Section 13 of Gray's Anatomy Part 4. This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information to the volunteer, please visit LibriVox.org. Recording by M. L. Cohen. Anatomy of the Human Body Part 4 by Henry Gray. The Forebrain Part 1. The Forebrain or Prozencephalon. The Forebrain or Prozencephalon consists of one, the Diancephalon corresponding in a large measure to the third ventricle and the structures which bound it. And two, the Telencephalon, comprising the largest part of the brain, that is the cerebral hemispheres. These hemispheres are intimately connected with each other across the middle line and each contains a large cavity named the lateral ventricle. The lateral ventricles communicate through the intervertebral foramen with the third ventricle but are separated from each other by a medial septum, the septum palusitum. This contains a slit-like cavity which does not communicate with the ventricles. The Diancephalon. The Diancephalon is connected above and in front with the cerebral hemispheres, behind with the midbrain. Its upper surface is concealed by the corpus callosum and is covered by a fold of Pia mater named the telacoridia of the third ventricle. Inferiorly, it reaches to the base of the brain. The Diancephalon comprises one, the thalamencephalon, two, the pars mammilaris hypothalamai, and three, the posterior part of the third ventricle. For descriptive purposes, however, it is more convenient to consider the whole of the third ventricle and its boundaries together. This necessitates the inclusion under this heading of the parzoptica hypothalamai and the corresponding part of the third ventricle, structures which properly belong to the telencephalon. The Thalamencephalon. The thalamencephalon comprises one, the thalamus, two, the metathalamus or corporeginiculata, and three, the epithalamus, consisting of the trigonhebenulae, the pineal body, and the posterior commissure. The thalamai, optic thalamus, are two large ovoid masses situated one on either side of the third ventricle and reaching for some distance behind that cavity. Each measures about four centimeters in length and presents two extremities, an anterior and a posterior, and four surfaces, superior, inferior, medial, and lateral. The anterior extremity is narrow. It lies close to the middle line and forms the posterior boundary of the interventricular foramen. The posterior extremity is expanded, directed backward and lateralward, and overlaps the superior colliculus. Medially, it presents an angular prominence, the pulvanar, which is continued laterally into an oval swelling, the lateral geniculate body, while beneath the pulvanar, but separated from it by the superior brachium, is the second oval swelling, the medial geniculate body. The superior surface is free, slightly convex, and covered by a layer of white substance, termed a stratum zonale. It is separated laterally from the caudate nucleus by a white band, the striaterminalis, and by the terminal vein. It is divided into a medial and a lateral portion by an oblique shallow furrow, which runs from behind forward and medialward and corresponds with the lateral margin of the fornex. The lateral part forms a portion of the floor of the lateral ventricle, and is covered by the epithelial lining of this cavity. The medial part is covered by the telecoridia of the third ventricle and its destitute of an epithelial covering. In front, the superior is separated from the medial surface by a salient margin, the tinea thalamai, along which the epithelial lining of the third ventricle is reflected onto the undersurface of the telecoridia. Behind, it is limited medially by a groove, the sulcus habenule, which intervenes between it and a small triangular area termed the trigrome habenule. The inferior surface rests upon and is continuous with the upward prolongation of the tegmentum, subthalamic tegmental region, in front of which it is related to substancia anomenata of minert. The medial surface constitutes the upper part of the lateral wall of the third ventricle and is connected to the corresponding surface of the opposite thalamus by a flattened gray band, the mass intermedia, middle or gray commissure. This mass averages about one centimeter in its anterior posterior diameter. It sometimes consists of two parts and occasionally is absent. It contains nerve bundles and nerve fibers. Some of the latter may cross the middle line, but most of them pass towards the middle line and then curve lateral ward on the same side. The lateral surface is in contact with the thick band of white substance which forms the occipital part of the internal capsule and separates the thalamus from the lentiform nucleus of the corpus striatum. Structure. The thalamus consists chiefly of gray substance, but its upper surface is covered by a layer of white substance named stratum zonale and its lateral surface by a similar layer termed the lateral medullary lamina. Its gray substance is incompletely subdivided into three parts, anterior, medial and lateral by a white layer, the medial medullary lamina. The anterior part comprises the anterior tubercle. The medial part lies next to the lateral wall of the third ventricle while the lateral and largest part is interposed between the medullary laminae and includes the pulvanar. The lateral part is traversed by numerous fibers which radiate from the thalamus into the internal capsule and pass through the ladder into the cerebral cortex. These three parts are built up of numerous nuclei, the connections of many of which are imperfectly known. Connections. The thalamus may be regarded as a large ganglionic mass in which the ascending tracts of the tegmentum and a considerable portion of the fibers of the optic tract end and from the cells in which numerous fibers, thalamic cortical, take origin and radiate to almost every part of the cerebral cortex. The lamniscus together with other longitudinal strands of the tegmentum enters its ventral part, the thalamic mammary fasciculus, bundle of Vic d'Azur. From the corpus mammillary enters its anterior tubercle while many of its fibers of the optic tract terminate in its posterior ends. The thalamus also receives numerous fibers, cortical thalamic, from the cells of the cerebral cortex. The fibers that arise from the cells of the thalamus form four principal groups or stalks. A. Those of the anterior stalk pass through the frontal part of the internal capsule to the frontal lobe. B. The fibers of the posterior stalk, optic radiations, arise in the pulvanar and are conveyed through the occipital part of the internal capsule to the occipital lobe. C. The fibers of the inferior stalk leave the undermedial surface of the thalamus and pass beneath the lentiform nucleus to the temporal lobe and insula. D. Those of the parietal stalk pass from the lateral nucleus of the thalamus to the parietal lobe. Fibers also extend from the thalamus into the corpus striatum. Those destined for the caudate nucleus leave the lateral surface and those from the lentiform nucleus, the inferior surface of the thalamus. The metathalamus comprises the geniculate bodies which are to a number, a medial and a lateral, on each side. The medial geniculate body, corpus geniculatum mediale, internal geniculate body, post geniculatum, lies under cover of the pulvanar of the thalamus and on the lateral aspect of the corpore aquageminum. Oval in shape, with its long axis directed forward and lateral word, it is lighter in color and smaller in size than the lateral. The inferior brachium from the inferior colliculus disappears under cover of it, while from its lateral extremity a strand of fibers passes to join the optic tract. Entering it are many acoustic fibers from the lateral lamniscus. The medial geniculate bodies are connected with one another by the commissure of goudin, which passes through the posterior part of the optic chiasma. The lateral geniculate body, corpus geniculatum lateralae, external geniculate body, pre-geniculatum, is an oval elevation on the lateral part of the posterior end of the thalamus and is connected with the superior colliculus by the superior brachium. It is of a dark color and presents a laminated arrangement consisting of alternating layers of grain white substance. It receives numerous fibers from the optic tract, while other fibers of this tract pass over or through it into the pulvanar. Its cells are large and pigmented, their axons pass to the visual area in the occipital part of the cerebral cortex. The superior colliculus, the pulvanar and the lateral geniculate body receive many fibers from the optic tracts and are therefore intimately connected with sight, constituting what are termed the lower visual centers. Extirpation of the eyes in the newly born animal entails an arrest to the development of these centers, but has no effect on the medial geniculate bodies or on the inferior colliculi. Moreover, the lateral well developed in the mole, an animal in which the superior colliculi are rudimentary. The epithalamus comprises the trigonum habenule, the pineal body and the posterior commissure. The trigonum habenule is a small depressed triangular area situated in front of the superior colliculus and on the lateral aspect of the posterior part of the tiniathalamae. It contains a group of nerve cells termed the ganglion habenule. Fibers enter it from the stalk of the pineal body and others forming what is termed the habenule commissure pass across the middle line to the corresponding ganglion of the opposite side. Most of its fibers are, however, directed downward and form a bundle, the fasciculus retroflexus of minor, which passes medial to the red nucleus and, after decasating with the corresponding fasciculus of the opposite side, ends in the interpeduncular ganglion. The pineal body, corpus pineale epithesis, is a small, conical, reddish gray body which lies in the depression between the superior colliculi. It is placed beneath the splenia of the corpus callosum but is separated from this by the telacoridia of the third ventricle, the lower layer of which envelops it. It measures about eight millimeters in length and its base, directed forward, is attached by a stalk or peduncle of white substance. The stalk of the pineal body divides anteriorly into two laminae, a dorsal and a ventral, separated from one another by the pineal recess of the third ventricle. The ventral lamina is continuous with the posterior commissure. The dorsal lamina is continuous with the habendula commissure and divides into two strands, the medullary striae, which run forward, one on either side, along the junction of the medial and upper surface of the thalamus to blend in front with the columns of the fornix. The posterior commissure is a rounded band of white fibers crossing the middle line on the dorsal aspect of the upper end of the cerebral aqueduct. Its fibers acquire their medullary sheaths early and the connections have not been definitively determined. Most of them have their origin in a nucleus, the nucleus of the posterior commissure, nucleus of darkshewitch, which lies in the central gray substance of the upper end of the cerebral aqueduct, in front of the nucleus of the ocular motor nerve. Some are probably derived from the posterior part of the thalamus and from the superior colliculus, while others are believed to be continued downward into the medial longitudinal fasciculus. The hypothalamus includes the subthalamic tegmental region and the structures forming the greater part of the floor of the third ventricle, that is the corpora mamillaria, tuber sinerium, infundibulum hypothesis and optic chiasma. The subthalamic tegmental region consists of the upper continuation of the tegmentum. It lies on the ventralateral aspect of the thalamus and separates it from the fibers of the internal capsule. The red nucleus and the substantia nigra are prolonged into its lower part. Once it is continuous with the substantia nominata of minert, immediately with the gray substance of the floor of the third ventricle. It consists from above downward of three strata. One, stratum dorsale, directly applied to the under surface of the thalamus and consisting of fine longitudinal fibers. Two, zona inserta, a continuation forward of the formacea reticularis of the tegmentum. And three, the corpus subthalamicum, nucleus of lewis, a brownish mass presenting a lenticulous shape on transverse section and situated on the dorsal aspect of the fibers of the base of the cerebral peduncle. It is encapsulated by a lamina of nerve fibers and contains numerous medium-sized nerve cells, the connections of which are not as yet fully determined. The corpora mammilaria, corpus albicantia, are two round white masses each about the size of a small pea placed side-by-side below the gray substance of the floor of the third ventricle in front of the posterior perforated substance. They consist of white substance externally and gray substance internally, the cells of the latter forming two nuclei, a medial of smaller and a lateral of larger cells. The white substance is mainly formed by the fibers of the columns of the fornix, which descend to the base of the brain and end partly in the corpora mammilaria. From the cells of the gray substance of each of the mammillary bodies, two fasciculi arise. One, the thalamumammillary fasciculus, bundle of Vic d'Azur, passes upward into the anterior nucleus of the thalamus. The other is directed downward into the tegmentum. Afferent fibers are believed to reach the corpora mammilaria from the medial amniscus and from the tegmentum. The tuberosinarium is a hollow eminence of gray substance situated between the corpora mammilaria behind and the optic chiasma in front. Laterally, it is continued with the anterior perforated substance and anteriorly with the thin lamina, the lamina terminalis. From the undersurface of the tuberosinarium, a holoconical process, the infundibulum projects downward and forward and is attached to the posterior lobe of the hypothesis. In the lateral part of the tuberosinarium is a nucleus of nerve cells, the basal optic nucleus of minord, while close to the cavity of the third ventricle are three additional nuclei. Between the tuberosinarium and the corpora mammilaria, a small elevation with a corresponding depression in the third ventricle is sometimes seen. Reftius has named it the eminenceus sacularis in regards it as a representative of the saccus vasculosis found in this situation in some of the lower vertebrates. The hypothesis, pituitary body, is a reddish gray somewhat oval mass measuring about 12.5 millimeter in its transverse and about 8 millimeter in its anterior posterior diameter. It is attached to the end of the infundibulum and is situated in the fossa hipafacios of the sphenytal bone, where it is retained by a circular fold of dura mater, the diaphragma cella. This fold almost completely roofs in the fossa leaving only a small central aperture through which the infundibulum passes. Optic chiasma. Chiasma opticum, optic commissure. The optic chiasma is a flattened and somewhat quadrilateral band of fibers situated at the junction of the floor of the anterior wall of the third ventricle. Most of its fibers have their origins in the retina and reach the chiasma through the optic nerves which are continuous with its anterior lateral angles. In the chiasma they undergo a partial decusation. The fibers from the nasal half of the retina decusate and enter the optic track of the opposite side while the fibers from the temporal half of the retina do not undergo decusation but pass back into the optic tract of the same side. Occupying the posterior part of the commissure however the strand of fibers, the commissure of goudon which is not derived from the optic nerves it forms a connecting link between the medial geniculate bodies. Optic tracts. The optic tracts are continued backward and lateral from the posterior lateral angles of the optic chiasma. Each passes between the anterior perforated substance and the tuber synerium and winding around the ventral idol aspect of this ribopedoncle divides into a medial and a lateral root. This is the fibers of goudon's commissure. The lateral root consists mainly of afferent fibers which arise in the retina and undergo partial decusation in the optic chiasma as described. But it also contains a few fine efferent fibers which have their origin in the brain and their terminations in the retina. When traced backward the afferent fibers of the lateral root are found to end in the lateral geniculate body and pulvenar of the thalamus and in the superior colliculus These three structures constitute the lower visual centers. Fibers arise from the nerve cells in these centers and pass through the occipital part of the internal capsule under the name of the optic radiations to the cortex of the occipital lobe of the cerebrum where the higher or cortical visual center is situated. Some of the fibers of the optic radiations take an opposite course arising from the cells of the occipital cortex and passing to the lower visual centers. Some fibers are detached from the optic tract and pass through the cerebral peduncle to the nucleus of the ocular motor nerve. These may be regarded as the afferent branches for the sphincter pupulae and ciliaris muscles. Other fibers have been described as reaching the cerebrum through the superior peduncle while others again are lost in the ponds. The third ventricle Ventriculus tertius The third ventricle is a median cleft between the two thalami. Behind it it communicates with the fourth ventricle in its cerebral aqueduct and in front with the lateral ventricles through the interventricular foramen. Somewhat triangular in shape with the apex directed backwards it has a roof, a floor an anterior and a posterior boundary and a pair of lateral walls. The roof is formed by a layer of epithelium which stretches between the upper edges of the lateral wall of the cavity and is continuous with the epithelial lining of the ventricle. It is covered by an adherent to a fold pattern named a telacoridia of the third ventricle. From the undersers of which a pair of vascular fringe processes the chloride plexuses of the third ventricle project downward one on either side of the middle line and invaginate the epithelial roof into the ventricular cavity. The floor slopes downward and forward and is formed mainly by the structures which constitute the hypothalamus. From before backwards these are the optic chiasma the tuberosinarium and infundibulum and a corpus mammilaria. Behind the last the floor is formed by the interbeduncular fossa and the tegmenta of the cerebro pinuncles. The ventricle is prolonged downward as the funnel shaped recess the recessus infundibuli into the infundibulum and to the apex of the ladder the hypothesis is attached. The anterior boundary is constituted below by the lamina terminalis a thin layer of gray substance stretching from the upper surface of the optic chiasma to the rostrum of the corpus callosum at the columns of the fornix and the anterior commissure. At the junction of the floor and anterior wall immediately above the optic chiasma the ventricle presents a small angular recess or diverticulum the optic recess. Between the columns of the fornix and just above the anterior commissure is the second recess termed the vulva. At the junction of the roof and anterior wall of the ventricle and situated between the thalamai behind and the columns of the fornix is the particular foramen foramen of Monroe through which the third communicates with the lateral ventricles. The posterior boundary is constituted by the pineal body the posterior commissure and the cerebral aqueduct. A small recess the recessus pinealis projects into the stalk of the pineal body while in front of and above the pineal body is a second recess the recess super pinealalis is the epithelium of the epithelium which forms the ventricular roof. Each lateral wall consists of an upper portion formed by the medial surface of the anterior through thirds of the thalamus and a lower consisting of an upward continuation of gray substance of the ventricular floor. These two parts correspond to the alar and basal laminate respectively of the lateral wall of the forebrain, vesicle and are separated from each other by a furrow the sulcus of Monroe and aqueduct. The lateral wall is limited above by the taniathalomy. The columns of the fornix curve downward in front of the interventricular foramen and then run in the lateral walls of the ventricle where at first they form distinct prominences but subsequently are lost to sight. The lateral walls are joined to each other across the cavity of the ventricle by a band of gray substance the massa intermedia. Interpeduncular fossa This is a somewhat lozen shaped area of the base of the brain limited in front by the optic chiasma behind by the anterior superior surface of the pons enter laterally by the converging optic tracts and posterior laterally by the diverging cerebral peduncles. The structures contained in it have already been described. From behind forward they are the posterior perforated substance corpora mammilaria tuberosinarium infundibulum and hypothesis. End of section 13 Section 14 of Gray's Anatomy Part 4 This is a LibriVox recording. All LibriVox recordings are in a public domain. For more information or to volunteer please visit LibriVox.org ML Cohen Anatomy the Human Body Part 4 by Henry Gray The Four Brain Part 2 The telencephalon The telencephalon includes one cerebral ventricles and two the pars optica hopothalamae and the anterior portion of the third ventricle already described under the diencephalon. As previously stated each cerebral hemisphere may be divided into three fundamental parts that is the rhinencephalon the corpus traetum and the neopallium. The rhinencephalon associated with the sense of smell is the oldest part of the telencephalon and forms almost the whole of the hemisphere in some of the lower animals that is fishes, amphibians, and reptiles. In man it is rudimentary whereas the neopallium undergoes great development and forms the chief part of the hemisphere. The cerebral hemispheres The cerebral hemispheres constitute the largest part of the brain and when viewed together from above assume the form of an ovoid mass broader behind than in front the greatest transverse diameter corresponding with a line connecting the two parietal eminences. The hemispheres are separated medially by a deep cleft termed a longitudinal cerebral fissure and each possesses a central cavity the lateral ventricle. The longitudinal cerebral fissure Fissurus cerebri longitudinalis, great longitudinal fissure contains a sickle shaped process of Duramata, the falc cerebrae. In front and behind the fissure extends from the upper to the under surfaces of the hemispheres and it neatly separates them but its middle portion separates them for only about one half of their vertical extent for at this part they are connected across the middle line by a great central white commissure the corpus callosum. In a median sagittal section the cut corpus callosum presents the appearance of a broad arched band its thick posterior end termed a splenium overlaps the midbrain but is separated from it by the telecoridia of the third ventricle its anterior curved end termed a genu gradually tapers into a thinner portion the rostrum which has continued downward and backward in front of the anterior commissure to join the lamina terminalis arching backward from immediately behind the anterior commissure to the under surface of the splenium is a second white band named the fornix between this and the corpus callosum are the lamin A and cavity of the septum plucidum surfaces of the cerebral hemispheres each hemisphere presents three surfaces lateral, medial and inferior the lateral surface is convex in adaptation to the concavity of the corresponding half of the vault of the cranium the medial surface is flat and vertical and is separated from that of the opposite hemisphere by the great longitudinal fissure and the falc cerebrae the inferior surface is a regular form and may be divided into three areas anterior, middle and posterior the anterior area formed by the orbital surface of the frontal lobe is concave and rests on the roof of the orbit and nose the middle area is convex and consists of the under surface of the temporal lobe it is adapted to the corresponding half of the middle cranial fossa the posterior area is concave directed medial word as well as downward and is termed the tentorial surface since it rests upon the tentorium cerebelli which intervenes between it and the upper surface of the cerebellum these three surfaces are separated from each other by the following borders a superior medial between the lateral and medial surfaces b inferior lateral between the lateral and inferior surfaces the anterior part of this border separating the lateral from the orbital surface is known as the supercillary border c medial occipital separating the medial and tentorial surfaces and d medial orbital separating the orbital from the medial surface the anterior end of the hemisphere is named the frontal pole the posterior of the occipital pole and the anterior end of the temporal lobe the temporal pole about five centimeters in front of the occipital pole on the inferior lateral border d indentation or notch named the preoccipital notch the surfaces of the hemispheres are molded into a number of irregular eminences named gyrior convolutions and separated by furrows termed fissures and salsi furrows are of two kinds complete and incomplete the former appear earlier in fetal life are few in number and are produced by infoldings of the entire thickness of the brain wall and give rise to the corresponding elevations in the interior of the ventricle. They comprise the hippocampal fissure and parts of the calcarine and collateral fissures. The incomplete furrows are very numerous and only indent the subjacent white substance without producing any corresponding elevations in the ventricular cavity. The gyri and their intervening fissures and the sulci are fairly constant in their arrangement. At the same time they vary within certain limits, not only in different individuals, but on the two hemispheres of the same brain. The convoluted condition of the surface permits a great expansion of the gray matter without the sacrifice of much additional space. The number and extent of the gyri, as well as the depth of the intervening furrows, appear to bear a direct relation to the intellectual powers of the individual. Certain of the fissures and sulci are utilized for the purpose of dividing the hemisphere into lobes and are therefore termed interlobular. Included under this category are the lateral cerebral, parietal, occipital, calcarine, and collateral fissures, the central and cingulate sulci, and the sulcus circularis. The lateral cerebral fissure, fissura cerebrilateralis silvii, fissure of sylvius, is a well-marked cleft on the inferior and lateral surfaces of the hemisphere and consists of a short stem which divides into three ramae. The stem is situated at the base of the brain and commences in a depression at the lateral angle of the anterior perforated substance. From this point it extends between the anterior part of the temporal lobe and the orbital surface of the frontal lobe and reaches the lateral surface of the hemisphere. Here it divides into three ramae, an anterior horizontal, an anterior ascending, and a posterior. The anterior horizontal ramae passes forward about 2.5 centimeters into the inferior frontal gyrus while the anterior ascending ramae extends upward into the same convolution for about an equal distance. The posterior ramae is the longest. It runs backward and slightly upward for about seven centimeters and ends by an upward inflection in the parietal lobe. The central sulcus, sulcus centralis rollandi, fissure of Rolando, central fissure, is situated about the middle of the lateral surface of the hemisphere and begins in or near the longitudinal cerebral fissure, a little behind its midpoint. It runs sinuously downward and forward and ends a little above the posterior ramae of the lateral fissure and about 2.5 centimeters behind the anterior ascending ramae of the same fissure. It describes two chief curves, a superegenu with its concavity directed forward and an inferegenu with its concavity directed backward. The central sulcus forms an angle opening forward of about 70 degrees with the median plane. The parietal occipital fissure, fissure of parietal occipitalis, only a small part of this fissure is seen on the lateral surface of the hemisphere, its chief part being on the medial surface. The lateral part of the parietal occipital fissure is situated about 5 centimeters in front of the occipital pole of the hemisphere and measures about 1.25 centimeters in length. The medial part of the parietal occipital fissure runs downward and forward as a deep cleft on the medial surface of the hemisphere and joins the calcarine fissure below and behind the posterior end of the corpus callosum. In most cases it contains the submerged gyros. The calcarine fissure, viscera calcorina, is on the medial surface of the hemisphere. It begins near the occipital pole and to converging rami and runs forward to a point a little below the splenium of the corpus callosum where it is joined at an acute angle by the medial part of the parietal occipital fissure. The anterior part of this fissure gives rise to the prominence of the calcar aevis and the posterior corneal of the lateral ventricle. The cingulate sulcus, sulcus cinguli, callosum marginal fissure, is on the medial surface of the hemisphere. It begins below the anterior end of the corpus callosum and runs upward and forward nearly parallel to the rostrum of this body and, curving in front of the genu, is continued backward above the corpus callosum and finally ascends to the superior medial border of the hemisphere a short distance behind the upper end of the central sulcus. It separates the superior frontal from the cingulate gyros. The collateral fissure, fissure collateralis, is on the tentorial surface of the hemisphere and extends from near the occipital pole to within a short distance of the temporal pole. Behind it lies below and lateral to the calcar aevis fissure from which it is separated by the lingual gyros. In front it is situated between the hippocampal gyros and the anterior part of the fusiform gyros. The sulcus circularis, circuminsular fissure, is on the lower and lateral surfaces of the hemisphere. It surrounds the insula and separates it from the frontal, parietal, and temporal lobes. The lobes of the hemispheres. By means of these fissures and sulci, assisted by certain arbitrary lines, each hemisphere is divided into the following lobes. The frontal, the parietal, the temporal, the occipital, the limbic, and the insula. Frontal lobe, lobe is frontalis. On the lateral surface of the hemisphere this lobe extends from the frontal pole to the central sulcus, the latter separating it from the parietal lobe. Below it is limited by the posterior ramus of the lateral fissure which intervenes between it and the central lobe. On the medial surface it is separated from the cingulate gyrus by the cingulate sulcus and on the inferior surface it is bounded behind by the stem of the lateral fissure. The lateral surface of the frontal lobe is traversed by three sulci which divided into four gyri. The sulci are named the precentral and the superior and inferior frontal. The gyri are the anterior central and the superior middle and inferior frontal. The precentral sulcus runs parallel to the central sulcus and is usually divided into an upper and a lower part. Between it and the central sulcus is the anterior central gyrus. From the precentral sulcus the superior and inferior frontal sulci run forward and downward and divide the remainder of the lateral surface of the lobe into three parallel gyri named respectively the superior middle and inferior frontal gyri. The anterior central gyrus gyris centralis anterior ascending frontal convolution precentral gyri is bounded in front by the precentral sulcus behind by the central sulcus. It extends from the superior medial border of the hemisphere to the posterior ramus of the lateral fissure. The superior frontal gyrus gyrus frontalis superior superior frontal gyrus is situated above the superior frontal sulcus and it's continued on to the medial surface of the hemisphere. The portion on the lateral surface of the hemisphere is usually more or less completely subdivided into an upper and a lower part by the anterior posterior sulcus the paramedian sulcus which however is frequently interrupted by bridging gyri. The middle frontal gyrus gyrus frontalis medius medial frontal gyre between the superior and inferior frontal sulci is continuous with the anterior orbital gyrus on the inferior surface of the hemisphere. It is frequently subdivided into two by a horizontal sulcus the medial frontal sulcus of iberstaller which ends anteriorly in a wide bifurcation. The inferior frontal gyrus gyrus frontalis inferior subfrontal gyre lies below the inferior frontal sulcus and extends forward from the lower part of the precentral sulcus. It is continuous with the lateral and posterior orbital gyri on the undersurface of the lobe. It is subdivided by the anterior horizontal and ascending ramai of the lateral fissure into three parts. One, the orbital part below the anterior horizontal ramus of the fissure. Two, the triangular part cap of broca between the ascending and horizontal ramai and three the basilar part behind the anterior ascending ramus. The left inferior frontal gyrus is as a rule more highly developed than the right and is named the gyrus of broca from the fact that broca described it as the center for articulate speech. The inferior or orbital surface of the frontal lobe is concave and rests on the orbital plate of the frontal bone. It is divided into four orbital gyri by a well-marked H-shaped orbital sulcus. These are named from the position the medial anterior lateral and posterior orbital gyri. The medial orbital gyrus presents a well-marked anterior posterior sulcus, the olfactory sulcus, for the olfactory tract. The portion medial to this is termed a straight gyrus and is continuous with the superior frontal gyrus on the medial surface. The medial surface of the frontal lobe is occupied by the medial part of the superior frontal gyrus, marginal gyrus. It lies between the singlet sulcus and the superior medial margin of the hemisphere. The posterior part of this gyrus is sometimes marked off by a vertical sulcus and is distinguished as the paracentral lobule because it is continuous with the anterior and posterior central gyri. Parietal lobe, lobis parietalis. The parietal lobe is separated from the frontal lobe by the central sulcus, but its boundaries below and behind are not so definite. Posteriorly, it is limited by the parietal occipital fissure and by a line carried across the hemisphere from the end of the fissure towards the preoccipital notch. Below, it is separated from the temporal lobe by the posterior ramus of the lateral fissure and by a line carried backward from it to meet the line passing downward to the preoccipital notch. The lateral surface of the parietal lobe is cleft by a well marked furrow, the intra parietal sulcus of Turner, which consists of an oblique and a horizontal portion. The oblique part is named a post-central sulcus and commences below about midway between the lower end of the central sulcus and the upturned end of the lateral fissure. It runs upward and backward parallel to the central sulcus and is sometimes divided into an upper and a lower ramus. It forms the hindal limit of the posterior central gyrus. From about the middle of the post-central sulcus, or from the upper end of its inferior ramus, the horizontal portion of the intra parietal sulcus is carried backward and slightly upward on the parietal lobe and is prolonged under the name of the occipital ramus onto the occipital lobe where it divides into two parts, which form nearly a right angle with the main stem and constitute the transverse occipital sulcus. The part of the parietal lobe above the horizontal portion of the intra parietal sulcus is named the superior parietal lobule, the part below the inferior parietal lobule. The posterior central gyrus, gyrus centralis posterior, ascending parietal convolution, post-central gyrus, extends from the longitudinal fissure above to the posterior ramus of the lateral fissure below. It lies parallel with the anterior central gyrus with which it is connected below and also sometimes above the central sulcus. The superior parietal lobule, lobulis parietalis superior, is bounded in front by the upper part of the post-central sulcus but is usually connected with the posterior central gyrus above the end of the sulcus. Behind it is the lateral part of the parietal occipital fissure, around the end of which it is joined to the occipital lobe by a curved gyrus, the arcus parietal occipitalis. Below it is separated from the inferior parietal lobule by the horizontal portion of the intra parietal sulcus. The inferior parietal lobule, lobulis parietalis inferior, sub-parietal district or lobule, lies below the horizontal portion of the intra parietal sulcus and behind the lower part of the post-central sulcus. It is divided from before backward into two gyri. One, the super marginal arches over the upturned end of the lateral fissure. It is continuous in front with the post-central gyrus and behind with the superior temporal gyrus. The second, the angular, arches over the post-year end of the superior temporal sulcus, behind which it is continuous with the middle temporal gyrus. The medial surface of the parietal lobe is bounded behind the medial part of the parietal occipital fissure. In front, by the post-year end of the cingulate sulcus and below, it is separated from the cingulate gyrus by the sub-parietal sulcus. It is of small size and consists of a square-shaped convolution, which is termed a pre-cunius or quadrate lobe, lobus occipitalis. The occipital lobe is small and pyramidal in shape. It presents three surfaces, lateral, medial, and tentorial. The lateral surface is limited in front by the lateral part of the parietal occipital fissure and by a line carried from the end of this fissure to the pre-occipital notch. It is traversed by the transverse occipital and lateral occipital sulci. The transverse occipital sulcus is continuous with the post-year end of the occipital ramus of the intra-parietal sulcus and runs across the upper part of the lobe a short distance behind the parietal occipital fissure. The lateral occipital sulcus extends from behind forward and divides the lateral surface of the occipital lobe into a superior and inferior gyrus, which are continuous in front with the parietal and temporal lobes. The medial surface of the occipital lobe is bounded in front by the medial part of the parietal occipital fissure and is traversed by the calcorine fissure, which subdivides it into the cuneus and the lingual gyrus. The cuneus is a wedge-shaped area between the calcorine fissure and the medial part of the parietal occipital fissure. The lingual gyrus lies between the calcorine fissure and the post-year part of the collateral fissure. Behind it reaches the occipital pole, in front it is continued on to the tentorial surface of the temporal lobe and joins the hippocampal gyrus. The tentorial surface of the occipital lobe is limited in front by an imaginary transverse line through the pre-occipital notch and consists of the post-year part of the fusiform gyrus, occipitotemporal convolution, and the lower part of the lingual gyrus, which are separated from each other by the post-year segment of the collateral fissure. End of Section 14. Section 15 of Gray's Anatomy Part 4. This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, please visit LibriVox.org. Recording by ML Cohen, Anatomy the Human Body Part 4 by Henry Gray, The Forebrain Part 3. Temporal lobe, lobus temporalis. The temporal lobe presents superior lateral and inferior surfaces. The superior surface forms the lower limit of the lateral fissure and overlaps the insula. On opening out the lateral fissure, three or four gyri will be seen springing from the depths of the hindor end of the fissure and running obliquely floored and outward on the post-year part of the upper surface of the superior temporal gyrus. These are named a transverse temporal gyri. Heschel. The lateral surface is bounded above by the post-year ramus of the lateral fissure and by the imaginary line continued backward from it. Below, it is limited by the inferior lateral border of the hemisphere. It is divided into superior middle and inferior gyri by the superior and middle temporal sulci. The superior temporal sulcus runs from before backwards across the temporal lobe and some little distance below, but parallel with the post-year ramus of the lateral fissure, and hence it is often termed the parallel sulcus. The middle temporal sulcus takes the same direction as the superior but is situated at a lower level and is usually subdivided into two or more parts. The superior temporal gyrus lies between the post-year ramus of the lateral fissure and the superior temporal sulcus and is continuous behind with the super marginal and angular gyri. The middle temporal gyrus is placed between the superior and middle temporal sulci and is joined posteriorly with the angular gyrus. The inferior temporal gyrus is placed below the middle temporal sulcus and is connected behind with the inferior occipital gyrus. It also extends around the inferior lateral border onto the inferior surface of the temporal lobe where it is limited by the inferior sulcus. The inferior surface is concave and is continuous posteriorly with the tentorial surface of the occipital lobe. It is traversed by the inferior temporal sulcus which extends from near the occipital pole behind to within a short distance of the temporal pole in front but is frequently subdivided by bridging gyri. Lateral to this fissure is the narrow tentorial part of the inferior temporal gyrus and medial to it the fusiform gyrus which extends from the occipital to the temporal pole. This gyrus is limited medially by the collateral fissure which separates it from the lingual gyrus behind and from the hippocampal gyrus in front. The insula island of rile central lobe lies deeply in the lateral occipulin fissure and can only be seen when the lips of that fissure are widely separated since it is overlapped and hidden by the gyri which bound the fissure. These gyri are termed the opercula of the insula. They are separated from each other by the three rami of the lateral fissure and are named the orbital frontal, frontotemporal, and temporal operculum. The orbital operculum lies below the anterior horizontal ramus of the fissure, the frontal between this and the anterior ascending ramus, the parietal between the anterior ascending ramus and the upturned end of the posterior ramus and the temporal below the posterior ramus. The frontal operculum is of small size in those cases where the anterior horizontal and ascending ramus of the lateral fissures arise from a common stem. The insula is surrounded by a deep circular sulcus which separates it from the frontal, parietal, and temporal lobes. When the opercula have been removed, the insula is seen as a triangular eminence, the apex of which is directed toward the anterior perforated substance. It is divided into a larger anterior and a smaller posterior part by a deep sulcus which runs backward and upward from the apex of the insula. The anterior part is subdivided by a shallow sulci into three or four short gyri while the posterior part is formed by one long gyris, which is often bifurcated at its upper end. The cortical gray substance of the insula is continuous with that of the different opercula while its deep surface corresponds with the lentiform nucleus of the corpus striatum. Limbic lobe The term limbic lobe was introduced by Broca and under it he included the cingulate and hippocampal gyri which together arch around the corpus callosum in the hippocampal fissure. These he separated on the morphological ground that they are well developed in animals possessing a keen sense of smell, osmotic animals such as the dog and the fox. They were thus regarded as part of the rhinocephalon but it is now recognized that they belong to the neopalium. The cingulate gyris is therefore sometimes described as part of the frontal lobe and the hippocampal as part of the temporal lobe. The cingulate gyris, gyris cinguli, colossal convolution is an arch-shaped convolution lying in close relation to the superior surface of the corpus callosum from which it is separated by a slit like fissure, the colossal fissure. It commences below the rostrum of the corpus callosum, curves around in front of the genu, extends along the upper surface of the body and finally turns downward behind the splenium where it is connected by a narrow isthmus with the hippocampal gyris. It is separated from the medial part of the superior frontal gyris by the cingulate sulcus and from the precuneus by the subparietal sulcus. The hippocampal gyris, gyris hippocampi, is bounded above by the hippocampal fissure and below by the anterior part of the collateral fissure. Behind it is continuous superiorly through the isthmus with the cingulate gyri and inferiorly with the lingual gyris. Running in the substance of the cingulate and hippocampal gyri and connecting them together is a tract of arched fibers named the cingulum. The anterior extremity of the hippocampal gyris is recurved in the form of a hook, uncus, which is separated from the apex of the temporal lobe by a slight fissure, the incisora semporalis. Although superficially continuous with the hippocampal gyris, the uncus forms morphologically a part of the rhinocephalon. The hippocampal fissure, fissura hippocampi dentate fissure, begins immediately behind the splenium of the corpus callosum and runs forward between the hippocampal and dentate gyri to end in the uncus. It is a complete fissure and gives rise to the prominence of the hippocampus in the inferior corneum of the lateral ventricle. Rhine and Cephalon The Rhine and Cephalon comprises the olfactory lobe, the uncus, the subcolosal and supercolosal gyri, the fascia dentata hippocampus, the septum pollucinum, the fornix and the hippocampus. 1. The olfactory lobe, lobis olfactorius, is situated under the inferior or orbital surface of the frontal lobe. In many vertebrates, it constitutes a well-marked portion of the hemisphere and contains an extension of the lateral ventricle, but in man and some other mammals it is rudimentary. It consists of the olfactory bulb and tract, the olfactory trigone, the parolfactory area of broca, and the anterior perforated substance. A. The olfactory bulb, lobis olfactorius, is an oval reddish-gray mass which rests on the cribiform plate of the ethmoid and forms the anterior-expanded extremity of the olfactory tract. Its undersurface receives the olfactory nerves which pass upward through the cribiform plate from the olfactory region of the nasal cavity. Its minute structure is described later. B. The olfactory tract, tractis olfactorius, is a narrow white band triangular on coronal section, the apex being directed upward. It lies in the olfactory sulcus on the inferior surface of the frontal lobe and divides posteriorly into two striae, a medial and a lateral. The lateral striae is directed across the lateral part of the anterior perforated substance and then bends abruptly medial toward the uncus of the hippocampal gyrus. The medial striae turns medial word behind the power olfactory area and ends in the subcolosal gyrus. In some cases a small intermediate striae is seen running backward to the anterior perforated substance. C. The olfactory trigone.  Its apex, directed forward, occupies the posterior part of the olfactory sulcus and is brought into view by throwing back the olfactory tract. D. The para olfactory area of Broca. Area para olfactoria is a small triangular field on the medial surface of the hemisphere in front of the subcolosal gyrus, from which it is separated by the posterior para olfactory sulcus. It is continuous below with the olfactory trigone and above and in front with the cingulate gyrus. It is limited anteriorly by the anterior para olfactory sulcus. E. The anterior perforated substance. Substantia perforata anterior is an irregularly quadrilateral area in front of the optic tract and behind the olfactory trigone, from which it is separated by the fissure primia. Medially and in front it is continuous with the subcolosal gyrus. Laterally it is bounded by the lateral stream of the olfactory tract and is continued into the uncus. Its gray substance is confluent above with that of the corpus triatum and is perforated anteriorly by numerous small blood vessels. 2. The uncus has already been described as the recurved, hook-like portion of the hippocampal gyrus. 3. The subcolosal supercolosal indentate gyri, form a rudimentary, arch-shaped lamina of gray substance, extending over the corpus colosum and above the hippocampal gyrus from the anterior perforated substance to the uncus. A. The subcolosal gyrus, gyris subcolosus pedicone of the corpus colosum, is a narrow lamina on the medial surface of the hemisphere in front of the lamina terminalis behind the para olfactory area and below the rostrum of the corpus colosum. It is continuous around the genu of the corpus colosum with the supercolosal gyrus. 4. B. The supercolosal gyrus, induzium grisium gyris epicolosus consists of a thin layer of gray substance in contact with the upper surface of the corpus colosum and continuously laterally with the gray substance of the cingulate gyrus. It contains two longitudinally directed strands of fibers turned respectively the medial and lateral longitudinal striae. The supercolosal gyrus is prolonged around the splenium of the corpus colosum as a delicate lamina, the fasciola sineria, which is continuous below with the fascia dentata hippocampi. C. The fascia dentata hippocampi, gyris dentatus, is a narrow band extending downward and forward above the hippocampal gyris but separated from it by the hippocampal fissure. Its free margin is notched and overlapped by the fimbria, the fimbrio dentate fissure, intervening. Anteriorly it is continued into the notch of the uncus where it forms a sharp bend and is then prolonged as a delicate band, the band of geocomani, over the uncus on the lateral surface of which it is lost. The remaining parts of the rhinencephalon, that is the septum polusum, phoenix and hippocampus, will be described in connection with the lateral ventricle. Interior of the cerebral hemispheres If the upper part of either hemisphere be removed at a level about 1.25 centimeters above the corpus callosum, the central white substance will be exposed as an oval shaped area, the centrom ovale minus, surrounded by a narrow convoluted margin of gray substance and studded with numerous minute red dots, puncta vasculosa, produced by the escape of blood from divided blood vessels. If the remaining portion of the hemisphere will be slightly drawn apart, a broad band of white substance, the corpus callosum will be observed connecting them at the bottom of the longitudinal fissure, the margins of the hemispheres which overlap the corpus callosum are called the labia cerebri. Each labrium is part of the cingulate gyrus already described and the like interval between it and the upper surface of the corpus callosum is termed a colossal fissure. If the hemispheres be sliced off to a level with the upper surface of the corpus callosum, the white substance of that structure will be seen connecting the two hemispheres. The large expanse of medullary matter now exposed, surrounded by a convoluted margin of gray substance, is called the centrum ovale magis. The corpus callosum is the great transverse commissure which ennites the cerebral hemispheres and roves the lateral ventricles. A good conception of position and size is obtained by examining a medial saginal section of the brain. When this seemed to form an arch straight structure about 10 centimeters long, its anterior end is about 4 centimeters from the frontal pole and its posterior end about 6 centimeters from the occipital pole of the hemisphere. The anterior end is named a genu and is bent downward and backward in front of the septum polycytum. Diminishing rapidly in thickness, it is prolonged backwards under the name of the rostrum, which is connected below with the lamina terminalis. The anterior cerebral arteries are in contact with the under surface of the rostrum. They then arch over the front of the genu and are carried backwards above the body of the corpus callosum. The posterior end is termed a splenium and constitutes the thickest part of the corpus callosum. It overlays the tilacoridia of the third ventricle and the midbrain and ends in a thick convex free border. A sagittal section of the splenium shows that the posterior end of the corpus callosum is actually bent forward, the upper and lower parts being applied to each other. The superior surface is convex from before backward and is about 2.5 centimeters wide. Its medial part forms the bottom of the longitudinal fissure and is in contact posteriorly with the lower border of the falc cerebrae. Laterally it is overlapped by the cingulate gyrus but is separated from it by the slit-like colossal fissure. It is traversed by numerous transverse ridges and furrows and is covered by a thin layer of gray matter, the super colossal gyrus, which exhibits on either side of the middle line, the medial and lateral longitudinal striae already described. The inferior surface is concave and forms on either side of the middle line of the roof of the lateral ventricle. Immediately this surface is attached in front to the septum pelusinum. Behind this it is fused with the upper surface of the body of the fornix while the splenium is in contact with the telacore idea. On either side the fibers of the corpus callosum radiate in the white substance and pass to the various parts of the cerebral cortex. Those curving forward from the genu to the frontal lobe constitute the forceps anterior and those curving backward into the occipal lobe, the forceps posterior. Between these two parts is the main body of the fibers which constitute the topetum and extends laterally on either side into the temporal lobe and cover in the central part of the lateral ventricle, the lateral ventricles, ventriculus lateralis. The two lateral ventricles are irregular cavities situated in the lower medial parts of the cerebral hemisphere, one on either side of the middle line. They are separated from each other by a median vertical partition, the septum pelusinum, but communicate with the third ventricle and indirectly with each other through the interventricular foramen. They are lined by a thin diaphanous membrane, the appendoma, covered by ciliated epithelium and contains cerebrospinal fluid, which even in health may be secreted in considerable amount. Each lateral ventricle consists of a central part or body and three prolongations from it term corneal. The central part, paracentralis ventricular lateralis, cella, of the lateral ventricle extends from the interventricular foramen to the splenium of the corpus callosum. It is in a regularly curved cavity, triangular on transverse section, with a roof, a floor, and a medial wall. The roof is formed by the undersurface of the corpus callosum, the floor by the following parts enumerated in order of their position from before backward, the caudate nucleus of the corpus striatum, distria terminalis and the terminal vein, the lateral portion of the upper surface of the thalamus, the coreate plexus, and the lateral part of the fornix. The medial wall is the posterior part of the septum pelusinum, which separates it from the opposite ventricle. The anterior corneu, corneu anterior, anterior horn pre-corneu, passes forward in lateral word with a slight inclination downward from the intraventricular foramen into the frontal lobe, curving around the anterior end of the caudate nucleus. Its floor is formed by the upper surface of the reflected portion of the corpus callosum, the rostrum. It is bounded medially by the anterior portion of the septum pelusinum, and laterally by the head of the caudate nucleus. Its apex reaches the posterior surface of the genu of the corpus callosum. The posterior corneu, corneuposterius postcorneu, passes into the occipital lobe, its direction being backward in lateral word and then medial word. Its roof is formed by the fibers of the corpus callosum passing to the temporal and occipital lobes. On its medial wall is the longitudinal eminence, the calcar avris, hippocampus minor, which is an involution of the ventricular wall produced by the calcarine fissure. Above this, the forceps posterior of the corpus callosum sweeping around to enter the occipital lobe causes another projection, termed the bulb of the posterior corneu. The calcar avris and bulb of the posterior corneu are extremely variable in a degree of development, in some cases they are ill-defined, and others prominent. The inferior corneu, corneu inferior, descending horn, middle horn, medial corneu, is the largest of the three, transverses the temporal lobe of the brain forming in its course a curve around and at posterior end of the thalamus. It passes at first backward, lateral world and downward, and then curves forward to within 2.5 centimeters of the apex of the temporal lobe, its direction being fairly well indicated on the surface of the brain by that of the superior temporal sulcus. Its roof is formed chiefly by the inferior surface of the tapitum of the corpus callosum, but the tail of the caudate nucleus and the striaterminalis also extend forward in the roof of the inferior corneu to its extremity, where they end in a massive gray substance, the nucleus amygdalae. Its floor presents the following parts, the hippocampus, the fimbria hippocampi, the collateral eminence, and the corid plexus. When the corid plexus is removed, a cleft-like opening is left along the medial wall of the inferior corneu. This cleft constitutes the lower part of the coroidal fissure. End of section 15. Section 16 of Gray's Anatomy part 4. This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information to volunteer, please visit LibriVox.org. Recording by M. L. Cohen, Anatomy the Human Body part 4 by Henry Gray, the forebrain part 4. The hippocampus, the hippocampus major, is a curved eminence about five centimeters long, which extends throughout the entire length of the floor of the inferior corneu. Its lower end is enlarged and presents two or three rounded elevations or digitations, which give it a paw-like appearance, and hence it is named a Pez hippocampi. If a transverse section be made through the hippocampus, it will be seen that this eminence is produced by the folding of the wall of the hemisphere to form the hippocampal fissure. The main mass of the hippocampus consists of gray substance, but on its ventricular surface is a thin white layer, the alveus, which is continuous with the fimbria hippocampi. The collateral eminence, eminencia collateralis, is an elongated swelling-lying lateral and parallel with the hippocampus. It corresponds with the middle part of the collateral fissure, and its size depends on the depth and direction of this fissure. It is continuous behind with the flattened triangular area of the trigonum collaterali situated between the posterior and inferior corneua. The fimbria hippocampi is a continuation of the crux of the fornix and will be discussed with that body. A description of the quariplexus will be found later. The corpostriatum has received its name from the striped appearance which a section of its anterior part presents, in consequence of diverging white fibers being mixed with the gray substance which forms its chief mass. A part of the corpostriatum is embedded in the white substance of the hemisphere and is therefore external to the ventricle. It is termed the extraventricular portion or the lentiform nucleus. The remainder, however, projects into the ventricle and is named the intraventricular portion or the caudate nucleus. The caudate nucleus, nucleus caudatus caudatum, is a pear-shaped, highly arched gray mass. Its broad extremity or head is directed forward into the anterior cornea of the lateral ventricle and is continuous with the anterior perforated substance and with the anterior end of the lentiform nucleus. Its narrow end, or tail, is directed backwards on the lateral side of the thalamus from which it is separated by the striaterminalis and the terminal vein. It is then continued downward into the roof of the inferior corneal and ends in the nucleus amygdalae at the apex of the temporal lobe. It is covered by the lining of the ventricle and crossed by some veins of considerable size. It is separated from the lentiform nucleus in its greater part of its extent by a thick lamina of white substance called the internal capsule, but the two portions of the corpostriatum are united in front. The lentiform nucleus. Nucleus lentiformis lenticular nucleus lenticula is lateral to the caudate nucleus and thalamus and is seen only in sections of the hemisphere. When divided horizontally, it exhibits to some extent the appearance of a biconvex lens, while a coronal section of its central part presents a somewhat triangular outline. It is shorter than the caudate nucleus and does not extend as far forward. It is bounded laterally by a lamina of white substance called the external capsule and lateral to this is a thin layer of gray substance termed the claustrum. Its anterior end is continuous with the lower part of the head of the caudate nucleus and with the anterior perforated substance. In a coronal section through the middle of the lentiform nucleus, two medullary laminate are seen dividing it into three parts. The lateral and largest part is of a reddish color and is known as the putamen, while the medial and intermediate area of a yellowish tint and together constitute the globus pallidus. All three are marked by fine radiating white fibers which are most distinct in the putamen. The gray substance of the corpostriatum is traversed by nerve fibers some of which originate in it. The cells are multipolar both large and small. Those of the lentiform nucleus contain yellow pigment. The caudate and lentiform nuclei are not only directly continuous with each other anteriorly but are connected to each other by numerous fibers. The corpostriatum is also connected one to the cerebral cortex by what are termed corticostriate fibers. Two to the thalamus by fibers which pass through the internal capsule and by a strand named anselentiformis. Three to the cerebral peduncle by fibers which leave the lower aspect of the caudate and lentiform nuclei. The claustrum is a thin layer of gray substance situated on the lateral surface of the external capsule. Its transverse section is triangular with the apex directed upward. Its medial surface contiguous to the external capsule is smooth but its lateral surface presents ridges and furrows corresponding with the gyri and sulci of the insula with which it is in close relationship. The claustrum is regarded as a detached portion of the gray substance of the insula from which it is separated by a layer of white fibers. The capsule extrema band a ballerger. It sells a small and spindle shaped and contain yellow pigment. They are similar to those of the deepest layer of the cortex. The nucleus amygdala is an ovoid gray mass situated at the lower end of the roof of the inferior cornu. It is merely a localized thickening of the gray cortex continuous without of the uncus. In front it is continuous with the putamen behind with the striaterminalis and tail of the caudate nucleus. The internal capsule, capsula interna is a flattened band of white fibers between the lentiform nucleus on the lateral side and the caudate nucleus and thalamus on the medial side. In horizontal section it is seen to be somewhat abruptly curved with its convexity inward. The prominence of the curve is called the genu and projects between the caudate nucleus and the thalamus. The portion in front of the genu is termed the frontal part and separates the lentiform from the caudate nucleus. The portion behind the genu is the occipital part and separates the lentiform nucleus from the thalamus. The front part of the internal capsule contains 1. Fibers running from the thalamus to the frontal lobe. 2. Fibers connected to lentiform and caudate nuclei. 3. Fibers connecting to cortex with the corpus striatum. And 4. Fibers passing from the frontal lobe through the medial fifth of the base of the cerebral peduncle to the nucleus pontus. The fibers in the region of the genu are named the geniculate fibers. They originate in the motor part of the cerebral cortex and after passing downward through the base of the cerebral peduncle with the cerebral spinal fibers undergo decastation and end in the motor nuclear of the cranial nerves of the opposite side. The anterior two-thirds of the occipital part of the internal capsule contain the cerebral spinal fibers which arise in the motor area of the cerebral cortex and passing downward through the middle three-fifths of the base of the cerebral peduncle are continued into the pyramids of the medulla oblongata. The posterior third of the occipital part contains 1. Sensory fibers largely derived from the thalamus though some may be continued upward from the medial lemniscus. 2. The fibers of the optic radiation from the lower visual centers to the cortex of the occipital lobe. 3. Acoustic fibers from the lateral lemniscus to the temporal lobe. And 4. Fibers which pass from the occipital and temporal lobes to the nuclei pontis. The fibers of the internal capsule radiate widely as they pass to and from the various parts of the cerebral cortex forming the corona radiata and intermingling with the fibers of the corpus callosum. The external capsule, capsula externa, is a lamina of white substance situated lateral to the length of form nucleus between it and the claustrum and continuous with the internal capsule below and behind the lentiform nucleus. It probably contained fibers derived from the thalamus the anterior commissure and the subthlamic region. The substantia anomenata of minert is a stratum consisting partly of gray and partly of white substance which lies below the anterior part of the thalamus and lentiform nucleus. It consists of three layers superior middle and inferior. The superior layer is named ancelentiformis and its fibers derived from the medullary lamina of the lentiform nucleus pass medially to end in the thalamus and subthlamic region while others are said to end in the tegmentum and red nucleus. The middle layer consists of nerve cells and nerve fibers. Fibers enter it from the parietal lobe through the external capsule while others are said to connect it with the medial longitudinal fasciculus. The inferior layer forms the main part of the inferior stalk of the thalamus and connects this body with the temporal lobe and insula. The striaterminalis tanius semicircularis is a narrow band of white substance situated in the depression between the caudate nucleus and the thalamus. Anteriorly its fibers are partly continued into the column of the fornix some however pass over the anterior commissure to the gray substance between the caudate nucleus and the septum pollucinum while others are said to enter the caudate nucleus. Posteriorly it is continued into the roof of the inferior corner of the lateral ventricle at the extremity of which it enters the nucleus amygdalae. Superficial to it is a large vein, the terminal vein, vein of the corpus striatum, which receives numerous tributaries from the corpus striatum and thalamus. It runs forward to the interventricular foramen and there joins with the vein of the corioplexus to form the corresponding internal cerebral vein. On the surface of the terminal vein is a narrow white band named the lamina The fornix is a longitudinal arch-shaped lamella of white substance situated below the corpus callosum and continuous with it behind but separated from it in front by the septum pollucinum. Made to describe is consisting of two symmetrical bands, one for either hemisphere. The two portions are not united to each other in front and behind but their central parts are joined together in the middle line. The anterior parts are called the columns of the fornix, the intermediate united portions the body and the posterior parts the crura. The body corpus fornicus of the fornix is triangular, narrow in front and broad behind. The medial part of its upper surface is connected to the septum pollucinum in front and to the corpus callosum behind. The lateral portion of this surface forms part of the floor of the lateral ventricle and is covered by the ventricular epithelium. Its lateral edge overlaps the corioplexus and is continuous with the epithelium covering of the structure. The undersurface rests upon the telecoridia of the third ventricle which separates it from the epithelial roof of that cavity and from the medial portions of the upper surfaces of the thalamai. Below, the lateral portions of the body of the fornix are joined by a thin triangular lamina named a sultarium, lyrim. This lamina contains some transverse fibers which connect to two hippocampi across the middle line and constitutes a hippocampal commissure. Between the sultarium and the corpus callosum is a horizontal cleft, the so-called ventricle of the fornix. Ventricle of virga is sometimes found. The columns, colomna fornicus, anterior pullers, fornicolums, of the fornix arch downward in front of the intrantricular foramen and behind the anterior commissure and each descends through the gray substance in the lateral wall of the third ventricle to the base of the brain where it ends in the corpus mammillare. From the cells of the corpus mammillare, the thalamol mammillare fasciculus, bundle avic d'azur, takes origin and is prolonged into the anterior nucleus of the thalamus. The columns of the fornix and the thalamol mammillare fasciculus together form a loop resembling the figure 8, but the continuity of the loop is broken in the corpus mammillare. The column of the fornix is drawn by the striomedularis of the pineal body and by the superficial fibers of the striaterminalis and is said to receive also fibers in the septum pelucidum. Sococondal describes an olfactory fasciculus which becomes detached from the main portion of the columns of the fornix and passes downward in front of the anterior commissure to the base of the brain where it divides into two bundles, one joining the medial stria of the olfactory tract, the other joins the subcolosal gyrus and through it reaches the hippocampal gyrus. The crura, cruse fornicus, posterior pillars of the fornix are prolonged backward from the body. They are flattened bands and at their commencement are intimately connected with the undersurface of the corpus callosum. Diverging from one another, each curves around the posterior ends of the thalamus and passes downward and forward into the inferior corner of the lateral ventricle. Here it lies along the concavity of the hippocampus on the cersus which some of its fibers are spread out to form the alveus. While the remainder are continued as a narrow white band, the fimbria hippocampi, which is prolonged into the uncus of the hippocampal gyrus. The inner edge of the fimbria overlaps the fascia dentata hippocampi, dentate gyrus, from which it is separated by the fimbrio dentate fissure. From its lateral margin, which is thin and ragged, the ventricular epithelium is reflected over the quaria plexus as the lateral projects to the coroidal fissure. Interventricular foramen, foramen of Monroe. Between the columns of the fornix and the anterior ends of the thalamus and over aperture is present on either side, this is the interventricular foramen and through it the lateral ventricles communicate with the third ventricle. Behind the epithelial lining of the foramen, the quaria plexus of the lateral ventricles are joined across the middle line.  On sagittal section it is oval in shape, its long diameter being vertical and measuring about five millimeters. Its fibers can be traced lateralward and backward on either side beneath the corpus striatum into the subsins of the temporal lobe. It serves in this way to connect to two temporal lobes but it also contains decasating fibers from the olfactory tracts. The septum palusitum, septum lucidum is a thin vertically placed partition consisting of two laminate separating in the greater part of their extent by a narrow chunk or interval, the cavity of the septum palusitum. It is attached above to the undersurface of the corpus colosum, below to the anterior part of the fornix behind and the reflected part of the corpus colosum in front. It is triangular in form, broad in front and narrow behind. Its inferior angle corresponds with the upper part of the anterior commissure. The lateral surface of each laminate is directed towards the body and anterior corneum of the lateral ventricle and is covered by the appendema of that cavity. The cavity of the septum palusitum, caivum septum palusidae, pseudosial fifth ventricle, is generally regarded as part of the longitudinal cerebrofissure which has become shut off by the union of the hemispheres in the formation of the corpus colosum above and the fornix below. Each half of the septum therefore forms part of the medial wall of the hemisphere and consists of a medial layer of gray substance derived from that of the cortex and a lateral layer of white substance continuous without the cerebral hemisphere. This cavity is not developed from the cavity of the cerebral vesicles and never communicates with the ventricles of the brain. The cori plexus of the lateral ventricle, plexus cordius ventriculus lateralis, paraplexus, is a highly vascular fringe-like process of pia mater which projects into the ventricular cavity. The plexus, however, is everywhere covered by a layer of epithelium continuous with the epithelial lining of the ventricle. It extends from the interventricular foramen where it is joined with the plexus of the opposite ventricle to the end of the inferior cornu. The part in relation to the body of the ventricle forms the vascular fringe margin of a triangular process of pia mater named the telecoridia of the third ventricle and projects from undercover the lateral edge of the fornix. It lies upon the upper surface of the thalamus from which the epithelium is reflected over the plexus onto the edge of the fornix. This portion, in relation to the inferior cornu, lies in the concavity of the hippocampus and overlaps the fimbria hippocampi. From the lateral edge of the fimbria, the epithelium is reflected over the plexus onto the roof of the cornu. It consists of minute and highly vascular villus processes, each with an afferent and an efferent vessel. The arteries of the plexus are A, the anterior coroidal, a branch of the internal carotid which answers the plexus at the end of the inferior cornu, and B, the posterior coroidal, one or two small branches of the posterior cerebral which passes forward under the splenium. The veins of the coroid plexus unite to form a tortuous vein which courses from behind forward to the interventricular foramen and there joins with the terminal vein to form the corresponding intersurable vein. When the coroid plexus is pulled away, the continuity between its epithelial covering and the epithelial aligning of the ventricle is severed and a cleft-like space is produced. This is named the carotidal fissure. Like the plexus, it extends from the interventricular foramen to the end of the inferior cornu. The upper part of the fissure, that is the part nearest the interventricular foramen, is situated between the lateral edge of the fornix and the upper surface of the thalamus. Farther back, at the beginning of the inferior cornu, is between the commencement of the fimbria hippocampi and the posterior end of the thalamus. While in the inferior cornu, it lies between the fimbria in the floor and astrea terminalis in the roof of the cornu. The tila coridae of the third ventricle, tila coridae ventriculus tertii velem interpositum, is a double fold of pia mater, triangular in shape which lies beneath the fornix. The lateral portions of its lower surface rest upon the thalami, while its medial portion is in contact with the epithelial roof of the third ventricle. Its apex is situated at the interventricular foramen, its base corresponds with the splenium of the corpus callosum and occupies the interval between that structure above and the corporequagigemini and pineal body below. This interval, together with the lower portions of the coroidal fissures, is sometimes spoken of as the transverse fissure of the brain. At its base, the two layers of the velem separate from each other and are continuous with the pia mater investing the brain in this region. Its lateral margins are modified to form the highly vascular coroid plexuses of the lateral ventricles. It is supplied by the anterior and posterior coroidal arteries already described. The veins of the tila coridae are named the internal cerebral veins, vinaigalenae. They are two in number and run backward between its layers, each being formed at the interventricular foramen by the union of the terminal vein with the coroidal vein. The internal cerebral veins unite posteriorly in a single trunk, the great cerebral vein, vinaigalenae, which passes backward beneath the splenium and ends in the straight sinus. Section 17 of Gray's Anatomy Part 4. This is LibriVox Recording. All LibriVox recordings are in the public domain. For more information or to volunteer, please visit LibriVox.org. Recording by M. L. Cohen. Anatomy to Human Body Part 4 by Henry Gray. The Four Brain. Section 5. Structure of the Cerebral Hemispheres. The cerebral hemispheres are composed of gray and white substance. The former covers their surface and is termed a cortex. The latter occupies the interior of the hemispheres. The white substance consists of medulated fibers varying in size and arranged in bundles separated by neuroglia. They may be divided according to their course and connections into three distinct systems. One, projection fibers, connect the hemispheres with the lower parts of the brain and with the medulla spinalis. Two, transverse or commissural fibers unite to two hemispheres. Three, association fibers connect different structures in the same hemisphere. These are, in many instances, collateral branches of the projection fibers, but others are the axons of independent cells. One, the projection fibers consist of efferent and afferent fibers uniting the cortex with the lower part of the brain and with the medulla spinalis. The principal efferent strands are one, the motor tract occupying the genu and the anterior thirds of the occipital part of the internal capsule and consisting of A, the geniculate fibers which decasate and end in the motor nuclei the cranial nerves of the opposite side and B, the cerebrospinal fibers which are prolonged through the pyramid of the medulla oblongata into the medulla spinalis. Two, the corticopontine fibers ending in a nuclei pontus. The chief afferent fibers are one, those of the lemniscus which are not interrupted in the thalamus. Two, those of the superior cerebellar peduncle which are not interrupted in the red nucleus and thalamus. Three, numerous fibers are rising within the thalamus and passing through its stalks to the different parts of the cortex. Four, optic and acoustic fibers, the former passing to the occipital, the latter to the temporal lobe. Two, the transverse or commissural fibers connect the two hemispheres. They include A, the transverse fibers of the corpus callosum, B, the anterior commissure, C, the posterior commissure and D, the lyra or hippocampal commissure. They have already been described. Three, the association fibers unite different parts of the same hemisphere and are of two kinds. Those connecting adjacent gyri, short association fibers. Two, those passing between more distant parts, long association fibers. The short association fibers lie immediately beneath the gray substance of the cortex of the hemispheres and connect together adjacent gyri. The long association fibers include the following, A, the unsonate fasciculus, B, the singulum, C, the superior longitudinal fasciculus, D, the inferior longitudinal fasciculus, E, the perpendicular fasciculus, F, the occipital frontal fasciculus, and G, the fornix. A, the unsonate fasciculus passes across the bottom of the lateral fissure and unites the gyri of the frontal lobe with the anterior end of the temporal lobe. B, the singulum is a band of white matter contained within the singular gyrus. Beginning in front of the anterior perforated substance, it passes forward and upward parallel with the rostrum, winds around the genu, runs backward above the corpus callosum, turns around the splenium, and ends in the hippocampal gyrus. C, the superior longitudinal fasciculus passes backwards from the front lobe above the lentiform nucleus and insula. Some of its fibers end in the occipital lobe, and others curve downward and forward into the temporal lobe. D, the inferior longitudinal fasciculus connects to temporal and occipital lobes, running along the lateral walls of the inferior and posterior corneus of the lateral ventricle. E, the perpendicular fasciculus, runs vertically through the front part of the occipital lobe, and it connects the inferior parietal lobe with the fusiform gyrus. F, the occipital frontal fasciculus passes backward from the frontal lobe along the lateral border of the caudate nucleus and on the mesial aspect of the coronaraniata. Its fibers radiate in a fan-like manner and pass into the occipital and temporal lobes lateral to the posterior and inferior corneua. Deserene regards the fibers of the topetum as being derived from this fasciculus and not from the corpus callosum. G, the fornix connects the hippocampal gyrus with the corpus mammillary and by means of the thalamel mammillary fasciculus with the thalamus. Through the fibers of the hippocampal commissure, it probably also unites the opposite hippocampal gyri. The gray substance of the hemisphere is divided into 1, that of the cerebral cortex, and 2, that of the caudate nucleus, the lentiform nucleus, the claustrum, and the nucleus amygdalae. Structure of the cerebral cortex. The cerebral cortex differs in thickness and structure in different parts of the hemisphere. It is thinner in the occipital region than in the anterior and posterior central gyri, and is also much thinner at the bottom of the sulci than on the top of the gyri. Again, the minute structure of the anterior central differs from now to the posterior central gyrus, and areas possessing a special type of cortex can be mapped out in the occipital lobe. On examining a section of the cortex with the lens, it is seen to consist of alternating white and gray layers thus disposed from the surface inward. One, a thin layer of white substance. Two, a layer of gray substance. Three, a second white layer, outer band of balinger or band of generi. Four, a second gray layer. Five, a third white layer, inner band of balinger. Six, a third gray layer which rests on the medullary substance of the gyrus. The cortex is made up of nerve cells of varying size and shape, and of nerve fibers which are either medulated or naked-axis cylinders embedded in the matrix of neuroglia. Nerve cells. According to Gajal, the nerve cells are arranged in four layers, named from the surface inward as follows. One, the molecular layer. Two, the layer of small pyramidal cells. Three, the layer of large pyramidal cells. Four, the layer of polymorphous cells. The molecular layer. In this layer, the cells are polygonal triangular or fusiform in shape. Each polygonal cell gives off some sore five dendrites while its axon may arise directly from the cell or from one of its dendrites. Each triangular cell gives off two or three dendrites from one of which the axon arises. The fusiform cells are placed with the long axis parallel to the surface and are mostly bipolar, each pole being prolonged into a dendrite which runs horizontal for some distance and furnishes ascending branches. Their axons, two or three in number, arise from the dendrites and, like them, take a horizontal course giving off numerous ascending collaterals. The distribution of the axons and dendrites of all three sets of cells is limited to the molecular layer. The layer of small and the layer of large pyramidal cells. The cells in these two layers may be studied together, since with the exception of the differentiation in size and the more superficial position of the smaller cells, they resemble each other. The average length in the small cells is from 10 to 15 microns, that of the large cells from 20 to 30 microns. The body of each cell is a pyramidal in shape, its base being directed to the deeper parts and its apex towards the surface. It contains granular pigment and stains deeply with ordinary reagents. The nucleus is of large size in round or oval in shape. The base of the cell gives off the axis cylinder and this runs into the central white substance giving off collaterals in its course and is distributed as a projection, commissural, or association fiber. The apical and basal parts of the cell give off dendrites. The apical dendrite is directed towards the surface and ends in the molecular layer by dividing it to numerous branches, all of which may be seen when prepared by the silver or methylene blue method to be studied with projection bristle-like processes. The largest pyramidal cells are found in the upper part of the anterior central gyrus and in the paracentral lobule. They are often arranged in groups or nests from three to five and are named the giant cells of bets. In the former situation, they may exceed 50 microns in length and 40 microns in breadth. While in the paracentral lobule, they may attain a length of 65 microns. Layer of polymorphous cells. The cells of this layer, as their name implies, are very irregular in contour. They may be fusiform, oval, triangular, or star-shaped. Their dendrites are directed outward but do not reach so far as the molecular layer. Their axons pass into the subjacent white matter. There are two other kinds of cells in the cerebral cortex. They are A, the cells of Golgi, the axons of which divide immediately after their origins into large number of branches which are directed towards the surface of the cortex. B, the cells of Martinati, which are chiefly found in the polymorphous layer. Their dendrites are short and may have an ascending or descending course, while their axons pass out into the molecular layer and form an extensive horizontal arborization. Nerve fibers. These fill up a large part of the intervals between the cells and may be medulated or non-medulated. The latter comprising the axons of the smallest pyramidal cells and the cells of Golgi. In their direction, the fibers may be either tangential or radial. The tangential fibers run parallel to the surface of the hemispheres intersecting the radial fibers at right angles. They constitute several striata of which the following are the more important. One, a striatum of white fibers covering the superficial aspect of the molecular layer, plexus of X-ner. Two, the band of Bectero in the outer part of the layer of small pyramidal cells. Three, the band of Generi or external band of Ballinger running through the latter of large pyramidal cells. Four, the interior band of Ballinger between the layers of the large pyramidal cells in the polymorphous layer. Five, the deep tangential fibers and the lower part of the polymorphous layer. The tangential fibers consist of A, the collateral of the pyramidal and polymorphous cells and the cells of Martinati. B, the branching axons of Golgi cells. C, the collateral and terminal arborizations of the projection, commissural and association fibers. The radial fibers. Some of these, that is the axons of the pyramidal and polymorphous cells, descend into the central white matter while others, the terminations of the projection, commissural or association fibers, ascend to end in the cortex. The axons of the cells of Martinati are also ascending fibers, special types of cerebral cortex. It has already been pointed out that the minute structure of the cortex differs in different regions of the hemisphere. An AW Campbell has endeavored to prove, as the result of an exhaustive examination of a series of humans and anthropoid brains, quote, that there exists a direct correlation between the physiologic function and histologic structure, end quote. The principal regions where the typical structure is departed from will now be referred to. One, in the calcorine fissure and the gyre bounding it, the internal line of ballager is absent, while the band of generi is of considerable thickness and forms a characteristic feature of this region of the cortex. If a section be examined microscopically, an additional layer of cells is seen to be interpolated between the molecular layer and the layer of small pyramidal cells. This extra layer consists of two or three strata of fusiform cells, the long axis of which are at right angles to the surface. Each cell gives off two dendrites, external and internal, from the latter of which the axon arises and passes into the white central substance. In the layer of small pyramidal cells, fusiform cells identical with the above are seen, as well as ovoid or star-like cells with ascending axons, cells of Martinati. This is the visual area of the cortex and has been shown by J.S. Bolton that in old standing cases of optic atrophy, the thickness of generi's band is reduced by nearly 50%. A.W. Campbell says, quote, histologically, two distinct types of cortex can be made out in the occipital lobe. The first of these coats the walls and bounding convolutions of the calcorine fissure and is distinguished by the well-known line of generi or victesur. The second area forms an investing zone a centimeter or more broad around the first and is characterized by a remarkable wealth of fibers, as well as by a curious piriform cells of large size, richly stocked with chromophob elements. Cells which seem to have escaped the observation of Ramani Kahal, Bolton, and others who have worked at this region. As to the functions of these two regions, there is abundant evidence anatomical, embryological and pathological to show that the first or calcorine area is that to which visual sensations primarily pass and we are gradually obtaining proof to the effect that the second investing area is constituted for the interpretation and further elaboration of these sensations. These areas therefore deserve the name Visio-sensory and Visio-psychic, end quote. Two, the anterior central gyrus is characterized by the presence of the giant cells of bets and by, quote, a wealth of nerve fibers and measurely superior to that of any other part, end quote, Campbell. And in these respects differs from the posterior central gyrus. These two gyri, together with the paracentral lobule, were long regarded as constituting the, quote, motor areas, end quote of the hemispheres. But Sherrington and Grumbam have shown that in the chimpanzee, the motor area never extends onto the free face of the posterior central gyrus, but occupies the entire length of the anterior central gyrus and in most cases, the greater part or whole of its width. It extends into the depth of the central sulcus occupying the anterior wall and in some places the floor and in some extending even into the deeper part of the posterior wall of the sulcus. Three, in the hippocampus, the molecular layer is very thick and contains a large number of Golgi cells. It has been divided into three strata. A, S convolution or S granulosum containing many tangential fibers. B, S lacunosum, presenting numerous fascicolor spaces. C, S radiodum, exhibiting a rich plexus of fibrils. The two layers of pyramidal cells are condensed into one and the cells are mostly of large size. The axons of the cells of the polymorphous layer may run in an ascending, a descending, or a horizontal direction. Between the polymorphous layer and the ventricular appenduma is the white substance of the alveas. Four, in the fascia dentata hippocampi or dentate gyrus, the molecular layer contains some pyramidal cells while the layer of pyramidal cells is almost entirely represented by small ovoid cells. Five, the olfactory bulb. In many of the lower animals this contains a cavity which communicates through the olfactory tract with the lateral ventricle. In man, the original cavity is filled up by neuroglia and its wall becomes thickened but it's more and more so on the ventral than on the dorsal aspect. Its dorsal part contains a small amount of gray and white substance but it is scanty and ill-defined. A section through the ventral part shows it to consist of the following layers from without inward. One, a layer of olfactory nerve fibers which are the non-medulated axons prolonged from the olfactory cells of the natal cavity and reached the bulb by passing through the criberform plate of the ethmoid bone. At first they cover the bulb and then penetrate it to end by forming synapses with the dendrites of the mitral cells presently to be described. Two, glomerular layer. This layer contains numerous ferroidal reticulated enlargements termed glomeruli produced by the branching and arborizations of the processes of the olfactory nerve fibers with the descending dendrites of the mitral cells. Three, molecular layer. This is formed of a matrix of neuroglia embedded in which are the mitral cells. These cells are pyramidal in shape and the basal part of each gives off a thick dendrite which descends into the glomerular layer where it arborizes as indicated above and others which interlace with similar dendrites of neighboring mitral cells. The axons pass through the next layer into the white matter of the bulb and after becoming bent on themselves at right angle are continued into the olfactory tract. Four, nerve fiber layer. This lies next to the central core of neuroglia and its fibers consist of the axons or afferent processes of the mitral cells passing into the brain. Some efferent fibers are however also present and end in the molecular layer but nothing is known as to their exact origin. Weight of the encephalon. The average weight of the brain in the adult male is about 1,380 grams. That of the female about 1,250 grams. In the male the maximum weight out of 278 cases was 1,840 grams and the minimum weight 964 grams. The maximum weight of the adult female brain out of 191 cases was 1,585 grams and a minimum weight 879 grams. The brain increases rapidly during the first four years of life and reaches its maximum weight by about the 20th year. As age advances the brain decreases slowly in weight. In old age the decrease takes place more rapidly to the extent of about 28 grams per year. The human brain is heavier than that of any of the lower animals except the elephant and whale. The brain of the former weighs from 3.5 to 5.4 kilograms and that of the whale in a specimen 19 meters long weighed rather more than 6.7 kilograms. Cerebral localization. Physiological and pathological research have now gone far to prove that a considerable part of the surface of the brain may be mapped out into a series of more or less definite areas each of which is intimately connected with some well-defined function. Motor areas. The motor area occupies the anterior central and frontal gyri and the paracentral lobule. The centers for the lower limb are located on the uppermost part of the anterior central gyrus and its continuation onto the paracentral lobule. Those for the trunk are on the upper portion and those for the upper limb on the middle portion of the anterior central gyrus. The facial centers are situated on the lower part of the anterior central gyrus. Those for the tongue, larynx, muscles of mastication and pharynx on the frontal operculum while those for the head and neck occupy the posterior end of the middle frontal gyrus. Sensory areas. Tactile and temperature senses are located on the posterior central gyrus while the sense of form and solidity is on the superior pride of lobule and precuneus. With regard to the special senses, the area for the sense of taste is probably related to the oncus and hippocampal gyrus. The auditory area occupies the middle third of the superior temporal gyrus and adjacent gyri in the lateral fissure. The visual area, the calcorine fissure and cuneus, the olfactory area, the rhinocephalon. As special centers of much importance may be noted, the emissive center for speech on the left inferior frontal and anterior central gyri, Broca, the auditory receptive center on the transverse and superior temporal gyri, and the visual receptive center on the lingual gyrus and cuneus. End of section 17.