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http://rgm22.nig.ac.jp/mediawiki-ogareport/index.php/For_Gray_anatomy_normalization
 * The Insula (island of Reil; central lobe) (Fig. 731) lies deeply in the lateral or Sylvian 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, frontoparietal, and temporal opercula. 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 rami of the lateral fissure 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 shallow sulci into three or four short gyri, while the posterior part is formed by one long gyrus, 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 (Fig. 727).—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 and the hippocampal fissure. These he separated on the morphological ground that they are well-developed in animals possessing a keen sense of smell (osmatic animals), such as the dog and fox. They were thus regarded as a part of the rhinencephalon, but it is now recognized that they belong to the neopallium; the cingulate gyrus is therefore sometimes described as a part of the frontal lobe, and the hippocampal as a part of the temporal lobe.	  82
 * The cingulate gyrus (gyrus cinguli; callosal convolution) is an arch-shaped convolution, lying in close relation to the superficial surface of the corpus callosum, from which it is separated by a slit-like fissure, the callosal 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 gyrus. It is separated from the medial part of the superior frontal gyrus by the cingulate sulcus, and from the precuneus by the subparietal sulcus.	  83
 * The hippocampal gyrus (gyrus 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 gyrus and inferiorly with the lingual gyrus. Running in the substance of the cingulate and hippocampal gyri, and connecting them together, is a tract of arched fibers, named the cingulum (page 843). The anterior extremity of the hippocampal gyrus is recurved in the form of a hook (uncus), which is separated from the apex of the temporal lobe by a slight fissure, the incisura temporalis. Although superficially continuous with the hippocampal gyrus, the uncus forms morphologically a part of the rhinencephalon.	  84
 * 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 (page 819), and gives rise to the prominence of the hippocampus in the inferior cornu of the lateral ventricle.	  85
 * Rhinencephalon (Fig. 732).—The rhinencephalon comprises the olfactory lobe, the uncus, the subcallosal and supracallosal gyri, the fascia dentata hippocampi, the septum pellucidum, the fornix, and the hippocampus.	  86
 * 1. The Olfactory Lobe (lobus 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.	  87
 * (a) The olfactory bulb (bulbus olfactorius) is an oval, reddish-gray mass which rests on the cribriform plate of the ethmoid and forms the anterior expanded extremity of the olfactory tract. Its under surface receives the olfactory nerves, which pass upward through the cribriform plate from the olfactory region of the nasal cavity. Its minute structure is described on page 848.	  88
 * (b) The olfactory tract (tractus 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 striæ, a medial and a lateral. The lateral stria is directed across the lateral part of the anterior perforated substance and then bends abruptly medialward toward the uncus of the hippocampal gyrus. The medial stria turns medialward behind the parolfactory area and ends in the subcallosal gyrus; in some cases a small intermediate stria is seen running backward to the anterior perforated substance.	  89
 * (c) The olfactory trigone (trigonum olfactorium) is a small triangular area in front of the anterior perforated substance. Its apex, directed forward, occupies the posterior part of the olfactory sulcus, and is brought into view by throwing back the olfactory tract.	  90
 * (d) The parolfactory area of Broca (area parolfactoria) is a small triangular field on the medial surface of the hemisphere in front of the subcallosal gyrus, from which it is separated by the posterior parolfactory 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 parolfactory sulcus.	  91
 * (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 prima; medially and in front it is continuous with the subcallosal gyrus; laterally it is bounded by the lateral stria of the olfactory tract and is continued into the uncus. Its gray substance is confluent above with that of the corpus striatum, and is perforated anteriorly by numerous small bloodvessels.	  92
 * 2. The Uncus has already been described (page 826) as the recurved, hook-like portion of the hippocampal gyrus.	  93
 * 3. The Subcallosal, Supracallosal, and Dentate Gyri form a rudimentary arch-shaped lamina of gray substance extending over the corpus callosum and above the hippocampal gyrus from the anterior perforated substance to the uncus.	  94
 * (a) The subcallosal gyrus (gyrus subcallosus; peduncle of the corpus callosum) is a narrow lamina on the medial surface of the hemisphere in front of the lamina terminalis, behind the parolfactory area, and below the rostrum of the corpus callosum. It is continuous around the genu of the corpus callosum with the supracallosal gyrus.	  95
 * (b) The supracallosal gyrus (indusium griseum; gyrus epicallosus) consists of a thin layer of gray substance in contact with the upper surface of the corpus callosum and continuous laterally with the gray substance of the cingulate gyrus. It contains two longitudinally directed strands of fibers termed respectively the medial and lateral longitudinal striæ. The supracallosal gyrus is prolonged around the splenium of the corpus callosum as a delicate lamina, the fasciola cinerea, which is continuous below with the fascia dentata hippocampi.	  96
 * (c) The fascia dentata hippocampi (gyrus dentatus) is a narrow band extending downward and forward above the hippocampal gyrus but separated from it by the hippocampal fissure; its free margin is notched and overlapped by the fimbria—the fimbriodentate 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 Giacomini, over the uncus, on the lateral surface of which it is lost.	  97
 * The remaining parts of the rhinencephalon, viz., the septum pellucidum, fornix, and hippocampus, will be described in connection with the lateral ventricle.	  98
 * Interior of the Cerebral Hemispheres.—If the upper part of either hemisphere be removed, at a level about 1.25 cm. above the corpus callosum, the central white substance will be exposed as an oval-shaped area, the centrum 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 bloodvessels. If the remaining portions of the hemispheres 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 slit-like interval between it and the upper surface of the corpus callosum is termed the callosal fissure (Fig. 727). 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 the convoluted margin of gray substance, is called the centrum ovale majus.	  99
 * The Corpus Callosum (Fig. 733) is the great transverse commissure which unites the cerebral hemispheres and roofs in the lateral ventricles. A good conception of its position and size is obtained by examining a median sagittal section of the brain (Fig. 720), when it is seen to form an arched structure about 10 cm. long. Its anterior end is about 4 cm. from the frontal pole, and its posterior end about 6 cm. from the occipital pole of the hemisphere.	  100

after
The {Insula [FMA67329:Insula]} ({island of Reil [FMA67329:Insula]}; {central lobe [FMA67329:Insula]}) (Fig. 731) lies deeply in the lateral or {Sylvian fissure [FMA77801:Lateral sulcus]}, and can only be seen when the {lips [FMA59815:Labial part of mouth]} 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 [FMA67329:Insula]}; they are separated from each other by the three rami of the {lateral fissure [FMA77801:Lateral sulcus]}, and are named the {orbital [FMA49034:Orbitalis]}, {frontal [FMA46757:Frontalis]}, frontoparietal, and {temporal opercula [FMA74891:Temporal operculum]}. The {orbital operculum [FMA74887:Orbital operculum]} lies below the anterior horizontal ramus of the fissure, the {frontal [FMA46757:Frontalis]} 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 [FMA74886:Frontal operculum]} is of small size in those cases where the anterior horizontal and ascending rami of the {lateral fissure [FMA77801:Lateral sulcus]} arise from a common stem. The {insula [FMA67329:Insula]} is surrounded by a deep {circular sulcus [FMA83753:Circular sulcus of insula]} which separates it from the {frontal [FMA46757:Frontalis]}, parietal, and {temporal lobes [FMA61825:Temporal lobe]}. When the opercula have been removed, the {insula [FMA67329:Insula]} is seen as a triangular eminence, the apex of which is directed toward the {anterior perforated substance [FMA61891: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 [FMA67329:Insula]}. The anterior part is subdivided by shallow sulci into three or four short gyri, while the posterior part is formed by one long gyrus, which is often bifurcated at its upper end. The cortical {gray substance [FMA67242:Gray matter of neuraxis]} of the {insula [FMA67329:Insula]} is continuous with that of the different opercula, while its deep surface corresponds with the {lentiform nucleus [FMA77615:Lentiform nucleus]} of the {corpus striatum [FMA77616:Corpus striatum]}. {Limbic Lobe [FMA72719:Limbic lobe]} (Fig. 727).—The term {limbic lobe [FMA72719:Limbic lobe]} was introduced by Broca, and under it he included the cingulate and {hippocampal gyri [FMA61918:Parahippocampal gyrus]}, which together arch around the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]} and the {hippocampal fissure [FMA83747:Hippocampal sulcus]}. These he separated on the morphological ground that they are well-developed in animals possessing a keen sense of smell (osmatic animals), such as the dog and fox. They were thus regarded as a part of the {rhinencephalon [FMA62430:Paleocortex]}, but it is now recognized that they belong to the {neopallium [FMA62429:Neocortex]}; the {cingulate gyrus [FMA62434:Cingulate gyrus]} is therefore sometimes described as a part of the {frontal lobe [FMA61824:Frontal lobe]}, and the {hippocampal [FMA62493:Hippocampus]} as a part of the {temporal lobe [FMA61825:Temporal lobe]}. 82   The {cingulate gyrus [FMA62434:Cingulate gyrus]} ({gyrus cinguli [FMA62434:Cingulate gyrus]}; callosal convolution) is an arch-shaped convolution, lying in close relation to the superficial surface of the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]}, from which it is separated by a slit-like fissure, the callosal fissure. It commences below the {rostrum of the corpus callosum [FMA61945:Rostrum of corpus callosum; FMA61946:Genu of corpus callosum]}, curves around in front of the {genu [FMA24974:Knee]}, extends along the upper {surface of the body [FMA61695:Body surface]}, and finally turns downward behind the {splenium [FMA7196:Spleen]}, where it is connected by a narrow isthmus with the {hippocampal gyrus [FMA61918:Parahippocampal gyrus]}. It is separated from the medial part of the {superior frontal gyrus [FMA61857:Superior frontal gyrus]} by the {cingulate sulcus [FMA83748:Cingulate sulcus]}, and from the {precuneus [FMA61900:Precuneus]} by the {subparietal sulcus [FMA83777:Subparietal sulcus]}. 83   The {hippocampal gyrus [FMA61918:Parahippocampal gyrus]} ({gyrus hippocampi [FMA61918:Parahippocampal gyrus]}) is bounded above by the {hippocampal fissure [FMA83747:Hippocampal sulcus]}, and below by the anterior part of the {collateral fissure [FMA83751:Collateral sulcus]}. Behind, it is continuous superiorly, through the isthmus, with the {cingulate gyrus [FMA62434:Cingulate gyrus]} and inferiorly with the {lingual gyrus [FMA61904:Lingual gyrus]}. Running in the substance of the cingulate and {hippocampal gyri [FMA61918:Parahippocampal gyrus]}, and connecting them together, is a tract of arched fibers, named the {cingulum [FMA56731:Cingulum of tooth]} (page 843). The anterior extremity of the {hippocampal gyrus [FMA61918:Parahippocampal gyrus]} is recurved in the form of a hook ({uncus [FMA74884:Uncus]}), which is separated from the apex of the {temporal lobe [FMA61825:Temporal lobe]} by a slight fissure, the {incisura [FMA74524:Anterior cerebellar incisure; FMA75036:Notch]} {temporalis [FMA49006:Temporalis]}. Although superficially continuous with the {hippocampal gyrus [FMA61918:Parahippocampal gyrus]}, the {uncus [FMA74884:Uncus]} forms morphologically a part of the {rhinencephalon [FMA62430:Paleocortex]}. 84   The {Hippocampal Fissure [FMA83747:Hippocampal sulcus]} (fissura {hippocampi [FMA62493:Hippocampus; FMA74038:Hippocampal formation]}; {dentate fissure [FMA83747:Hippocampal sulcus]}) begins immediately behind the {splenium of the corpus callosum [FMA61948:Splenium of corpus callosum]}, and runs forward between the {hippocampal [FMA62493:Hippocampus]} and {dentate gyri [FMA61922:Dentate gyrus of hippocampal formation]} to end in the {uncus [FMA74884:Uncus]}. It is a complete fissure (page 819), and gives rise to the prominence of the {hippocampus [FMA62493:Hippocampus; FMA74038:Hippocampal formation]} in the {inferior cornu of the lateral ventricle [FMA83701:Temporal horn of lateral ventricle]}. 85   {Rhinencephalon [FMA62430:Paleocortex]} (Fig. 732).—The {rhinencephalon [FMA62430:Paleocortex]} comprises the olfactory lobe, the {uncus [FMA74884:Uncus]}, the subcallosal and {supracallosal gyri [FMA61920:Supracallosal gyrus]}, the {fascia dentata hippocampi [FMA61922:Dentate gyrus of hippocampal formation]}, the {septum pellucidum [FMA61842:Septum of telencephalon; FMA61844:Septum pellucidum]}, the {fornix [FMA61965:Fornix of forebrain]}, and the {hippocampus [FMA62493:Hippocampus; FMA74038:Hippocampal formation]}. 86   1. The Olfactory Lobe ({lobus [FMA13367:Lobe of thyroid gland; FMA45728:Anatomical lobe]} olfactorius) is situated under the inferior or {orbital surface of the frontal lobe [FMA57406:Cerebral surface of orbital part of frontal bone]}. In many vertebrates it constitutes a well-marked portion of the hemisphere and contains an extension of the {lateral ventricle [FMA78448:Lateral ventricle]}; but in man and some other mammals it is rudimentary. It consists of the {olfactory bulb [FMA77624:Olfactory bulb]} and tract, the {olfactory trigone [FMA74883:Olfactory trigone]}, the {parolfactory area [FMA61890:Subcallosal area]} of Broca, and the {anterior perforated substance [FMA61891:Anterior perforated substance]}. 87   (a) The {olfactory bulb [FMA77624:Olfactory bulb]} ({bulbus olfactorius [FMA77624:Olfactory bulb]}) is an oval, reddish-gray mass which rests on the {cribriform plate [FMA52890:Cribriform plate]} of the {ethmoid [FMA52740:Ethmoid]} and forms the anterior expanded extremity of the {olfactory tract [FMA46787:Olfactory nerve]}. Its under surface receives the {olfactory nerves [FMA75450:Set of olfactory nerves]}, which pass upward through the {cribriform plate [FMA52890:Cribriform plate]} from the olfactory region of the {nasal cavity [FMA54378:Nasal cavity]}. Its minute structure is described on page 848. 88   (b) The {olfactory tract [FMA46787:Olfactory nerve]} ({tractus olfactorius [FMA77626:Olfactory tract]}) is a narrow white band, triangular on {coronal [FMA264717:Coronale]} section, the apex being directed upward. It lies in the {olfactory sulcus [FMA83769:Olfactory sulcus]} on the inferior {surface of the frontal lobe [FMA256267:Surface of frontal lobe]}, and divides posteriorly into two striæ, a medial and a lateral. The lateral stria is directed across the lateral part of the {anterior perforated substance [FMA61891:Anterior perforated substance]} and then bends abruptly medialward toward the {uncus [FMA74884:Uncus]} of the {hippocampal gyrus [FMA61918:Parahippocampal gyrus]}. The medial stria turns medialward behind the {parolfactory area [FMA61890:Subcallosal area]} and ends in the {subcallosal gyrus [FMA61919:Paraterminal gyrus]}; in some cases a small intermediate stria is seen running backward to the {anterior perforated substance [FMA61891:Anterior perforated substance]}. 89   (c) The {olfactory trigone [FMA74883:Olfactory trigone]} ({trigonum olfactorium [FMA74883:Olfactory trigone]}) is a small triangular area in front of the {anterior perforated substance [FMA61891:Anterior perforated substance]}. Its apex, directed forward, occupies the posterior part of the {olfactory sulcus [FMA83769:Olfactory sulcus]}, and is brought into view by throwing {back [FMA24205:Surface of back]} the {olfactory tract [FMA46787:Olfactory nerve]}. 90   (d) The {parolfactory area [FMA61890:Subcallosal area]} of Broca ({area parolfactoria [FMA61890:Subcallosal area]}) is a small triangular field on the medial surface of the hemisphere in front of the {subcallosal gyrus [FMA61919:Paraterminal gyrus]}, from which it is separated by the {posterior parolfactory sulcus [FMA83745:Posterior parolfactory sulcus]}; it is continuous below with the {olfactory trigone [FMA74883:Olfactory trigone]}, and above and in front with the {cingulate gyrus [FMA62434:Cingulate gyrus]}; it is limited anteriorly by the {anterior parolfactory sulcus [FMA83744:Anterior parolfactory sulcus]}. 91   (e) The {anterior perforated substance [FMA61891:Anterior perforated substance]} ({substantia perforata anterior [FMA61891:Anterior perforated substance]}) is an irregularly quadrilateral area in front of the {optic tract [FMA62046:Optic tract]} and behind the {olfactory trigone [FMA74883:Olfactory trigone]}, from which it is separated by the {fissure prima [FMA83729:Primary fissure of cerebellum]}; medially and in front it is continuous with the {subcallosal gyrus [FMA61919:Paraterminal gyrus]}; laterally it is bounded by the lateral stria of the {olfactory tract [FMA46787:Olfactory nerve]} and is continued into the {uncus [FMA74884:Uncus]}. Its {gray substance [FMA67242:Gray matter of neuraxis]} is confluent above with that of the {corpus striatum [FMA77616:Corpus striatum]}, and is perforated anteriorly by numerous small bloodvessels. 92   2. The {Uncus [FMA74884:Uncus]} has already been described (page 826) as the recurved, hook-like portion of the {hippocampal gyrus [FMA61918:Parahippocampal gyrus]}. 93   3. The Subcallosal, Supracallosal, and {Dentate Gyri [FMA61922:Dentate gyrus of hippocampal formation]} form a rudimentary arch-shaped lamina of {gray substance [FMA67242:Gray matter of neuraxis]} extending over the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]} and above the {hippocampal gyrus [FMA61918:Parahippocampal gyrus]} from the {anterior perforated substance [FMA61891:Anterior perforated substance]} to the {uncus [FMA74884:Uncus]}. 94   (a) The {subcallosal gyrus [FMA61919:Paraterminal gyrus]} ({gyrus subcallosus [FMA61919:Paraterminal gyrus]}; peduncle of the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]}) is a narrow lamina on the medial surface of the hemisphere in front of the {lamina terminalis [FMA61975:Lamina terminalis]}, behind the {parolfactory area [FMA61890:Subcallosal area]}, and below the {rostrum of the corpus callosum [FMA61945:Rostrum of corpus callosum; FMA61946:Genu of corpus callosum]}. It is continuous around the {genu of the corpus callosum [FMA61946:Genu of corpus callosum]} with the {supracallosal gyrus [FMA61920:Supracallosal gyrus]}. 95   (b) The {supracallosal gyrus [FMA61920:Supracallosal gyrus]} ({indusium griseum [FMA62488:Induseum griseum]}; gyrus epicallosus) consists of a thin layer of {gray substance [FMA67242:Gray matter of neuraxis]} in contact with the upper surface of the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]} and continuous laterally with the {gray substance [FMA67242:Gray matter of neuraxis]} of the {cingulate gyrus [FMA62434:Cingulate gyrus]}. It contains two longitudinally directed strands of fibers termed respectively the medial and {lateral longitudinal stri [FMA62439:Lateral longitudinal stria]}æ. The {supracallosal gyrus [FMA61920:Supracallosal gyrus]} is prolonged around the {splenium of the corpus callosum [FMA61948:Splenium of corpus callosum]} as a delicate lamina, the {fasciola cinerea [FMA61921:Fasciolar gyrus]}, which is continuous below with the {fascia dentata hippocampi [FMA61922:Dentate gyrus of hippocampal formation]}. 96   (c) The {fascia dentata hippocampi [FMA61922:Dentate gyrus of hippocampal formation]} ({gyrus dentatus [FMA61922:Dentate gyrus of hippocampal formation]}) is a narrow band extending downward and forward above the {hippocampal gyrus [FMA61918:Parahippocampal gyrus]} but separated from it by the {hippocampal fissure [FMA83747:Hippocampal sulcus]}; its free margin is notched and overlapped by the fimbria—the {fimbriodentate fissure [FMA83728:Fimbriodentate fissure]} intervening. Anteriorly it is continued into the {notch [FMA75036:Notch]} of the {uncus [FMA74884:Uncus]}, where it forms a sharp bend and is then prolonged as a delicate band, the band of Giacomini, over the {uncus [FMA74884:Uncus]}, on the lateral surface of which it is lost. 97   The remaining parts of the {rhinencephalon [FMA62430:Paleocortex]}, viz., the {septum pellucidum [FMA61842:Septum of telencephalon; FMA61844:Septum pellucidum]}, {fornix [FMA61965:Fornix of forebrain]}, and {hippocampus [FMA62493:Hippocampus; FMA74038:Hippocampal formation]}, will be described in connection with the {lateral ventricle [FMA78448:Lateral ventricle]}. 98   Interior of the {Cerebral Hemispheres [FMA61817:Cerebral hemisphere]}.—If the upper part of either hemisphere be removed, at a level about 1.25 cm. above the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]}, the central {white substance [FMA83929:White matter of neuraxis]} will be exposed as an oval-shaped area, the {centrum ovale [FMA61939:Semioval center]} minus, surrounded by a narrow convoluted margin of {gray substance [FMA67242:Gray matter of neuraxis]}, and studded with numerous minute red dots (puncta vasculosa), produced by the escape of blood from divided {blood [FMA9670:Portion of blood]}vessels. If the remaining portions of the hemispheres be slightly drawn apart a broad band of {white substance [FMA83929:White matter of neuraxis]}, the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]}, will be observed, connecting them at the bottom of the {longitudinal fissure [FMA83727:Longitudinal fissure]}; the margins of the hemispheres which overlap the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]} are called the labia {cerebri [FMA62000:Telencephalon]}. Each labrium is part of the {cingulate gyrus [FMA62434:Cingulate gyrus]} already described; and the slit-like interval between it and the upper surface of the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]} is termed the callosal fissure (Fig. 727). If the hemispheres be sliced off to a level with the upper surface of the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]}, the {white substance [FMA83929:White matter of neuraxis]} of that structure will be seen connecting the two hemispheres. The large expanse of medullary matter now exposed, surrounded by the convoluted margin of {gray substance [FMA67242:Gray matter of neuraxis]}, is called the {centrum ovale [FMA61939:Semioval center]} majus. 99   The {Corpus Callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]} (Fig. 733) is the great transverse commissure which unites the {cerebral hemispheres [FMA61817:Cerebral hemisphere]} and roofs in the {lateral ventricles [FMA78448:Lateral ventricle]}. A good conception of its position and size is obtained by examining a median sagittal section of the {brain [FMA50801:Brain]} (Fig. 720), when it is seen to form an arched structure about 10 cm. long. Its anterior end is about 4 cm. from the {frontal pole [FMA71028:Frontal pole (FP); FMA74885:Frontal pole]}, and its posterior end about 6 cm. from the {occipital pole [FMA71036:Occipital pole (OP); FMA74892:Occipital pole]} of the hemisphere. 100