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 * In a median sagittal section (Fig. 720) the cut corpus callosum presents the appearance of a broad, arched band. Its thick posterior end, termed the splenium, overlaps the mid-brain, but is separated from it by the tela chorioidea of the third ventricle and the pineal body. Its anterior curved end, termed the genu, gradually tapers into a thinner portion, the rostrum, which is 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 laminæ and cavity of the septum pellucidum.	  41
 * Surfaces of the Cerebral Hemispheres.—Each hemisphere presents three surfaces: lateral, medial, and inferior.	  42
 * 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 falx cerebri. The inferior surface is of an irregular 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 medialward as well as downward, and is named 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) supero-medial, between the lateral and medial surfaces; (b) infero-lateral, between the lateral and inferior surfaces; the anterior part of this border separating the lateral from the orbital surface, is known as the superciliary 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, the occipital pole; and the anterior end of the temporal lobe, the temporal pole. About 5 cm. in front of the occipital pole on the infero-lateral border is an indentation or notch, named the preoccipital notch.	  44
 * The surfaces of the hemispheres are moulded into a number of irregular eminences, named gyri or convolutions, and separated by furrows termed fissures and sulci. The furrows are of two kinds, complete and incomplete. The former appear early in fetal life, are few in number, and are produced by infoldings of the entire thickness of the brain wall, and give rise to 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.	  45
 * 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 of a great increase 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.	  46
 * 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, parietoöccipital, calcarine, and collateral fissures, the central and cingulate sulci, and the sulcus circularis.
 * The Lateral Cerebral Fissure (fissura cerebri lateralis [Sylvii]; fissure of Sylvius) (Fig. 726) is a well-marked cleft on the inferior and lateral surfaces of the hemisphere, and consists of a short stem which divides into three rami. The stem is situated on 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 rami: an anterior horizontal, an anterior ascending, and a posterior. The anterior horizontal ramus passes foward for about 2.5 cm. into the inferior frontal gyrus, while the anterior ascending ramus extends upward into the same convolution for about an equal distance. The posterior ramus is the longest; it runs backward and slightly upward for about 7 cm., and ends by an upward inflexion in the parietal lobe.	  48
 * The Central Sulcus (sulcus centralis [Rolandi]; fissure of Rolando; central fissure) (Figs. 725, 726) 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 mid-point. It runs sinuously downward and forward, and ends a little above the posterior ramus of the lateral fissure, and about 2.5 cm. behind the anterior ascending ramus of the same fissure. It described two chief curves: a superior genu with its concavity directed forward, and an inferior genu with its concavity directed backward. The central sulcus forms an angle opening forward of about 70° with the median plane.	  49
 * The Parietoöccipital Fissure (fissura parietoöccipitalis).—Only a small part of this fissure is seen on the lateral surface of the hemisphere, its chief part being on the medial surface.	  50
 * The lateral part of the parietoöccipital fissure (Fig. 726) is situated about 5 cm. in front of the occipital pole of the hemisphere, and measures about 1.25 cm. in length.
 * The medial part of the parietoöccipital fissure (Fig. 727) 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 a submerged gyrus.	  52
 * The Calcarine Fissure (fissura calcarina) (Fig. 727) is on the medial surface of the hemisphere. It begins near the occipital pole in two 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 parietoöccipital fissure. The anterior part of this fissure gives rise to the prominence of the calcar avis in the posterior cornu of the lateral ventricle.	  53
 * The Cingulate Sulcus (sulcus cinguli; callosomarginal fissure) (Fig. 727) 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 supero-medial border of the hemisphere a short distance behind the upper end of the central sulcus. It separates the superior frontal from the cingulate gyrus.	  54
 * The Collateral Fissure (fissura collateralis) (Fig. 727) 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 calcarine fissure, from which it is separated by the lingual gyrus; in front, it is situated between the hippocampal gyrus and the anterior part of the fusiform gyrus.	  55
 * The Sulcus Circularis (circuminsular fissure) (Fig. 731) is on the lower and lateral surfaces of the hemisphere: it surrounds the insula and separates it from the frontal, parietal, and temporal lobes.	  56
 * 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.	  57
 * Frontal Lobe (lobus 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 (Fig. 726) is tranversed by three sulci which divide it 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.	  59
 * The anterior central gyrus (gyrus centralis anterior; ascending frontal convolution; precentral gyre) is bounded in front by the precentral sulcus, behind by the central sulcus; it extends from the supero-medial border of the hemisphere to the posterior ramus of the lateral fissure.	  60