See also:part of the central
See also:system which in vertebrate animals is contained within the cranium or
See also:skull; it is divided into the
See also:brain or cerebrum, the
See also:hind brain or cerebellum, and the medulla oblongata, which is the transitional part between the
See also:cord and the other, 392 two parts already named . Except where stated, we
See also:deal here primarily with the brain in man . 1 . ANATOMY Membranes of the Human Brain . Three membranes named the dura mater, arachnoid and pia mater cover the brain and lie between it and the
See also:cranial cavity . The most
See also:external of the three is the dura mater, which consists of a cranial and a spinal portion . The cranial part is in contact with the inner table i . Falx cerebri . 9 and io .
See also:Superior and inferior 2 . Tentorium. petrosal sinus . 3,3 .
See also:longitudinal sinus . 11 . Cavernous sinus . 4 . Lateral sinus . 12 . Circular sinus which connects 5 .
See also:Internal jugular vein. the two cavernous sinuses 6 . Occipital sinus. together . 6' . Torcular Herophili . 13 .
Ophthalmic vein, from 15, 7 . Inferior longitudinal sinus. the eyeball . 8 .
See also:Veins of Galen . 14 . Crista galli of ethmoid
See also:bone . of the skull, and is adherent along the lines of the sutures and to the margins of the foramina, which transmit the nerves, more especially to the foramen magnum . If forms, therefore, for these bones an internal periosteum, and the meningeal
See also:arteries which ramify in it are the nutrient arteries of the inner table . As the growth of bone is more active in
See also:infancy and youth than in the adult, the adhesion between the dura mater and the cranial bones is greater in early
See also:life than at maturity . From the inner
See also:surface of the dura mater strong bands pass into the cranial cavity, and
See also:form partitions between certain of the subdivisions of the brain . A vertical longitudinal mesial
See also:band, named, from its sickle shape, falx cerebri, dips between the two hemispheres of the cerebrum . A smaller sickle-shaped vertical mesial band, the falx cerebelli, attached to the internal occipital crest, passes between the two hemispheres of the cerebellum .
A large band
See also:arches forward in the
See also:plane of the cavity, from the transverse groove in the occipital bone to the clinoid processes of the sphenoid, and is attached laterally to the upper border of the petrous part of each temporal bone . It separates the cerebrum from the cerebellum, and, as it forms a
See also:tent-like covering for the latter, is named tentorium cerebelli . Along certain lines the cranial dura mater splits into two layers to form tubular passages for the transmission of venous
See also:blood . These passages are named the venous blood sinuses of the dura mater, and they are lodged in the grooves on the inner surface of the skull referred to in the description of the cranial bones . Opening into these sinuses are numerous veins which convey from the brain the blood that has been circulating through it; and two of these sinuses, called cavernous, which lie at the sides of the
See also:body of the sphenoid bone, receive the ophthalmic veins from the eyeballs situated in the orbital cavities . These blood sinuses pass usually from before backwards: a superior longitudinal along the upper border of the falx cerebri as far as the internal occipital protuberance; an inferior longitudinal along its
See also:lower border as far as the tentorium, where it joins the straight sinus, which passes back as far as the same protuberance . One or two small occipital sinuses, which lie in the falx cerebelli, also pass to join the straight and longitudinal sinuses opposite this protuberance; several currents of blood meet, therefore, at this spot, and as Herophilus supposed that a sort of whirlpool was formed in the blood, the name torcular Herophili has been used to
See also:express the
See also:meeting of these sinuses . From the torcular the blood is drained away by two large sinuses, named lateral, which
See also:curve forward and downward to the jugular foramina to terminate in the internal jugular veins . In Its course each lateral sinus receives two petrosal sinuses, which pass from the cavernous sinus backwards along the upper and lower
See also:borders of the petrous part of the temporal bone, The dura mater [ANATOMY consists of a tough, fibrous membrane, somewhat flocculent externally, but smooth, glistening, and
See also:free on its inner surface . The inner surface has the appearance of a serous membrane, and when examined microscopically is seen to consist of a layer of squamous endothelial cells . Hence the dura mater is sometimes called a fibroserous membrane . The dura mater is well provided with
See also:lymph vessels, which in all probability open by stomata on the free inner surface .
Between the dura mater and the subjacent arachnoid membrane is a
See also:fine space containing a minute quantity of limpid serum, which moistens the smooth inner surface of the dura and the corresponding smooth
See also:outer surface of the arachnoid . It is regarded as equivalene to the cavity of a serous membrane, and is named the sub-ducal space . Arachnoid Mater.—The arachnoid is a membrane of great delicacy and transparency, which loosely envelops both the brain and spinal cord . It is separated from these
See also:organs by the pia mater; but between it and the latter membrane is a distinct space, called subarachnoid . The sub-arachnoid space is more distinctly marked beneath the spinal than beneath the cerebral parts of the membrane, which forms a looser investment for the cord than for the brain . At the
See also:base of the brain, and opposite the fissures between the convolutions of the cerebrum, the
See also:interval between the arachnoid and the pia mater can, however, always be seen, for the arachnoid does not, like the pia mater, clothe the sides of the fissures, but passes directly across between the summits of adjacent convolutions . The subarachnoid space is subdivided into numerous freely-communicating loculi by bundles of delicate areolar tissue, which bundles are in-vested, as
See also:Key and Retzius have shown, by a layer of squamous endothelium . The space contains a limpid cerebro-spinal fluid, which varies in quantity from 2 drachms to 2 oz., and is most plentiful in the dilatations at the base of the brain known as cisternae . It should be clearly understood that there is no communication between the subdural and sub-arachnoid spaces, but that the latter communicates with the ventricles through openings in the roof of the
See also:fourth, and in the descending cornua of the lateral ventricles . When the skull cap is removed, clusters of granular bodies are usually to be seen imbedded in the dura mater on each side of the superior longitudinal sinus; these are named the Pacchionian bodies . When traced through the dura mater they are found to
See also:spring from the arachnoid . The observations of Luschka and
See also:Cleland have proved that villous processes invariably grow from the free surface of that membrane, and that when these villi greatly increase in
See also:size they form the bodies in question .
Sometimes the Pacchionian bodies greatlyhypertrophy, occasioning absorption of the bones of the cranial vault and depressions on the upper surface of the brain . Pia Mater.—This membrane closely invests the whole outer surface of the brain . It dips into the fissures between the convolutions, and After D . J .
See also:Cunningham's Text-
See also:book of Anatomy . a wide prolongation, named velum inter positum, lies in the interior of the cerebrum . With a little care it can be stripped off the brain without causing injury to its substance . At the base of the brain the pia mater is prolonged on to the roots of the cranial nerves . This membrane consists of a delicate connective tissue, in which the arteries of the brain and spinal cord ramify and subdivide into small branches before they penetrate the nervous substance, and in which the veins conveying the blood from the nerve centres lie before they open into the blood sinuses of the cranial dura mater and the extradural
See also:venus plexus of the spinal canal . Optic chiasma-Optic
See also:tract Corpus geniculatum i externum Corpus geniculatum internum Locus perforatus posticus Restiform body
See also:Pyramid Anterior superficial arcuate
See also:fibres Decussation of pyramids Optic nerve Infundibulum Tuber cinereum Corpora
See also:mammillaria Oculo-rnotor nerve (III.) Trochlear nerve(IV.) winding
See also:round the crus cerebri Ttigeminal nerve (V.) Abducent nerve (VI.) Facial nerve (VII.) Auditory nerve (VIII.) V a go-gl osso ph aryngea l nerve (IX. and X.) Hypoglossal (nerve XII.) most anterior is the pyramid or motor tract, the decussation of which has been seen . Behind this is the mesial fillet or sensory tract, The Medulla Oblongata rests upon the basi-occipital . It is somewhat which has also decussated a little below the point of section, while pyramidal in form, about I4 in. long, and I in. broad in its widest farther back still is the posterior longitudinal bundle which is coming part .
It is a bilateral
See also:organ, and is divided into a right and a
See also:half by shallow anterior and posterior median fissures, continuous with the corresponding fissures in the spinal cord; the posterior fissure ends above in the fourth ventricle . Each half is subdivided into elongated tracts of nervous
See also:matter . Next to, and parallel with the anterior fissure is the anterior pyramid (see fig . 2) . This pyramid is continuous below with the cord, and the place of continuity is marked by the passage across Fasciculus solitarius the fissure of three or four bundles of nerve fibres, Spinal
See also:root of trigeminal nerve from each half of the cord to the opposite anterior pyramid; this
See also:crossing is called the decussation of the pyramids . To the side of the pyramid, and separated posterior from it by a faint fissure, is the olivary fasciculus, Deep arcuate fibres laetudmal which at its upper end is elevated into the projecting fasciculus
See also:oval-shaped olivary body . Behind the olivary body in the lower half of the medulla are three tracts named from before backward the funiculus of Rolandp, the funiculus cuneatus and the funiculus Anterior superficial gracilis (see fig . 3) . The two funiculi graciles of opposite sides are in contact in the
See also:mid dorsal
See also:line and have between them the postero median fissure . When the fourth ventricle is reached they diverge to form the lower limit of that
See also:diamond-shaped space and are slightly swollen to form the clavae . All these three bundles appear to be continued up into the cerebellum as the restiform bodies or inferior cerebellar peduncles, but really the continuity is very slight, as the restiform bodies are formed from the
See also:direct cerebellar tracts of the spinal cord joining with the superficial arcuate fibres which curve back just below the olivary bodies . The upper part of the fourth ventricle is bounded by the superior cerebellar From Cunningham, Text book of Anatomy .
peduncles which meet just before the inferior quadri- FIG . 4,-Transverse Section through the Human geminal bodies are reached . Stretching across between Lower Olivary Region. them is the superior medullary velum or
See also:valve of Vieussens, forming the upper part of the roof, while the inferior velum forms the lower part, and has an opening called the foramen of Majendie, through which the sub-arachnoid space communicates with the ventricle . The
See also:floor (see fig . 3) has two triangular depressions on each side of a median furrow; these are the superior and inferior fovea, the significance of which will be noticed in the development of the rhombencephalon .
See also:Running horizontally across the
See also:middle of the floor are the striae acusticae which are continued into the auditory nerve . The floor of the fourth ventricle is of
See also:special Medulla Oblongata . Superior quadrigeminal body Inferior quadrigeminal body Crus cerebri Pontine part of floor of ventricle IV . Eminentia
See also:Ceres Fovea superior Restiform body Trigonum hypoglossi Clava Rolandic tubercle Funiculus cuneatus From Cunningham, Text-book of Anatomy .
See also:interest because a little way from the surface are the deep origins of all the cranial nerves from the fifth to the twelfth . (See NERVE: cranial) . If a section is made transversely through the medulla about the
See also:apex of the fourth ventricle three important bundles of fibres are cut close to the mid line on each side (see fig .
4) . The up from the anterior basis bundle of the cord . External to and behind the pyramid is the crenated section of the olivarynucleus, the surface bulging of which forms the olivary body . The
See also:grey matter of the medulla oblongata, which contains numerous multipolar nerve cells, is in part continuous with the grey matter of the spinal cord, and in part consists of
See also:independent masses . As the grey matter of the cord enters the medulla it loses its crescentic arrangement . The posterior cornua are thrown outwards towards the surface, lose their pointed form, and dilate into rounded masses named the grey tubercles of Rolando . The grey matter of the anterior cornua is cut off from the
See also:rest by the decussating pyramids and finally disappears . The formatio reticularis which is feebly
See also:developed in the cord becomes well developed in the medulla . In the lower part of the medulla a central canal continuous with that of the cord exists, but when the clavae on the opposite sides of the medulla diverge from each other, the central canal loses its posterior boundary, and dilates into the cavity of the fourth ventricle . The grey matter in the interior of the medulla appears, therefore, on the floor of the ventricle and is continuous with the grey matter near the central canal of the cord . This grey matter forms collections of nerve cells, which are the centres of origin of several cranial nerves . Crossing the anterior surface of the medulla oblongata, immediately below the pons, in the majority of mammals is a trans-
See also:verse arrangement of fibres forming the trapezium, which contains a grey nucleus, named by
See also:van der Kolk the superior olive .
In the human brain the trapezium is concealed by the lower transverse fibres of the pons, but when sections are made through it, as L .
See also:Clarke pointed out, the grey matter of the superior olive can be seen . These fibres of the trapezium come from the cochlear nucleus of the auditory nerve, and run up as the lateral fillet . The Pons Varolii or
See also:BRIDGE is cuboidal in form (see fig . 2): its anterior surface rests upon the dorsum sellae of the sphenoid, and is marked by a median longitudinal groove; its inferior surface receives the pyramidal and olivary tracts of the medulla oblongata; at its superior surface are the two crura cerebri; each lateral surface is in relation to a hemisphere of the cerebellum, and a peduncle passes from the pons into the interior of each hemisphere; the posterior surface forms in part the upper portion of the floor of the fourth ventricle, and in part is in contact with the corpora quadrigemina . The pons consists of
See also:white and grey matter: the nerve fibres of the white matter pass through the substance of the pons, in either a transverse or a longitudinal direction . The transverse fibres go from one hemisphere of the cerebellum to that of the opposite side; some are situated on the anterior surface of the pons, and form its superficial transverse fibres, whilst others pass through its substance and form the deep transverse fibres . The longitudinal fibres ascend from the medulla oblongata and leave the pons by emerging from its upper surface as fibres of the two crura cerebri . The pons possesses a median raphe continuous with that of the medulla oblongata, and formed like it by a decussation of fibres in the mesial plane . Superior peduncle of the cerebellum Middle peduncle of the cerebellum Striae acusticae
See also:Area acusticae Trigonum vagi
See also:Taenia thalami Pineal body Mesial
See also:accessory olivary nucleus Medulla in the In a horizontal section through the pons and upper part of the fourth ventricle the superficial transverse fibres are seen most anteriorly; then come the anterior pyramidal fibres, then the deep transverse pontine fibres, then the fillet, while most posteriorly and close to the floor of the fourth ventricle the posterior longitudinal bundle is seen (see fig . 5) . The grey matter of the pons is scattered irregularly through its substance, and appears on its posterior surface; but not on the anterior surface, composed exclusively of the superficial transverse fibres .
The Cerebellum.lobes, of which the most important are the amygdala or tonsil, which forms the lateral boundary of the anterior part of the vallecula, and the flocculus, which is situated immediately behind the middle peduncle of the cerebellum . The inferior vermiform
See also:process is subdivided into a posterior part or pyramid ; an
See also:elevation or uvula, situated between the two tonsils; and an anterior pointed process or nodule . Stretching between the two flocculi, and attached midway to the sides of the nodule, is a thin, white, semilunarshaped
See also:plate of nervous matter, called the inferior medullary velum . The whole outer surface of the cere- bellum possesses a characteristic foliated or laminated appearance, due to its sub- division into multitudes of thin plates or lamellae by numerous fissures . The cerebellum consists of both grey and white matter . The grey matter forms the exterior or cortex of the lamellae, and passes from one to the other across the bottoms of the several fissures . The white matter lies in the interior of the organ, and extends into the core of each lamella . When a vertical section is made through the organ, the prolongations of white matter branching off into the in- terior of the several lamellae give to the section an arborescent appearance, known by the fanciful name of. arbor vitae (see fig . 6) . Independent masses of grey matter are, however, found in the in- terior of the cerebellum . If the hemi- sphere be cut through a little to the outer side of the median
See also:lobe, a zigzag arrange- ment of grey matter, similar in appear- ance and structure to the nucleus of the olivary body in the medulla oblongata, and known as the corpus dentatum of the cerebellum, is seen; it lies in the midst of the white core of the hemisphere, and encloses white fibres, which leave the interior of the corpus at its inner and lower side . On the mesial side of this corpus dentatum lie three smaller nuclei .
The white matter is more abundant in the hemispheres than in the median lobe, and is for the most part directly continuous with the fibres of the pe- duncles of the cerebellum . Thus the restiform or inferior peduncles pass from below upward through the white core, to end in the grey matter of the tentorial surface of the cerebellum, more especially in that of the central lobe; on their way they are connected with the Middle peduncle of cerebellum From Cunningham, Text-book of Anatomy . The Cerebellum, LITTLE BRAIN, Or AFTER BRAIN occupies the inferior pair of occipital fossae, and lies below the plane of the tentorium cerebelli . It consists of two hemispheres or lateral lobes, and of a median or central lobe, which in human anatomy is called the vermis . It is connected below with the medulla oblongata by the two callosum restiform bodies which form its inferior peduncles, and above with the corpora quadrigemina of the cerebrum by two bands, which form its superior peduncles; whilst the two hemispheres are connected together by the trans-verse fibres of the pons, which form the middle peduncles of the cerebellum . On the superior or tentorial surface of the cerebellum the median or vermiform lobe is amere elevation, but on its inferior or occipital surface this lobe forms a well-defined process, which lies at the bottom of a deep fossa or vallecula; this fossa is prolonged to the posterior border of the cerebellum, From Cunningham, Text-book of Anatomy. and forms there a deep notch which separates the two hemispheres from FIG . 6.-Mesial Section through the Corpus Callosum, the Mesencephalon, the Pons, Medulla and each other; in this notch the falx Cerebellum . Showing the third and fourth ventricles joined by the aqueduct of Sylvius. cerebelli is lodged . Extending hori- zontally backwards from the middle cerebellar peduncle, along the grey matter of the corpus dentatum . The superior peduncles, which outer border of each hemisphere is the great horizontal fissure, which descend from the corpora quadrigemina of the cerebrum, form divides the hemisphere into its tentorial and occipital surfaces. connexions mainly with the corpus dentatum . The middle peduncles Each of these surfaces is again subdivided by fissures into smaller form a large proportion of the white core, and their fibres terminate Forni; Foramen of
See also:Monro Septum lucidum Anterior commissure Corpus mammillare Lamina cinerea Optic nerve Pituitary body Tuber cinereum Third nerve 1 d Uvula Pons , ~ i l Central lobule Valve of Vieussens , I Nodule Ventricle IV . I bfedulla Choroid plexus in ventricle IV .
in the grey matter of the foliated cortex of the hemispheres . It has been noticed that those fibres which are lowest in the pons go to the upper surface of the cerebellum and
See also:vice versa .
See also:Histology of the Cerebellum.—The white centre of the cerebellum is composed of numbers of medullated nerve fibres coursing to and from the grey matter of the cortex . These fibres are supported in a groundwork of neuroglial tissue, their
See also:nutrition being supplied by a small number of blood vessels . The cortex (see fig . 7) consists of a thin layer of grey material forming an outer coat of somewhat varying thickness over the whole external surface of the laminae of the organ . When examined microscopically it is found to be made up of two layers, an outer " molecular " and an inner " granular " layer . Forming a layer lying at the junction of these two are a number of cells, the cells of Purkinje, which constitute the most characteristic feature of the cerebellum . The bodies of these cells are
See also:pear-shaped . Their inner ends taper and finally end-in a nerve fibre which may be traced into the white centre . In their course through the granule layer they give off a number of branching collaterals, some turning back and passing between the cells of Purkinje into the molecular layer . Their inner ends terminate in one or sometimes two stout processes which repeatedly branch dichotomously, thus forming a very elaborate dendron in the molecular layer .
The branchings of this dendron From Cunningham, Text-book of Anatomy .Kolliker) . Treated by the Golgi method . P . Axon of
See also:cell of Purkinje . GRI . Axons of granule cells in F .
See also:Moss fibres. molecular layer cut K and K' . Fibres from white core transversely. of
See also:folium ending in molecular M' .
See also:Basket-cells . layer in connexion with the ZK . Basket-
See also:work around the dendrites of the cells of cells of Purkinje .
Purkinje . GL . Neuroglial cell . M . Small cell of the molecular N . Axon of an association GR . Granule cell . [layer. cell . are also highly characteristic in that they are approximately restricted to a single plane like an
See also:espalier fruit
See also:tree, and those for neighbouring cells are all parallel to one another and at right angles to the general direction of the folium to which they belong . In the molecular layer are found two types of cells . The most abundant are the so-called basket cells which are distributed through the whole thickness of the layer . They have a rounded body giving off many branching dendrons to their immediate neighbourhood and one long neuraxon which runs parallel to the surface and to the long
See also:axis of the lamina .
In its course, this gives off numerous collaterals which run downward to the bodies of Purkinje's cells . Their terminal branchings together with similar terminals of other collaterals form the basket-work around the bodies of these cells . The granular layer is sometimes termed the
See also:rust-coloured layer from its appearance to the naked
See also:eye . It contains two types of nerve cells, the small granule cells and the large granule cells . The former are the more numerous . They give off a number of
See also:short dendrites with claw-like endings, and a fine non-medullated neuraxon process . This runs upward to the cortex, where it divides into two branches in the form of a T . The branches run for some distance parallel to the axis of the folium and terminate in unbranched ends . The large granule cells are multipolar cells, many of the branchings penetrating well into the molecular layer . The neuraxon process turns into the opposite direction and forms a richly branching system through the entire thickness of the granular layer . There is also an abundant plexus of fine medullated fibres within the granule layer . The fibres of the white central matter are partly centrifugal, the neuraxons of the cells of Purkinje, and partly centripetal .
The position of the cells of these latter fibres is not known . The fibres give rise to an abundant plexus of fibrils in the granular layer, and many reaching into the molecular layer ramify there, especially in the immediate neighbourhood of the dendrites of Purkinje's cells . From the appearance of their plexus of fibrils these are sometimes called moss fibres . The Fourth Ventricle is the'dilated upper end of the central canal of the medulla oblongata . Its shape is like an heraldic
See also:lozenge . Its floor is formed by the grey matter of the posterior surfaces of the medulla oblongata and pons, already described (see
See also:figs . 3 and 6) ; its roof partly by the inferior vermis of the cerebellum, the nodule of which projects into its cavity, and partly by a thin layer, called valve of Vieussens, or superior medullary velum; its lower lateral boundaries by the divergent clavae and restiform bodies; its upper lateral boundaries by the superior peduncles of the cerebellum . The inferior medullary velum, a reflection of the pia mater and epithelium from the back of the medulla to the inferior vermis, closes it in below . Above, it communicates with the aqueduct of Sylvius, which is tunnelled below the substance of the corpora quadrigemina . Along the centre of the floor is the median furrow, which terminates below in a
See also:pen-shaped form, the so-called calamus scriptorius . Situated on its floor are the fasciculi teretes, striae acusticae, and deposits of grey matter described in connexion with the medulla oblongata . Its
See also:epithelial lining is continuous with that of the central canal .
The Cerebrum . The Cerebrum or GREAT BRAIN lies above the plane of the tentorium, and forms much the largest division of the encephalon . It is customary in human anatomy to include under the name of cerebrum, not only the convolutions, the corpora striata, and the optic thalami, developed in the anterior cerebral vesicle, but also the corpora quadrigemina and crura cerebri developed in the mesencephalon or middle cerebral vesicle . The cerebrum is ovoid in shape, and presents superiorly, anteriorly and posteriorly a deep median longitudinal fissure, which subdivides it into two hemispheres . Inferiorly there is a continuity of structure between the two hemispheres across the mesial plane, and if the two hemispheres be
See also:drawn asunder by opening out the longitudinal fissure, a broad white band, the corpus callosum, may be seen at the bottom of the fissure passing across the mesial plane from one hemisphere to the other . The outer surface of each hemisphere is
See also:convex, and adapted in shape to the concavity of the inner table of the cranial bones; its inner surface, which
See also:bounds the longitudinal fissure, is
See also:flat and is separated from the opposite hemisphere by the falx cerebri; its under surface, where it rests on the tentorium, is
See also:concave, and is separated by that membrane from the cerebellum and pons . From the front of the pons two strong white bands, the crura cerebri or cerebral peduncles, pass forward and upward (see fig . 2) . Winding round the outer side of each crus is a flat white band, the optic tract . These tracts
See also:verge in front, and join to form the optic commissure, from which the two optic nerves arise . The crura cerebri, optic tracts, and optic commissure enclose a lozenge-shaped space, which includes—(a) a grey layer, which, from being perforated by several small arteries, is called locus perforatus posticus; (b) two white mammillae, the corpora albicantia; (c) a grey nodule, the tuber cinereum, from which (d) the infundibulum projects to join the pituitary body . Immediately in front of the optic commissure is a grey layer, the lamina cinerea of the third ventricle; and between the optic commissure and the inner end of each Sylvian fissure is a grey spot perforated by small arteries, the locus perforatus anticus .
If a transverse section is made at right angles to the surface of the crura cerebri it will pass right through the mesencephalon and come out on the dorsal side through the corpora quadrigemina (see fig . 8) . The ventral part of each crus forms the crusta, which is the continuation forward of the anterior pyramidal fibres of the medulla and pons, and is the great motor path from the brain to the cord . Dorsal to this is a layer of pigmented grey matter, called the substantia
See also:nigra, and dorsal to this again is the tegmentum, which is a continuation upward of the formatio reticularis of the medulla, and passing through it are seen three important nerve bundles . The superior cerebellar peduncle is the most internal of these and decussates with its
See also:fellow of the opposite side so that the two tegmenta are continuous across the middle line . More externally the mesial fillet is seen, while dorsal to the cerebellar peduncle is the posterior longitudinal bundle . If the section happens to pass through the superior corpus quadrigeminum a characteristic circular area appears between the cerebellar peduncle and the fillet, which, from its tint, is called the red nucleus . More dorsally still the section will pass through the Sylvian aqueduct or passage from the third to the fourth ventricle, and this is surrounded by a mass of grey matter in the ventral part of which are the nuclei of the third and fourth nerves . The third nerve is seen at the level of the superior corpus quadrigeminum running from its nucleus of origin, through the red nucleus, to a groove on the inner side of the crus called the oculomotor groove, which marks the separation between the crusta and tegmentum . Dorsal to the Sylvian aqueduct is a layer called the lamina quadrigemina and on this the corpora quadrigemina rest . The superior pair of these bodies is overlapped by the pineal body and forms part of the lower visual centres . Connexions can be traced to the optic tract, the higher visual centre on the mesial surface of the occipital lobe, the deep origin of the third or oculo-motor nerve as well as to the mesial and lateral fillet .
The inferior pair of quadrigeminal bodies are more closely in
See also:touch with the organs of
See also:hearing, and are connected by the lateral fillet with the cochlear nucleus of the auditory nerve . Surface of the Brain . The peripheral part of each hemisphere, which consists of grey matter, exhibits a characteristic folded appearance, known as gyri (or convolutions) of the cerebrum . These gyri are separated from each other by fissures and
See also:sulci, some of which are considered to subdivide the hemisphere into lobes, whilst others
See also:separate the gyri in each lobe from each other . In each hemisphere of the human brain five lobes are recognized: the temporo-sphenoidal, frontal, parietal, occipital, and the central lobe or
See also:Island of Reil; it should, however, be realized that these lobes do not exactly correspond to the outlines of the bones after which they are named . Passing obliquely on the outer
See also:face of the hemisphere from before, upward and backward, is the well marked Sylvian fissure (fig . 9, s), which is the first to appear in the development of the hemisphere . Below it lies the temporo-sphenoidal lobe, and above and in front of it, the parietal and frontal lobes . As soon as it appears on the external surface of the brain the fissure divides into three limbs, anterior horizontal (si), ascending (s2), and posterior horizontal (s3), the latter being by far the longest . The place whence these diverge is the Sylvian point and corresponds to the pterion on the surface of the skull (see ANATOMY: Superficial and
See also:Artistic) . Between these three limbs and the vallecula or
See also:stem of the fissure are four triangular tongues or opercula; these are named, according to their position, orbital (fig . 9, C), frontal (pars triangularis) (B), fronto-parietal (pars Superior quadrigeminal basilaris) (A) and temporal .
The frontal lobe body is separated from the parietal by the fissure of Rolando (fig . 9, r) which extends on the outer face of the hemisphere from the Sylvian grey matter longitudinal fissure obliquely downward and forward towards the Sylvian fissure . About 2 in. from the hinder end of the hemisphere is the parieto-occipital fissure, which, commencing at the longitudinal fissure, passes down the inner surface of the hemisphere, and transversely outwards for Nucleus of third nerve a short distance on the outer surface of the hemisphere; it separates the parietal and occipital lobes from each other . The Temporo-Sphenoidal Lobe presents on the outer surface of the hemisphere three convolutions, arranged in parallel tiers from above downward, and named superior, middle and inferior temporal gyri . The fissure which separates the superior and Fibres of superior middle of these convolutions is called the parallel fissure (fig . 9, tf) . The Occipital Lobe also consists from above downwards of three parallel gyri, named superior, middle and inferior occipital . The Frontal Lobe is more complex; immediately in front of the fissure of Rolando, and forming indeed its anterior boundary, is a convolution named ascending frontal or pre-central, which ascends obliquely backward and upward from the Sylvian to the longitudinal fissure . Springing from the front of this gyrus, and passing forward to the anterior end of the cerebrum, are three gyri, arranged in parallel tiers from above downwards, and named superior, middle and inferior frontal gyri, which are also prolonged on to the orbital face of the frontal lobe . The Parietal Lobe is also complex; its most anterior gyrus, named ascending parietal or
See also:post-central, ascends parallel to and immediately behind the fissure of Rolando . Springing from the upper end of the back of this gyrus is the supra-parietal lobule, which, forming the boundary of the longitudinal fissure, extends as far back as the parieto-occipital fissure; springing from the lower end of the back of this gyrus is the supra-marginal, which forms the From Cunningham, Text-book of Anatomy . superior Quadrigeminal Body .
Po<E From Cunningham, Text-book of Anatomy . ff, Sulcus frontalis superior .
See also:f2, Sulcus frontalis inferior. f.m, Sulcus frontalis medius. p.m, Sulcus paramedialis . A, Pars basilaris . B, Pars triangularis . C, Pars orbitalts . S, Sylvian fissure . [fissure). st, Anterior horizontal
See also:limb (Sylvian s2, Ascending limb (Sylvian fissure) . .0, Posterior horizontal limb (Sylvian fissure) . s.asc, Ascending terminal part of the posterior horizontal limb of the Sylvian fissure . p.c.i, Inferior praecentral sulcus . p.c.s, Superior praecentral sulcus .
r, Fissure of Rolando . g.s, Superior genu . g.i, Inferior genu . d, Sulcus diagonalis . ti, Superior temporal sulcus (parallel t2, Inferior temporal sulcus . [sulcus). pf, Inferior postcentral sulcus . p2, Superior postcentral sulcus . p3,Ramus horizontalis . p4, Ramus occipitalis . s.o-t, Sulcus occipitalis transversus . occ. tat, Sulcus occipitalis lateralis (the sulcus lunatus of Elliot
See also:Smith). c.m, Calloso-marginal sulcus . c.t.r, Inferior transverse furrow .
upper boundary of the hinder part of the Sylvian fissure; as this part in front of the junction is called the pre-calcarine, and that behind gyrus occupies the hollow in the parietal bone, which corresponds the post-calcarine fissure . The internal parieto-occipital and cal-to the
See also:eminence, it may appropriately be named the gyrus of the carine are real fissures, because they cause an elevation in the parietal eminence . Above and behind the gyrus of the parietal interior of the brain, known as the hippocampus minor . Just in eminence is the angular front of the anterior end of the calcarine fissure the callosal gyrus is gyrus, which bends round constricted to form the
See also:isthmus which connects it with the
See also:hippo-the posterior extremity of campal or uncinate gyros . Below the calcarine fissure is a gyrus the parallel fissure, while called the gyrus lingualis, and this is bounded below by another arching over the hinder end true fissure, the
See also:collateral, which runs parallel to the calcarine, but of the inferior temporo- is continued much farther forward into the temporal lobe and so sphenoidal sulcus is the forms the lower boundary of the hippocampal gyrus . It will thus post-parietal gyrus . Lying be seen that the hippocampal gyrus is continuous posteriorly with in the parietal lobe is the the callosal gyros above by means of the isthmus, and with the gyrus infra-parietal fissure (fig . 9, lingualis below . The hippocampal gyrus is bounded above by the p3 and p4), which separates dentate or hippocampal fissure which causes the hippocampus major the gyrus of the parietal in the descending
See also:cornu and so is a
See also:complete fissure . If its lips are eminence from the supra- separated the fascia dentata or gyrus
See also:dentatus and the
See also:fimbria parietal lobule. continued from the posterior pillar of the fornix are seen . Anteriorly The Central Lobe of the the fissure is arrested by the recurved process of the upper part of the hemisphere, more usually hippocampal gyrus, called the uncus, and in front of this a slight called the insula or island sulcus, the incisura temporalis, marks off the temporal
See also:pole or tip of Reil, does not come to the of the temporal lobe from the region of the uncus . It will be seen surface of the hemisphere, that the callosal gyros, isthmus, and hippocampal gyrus form but lies deeply within the nearly a complete
See also:ring, and to this the name of limbic lobe is given .
Sylvian fissure, the oper- cula forming the margin of Interior of the Cerebrum . which, conceal it . It con- If a horizontal slice be removed from the upper part of each sists of four or five short hemisphere (see fig . 12), the peripheral grey matter of the gyri will gyri, which radiate from be seen to follow their various windings, whilst the core of each gyrus the locus perforatus anticus, consists of white matter continuous with a mass of white matter situated at the inner end of in the interior of the hemisphere . If a deeper slice be now made the fissure . This lobe is down to the plane of the corpus callosum, the white matter of that almost entirely surrounded structure will be seen to be continuous with the white centre of by a deep sulcus called each hemisphere known as the centrum ovale . The corpus callosum longitudinal fissure. articulates with the parietal brain which has been hardened in spirit, the corpus callosum is seen 0 . Olfactory fissure, over which the and squamous-temporal. to consist almost entirely of bundles of nerve fibres, passing trans- olfactory peduncle and lobe are In front of the central versely across the mesial plane between the two hemispheres; these situated. lobe, on the base of the fibres may be traced into the white cores and grey matter of the TR . Orbital sulcus . [surface. brain, are the orbital gyri, gyri, and connect the gyri, though by no means always corresponding i" 1" . Convolutions on the orbital which are separated from ones, in the opposite hemispheres . Hence the corpus callosum is a con-e, I, I, i .
Under surface of infero- one another by the orbital necting or commissural structure, which brings the gyri of the two frontal convolution. sulcus . This is usually hemispheres into anatomical and physiological relation with each 4 . Under surface of ascending frontal; H-shaped, and the gyri other . On the surface of the corpus callosum a few fibres, the striae and 5, of ascending parietal con- are therefore anterior, longitudinales, run in the antero-posterior or longitudinal direction volutions. posterior, external and in- (see fig . 12, b) . Their morphological interest is referred to in the C . Central lobe or insula. ternal . Bisecting the in- section below on
See also:Comparative Anatomy . In the sulcus between the ternal orbital gyrus is an corpus callosum and the limbic lobe a narrow band of fibres called antero-posterior sulcus (s. rectus), beneath which lies the olfactory the cingulum is seen, most of its fibres only run a short distance in lobe, bulbous in front, for the olfactory nerves to arise from. it and
See also:link together adjacent parts of the brain . If the corpus On the mesial surface of the hemisphere, as seen when the brain is callosum be now cut through on each side of its mesial line, the large longitudinally bisected and the cerebellum and medulla removed by cavity or lateral ventricle in each hemisphere will be opened into. cutting through the crus cerebri (see fig . II), the divided corpus callosum is the most central
See also:object, while below it are seen the fornix, septum lucidum and third ventricle, the description of which will follow . The cerebral surface, above and in front of the corpus callosum, is divided into two by a sulcus, the
See also:contour of which closely resembles that of the upper margin of the corpus callosum .
This is the calloso-marginal sulcus, so called because it separates the callosal gyros, which lies between it and the corpus callosum, from the marginal gyri nearer the margin of the brain . When the sulcus reaches a point vertically above the hind end of the corpus callosum it turns sharply upward and so forms the hinder limit of the marginal gyri, the posteriorinch or two of which is more or less distinctly marked off to form the paracentral lobule, where the upper part of the central fissure of Rolando turns over the margin of the brain . The callosal gyrus, which is also called the gyros fornicatus from its arched appearance, is continued backward round the posterior end of the corpus callosum, and so to the mesial surface of the temporal lobe . Behind the upturned end of the calloso-marginal sulcus there is a square area which is called the precuneus or quadrate From Cunningham, Text-book of Anatomy . lobe; it is bounded behind by the deeply cut FIG . II.—The Gyri and Sulci on the Mesial Aspect of the Cerebral Hemisphere . internal parieto-occipital fissure and this runs r, Fissure of Rolando. r,o, Rostral sulcus. i,t, Incisura temporalis. from the margin of the brain downward and forward to join another fissure, the calcarine, at an acute
See also:angle, . The lateral ventricle is subdivided into a central space or body, thus enclosing a
See also:wedge-shaped piece of brain called the cuneus and three bent prolongations or cornua; the anterior cornu extends between them . The calcarine fissure is fairly horizontal, and is forward, outward and downward into the frontal lobe; the posterior joined about its middle by the internal parieto-occipital, so that the cornu curves backward, outward and inward into the occipital lobe; the descending cornu curves backward, outward, downward, forward and inward, behind and below the optic thalamus into the temporosphenoidal lobe . On the floor of the central space may be seen from before backward the grey upper surface of the pear-shaped caudate nucleus of the corpus striatum (figs . 12 and 13, f), and to its inner and posterior part a small portion of the optic thalamus, whilst between the two is the curved flat band, the taenia semicircularis (figs . 12 and 13, g) .
Resting on the upper surface of the thalamus Corpus Callosum . a, Transverse fibres, and g, Taenia semicircularis . b, Longitudinal fibres of corpus h, Optic thalamus . callosum. k, Choroid plexus . c, Anterior, and [ventricle . 1, Taenia hippocampi . d, Posterior cornua of lateral m, Hippocampus major . e, Septum lucidum. n, Hippocampus minor . f, Corpus striatum. o, Eminentia collateralis. is the vascular fringe of the velum interpositum, named choroid plexus, and immediately internal to this fringe is the free edge of the white posterior pillar of the fornix . The anterior cornu has the anterior end of the corpus striatum projecting into it . The posterior cornu has an elevation on its floor, the hippocampus minor (fig . 12, n), and between this cornu and the descending cornu is the elevation called eminentia collateralis, formed by the collateral fissure (fig .
12, o) . Extending down the descending cornu and following its curvature is the hippocampus major, which terminates below in a nodular end, the pes hippocampi; on its inner border is the white taenia hippocampi, continuous above with the posterior pillar of the fornix . If the taenia be drawn to one side the hippocampal fissure is exposed, at the bottom of which the grey matter of the gyrus hippocampi may be seen to form a well-defined dentated border (the so-called fascia dentata) . The choroid plexus of the pia mater turns round the gyrus hippocampi, and enters the descending cornu through the lateral part of the great transverse fissure between the taenia hippocampi and optic thalamus . The lateral ventricle is lined by a ciliated epithelium called the ependyma . This lining is continuous through the foramen of Monro with that of the third ventricle, which again is continuous with the lining of the fourth ventricle through the aqueduct of Sylvius . A little fluid is contained in the cerebral ventricles, which, under some pathological conditions, may increase greatly in quantity, so as to occasion considerabledilatation of the ventricular cavities . If the corpus callosum be now divided about its middle by a transverse incision, and the posterior half of this structure be turned back (see fig . 13), the body of the fornix on which the corpus callosum rests is exposed . If the anterior half of the corpus callosum be now turned forward, the grey
See also:partition, or septum lucidum, between the two lateral ventricles is exposed . This septum fits into the interval between the under surface of the corpus callosum and the upper surface of the anterior part of the fornix . It consists of two layers of grey matter, between which is a narrow vertical mesial space, the fifth ventricle (fig .
13, e), and this space does not communicate with the other ventricles nor is it lined with ependyma . If the septum be now removed, the anterior part of the fornix is brought into view . The fornix is anarch-shaped band of nerve fibres extending in theantero-posterior direction . Its anterior end forms the anterior pillars of the arch, its posterior end the posterior pillars, whilst the intermediate body of the fornix forms the
See also:crown of the arch . It consists of two lateral halves, one belonging to each hemisphere . At the
See also:summit of the arch the two lateral halves are joined to form the body; but in front the two halves separate from each other, and form two anterior pillars, which descend in front of the third ventricle to the base of the cerebrum, where they form the corpora albicantia, and from these some white fibres called the bundle of Vicq d'Azyr ascend to the optic thalamus (see fig . II) . Behind the body the two halves diverge much more from each other, and form the posterior pillars, in the triangular interval between which is a thin lamina of commissural fibres called the
See also:lyra (fig . 13, a) . Each posterior pillar curves downward and outward into the descending cornu of the ventricle, and, under the name of taenia hippocampi, forms the mesial free border of the hippocampus major (fig . 13, l) . Eventually it ends in the substance of the hippocampus and in the uncus of the temporal lobe .
If the body of the fornix be now divided by a transverse incision, its anterior part thrown forward, and its posterior part backward, the great transverse fissure of the cerebrum is opened into, and the velum interpositum lying in that fissure is exposed . The velum inter positum is an
See also:fold of pia mater, which passes into the anterior of the hemispheres through the great trans-verse fissure . It is triangular in shape; its base is 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; and the blood from these is returned by small veins, which join to form the veins of Galen . These veins pass along the centre of the velum, and, as is shown in fig . 1, open into the straight sinus . If the velum interpositum be now carefully raised from before backward, the optic thalami, third ventricle, pineal body and corpora quadrigemina are exposed . Velum Interpositum . a, Lyra, turned back. gg g, Taenia semicircularis . b, b, Posterior pillars of the h, h, Optic thalamus .
fornix, turned back. k, Choroid plexus . c, c, Anterior pillars of the fornix . 1, Taenia hippocampi . d, Velum interpositum and m, Hippocampus major in de-veins of Galen. scending cornu . e, Fifth ventricle. n, Hippocampus minor . f, f, Corpus striatum. o, Eminentia collateralis . 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 postero-inferior surface forms the roof of the descending cornu and posteriorly at the splenium, but the body is above the plane of section . Behind the genu the fifth ventricle is cut, and behind that the two pillars of the fornix which here form the anterior boundary of the third ventricle . At the posterior end of this is the pineal body, which the section has just escaped . To the outer side of the fornix is seen the foramen of
See also:Munro, leading into the front of the body and. anterior
See also:horn of the lateral ventricle .
It will be seen that the lateral boundary of this horn is the cut caudate nucleus of the corpus striatum, while the lateral boundary of the third ventricle is the cut optic thalamus, both of which bodies have been already described, but external to these is a third triangular grey mass, with its apex directed inward, which cannot be seen except in a section . This is the lenticular nucleus of the corpus striatum, the inner or apical half of which is of a
See also:colour and is called the globus pallidus, while the basal half is redder and is known as the putamen . External to the putamen is a long narrow
See also:strip of grey inattet called the claustrum, which is sometimes regarded as a third nucleus of the corpus striatum . These masses of grey matter, taken together, are the basal nuclei of the brain . Internal to the lenticular nucleus, and between it and the caudate nucleus in front and the thalamus behind, is the internal capsule, through which run most of the fibres connecting the cerebral cortex with the crus cerebri . The capsule adapts itself to the contour of the lenticular nucleus and has an anterior limb, a
See also:bend or genu, and a posterior limb . Just behind the genu of the internal capsule is a very important region, for here the great motor tract from the Rolandic region of the cortex passes on its way to the crusta and spinal cord . Besides this there are fibres passing from the cortex to the deep origins of the facial and hypo-glossal nerves . Behind the motor tracts Claustrum are the sensory, including the fillet, the superior cerebellar peduncle and the inferior quadrigeminal tract, while quite at Insula the back of the capsule are found the auditory and optic radiations linking up the higher (cortical) and lower auditory -'putamen and visual centres . Between the putamen and the claustrum is the external capsule, which is smaller and of less importance than the internal, while on the lateral side of the claustrum is the white and then the grey matter of the central lobe . As the fibres of the internal capsule run up toward the cortex they decussate with the transverse fibres of the corpus callosum and spread out to form the
See also:corona radiate . It has only been possible to deal with a few of the more important bundles of fibres here, but it should be mentioned that much of the white Tail of matter of the brain is formed of association fibres which link caudate up different cortical areas, and which become medullated nucleus and functional after
See also:birth .
See also:Weight of the Brain .
See also:radiation . This has been the subject of a great deal of
See also:research, but Tafertum the results are not altogether conclusive; it seems, however, longitudinal that, although the male brain is 4 to 5 oz. heavier than that of bundle the
See also:female, its relative weight to that of the body is about the same in the two sexes . An
See also:average male brain weighs about 48 oz. and a female 431 oz . The greatest absolute weight is found between twenty-five and
See also:thirty-five years of age in the male and a little later in the female . At birth the brain weighs comparatively much more than it does later on, its proportion to the body weight being about I to 6 . At the tenth
See also:year it is about I to 14, at the twentieth I to 30, and after that about I to 36.5 . In old age there is a further slight decrease in proportion . In many men of great intellectual eminence the brain weight has been large—Cuvier's brain weighed 641 oz.,
See also:Goodsir's 571, for instance—but the exceptions are numerous . Brains over 60 oz. in weight are frequently found in quite undistinguished
See also:people, and even in idiots 60 oz. has been recorded . On the other
See also:hand, microcephalic idiots may have a brain as low as to or even 8 1 oz., but it is doubtful whether From Cunningham, Text-book of Anatomy. normal intelligence is possible with a brain weighing less than The weight of the cerebellum is usually one-eighth of that of the entire brain . Attempts have been made to estimate the surface area of the grey matter by dissecting it off and measuring it, and also by covering it with gold
See also:leaf and measuring that .
The results, however, have not been conclusive . Further details of the brain, abundantly illustrated, will be found in the later
See also:editions of any of the standard text-books on anatomy, references to which will be found in the article on ANATOMY :
See also:Modern Human . Das Menschenhirn, by G . Rdtzius (
See also:Stockholm, 1896), and numerous
See also:memoirs by G . Elliot Smith and D . J . Cunningham in the Journ . Anat. and Phys. and Anatomisch Anzeig., may be consulted . Histology of Cerebral Cortex . The cerebral cortex (see fig . 15) consists of a continuous
See also:sheet of grey matter completely enveloping the white matter of the hemispheres . It varies in thickness in different parts, and becomes thinner in old age, but all parts show a somewhat similar microscopic structure .
Thus, in vertical section, the following layers may be made out of the ventricle, whilst its inner surface forms the side
See also:wall of the third ventricle . At its outer and posterior part are two slight elevations, in close relation to the optic tract, and named respectively corpus geniculatum internum and externum . The posterior knob-like extremity of the thalamus is called the pulvinar; this, as well as the two corpora geniculata and the superior corpus quadrigeminum, is connected with the optic tract . The third ventricle (see fig . 6) is a cavity situated in the mesial plane between the two optic thalami . Its roof is formed by the velum interpositum and body of the fornix; its floor by the posterior perforated space, corpora albicantia, tuber cinereum, infundibulum, and optic commissure; its anterior boundary by the anterior pillars of the fornix, anterior commissure and lamina cinerea; its posterior boundary by the corpora quadrigemina and posterior commissure . The cavity of this ventricle is of small size in the living
See also:head, for the inner surfaces of the two thalami are connected together Gals of corpus callosum Anterior horn of lateral ventricle Caudate nucleus Anterior limb of internal capsule Ventricle V . Gene of internal capsule Anterior pillars of fornix Globus pallidus Bundle of Vicq d'Azyr Posterior limb of internal capsule Thalamus Retrolenticular part of internal capsule Hippocampus major Splenium Choroid plexus Band of Vicq d'Azyr Calcarine fissure by intermediate grey matter, named the middle or soft commissure . Immediately in front of the corpora quadrigemina, the white fibres of the posterior commissure pass across between the two optic thalami . If the anterior pillars of the fornix be separated from each other, the white fibres of the anterior commissure may be seen lying in front of them . The pineal body is a reddish
See also:cone-shaped body situated upon the anterior pair of the corpora quadrigemina (see figs . 3 and 6) .
From its broad anterior end two white bands, the peduncles of the pineal body, pass forward, one on the inner side of each optic thalamus . Each peduncle joins, along with the taenia semicircularis, the anterior pillar of the fornix of its own side . In its structure this body consists of tubular gland tissue containing gritty calcareous particles, constituting the brainsand . Its
See also:morphology will be referred to later . A general idea of the internal structure of the brain is best obtained by studying a horizontal section made just below the level of the Syivian point and just above the great transverse fissure (see fig . 14) . Such a section will cut the corpus callosum anteriorly at the genu 400 I . The Molecular Layer (Stratum zonale).—This is made up of a large number of fine nerve branchings both medullated and nonmedullated . The whole forms a close network, the fibres of which run chiefly a tangential course . The cells of this layer are the so-called cells of Cajal . They possess an irregular body, giving off 4 or 5 dendrites, which terminate within the molecular layer and a long nerve fibre process or neuraxon which runs parallel to the surface of the convolution . 2 .
The Layer of small Pyramidal Cells.—The typical cells of this layer are pyramid-shaped, the apices of the pyramids being directed towards the surface . The apex terminates in a dendron which reaches into the molecular layer, giving off several collateral horizontal branches in its course . The final branches in the molecular layer take a direction parallel to the surface . Smaller dendrites arise from the lateral and basal surfaces of these cells, but do not extend far from the body of the cell . .The neuraxon always arises from the base of the cell and passes towards the central white From Cunningham, Text-book of Anatomy . A . E . Small pyramidal cell . B Neuroglia cells . F . Large pyramidal cell . C .
Cell with short axon (N) which breaks G . Cell of Martinotti . up in a free arborization . H . Polymorphic cell . D . Spindle-shaped cell in stratum zonale . K . Corticipetal fibres . matter, thus forming one of the nerve-fibres of that substance . In its path it gives off a number of collaterals at right angles, which are distributed to the adjacent grey matter . 3 .
The Layer of large Pyramidal Cells.—This is characterized by the presence of numbers of cells of the same type as those of the preceding layer, but of larger size . The nerve-fibre process becomes a medullated fibre of the white matter . 4 . The Layer of Polymorphous Cells.—The cells of this layer are irregular in outline, and give off several dendrites branching into the surrounding grey matter . The neuraxon gives off a number of collaterals, and then becomes a nerve-fibre of the central white matter . Scattered through these three layers there are also a number of cells (cells of Golgi) whose neuraxon divides at once, the divisions terminating within the immediate vicinity of the cell-body . Some cells are also found in which the neuraxon, instead of running into[ANATOMY the white matter of the brain, passes toward the surface; these are called cells of Martinotti . The medullated nerve-fibres of the white matter when traced into the cortex are seen to enter in bundles set vertically to the surface . These bundles taper and are resolved into isolated fibres in the upper parts of the pyramidal layers . The fibres constituting the bundles form two sets . (a) The centrifugal fibres consist as above described of the fibre processes of the pyramidal and polymorphous cells . (b) The centripetal fibres ascend through the cortex to terminate within the molecular layer by horizontally running branches .
As they pass through they give off a number of collaterals . The position of the cells from which these fibres arise is not known . In addition to the radially arranged bundles of fibres, networks are formed by the interlacement with them of large numbers of fine medullated fibres running tangentially to the surface . These are derived chiefly from the collaterals of the pyramidal cells and of the centripetal fibres . They form two specially marked bundles, one within the layer of the polymorphous cells known as the inner band of Baillarger, and another in the layer of large pyramidal cells called the outer band of Baillarger . This latter is very thick in the calcarine region, and forms the white stria of Gennin, while the inner band is best seen in the precentral gyrus . As both these strands
See also:cross the already mentioned radial bundles at right angles, they are regarded as specialized parts of an interradial reticulum of fibres, but, nearer the surface than the radial bundles penetrate, tangential fibres are found, and here they are called the supraradial reticulum . In certain parts of the brain the fibres of this reticulum are more From The Museum
See also:Catalogue of the Royal
See also:College of Surgeons of England . closely set, and form the band of Bechterew in the superficial part of the small pyramidal cell zone . For further information on the structure of the cerebral cortex, see A . W .
See also:Campbell, Proc .
See also:Soc. vols. lxxii. and lxxiv . Comparative Anatomy . A useful introduction to the study of the vertebrate brain is that of the
See also:Amphioxus, one of the lowest of the Chordata or animals having a notochord . Here the brain is a very slightly modified part of the dorsal tubular nerve-cord, and, on the surface, shows no distinction from the rest of that cord . When a section is made the central canal is seen to be enlarged into a cavity, the neurocoele, which, in the
See also:young animal, communicates by an opening, the neuropore, with the bottom of the olfactory
See also:pit, and so with the exterior . More ventrally another slight diverticulum probably represents the infundibulum . The only trace of an eye is a patch of pigment at the anterior end of the brain, and there are no signs of any auditory apparatus . There are only two pairs of cerebral nerves, both of which are sensory (Willey, Amphioxus, 1894) . In the
See also:Cyclostomata, of which the
See also:lamprey (Petromyzon) is an example, the minute brain is much more complex, though it is still only a very slight enlargement of the anterior end of the cord . The single cavity seen in Amphioxus is here subdivided into three: an anterior or prosencephalon, a middle or mesencephalon, and a hinder or rhombencephalon . The rhombencephalon has a very slight transverse thickening in the fore-part of its roof, this is the rudimentary cerebellum (Cer.); the rest of this part of the brain is taken up by the large medulla, the cavity of which is the fossa rhomboidalis or fourth ventricle .
This fossa is roofed over by the epithelium lining the cavity of the ventricle, by pia mater and blood-vessels constituting a choroid plexus (fig . 16, B) . The fourth ventricle communicates with the parts in front by means of a passage known as the aqueduct of Sylvius . The mesencephalon or mid-brain, when looked at from the dorsal surface, shows a pair of large hollow swellings, the optic lobes or corpora bigemina . Their cavities open out from the aqueduct of B . Sylvius, and from the nervous tissue in their walls the optic nerves derive their fibres . From the front of the prosencephalon or anterior vesicle the olfactory nerves come off, and at the base of each of these are two hollow swellings; the larger and more anterior is the olfactory bulb, the smaller and more posterior the cerebral hemisphere . Both these swellings must be regarded as lateral outgrowths from the
See also:blind front end of the
See also:original single vesicle of the brain as seen in Amphioxus, and from the anterior subdivision or prosencephalon in the lamprey . The anterior vesicle, however, is now again sub-divided, and that part from which the cerebral hemispheres bud out, and the hemispheres themselves, is called the telencephalon, while the posterior part of the original prosencephalon is known as the thalamencephalon, or more rarely the diencephalon . On the dorsal surface of the thalamencephalon are two nervous masses called the ganglia habenulae; the right is much larger than the left, and from it a stalk runs forward and upward to end in the vestigial pineal body (or epiphysis), which contains rudiments of a pigmented retina and of a
See also:lens, and which is usually regarded as the remains of one of a pair of median eyes, though it has been suggested that it may be an organ for the appreciation of temperature . From the small left ganglion habenulae a still more rudimentary pineal stalk projects, and there are signs of a third out-growth (paraphysis) in front of these . On the floor of the thalamencephalon the blind pouch-like infundibulum is in contact with the pituitary body, an outgrowth from the combined pituitary and olfactory pouch, which in the adult opens on to the top of the head just itf front of the pineal area .
The anterior closed end of the nerve-
See also:tube, in front of the foramina of Munro or openings from which the hemispheres have grown out, is known as the lamina lerminalis, and in this is seen a little white commissure, connecting the hemispheres of opposite sides and belonging entirely to the telencephalon, known as the anterior commissure . The roof of the telencephalon is mainly epithelial, and contains no traces of cortical structure . In the posterior part of the roof of the thalamencephalon is the small posterior commissure (Ahlborn, Zeits. wiss . Zool . Bd, xxxix., 1883, p . 191) . In the Elasmobranch
See also:Fish, such as the sharks and rays, the cerebellum (Cer. fig . 17) is very large and contains the layers found in all the higher vertebrates . In the mesencephalon fibres corresponding with those of the fillet of higher vertebrates can be seen, and there is a nucleus in the hinder part of the corpora bigemina foreshadowing the separation into corpora quadrigemina . There is only one pineal stalk in the roof of the thalamencephalon, and the ganglia habenulae —very
See also:constant structures in the vertebrate brain—are not so marked as in Petromyzon, but are, as usual, connected with the olfactory parts of the cerebrum, with the surface of the optic lobes (tectum opticum), and with the corpus interpedunculare (Meynert's bundle) . They are
See also:united across the middle line by a small superior or habenular commissure . In the floor of the thalamencephalon are two masses of ganglionic tissue, the optic thalami .
The infundibulum dilates into two rounded bodies, the lobi inferiores, while the pituitary body or hypophysis cerebri has two lateral diverticula known as sacci vasculosi . Ganglia geniculata are found for the first
See also:time in connexion with the optic tracts in the lower part of the thalamus . The olfactory lobes (fig . 17,
See also:Olf . Bulb) are very large and often separated by long stalks from the cerebral hemispheres, which are comparatively much larger than those of the Cyclostomata; their roof or
See also:pallium is nervous, but devoid of cortical From Cat . R . C . S . England . structure, while in the floor in some
See also:species large anterior basal ganglia or corpora striata are found (Miklucho-Maclay, Beitrage z. vergl . Neurol., 1870; Edinger, Arch. mikr . Anat .
Bd. lviii., 1901, p . 661, " Cerebellum ") . The Teleostean Fish are chiefly remarkable for the great development of the optic lobes and suppression of the olfactory apparatus . The pallium is non-nervous, and the optic tracts merely cross one another instead of forming a commissure . A process of the cerebellum called valvula cerebelli projects into the cavity of each optic lobe (Rabl . Ruckhard, Arch . Anat. it . Phys., 1898, p . 345 [Pallium];Haller, Morph . Jahrb . Bd.
See also:xxvi., 1898, p . 632 [Histology and Bibliography]) .
The brain of the Dipnoi, or mud fish, shows no very important developments, except that the 40I anterior pineal organ or paraphysis is large (Saunders,
See also:Ann. and Mag . Nat . Hist.
See also:ser . 6, vol. iii., 1889, p . 157; Burkhardt, Centralnervensystem v . Protopterus, Berlin, 1892) . In the
See also:Amphibia the brain is of a low type, the most marked advances on that of the fish being that the anterior commissure is divided, into a dorsal and ventral part, of which the ventral is the true anterior commissure of higher vertebrates, while the dorsal is a hippocampal commissure and coincides in its appearance with the presence of a small mass of cells in the outer layer of the median wall of the pallium, which is probably the first indication of a hippocampal cortex or cortex of any kind (
See also:Osborn, Journ . Morph. vol. ii., 1889, p . 51) . In the Reptilia the medulla has a marked flexure with a ventral convexity, and an undoubted cerebral cortex for the first time makes its appearance . The mesial wall of the cerebral hemisphere is divided into a large dorsal hippocampal area (fig . 18,
See also:Hip.) and a smaller ventral olfactory tubercle .
Between these two a narrow area of ganglionic matter runs forward from the side of the lamina lerminalis and is known as the paraterminal or precommissural area (Elliot Smith, Journ . Anat. and Phys. vol. xxxii. p . 411) . To the upper lateral part of the hemisphere Elliot Smith has given the name of neopallium, while the lower lateral part, imperfectly separated from it, is called the pyriform lobe . In the Lacertilia the pineal eye, if it be an eye, is better developed than in any existing vertebrate, though even in them there is noevidence of its being used for sight . Behind the so-called pineal eye and its stalk is the epiphysis or pineal body, and sometimes there is a dorsal
See also:sac between them (see fig . 18).1 The middle or soft commissure appears in certain
See also:reptiles (Crocodilia and Chelonia), as does also the corpus mammillare (Edinger, Senckenberg, Naturf . Gesell . Bd. xix., 1896, and Bd . )xii., 1899; Haller, Morph . Jahrb . Bd.
See also:xxviii., 1900, p .
252) . Among the birds there is great unity of type, the cerebellum is large and, by its forward
See also:projection, presses the optic lobes down toward the ventro-lateral part of the brain . The cerebral hemispheres are also large, owing chiefly to the great size of the corpora striata, which already show a differentiation into caudate nucleus, putamen and globus pallidus . The pallium is reptilian in character, though its cortical area is more extensive . The geniculate bodies are very large (Bumm, Zeits. wiss . Zool . Bd. xxxviii., 1883, p . 430; Brandis, Arch. mikr . Anat . Bd. xli., 1893, p . 623, and xliii., 1894, p . 96, and xliv., 1895, p .
See also:Boyce and
See also:Warrington, Phil . Trans. vol. cxci., 1899, p..293) . Amongthe Mammalia the
See also:Monotremata have a cerebellum which shows, in addition to the central lobe of the lower vertebrates, a flocculus on each side, and the two halves of the cerebellum are united by a ventral commissure, the pons varolii . The pallium is reptilian in its arrangement, but that part of it which Elliot Smith has named the neo- pallium is very large, both in the Ornithorynchus and
See also:Echidna, a fact very difficult to account for . In the latter animal the cortical area is so extensive as to be thrown into many and deep sulci, and yet the Echidna is one of the lowliest of mammals in other respects . A well- marked rhinal fissure separates the pyriform lobe from the neopallium, while, on the mesial surface, the hippocampal fissure separates the neopallium from the hippocampal area . Just below the hippocampal fissure a specially coloured tract indicates 'The literature of the pineal region is enormous . Studnicka (in Oppels Vergleichende mikrosk . Anat . Teile 4-5, 1904, 1905) gives 285 references . The
See also:present conception of the generalized arrangement is: (a) A single glandular median organ from the fore-brain called the paraphysis . (,B) A pouch of the ependymal roof of the ventricle called the dorsal sac .
(y) A right and left epiphysis, one of which may be wholly or partially suppressed . These may
See also:change their position to anterior and posterior in some animals .
BRAILA (in Rumanian Braila, formerly IBRAILA)
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