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http://rgm22.nig.ac.jp/mediawiki-ogareport/index.php/For_Gray_anatomy_normalization
 * The internal capsule (capsula interna) (Figs. 745, 746) 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 (Figs. 742) 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.	  121
 * The frontal part of the internal capsule contains: (1) fibers running from the thalamus to the frontal lobe; (2) fibers connecting the lentiform and caudate nuclei; (3) fibers connecting the 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 nuclei pontis. 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 cerebrospinal fibers, undergo decussation and end in the motor nuclei of the cranial nerves of the opposite side. The anterior two-thirds of the occipital part of the internal capsule contains the cerebrospinal 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 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.	  122
 * 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 (Fig. 745) and intermingling with the fibers of the corpus callosum.	  123
 * The external capsule (capsula externa) (Fig. 742) is a lamina of white substance, situated lateral to the lentiform nucleus, between it and the claustrum, and continuous with the internal capsule below and behind the lentiform nucleus. It probably contains fibers derived from the thalamus, the anterior commissure, and the subthalamic region.
 * The substantia innominata of Meynert 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 the ansa lentiformis, and its fibers, derived from the medullary lamina of the lentiform nucleus, pass medially to end in the thalamus and subthalamic 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 the insula.	  125
 * The stria terminalis (tænia 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 septum pellucidum, while others are said to enter the caudate nucleus. Posteriorly, it is continued into the roof of the inferior cornu of the lateral ventricle, at the extremity of which it enters the nucleus amygdalæ. 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 choroid plexus to form the corresponding internal cerebral vein. On the surface of the terminal vein is a narrow white band, named the lamina affixa.	  126
 * The Fornix (Figs. 720, 747, 748) 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 pellucidum. It may be described as 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 fornicis) of the fornix is triangular, narrow in front, and broad behind. The medial part of its upper surface is connected to the septum pellucidum 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 choroid plexus, and is continuous with the epithelial covering of this structure. The under surface rests upon the tela chorioidea 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 thalami. Below, the lateral portions of the body of the fornix are joined by a thin triangular lamina, named the psalterium (lyra). This lamina contains some transverse fibers which connect the two hippocampi across the middle line and constitute the hippocampal commissure. Between the psalterium and the corpus callosum a horizontal cleft, the so-called ventricle of the fornix (ventricle of Verga), is sometimes found.	  128
 * The columns (columna fornicis; anterior pillars; fornicolumns) of the fornix arch downward in front of the interventricular 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 thalamomammillary fasciculus (bundle of Vicq d’Azyr) takes origin and is prolonged into the anterior nucleus of the thalamus. The column of the fornix and the thalamomammillary 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 joined by the stria medullaris of the pineal body and by the superficial fibers of the stria terminalis, and is said to receive also fibers from the septum pellucidum. Zuckerkandl describes an olfactory fasciculus which becomes detached from the main portion of the column 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 subcallosal gyrus, and through it reaches the hippocampal gyrus.	  129
 * The crura (crus fornicis; posterior pillars) of the fornix are prolonged backward from the body. They are flattened bands, and at their commencement are intimately connected with the under surface of the corpus callosum. Diverging from one another, each curves around the posterior end of the thalamus, and passes downward and forward into the inferior cornu of the lateral ventricle (Fig. 750). Here it lies along the concavity of the hippocampus, on the surface of 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) (page 827), from which it is separated by the fimbriodentate fissure; from its lateral margin, which is thin and ragged, the ventricular epithelium is reflected over the choroid plexus as the latter projects into the chorioidal fissure.	  130
 * Interventricular Foramen (foramen of Monro).—Between the columns of the fornix and the anterior ends of the thalami, an oval 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 choroid plexuses of the lateral ventricles are joined across the middle line.	  131
 * The Anterior Commissure (precommissure) is a bundle of white fibers, connecting the two cerebral hemispheres across the middle line, and placed in front of the columns of the fornix. On sagittal section it is oval in shape, its long diameter being vertical and measuring about 5 mm. Its fibers can be traced lateralward and backward on either side beneath the corpus striatum into the substance of the temporal lobe. It serves in this way to connect the two temporal lobes, but it also contains decussating fibers from the olfactory tracts.	  132
 * The Septum Pellucidum (septum lucidum) (Fig. 720) is a thin, vertically placed partition consisting of two laminæ, separated in the greater part of their extent by a narrow chink or interval, the cavity of the septum pellucidum. It is attached, above, to the under surface of the corpus callosum; below, to the anterior part of the fornix behind, and the reflected portion of the corpus callosum 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 lamina is directed toward the body and anterior cornu of the lateral ventricle, and is covered by the ependyma of that cavity.	  133
 * The cavity of the septum pellucidum (cavum septi pellucidi; pseudocele; fifth ventricle) is generally regarded as part of the longitudinal cerebral fissure, which has become shut off by the union of the hemispheres in the formation of the corpus callosum 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 with that of the cerebral hemispheres. This cavity is not developed from the cavity of the cerebral vesicles, and never communicates with the ventricles of the brain.	  134
 * The Choroid Plexus of the Lateral Ventricle (plexus chorioideus ventriculus lateralis; paraplexus) (Fig. 750) 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 fringed margin of a triangular process of pia mater, named the tela chorioidea of the third ventricle, and projects from under cover of the lateral edge of the fornix. It lies upon the upper surface of the thalamus, from which the epithelium is reflected over the plexus on to the edge of the fornix (Fig. 723). The 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 on to the roof of the cornu (Fig. 749). It consists of minute and highly vascular villous processes, each with an afferent and an efferent vessel. The arteries of the plexus are: (a) the anterior choroidal, a branch of the internal carotid, which enters the plexus at the end of the inferior cornu; and (b) the posterior choroidal, one or two small branches of the posterior cerebral, which pass forward under the splenium. The veins of the choroid 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 internal cerebral vein.
 * When the choroid plexus is pulled away, the continuity between its epithelial covering and the epithelial lining of the ventricle is severed, and a cleft-like space is produced. This is named the choroidal fissure; like the plexus, it extends from the interventricular foramen to the end of the inferior cornu. The upper part of the fissure, i.e., 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 it 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 the stria terminalis in the roof of the cornu.	  136
 * The tela chorioidea of the third ventricle (tela chorioidea ventriculi tertii; velum interpositum) (Fig. 750) 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 corpora quadrigemina and pineal body below. This interval, together with the lower portions of the choroidal fissures, is sometimes spoken of as the transverse fissure of the brain. At its base the two layers of the velum 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 choroid plexuses of the lateral ventricles. It is supplied by the anterior and posterior choroidal arteries already described, The veins of the tela chorioidea are named the internal cerebral veins (venæ Galeni); 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 choroidal vein. The internal cerebral veins unite posteriorly in a single trunk, the great cerebral vein (vena magna Galeni), which passes backward beneath the splenium and ends in the straight sinus.
 * Structure of the Cerebral Hemispheres.—The cerebral hemispheres are composed of gray and white substance: the former covers their surface, and is termed the cortex; the latter occupies the interior of the hemispheres.	  138
 * The white substance consists of medullated 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. (1) Projection fibers connect the hemisphere with the lower parts of the brain and with the medulla spinalis. (2) Transverse or commissural fibers unite the two hemispheres. (3) 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.	  139
 * 1. The projection fibers consist of efferent and afferent fibers uniting the cortex with the lower parts of the brain and with the medulla spinalis. The principal efferent strands are: (1) the motor tract, occupying the genu and anterior two-thirds of the occipital part of the internal capsule, and consisting of (a) the geniculate fibers, which decussate and end in the motor nuclei of 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: (2) the corticopontine fibers, ending in the nuclei pontis. The chief afferent fibers are: (1) those of the lemniscus which are not interrupted in the thalamus; (2) those of the superior cerebellar peduncle which are not interrupted in the red nucleus and thalamus; (3) numerous fibers arising within the thalamus, and passing through its stalks to the different parts of the cortex (page 810); (4) optic and acoustic fibers, the former passing to the occipital, the latter to the temporal lobe.	  140

after
The {internal capsule [FMA61950:Internal capsule]} ({capsula interna [FMA61950:Internal capsule; FMA61952:Anterior limb of internal capsule; FMA61954:Posterior limb of internal capsule]}) (Figs. 745, 746) is a flattened band of white fibers, between the {lentiform nucleus [FMA77615:Lentiform nucleus]} on the lateral side and the {caudate nucleus [FMA61833:Caudate nucleus]} and {thalamus [FMA62007:Thalamus]} on the medial side. In horizontal section (Figs. 742) it is seen to be somewhat abruptly curved, with its convexity inward; the prominence of the curve is called the {genu [FMA24974:Knee]}, and projects between the {caudate nucleus [FMA61833:Caudate nucleus]} and the {thalamus [FMA62007:Thalamus]}. The portion in front of the {genu [FMA24974:Knee]} is termed the {frontal [FMA46757:Frontalis]} part, and separates the lentiform from the {caudate nucleus [FMA61833:Caudate nucleus]}; the portion behind the {genu [FMA24974:Knee]} is the occipital part, and separates the {lentiform nucleus [FMA77615:Lentiform nucleus]} from the {thalamus [FMA62007:Thalamus]}. 121   The {frontal [FMA46757:Frontalis]} part of the {internal capsule [FMA61950:Internal capsule]} contains: (1) fibers running from the {thalamus [FMA62007:Thalamus]} to the {frontal lobe [FMA61824:Frontal lobe]}; (2) fibers connecting the lentiform and {caudate nuclei [FMA61833:Caudate nucleus]}; (3) fibers connecting the {cortex [FMA15632:Adrenal cortex; FMA61109:Cortex]} with the {corpus striatum [FMA77616:Corpus striatum]}; and (4) fibers passing from the {frontal lobe [FMA61824:Frontal lobe]} through the medial fifth of the {base of the cerebral peduncle [FMA242166:Base of midbrain peduncle]} to the {nuclei pontis [FMA72512:Pontine nuclear group]}. The fibers in the region of the {genu [FMA24974:Knee]} are named the {geniculate fibers [FMA61953:Genu of internal capsule]}; they originate in the motor part of the {cerebral cortex [FMA61830:Cerebral cortex]}, and, after passing downward through the {base of the cerebral peduncle [FMA242166:Base of midbrain peduncle]} with {the cerebrospinal fibers [FMA265580:Corticospinal tract]}, undergo decussation and end in the motor nuclei of the {cranial nerves [FMA63820:Set of cranial nerves]} of the opposite side. The anterior two-thirds of {the occipital part of the internal capsule [FMA61954:Posterior limb of internal capsule]} contains {the cerebrospinal fibers [FMA265580:Corticospinal tract]}, which arise in the motor area of the {cerebral cortex [FMA61830:Cerebral cortex]} and, passing downward through the middle three-fifths of the {base of the cerebral peduncle [FMA242166:Base of midbrain peduncle]}, are continued into the {pyramids of the medulla oblongata [FMA75254:Pyramid of medulla]}. The posterior third of the occipital part contains: (1) sensory fibers, largely derived from the {thalamus [FMA62007:Thalamus]}, though some may be continued upward from the {medial lemniscus [FMA83675:Medial lemniscus]}; (2) the fibers of {optic radiation [FMA61941:Optic radiation]}, from the lower visual centers to the {cortex of the occipital lobe [FMA242205:Cortex of occipital lobe]}; (3) acoustic fibers, from the {lateral lemniscus [FMA72502:Lateral lemniscus]} to the {temporal lobe [FMA61825:Temporal lobe]}; and (4) fibers which pass from the occipital and {temporal lobes [FMA61825:Temporal lobe]} to the {nuclei pontis [FMA72512:Pontine nuclear group]}. 122   The fibers of the {internal capsule [FMA61950:Internal capsule]} radiate widely as they pass to and from the various parts of the {cerebral cortex [FMA61830:Cerebral cortex]}, forming the {corona radiata [FMA18661:Corona radiata]} (Fig. 745) and intermingling with the fibers of the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]}. 123   The {external capsule [FMA61959:External capsule]} ({capsula externa [FMA61959:External capsule]}) (Fig. 742) is a lamina of {white substance [FMA83929:White matter of neuraxis]}, situated lateral to the {lentiform nucleus [FMA77615:Lentiform nucleus]}, between it and the {claustrum [FMA67440:Claustrum]}, and continuous with the {internal capsule [FMA61950:Internal capsule]} below and behind the {lentiform nucleus [FMA77615:Lentiform nucleus]}. It probably contains fibers derived from the {thalamus [FMA62007:Thalamus]}, the {anterior commissure [FMA61961:Anterior commissure]}, and the {subthalamic region [FMA62010:Subthalamus]}. The {substantia innominata of Meynert [FMA61885:Substantia innominata]} is a stratum consisting partly of gray and partly of {white substance [FMA83929:White matter of neuraxis]}, which lies below the anterior part of the {thalamus [FMA62007:Thalamus]} and {lentiform nucleus [FMA77615:Lentiform nucleus]}. It consists of three layers, superior, middle, and inferior. The superior layer is named the ansa lentiformis, and its fibers, derived from the medullary lamina of the {lentiform nucleus [FMA77615:Lentiform nucleus]}, pass medially to end in the {thalamus [FMA62007:Thalamus]} and {subthalamic region [FMA62010:Subthalamus]}, while others are said to end in the tegmentum and {red nucleus [FMA62407:Red nucleus]}. The middle layer consists of {nerve cells [FMA54527:Neuron]} and {nerve fibers [FMA5914:Nerve fiber]}; fibers enter it from the {parietal lobe [FMA61826:Parietal lobe]} through the {external capsule [FMA61959:External capsule]}, while others are said to connect it with the {medial longitudinal fasciculus [FMA83846:Medial longitudinal fasciculus]}. The inferior layer forms the main part of the inferior stalk of the {thalamus [FMA62007:Thalamus]}, and connects this body with the {temporal lobe [FMA61825:Temporal lobe]} and the {insula [FMA67329:Insula]}. 125   The {stria terminalis [FMA61974:Stria terminalis]} (tænia semicircularis) is a narrow band of {white substance [FMA83929:White matter of neuraxis]} situated in the depression between the {caudate nucleus [FMA61833:Caudate nucleus]} and the {thalamus [FMA62007:Thalamus]}. Anteriorly, its fibers are partly continued into the {column of the fornix [FMA61968:Body of fornix of forebrain]}; some, however, pass over the {anterior commissure [FMA61961:Anterior commissure]} to the {gray substance [FMA67242:Gray matter of neuraxis]} between the {caudate nucleus [FMA61833:Caudate nucleus]} and {septum pellucidum [FMA61842:Septum of telencephalon; FMA61844:Septum pellucidum]}, while others are said to enter the {caudate nucleus [FMA61833:Caudate nucleus]}. Posteriorly, it is continued into the roof of the {inferior cornu of the lateral ventricle [FMA83701:Temporal horn of lateral ventricle]}, at the extremity of which it enters the {nucleus amygdalæ [FMA61841:Amygdala]}. Superficial to it is a large {vein [FMA50723:Vein]}, the {terminal vein [FMA50997:Superior thalamostriate vein]} ({vein [FMA50723:Vein]} of the {corpus striatum [FMA77616:Corpus striatum]}), which receives numerous tributaries from the {corpus striatum [FMA77616:Corpus striatum]} and {thalamus [FMA62007:Thalamus]}; it runs forward to the {interventricular foramen [FMA75351:Interventricular foramen]} and there joins with the {vein [FMA50723:Vein]} of the {choroid plexus [FMA61934:Choroid plexus of cerebral hemisphere]} to form the corresponding {internal cerebral vein [FMA51003:Internal cerebral vein]}. On the surface of the {terminal vein [FMA50997:Superior thalamostriate vein]} is a narrow white band, named the {lamina affixa [FMA83709:Lamina affixa]}. 126   The {Fornix [FMA61965:Fornix of forebrain]} (Figs. 720, 747, 748) is a longitudinal, arch-shaped lamella of {white substance [FMA83929:White matter of neuraxis]}, situated below the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]}, and continuous with it behind, but separated from it in front by the {septum pellucidum [FMA61842:Septum of telencephalon; FMA61844:Septum pellucidum]}. It may be described as 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 [FMA61968:Body of fornix of forebrain]}; the intermediate united portions, the body; and the posterior parts, the crura. The {body (corpus fornicis) of the fornix [FMA61968:Body of fornix of forebrain]} is triangular, narrow in front, and broad behind. The medial part of its upper surface is connected to the {septum pellucidum [FMA61842:Septum of telencephalon; FMA61844:Septum pellucidum]} in front and to the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]} behind. The lateral portion of this surface forms part of the floor of the {lateral ventricle [FMA78448:Lateral ventricle]}, and is covered by the ventricular {epithelium [FMA9639:Portion of epithelium]}. Its lateral edge overlaps the {choroid plexus [FMA61934:Choroid plexus of cerebral hemisphere]}, and is continuous with the epithelial covering of this structure. The under surface rests upon the {tela chorioidea of the third ventricle [FMA78463:Tela choroidea of third ventricle]}, which separates it from the epithelial roof of that cavity, and from the medial portions of the upper surfaces of the {thalami [FMA62007:Thalamus]}. Below, the lateral portions of the {body of the fornix [FMA61968:Body of fornix of forebrain]} are joined by a thin triangular lamina, named the psalterium (lyra). This lamina contains some transverse fibers which connect the two {hippocampi [FMA62493:Hippocampus; FMA74038:Hippocampal formation]} across the middle line and constitute the {hippocampal commissure [FMA61970:Commissure of fornix of forebrain]}. Between the psalterium and the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]} a horizontal cleft, the so-called ventricle of the {fornix [FMA61965:Fornix of forebrain]} (ventricle of Verga), is sometimes found. 128   The {columns (columna fornicis; anterior pillars; fornicolumns) of the fornix [FMA61968:Body of fornix of forebrain]} arch downward in front of the {interventricular foramen [FMA75351:Interventricular foramen]} and behind the {anterior commissure [FMA61961:Anterior commissure]}, and each descends through the {gray substance [FMA67242:Gray matter of neuraxis]} in the lateral {wall of the third ventricle [FMA242776:Wall of third ventricle]} to the {base of the brain [FMA77700:Basal forebrain]}, where it ends in the {corpus mammillare [FMA74877:Mammillary body]}. From the cells of the {corpus mammillare [FMA74877:Mammillary body]} the {thalamomammillary fasciculus [FMA83849:Mammillothalamic tract]} ({bundle of Vicq d’Azyr [FMA83849:Mammillothalamic tract]}) takes origin and is prolonged into the {anterior nucleus of the thalamus [FMA62019:Anterior nuclear group of thalamus]}. The {column of the fornix [FMA61968:Body of fornix of forebrain]} and the {thalamomammillary fasciculus [FMA83849:Mammillothalamic tract]} together form a loop resembling the figure 8, but the continuity of the loop is broken in the {corpus mammillare [FMA74877:Mammillary body]}. The {column of the fornix [FMA61968:Body of fornix of forebrain]} is joined by the {stria medullaris [FMA62080:Stria medullaris of thalamus]} of the {pineal body [FMA62033:Pineal body]} and by the superficial fibers of the {stria terminalis [FMA61974:Stria terminalis]}, and is said to receive also fibers from the {septum pellucidum [FMA61842:Septum of telencephalon; FMA61844:Septum pellucidum]}. Zuckerkandl describes an {olfactory fasciculus [FMA61973:Diagonal band]} which becomes detached from the main portion of the {column of the fornix [FMA61968:Body of fornix of forebrain]}, and passes downward in front of the {anterior commissure [FMA61961:Anterior commissure]} to the {base of the brain [FMA77700:Basal forebrain]}, where it divides into two bundles, one joining the medial stria of the {olfactory tract [FMA46787:Olfactory nerve]}; the other joins the {subcallosal gyrus [FMA61919:Paraterminal gyrus]}, and through it reaches the {hippocampal gyrus [FMA61918:Parahippocampal gyrus]}. 129   The crura ({crus fornicis [FMA61969:Posterior column of fornix of forebrain]}; posterior pillars) of the {fornix [FMA61965:Fornix of forebrain]} are prolonged backward from the body. They are flattened bands, and at their commencement are intimately connected with the under surface of the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]}. Diverging from one another, each curves around the posterior end of the {thalamus [FMA62007:Thalamus]}, and passes downward and forward into the {inferior cornu of the lateral ventricle [FMA83701:Temporal horn of lateral ventricle]} (Fig. 750). Here it lies along the concavity of the {hippocampus [FMA62493:Hippocampus; FMA74038:Hippocampal formation]}, on the surface of which some of its fibers are spread out to form the {alveus [FMA83867:Alveus of hippocampus]}, while the remainder are continued as a narrow white band, the {fimbria hippocampi [FMA83866:Fimbria of hippocampus]}, which is prolonged into the {uncus [FMA74884:Uncus]} of the {hippocampal gyrus [FMA61918:Parahippocampal gyrus]}. The inner edge of the fimbria overlaps the {fascia dentata hippocampi [FMA61922:Dentate gyrus of hippocampal formation]} ({dentate gyrus [FMA61922:Dentate gyrus of hippocampal formation]}) (page 827), from which it is separated by the {fimbriodentate fissure [FMA83728:Fimbriodentate fissure]}; from its lateral margin, which is thin and ragged, the ventricular {epithelium [FMA9639:Portion of epithelium]} is reflected over the {choroid plexus [FMA61934:Choroid plexus of cerebral hemisphere]} as the latter projects into the chorioidal fissure. 130   {Interventricular Foramen [FMA75351:Interventricular foramen]} ({foramen of Monro [FMA75351:Interventricular foramen]}).—Between the {columns of the fornix [FMA61968:Body of fornix of forebrain]} and the anterior ends of the {thalami [FMA62007:Thalamus]}, an oval aperture is present on either side: this is the {interventricular foramen [FMA75351:Interventricular foramen]}, and through it the {lateral ventricles [FMA78448:Lateral ventricle]} communicate with the {third ventricle [FMA78454:Third ventricle]}. Behind the epithelial lining of the foramen the {choroid plexuses of the lateral ventricles [FMA83711:Choroid plexus of lateral ventricle]} are joined across the middle line. 131   The {Anterior Commissure [FMA61961:Anterior commissure]} (precommissure) is a bundle of white fibers, connecting the two {cerebral hemispheres [FMA61817:Cerebral hemisphere]} across the middle line, and placed in front of the {columns of the fornix [FMA61968:Body of fornix of forebrain]}. On sagittal section it is oval in shape, its long diameter being vertical and measuring about 5 mm. Its fibers can be traced lateralward and backward on either side beneath the {corpus striatum [FMA77616:Corpus striatum]} into the substance of the {temporal lobe [FMA61825:Temporal lobe]}. It serves in this way to connect the two {temporal lobes [FMA61825:Temporal lobe]}, but it also contains decussating fibers from the {olfactory tracts [FMA46787:Olfactory nerve]}. 132   The {Septum Pellucidum [FMA61842:Septum of telencephalon; FMA61844:Septum pellucidum]} ({septum lucidum [FMA61844:Septum pellucidum]}) (Fig. 720) is a thin, vertically placed partition consisting of two laminæ, separated in the greater part of their extent by a narrow chink or interval, the {cavity of the septum pellucidum [FMA61874:Cave of septum pellucidum]}. It is attached, above, to the under surface of the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]}; below, to the anterior part of the {fornix [FMA61965:Fornix of forebrain]} behind, and the reflected portion of the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]} in front. It is triangular in form, broad in front and narrow behind; its {inferior angle [FMA13315:Inferior angle of scapula]} corresponds with the upper part of the {anterior commissure [FMA61961:Anterior commissure]}. The lateral surface of each {lamina is [FMA242259:Plexiform layer of cerebral cortex]} directed toward the body and anterior cornu of the {lateral ventricle [FMA78448:Lateral ventricle]}, and is covered by the {ependyma [FMA242791:Ependyma of neuraxis]} of that cavity. 133   The {cavity of the septum pellucidum [FMA61874:Cave of septum pellucidum]} ({cavum septi pellucidi [FMA61874:Cave of septum pellucidum]}; pseudocele; {fifth ventricle [FMA61874:Cave of septum pellucidum]}) is generally regarded as part of the {longitudinal cerebral fissure [FMA83727:Longitudinal fissure]}, which has become shut off by the union of the hemispheres in the formation of the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]} above and the {fornix [FMA61965:Fornix of forebrain]} 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 [FMA67242:Gray matter of neuraxis]}, derived from that of the {cortex [FMA15632:Adrenal cortex; FMA61109:Cortex]}, and a lateral layer of {white substance [FMA83929:White matter of neuraxis]} continuous with that of the {cerebral hemispheres [FMA61817:Cerebral hemisphere]}. This cavity is not developed from the cavity of the cerebral vesicles, and never communicates with the {ventricles of the brain [FMA78447:Region of ventricular system of brain]}. 134   The {Choroid Plexus of the Lateral Ventricle [FMA83711:Choroid plexus of lateral ventricle]} (plexus chorioideus {ventriculus lateralis [FMA74520:Frontal horn of lateral ventricle; FMA83700:Occipital horn of lateral ventricle; FMA83701:Temporal horn of lateral ventricle; FMA83703:Body of lateral ventricle]}; paraplexus) (Fig. 750) is a highly vascular, fringe-like process of {pia mater [FMA9590:Pia mater]}, which projects into the {ventricular cavity [FMA13238:Cavity of ventricle]}. The plexus, however, is everywhere covered by a layer of {epithelium [FMA9639:Portion of epithelium]} continuous with the epithelial lining of the ventricle. It extends from the {interventricular foramen [FMA75351:Interventricular foramen]}, where it is joined with the plexus of the opposite ventricle, to the end of the {inferior cornu [FMA83701:Temporal horn of lateral ventricle]}. The part in relation to the body of the ventricle forms the vascular fringed margin of a triangular process of {pia mater [FMA9590:Pia mater]}, named the {tela chorioidea of the third ventricle [FMA78463:Tela choroidea of third ventricle]}, and projects from under cover of the lateral edge of the {fornix [FMA61965:Fornix of forebrain]}. It lies upon the upper surface of the {thalamus [FMA62007:Thalamus]}, from which the {epithelium [FMA9639:Portion of epithelium]} is reflected over the plexus on to the edge of the {fornix [FMA61965:Fornix of forebrain]} (Fig. 723). The portion in relation to the {inferior cornu [FMA83701:Temporal horn of lateral ventricle]} lies in the concavity of the {hippocampus [FMA62493:Hippocampus; FMA74038:Hippocampal formation]} and overlaps the {fimbria hippocampi [FMA83866:Fimbria of hippocampus]}: from the lateral edge of the fimbria the {epithelium [FMA9639:Portion of epithelium]} is reflected over the plexus on to the roof of the cornu (Fig. 749). It consists of minute and highly vascular villous processes, each with an afferent and an efferent vessel. The {arteries [FMA63812:Set of arteries]} of the plexus are: (a) the anterior choroidal, a branch of the internal carotid, which enters the plexus at the end of the {inferior cornu [FMA83701:Temporal horn of lateral ventricle]}; and (b) the posterior choroidal, one or two small branches of the posterior cerebral, which pass forward under the {splenium [FMA7196:Spleen]}. The {veins [FMA63814:Set of veins]} of the {choroid plexus [FMA61934:Choroid plexus of cerebral hemisphere]} unite to form a tortuous {vein [FMA50723:Vein]}, which courses from behind forward to the {interventricular foramen [FMA75351:Interventricular foramen]} and there joins with the {terminal vein [FMA50997:Superior thalamostriate vein]} to form the corresponding {internal cerebral vein [FMA51003:Internal cerebral vein]}. When the {choroid plexus [FMA61934:Choroid plexus of cerebral hemisphere]} is pulled away, the continuity between its epithelial covering and the epithelial lining of the ventricle is severed, and a cleft-like space is produced. This is named the {choroidal fissure [FMA74512:Choroidal fissure]}; like the plexus, it extends from the {interventricular foramen [FMA75351:Interventricular foramen]} to the end of the {inferior cornu [FMA83701:Temporal horn of lateral ventricle]}. The upper part of the fissure, i.e., the part nearest the {interventricular foramen [FMA75351:Interventricular foramen]} is situated between the lateral edge of the {fornix [FMA61965:Fornix of forebrain]} and the upper surface of the {thalamus [FMA62007:Thalamus]}; farther {back [FMA24205:Surface of back]} at the beginning of the {inferior cornu [FMA83701:Temporal horn of lateral ventricle]} it is between the commencement of the {fimbria hippocampi [FMA83866:Fimbria of hippocampus]} and the posterior end of the {thalamus [FMA62007:Thalamus]}, while in the {inferior cornu [FMA83701:Temporal horn of lateral ventricle]} it lies between the fimbria in the floor and the {stria terminalis [FMA61974:Stria terminalis]} in the roof of the cornu. 136   The {tela chorioidea of the third ventricle [FMA78463:Tela choroidea of third ventricle]} ({tela chorioidea [FMA242849:Tela choroidea]} {ventriculi tertii [FMA78454:Third ventricle]}; {velum interpositum [FMA78464:Velum interpositum]}) (Fig. 750) is a double fold of {pia mater [FMA9590:Pia mater]}, triangular in shape, which lies beneath the {fornix [FMA61965:Fornix of forebrain]}. The lateral portions of its lower surface rest upon the {thalami [FMA62007:Thalamus]}, while its medial portion is in contact with the epithelial roof of the {third ventricle [FMA78454:Third ventricle]}. Its apex is situated at the {interventricular foramen [FMA75351:Interventricular foramen]}; its base corresponds with the {splenium of the corpus callosum [FMA61948:Splenium of corpus callosum]}, and occupies the interval between that structure above and the {corpora quadrigemina [FMA242157:Set of colliculi]} and {pineal body [FMA62033:Pineal body]} below. This interval, together with the lower portions of the {choroidal fissures [FMA74512:Choroidal fissure]}, is sometimes spoken of as the transverse fissure of the {brain [FMA50801:Brain]}. At its base the two layers of the velum separate from each other, and are continuous with the {pia mater [FMA9590:Pia mater]} investing the {brain [FMA50801:Brain]} in this region. Its lateral margins are modified to form the highly vascular {choroid plexuses of the lateral ventricles [FMA83711:Choroid plexus of lateral ventricle]}. It is supplied by the anterior and {posterior choroidal arteries [FMA50657:Posterior choroidal artery]} already described, The {veins [FMA63814:Set of veins]} of the {tela chorioidea [FMA242849:Tela choroidea]} are named the {internal cerebral veins [FMA70876:Set of internal cerebral veins]} (venæ Galeni); they are two in number, and run backward between its layers, each being formed at the {interventricular foramen [FMA75351:Interventricular foramen]} by the union of the {terminal vein [FMA50997:Superior thalamostriate vein]} with the choroidal {vein [FMA50723:Vein]}. The {internal cerebral veins [FMA70876:Set of internal cerebral veins]} unite posteriorly in a single {trunk [FMA7181:Trunk]}, the {great cerebral vein [FMA50993:Great cerebral vein]} ({vena magna Galeni [FMA50993:Great cerebral vein]}), which passes backward beneath the {splenium [FMA7196:Spleen]} and ends in the {straight sinus [FMA50769:Straight sinus]}. Structure of the {Cerebral Hemispheres [FMA61817:Cerebral hemisphere]}.—The {cerebral hemispheres [FMA61817:Cerebral hemisphere]} are composed of gray and {white substance [FMA83929:White matter of neuraxis]}: the former covers their surface, and is termed the {cortex [FMA15632:Adrenal cortex; FMA61109:Cortex]}; the latter occupies the interior of the hemispheres. 138   The {white substance [FMA83929:White matter of neuraxis]} consists of {medullated fibers [FMA5915:Myelinated nerve fiber]}, varying in size, and arranged in bundles separated by {neuroglia [FMA54541:Set of neuroglial cells]}. They may be divided, according to their course and connections, into three distinct systems. (1) Projection fibers connect the hemisphere with the lower parts of the {brain [FMA50801:Brain]} and with the {medulla spinalis [FMA7647:Spinal cord]}. (2) Transverse or commissural fibers unite the two hemispheres. (3) 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 [FMA67308:Axon]} of independent cells. 139   1. The projection fibers consist of efferent and {afferent fibers [FMA76570:Set of afferent nerve fibers]} uniting the {cortex [FMA15632:Adrenal cortex; FMA61109:Cortex]} with the lower parts of the {brain [FMA50801:Brain]} and with the {medulla spinalis [FMA7647:Spinal cord]}. The principal efferent strands are: (1) the {motor tract [FMA72634:Pyramidal tract]}, occupying the {genu [FMA24974:Knee]} and anterior two-thirds of {the occipital part of the internal capsule [FMA61954:Posterior limb of internal capsule]}, and consisting of (a) the {geniculate fibers [FMA61953:Genu of internal capsule]}, which decussate and end in the motor nuclei of the {cranial nerves [FMA63820:Set of cranial nerves]} of the opposite side; and (b) {the cerebrospinal fibers [FMA265580:Corticospinal tract]}, which are prolonged through the {pyramid of the medulla oblongata [FMA75254:Pyramid of medulla]} into the {medulla spinalis [FMA7647:Spinal cord]}: (2) the {corticopontine fibers [FMA75190:Set of corticopontine fibers]}, ending in the {nuclei pontis [FMA72512:Pontine nuclear group]}. The chief {afferent fibers [FMA76570:Set of afferent nerve fibers]} are: (1) those of the {lemniscus [FMA83676:Lemniscus of neuraxis]} which are not interrupted in the {thalamus [FMA62007:Thalamus]}; (2) those of the {superior cerebellar peduncle [FMA72495:Superior cerebellar peduncle]} which are not interrupted in the {red nucleus [FMA62407:Red nucleus]} and {thalamus [FMA62007:Thalamus]}; (3) numerous fibers arising within the {thalamus [FMA62007:Thalamus]}, and passing through its stalks to the different parts of the {cortex [FMA15632:Adrenal cortex; FMA61109:Cortex]} (page 810); (4) optic and acoustic fibers, the former passing to the occipital, the latter to the {temporal lobe [FMA61825:Temporal lobe]}. 140