter separated from each other by numerous striæ to aid in the formation of the corona radiata. The direct of white fibres, which ascend from below upwards through continuity, therefore, of many of the peduncular fibres with its substance. The upper mass of grey matter projects those of the corona is broken or interrupted by the interinto the lateral ventricle, and is called the intra-ventricular position of the cerebral ganglia, which Meynert has named portion or nucleus caudatus. The lower extra-ventricular ganglia of interruption. The peduncular fibres and those White portion or nucleus lenticularis forms the outer and lower of the corona constitute the cerebral portion of the projection matter. part of the corpus striatum, and is separated by the system of fibres of Meynert, a term devised to express that claustrum from the island of Reil. Multipolar nerve cells they conduct upwards to the grey cortex of the hemispheres are found in both the caudate and lenticular masses, and in sensory impulses derived from the external world, the the latter cells of large size have been seen. The optic image of which is projected upon the cortex. But it should thalamus forms an almost continuous mass of grey matter also not be forgotten that many of the fibres of this system traversed by nerve fibres, which are not, however, collected conduct motor impulses downwards to be propagated along into definite striæ. The nerve cells in the grey matter are the motor cranial and spinal nerves. The peduncular fibres both multipolar and fusiform. The external corpus geni- of the crura cerebri are arranged in two groups, named culatum consists of alternate layers of grey and white respectively crusta and tegmentum, which are separated matter, due to the zig-zag folding of the grey matter; the from each other by the nerve cells of the locus niger. The nerve cells are multipolar, and contain pigment. In the crusta forms the superficial or anterior part of the crus, internal corpus geniculatum the cells are smaller in size Its fibres are in greater part continuous with the longiand fusiform. The grey matter of the corpora quadrigemina tudinal fibres of the pons derived from the anterior consists of two distinct inasses. One, the zonular layer, pyramids of the medulla; but it receives additional fibres lies near the surface, and contains small multipolar nerve from the grey matter of the locus niger, and from the cells cells; the other, the Sylvian or central layer, lies at the sides of the Sylvian layer in the corpora quadrigemina. Some of the Sylvian fissure and belongs to the grey matter of the of the fibres of the crusta pass directly upwards as radiating wall of the cerebro-spinal tube, and serves as a centre of fibres to the grey cortex of the occipital and temporal lobes, origin for the roots of both the 3d and 4th cranial nerves. but the larger number terminate in the nucleus caudatus The grey matter of the crus cerebri occupies the centre of and nucleus lenticularis of the corpus striatum. From the cerebral peduncle. Its cells are multipolar, and contain these nuclei a great mass of fibres radiates into the cortex dark brown or black pigment, so that the name locus niger of the fronto-parietal lobes, more especially the frontal, but is applied to this collection of nerve cells.
a few also, bearing the special name of stria cornea, pass to c, The central grey matter of the cerebrum is in series the grey matter of the apex of the temporal lobe ; fibres with the grey matter of the floor of the 4th ventricle and also enter the convolutions of the insula. In addition to the grey matter of the spinal cord. It is situated around the radiating fibres, the grey matter of the corpus striatum the Sylvian aqueduct, and at the sides and floor of the third gives origin to fibres of the middle root of the olfactory ventricle, which form the cerebral portion of the cerebro- peduncle, and to connecting fibres with the grey matter of spinal tube. That which is situated in relation with the the septum lucidum. The tegmentum forms the posterior aqueduct of Sylvius forms the Sylvian or central layer just or deeper part of the crus cerebri. Its fibres are continuous described in the corpora quadrigemina. That which lies in with the longitudinal fibres of the pons derived from the relation to the third ventricle forms the middle or soft com-Olivary fasciculi, fasciculi teretes, and posterior pyramids missure, and the well-defined grey layer which covers the of the medulla. A few of the fibres of the tegmentum inner wall of each optic thalamus; also the grey masses enter the corpora quadrigemina and corpora geniculata, but situated at the base of the brain between and in front of the the great majority enter the optic thalami, in the grey matter crura cerebri, viz., the pons Tarini, tuber cinereum, lamina of which many evidently terminate, though some may pass cinerea, infundibulum, and the grey matter of the pituitary through into the cortex of the hemispheres as fibres of the body. By some anatomists the grey matter of the pineal corona radiata. But the grey matter of the thalamus gives body is referred to the same category, but Arnold has pointed origin to numerous radiating fibres : those which arise in out that it is separated by its peduncle from the soft com its posterior part radiate into the occipital and temporal missure ; and Meynert is disposed to regard it as a ganglion lobes, whilst those proceeding out of its anterior part radiate of origin of the tegmentum. Both the pituitary and pineal into the frontal, parietal, and temporal lobes, and the insula. bodies contain, besides the nervous matter, structures of In the optic thalamus the fornix arises. Its fibres emerge the type of the glands without ducts.
from the under surface of the thalamus, form the corpus The White Matter of the cerebrum consists of tracts or albicans, and then pass backwards as the upper boundary fasciculi of nerve fibres, of which—a, some connect the cere of the great transverse fissure to end as the tænia hippobrum with the lower divisions of the encephalon; b, others campi in the gyrus hippocampi; hence this convolution has connect the two hemispheres together; c, others connect a special connection with the optic thalamus through the different structures in the same hemisphere; d, others serve fornix. In the corpus albicans the fibres of the fornix are as roots of origin for the more anterior encephalic nerves. arranged in loops, in the concavities of which nerve cells
a, The tracts of fibres which connect the cerebrum with are situated. The optic thalamus also gives origin to the the lower divisions of the encephalon are called peduncular middle root of the optic tract. Owing to the connections fibres. The largest of these peduncles are the two crura of the locus niger, nucleus caudatus, and nucleus lenticucerebri or cerebral peduncles. Continuous below with the laris with the crusta, Meynert has named them the ganglia longitudinal fibres of the pons they ascend into the optic of the crusta ; whilst the optic thalami, corpora quadrigethalami and corpora striata, and their fibres are named the mina, and geniculata are the ganglia of the tegmentum. peduncular fibres. From the corpora striata and optic The comparison of the human brain with those of different
mammals has shown that the development of the hemi- | other, for the grey matter forms a continuous layer over spheres bears a direct relation to the size of the crusta and the whole surface of the hemisphere. Hence a group of its ganglia, whilst the development of the hemispheres is cerebral convolutions differs from a group of muscles, each in inverse relation to the size of the tegmentum and its member of which is undoubtedly a distinct organ, for each ganglia.
muscle is isolated from those around it by a definite investThe superior peduncles of the cerebellum connect that ing sheath. As regards internal structure, evidence has organ with the cerebrum. They arise in the grey matter already been given that all the convolutions are not conof the vermiform process, ascend to the corpora quadri- structed on precisely the same plan, and it has also been gemina, and some fibres are even prolonged apparently pointed out that the convolutions are not all connected in into the tegmentum, and through it doubtless into the optic the same way with the great cerebral ganglia. These thalamus.
structural modifications unquestionably point to functional 6, The fibres which connect together the two hemispheres differences in the several parts in which they are found. are called commissural fibres. The largest of these com But further, special connections through the arcuate fibres inissures is the corpus callosum, which, as has already been are established between certain convolutions and not bedescribed, connects corresponding convolutions in the tween others, and it is possible not only that particular opposite hemispheres. As its fibres lie on a plane superior combinations of convolutions through an interchange of to those of the corona radiata, the two systems of fibres internuncial fibres may condition à particular state of intersect with each other on their way to the convolutions. | intellectual activity, but that these combinations associate The anterior commissure, though often described as con various convolutions together in the performance of a given necting the two corpora striata, yet, as Spurzheim pointed intellectual act, just as in the muscular system several out half a century ago, passes through these bodies to the muscles are as a rule associated together for the performance convolutions around the Sylvian fissure, and gives a root of a given movement. A clue to the special functions of of origin to the olfactory nerve. The posterior commissure the convolutions may perhaps be obtained by studying passes into the two optic thalami ; some of its fibres are their connections, just as the action of the members of said to extend into the tegmentum, and others into the sub a group of muscles is ascertained by examining the direcstance of the hemisphere.
tion of their fibres and the attachment of their terminal c, The tracts which connect different convolutions in the tendons. same hemisphere are named arcuate fibres, or fibræ propriæ. MASS AND WEIGHT OF THE BRAIN.—The human brain Weight of The arcuatē fibres are situated immediately beneath the is absolutely bigger and heavier than the brain of any
brain. inner surface of the cortex of the hemispheres, and connect animal, except the elephant and the larger whales. It is together the grey matter of adjacent convolutions. In also heavier relatively to the bulk and weight of the body some localities they are strongly marked, and have received than are the brains of lower animals, except in some small special names.
birds and mammals. Considerable variations, however, The fasciculus uncinatus passes across the Sylvian fissure, exist in the size and weight of the human brain, not only traverses the claustrum and amygdala, and connects the in the different races of mankind, but in individuals of the convolutions of the frontal with those of the temporo
same race and in the two sexes. The heaviest brains occur sphenoidal lobe. The fillet of the gyrus fornicatus extends in the white races. The average weight of the adult Eurolongitudinally in that convolution, immediately above the pean male brain is, 49 to 50 oz., that of the adult female corpus callosum, from its anterior to its posterior ends, and 44 to 45 oz. ; so that the brain of a man is on the average connects two different parts of its grey matter together. fully 10 per cent. heavier than that of a woman. The The longitudinal fibres of the corpus callosum, or nerves greater weight of the brain in man as compared with woman of Lancisi, also connect the anterior and posterior ends of is not in relation merely to his greater bulk, but is a fundathe callosal convolution. The longitudinal inferior fasci- mental sexual distinction; for, whilst there is a difference culus connects the convolutions of the occipital with those of 10 per cent. in the brain weight, the average stature of of the temporal lobe. Longitudinal fibres lie on the inner women is, as Thurnam has calculated, only 8 per cent. less surface of the septum lucidum, and extend into the gyrus than that of men. Dr Boyd states that the average weight fornicatus.
of the brain in the newly born male infant is 11.67 oz.; in The corpora quadrigemina are connected with the optic the female only 10 oz. The exact age at which the brain thalami by nervous tracts called brachia, and smaller tracts reaches its maximum size has been variously placed at from also connect the thalami with the corpora geniculata. The the 3d to the 8th years by different authors; but it conpeduncles of the pineal gland connect that body with the tinues to increase in weight to 25 or 30, or even 40. fornix, and are probably continued into the optic thalamus. After 60 the brain begins to diminish in weight; in aged The tænia semicircularis is also at one end apparently con males the average weight is about 45 oz., in females about nected with the optic thalamus, but its posterior termination 41 oz. In some cases the adult brain considerably exceeds is not well ascertained.
the average weight. The brains of several men distinguished The great cerebral ganglia and the central masses of grey for their intellectual attainments have been weighed : the matter are centres of origin for sensori-motor nerves. The brain of Cuvier weighed 64), oz.; of Dr Abercrombie, 63 hemispherical ganglia, again, are the parts of the brain oz.; of Professor Goodsir, 571 oz.; of Spurzheim, 55 oz. ; associated with the intellectual processes. The question of Sir J. Y. Simpson, 54 oz. ; of Agassiz, 53.4 oz. ; and of has often been put, Are not the individual convolutions Dr Chalmers, 53 oz. But high brain weights have also been distinct organs, each endowed with special properties ? and found where there was no evidence of great intellectual various arguments based on physiological, pathological, and capacity. Peacock weighed four male brains which ranged anatomical grounds have been advanced in support of this from 62.75 to 61 oz.; Boyd, a specimen of 60.75 oz.; and proposition. In connection with the anatomical branch of Turner has recorded one of a boy aged fifteen which the argument it may be stated that the convolutions possess, weighed 60 oz. In the brains of the insane high brain not only in man, but in all animals with convoluted brains, weights have also been observed. Bucknill met with a great regularity both in position and arrangement; but brain in a male epileptic which weighed 641 oz.; Thurnam, specialisation of form is not in itself a sufficient test of one which weighed 62 oz.; and in the West Riding Asylum, specialisation of function. Again, though the convolutions out of 375 males examined, the weight of the brain in 30 have definite forms they are not disconnected from each cases was 55 oz. or upwards, and the highest weights were
61 oz. in a case of senile dementia, 60} oz. in a case of ENCEPHALIC_NERVES.— Several pairs of nerves, called Cranial dementia, and 60 oz. in one of melancholia. No case has CRANIAL or ENCEPHALIC, arise from the under surface or nerves. as yet been recorded of the weight of the brain in a woman base of the encephalon, and pass outwards through foramina possessing intellectual eminence; but Boyd met with a situated in the floor of the cranial cavity. Continental woman's brain as high as 55.25 oz., and many instances of anatomists usually enumerate twelve pairs of cranial nerves; upwards of 50 oz. in women where there was no evidence of but because in one locality two of these nerves lie together high mental endowment. Skae, in a female monomaniac, and pass through the same foramen, and in another spot observed a brain which weighed 611 oz.; and of 300 three of these nerves emerge together from the skull, British females examined in the West Riding Asylum the weight anatomists have restricted the number to nine pairs. of the brain in 26 cases was 50 oz. or upwards, the highest These nerves are numbered from before backwards, in the weights being 56 and 55 oz. in two cases of mania. The order in which they are seen at the base of the brain. size and weight of the brain do not therefore, per se, give the names applied to the individual nerves, and their an exact method of estimating the intellectual power of the numerical designations, according to both the Continental individual, and a high brain weight and great intellectual and British methods, are given in the following table : capacity are not necessarily correlated with each other. It
British. seems certain, if the human brain, even amongst the most
Olfactory Nerves, ....
1st pair uncultivated peoples, falls below 30 oz., that this low weight Optic Nerves,
2d is not merely incompatible with intellectual power and Oculo-motor Nerves,
3rd Trochlear Nerves,
4th activity, but is invariably associated with idiocy or imbe
Trifacial or Trigeminal Nerves, ... 5th cility; so that the human brain has a minimum weight
6th below which intellectual action is impossible. Amongst the Facial Nerves (Portio dura), 7th
7th more cultivated races the minimum weight-limit of intelli Auditory Nerves (Portio mollis), 8th
It gence is, however, in all probability higher than 30 oz.
10th Pneumogastric Nerves (Vagus),
8th has been placed by Broca at 32 oz. for the female, and 37 oz.
Spinal Accessory Nerves, 11th for the male brain; and Thurnam's numbers are almost the
9th To how low a weight the brain in the microcephalous idiot may fall is well shown in a case recorded by Theile, These nerves may be arranged in three groups according where it weighed only 10:6 oz., in Gore's case of 10 oz. 5 to the presence or absence of motor and sensory fibres. grs., and in Marshall's case, 8} oz. But instances are not First group.-Sensory nerves, or nerves of special sense: wanting in which the brains of idiots have exceeded even a, olfactory, the nerve of smell ; b, optic, nerve of sight; 50 oz. Langdon Down observed the brain of a male idiot c, auditory, nerve of hearing. aged 22, which weighed 591 oz.; and J. B. Tuke has Second group. - Motor nerves : a, oculo-motor, the prin. recently met with a brain of 60 oz. in a male idiot aged 37, cipal nerve of supply for the muscles of the eyeball; b, the capacity of whose cranium was 110 cubic inches. In trochlear, the nerve for the superior oblique muscle ; c, the West Riding Asylum tables the brain weights in 10 abducent, the nerve for the external rectus; d, portio dura, idiots were not less than 34 oz., and in 5 cases exceeded 40 the nerve for the facial muscles of expression; e, spina) oz. As yet the opportunities of weighing the brain in the accessory, the nerve which gives a motor root to the coloured races of men have been but scanty. But from a pneumogastric, and supplies the sterno-mastoid and travery extensive series of observations made by Barnard Davis, pezius muscles; f, hypoglossal, the nerve for the muscles not on the brains themselves, but on the cubic capacities of of the tongue. crania, from which an approximate estimate of the brain Third group.—Mixed nerves : a, trifacial, distributed to weight may be obtained with a fair measure of accuracy, the muscles of mastication, the skin of the face, various the following facts are derived :—The average weight of mucous membranes, and to the anterior and lateral surfaces the male brain in the African races is 45.6 oz.; of the of the tongue, where it may play the part of a nerve of the female brain, 42.7 oz. : the average weight of the male special sense of taste; b, glosso-pharyngeal, distributed to brain in the Australian races is 42:8 oz. ; of the female the mucous membrane of the pharynx, to certain palatobrain, 39-2 oz.: the average weight of the male brain in pharyngeal muscles, and to the mucous membrane of the the Occanic races, 46.5 oz. ; of the female brain, 43 oz. back of the tongue, where it acts as a nerve of the special The conclusions which may legitimately be drawn from an sense of taste; C, the pneumogastric, conjoined with the analysis of Barnard Davis's observations are as follows : internal division of the spinal accessory, is distributed 1st, That the average brain weight is considerably higher to several muscles, mucous membranes, and internal in the civilised European than in the savage races ; 2d, organs. That the range of variation is much greater in the former The consideration of the 1st group of cranial nerves than in the latter ; 3d, That there is an absence, almost may appropriately be deferred until the organs of sense, complete, of specimens heavier than 54 oz. in the exotic in which they terminate, are described. The anatomy of races, so that the higher terms of the series are not repre- the motor nerves is as follows :sented ; 4th, That though the male brains are heavier than The Oculo-motor or third nerve springs out of the inner Motor the female, there is not the same amount of difference in surface of the crus cerebri. When its fibres are traced into cranial the average brain weight between the two sexes in the the crus, some are seen to pass to the nerve cells of the nerves. uncultivated as in the cultivated peoples.
locus niger, whilst others sink into the corpora quadriNo reliable determinations have as yet been made of the gemina, and extend as far as the Sylvian group of large exact proportion, as regards bulk and weight, which the
The nerve, after it has emerged from the convolutions bear to the corpora striata, optic thalami, and crus, runs forwards in the outer wall of the cavernous corpora quadrigemina, but data are obtainable of the rela- sinus, and enters the orbit through the sphenoidal fissure. tive weight of the pons, cerebellum, and medulla to the It supplies the levator palpebræ superioris, the superior, entire encephalon. Between the ages of 20 and 70 the inferior, and internal recti muscles, and the inferior oblique. ratio of weight of the pons, cerebellum, and medulla, to the It contributes the short or motor root to the ciliary ganglion, entire brain, is as 13 to 100, and this relative weight is and through it influences the iris and ciliary muscles within virtually the same in both sexes.
the eyeball. It also communicates with the caverrona ORIGIN, ARRANGEMENT, AND DISTRIBUTION OF THE plexus of the sympathetic.