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olfactory tract lies in the olfactory sulcus on the inferior surface of the frontal lobe. olfactory tract divides posteriorly into two striæ, a medial. olfactory tract divides posteriorly into two striæ, a lateral. The olfactory tract 's lateral stria is directed across the lateral part of the anterior perforated substance. The olfactory tract 's lateral stria then bends abruptly medialward toward the uncus of the hippocampal gyrus. The olfactory tract 's medial stria turns medialward behind the parolfactory area ; The olfactory tract 's medial stria ends in the subcallosal gyrus ; in some cases a small intermediate stria is seen running backward to the anterior perforated substance. ( c ) The olfactory trigone ) is a small triangular area in front of the anterior perforated substance . ( c ) trigonum olfactorium ) is a small triangular area in front of the anterior perforated substance. The olfactory trigone 's apex, directed forward , occupies the posterior part of the olfactory sulcus. The olfactory trigone 's apex, directed forward , is brought into view by throwing back the olfactory tract. ( d ) The parolfactory area of Broca ) is a small triangular field on the medial surface of the hemisphere in front of the subcallosal gyrus, ( d ) area parolfactoria ) is a small triangular field on the medial surface of the hemisphere in front of the subcallosal gyrus , from subcallosal gyrus parolfactory area of Broca is separated by the posterior parolfactory sulcus ; parolfactory area of Broca is continuous below with the olfactory trigone ; parolfactory area of Broca is continuous above with the cingulate gyrus ; parolfactory area of Broca is continuous in front with the cingulate gyrus ; parolfactory area of Broca is limited anteriorly by the anterior parolfactory sulcus. ( e ) The anterior perforated substance ) is an irregularly quadrilateral area in front of the optic tract, ( e ) substantia perforata anterior ) is an irregularly quadrilateral area in front of the optic tract , ( e ) The anterior perforated substance ) is an irregularly quadrilateral area behind the olfactory trigone, ( e ) substantia perforata anterior ) is an irregularly quadrilateral area behind the olfactory trigone , from the olfactory trigone anterior perforated substance is separated by the fissure prima ; medially anterior perforated substance is continuous with the subcallosal gyrus ; in front anterior perforated substance is continuous with the subcallosal gyrus ; laterally anterior perforated substance is bounded by the lateral stria of the olfactory tract. laterally anterior perforated substance is continued into the uncus. anterior perforated substance 's gray substance is confluent above with gray substance of the corpus striatum,. anterior perforated substance 's gray substance is perforated anteriorly by numerous small bloodvessels. 2 . The Uncus has already been described ( page 826 ) as the recurved, hook-like portion of the hippocampal gyrus. 3 . The Subcallosal, Supracallosal , and Dentate Gyri form a rudimentary arch-shaped lamina of gray substance extending over the corpus callosum. The Subcallosal, Supracallosal , and Dentate Gyri form a rudimentary arch-shaped lamina of gray substance extending above the hippocampal gyrus from the anterior perforated substance to the uncus. ( a ) The subcallosal gyrus is a narrow lamina on the medial surface of the hemisphere in front of the lamina terminalis, behind the parolfactory area. ( a ) gyrus subcallosus ) is a narrow lamina on the medial surface of the hemisphere in front of the lamina terminalis, behind the parolfactory area . ( a ) 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. ( a ) The subcallosal gyrus is a narrow lamina on the medial surface of the hemisphere in front of the lamina terminalis, below the rostrum of the corpus callosum. ( a ) gyrus subcallosus ) is a narrow lamina on the medial surface of the hemisphere in front of the lamina terminalis, below the rostrum of the corpus callosum . ( a ) peduncle of the corpus callosum ) is a narrow lamina on the medial surface of the hemisphere in front of the lamina terminalis , below the rostrum of the corpus callosum. subcallosal gyrus is continuous around the genu of the corpus callosum with the supracallosal gyrus. ( b ) The supracallosal gyrus consists of a thin layer of gray substance in contact with the upper surface of the corpus callosum. ( b ) indusium griseum ) consists of a thin layer of gray substance in contact with the upper surface of the corpus callosum . ( b ) gyrus epicallosus ) consists of a thin layer of gray substance in contact with the upper surface of the corpus callosum. ( b ) The supracallosal gyrus consists of a thin layer of gray substance continuous laterally with the gray substance of the cingulate gyrus. ( b ) indusium griseum ) consists of a thin layer of gray substance continuous laterally with the gray substance of the cingulate gyrus . ( b ) gyrus epicallosus ) consists of a thin layer of gray substance continuous laterally with the gray substance of the cingulate gyrus. supracallosal gyrus 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 supracallosal gyrus is prolonged around the splenium of the corpus callosum as the fasciola cinerea , the fasciola cinerea is continuous below with the fascia dentata hippocampi. ( c ) The fascia dentata hippocampi is a narrow band extending downward and forward above the hippocampal gyrus ; ( c ) The gyrus dentatus ) is a narrow band extending downward and forward above the hippocampal gyrus ; ( c ) The fascia dentata hippocampi is a narrow band separated from hippocampal gyrus by the hippocampal fissure ; ( c ) The gyrus dentatus ) is a narrow band separated from hippocampal gyrus by the hippocampal fissure ; fascia dentata hippocampi 's free margin is notched and overlapped by the fimbria - the fimbriodentate fissure intervening. Anteriorly gyrus dentatus is continued into the notch of the uncus, where gyrus dentatus forms a sharp bend Anteriorly gyrus dentatus is continued into the notch of the uncus, where gyrus dentatus is then prolonged as a delicate band , over the uncus , Anteriorly gyrus dentatus is continued into the notch of the uncus, where gyrus dentatus is then prolonged as the band of Giacomini , over the uncus , on the lateral surface of uncus gyrus dentatus is lost. The remaining parts of the rhinencephalon, viz. , the septum pellucidum, will be described in connection with the lateral ventricle. The remaining parts of the rhinencephalon, viz. , the fornix, will be described in connection with the lateral ventricle. The remaining parts of the rhinencephalon, viz. , the hippocampus, will be described in connection with the lateral ventricle. Interior of the Cerebral Hemispheres. - If the upper part of Cerebral Hemispheres 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 , surrounded by a narrow convoluted margin of gray substance. - If the upper part of Cerebral Hemispheres be removed, at a level about 1.25 cm. above the corpus callosum, the central white substance will be exposed as the centrum ovale minus , surrounded by a narrow convoluted margin of gray substance. - If the upper part of Cerebral Hemispheres 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 , studded with numerous minute red dots , produced by the escape of blood from divided bloodvessels. - If the upper part of Cerebral Hemispheres be removed, at a level about 1.25 cm. above the corpus callosum, the central white substance will be exposed as the centrum ovale minus , studded with numerous minute red dots , produced by the escape of blood from divided bloodvessels. - If the upper part of Cerebral Hemispheres 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 , studded with puncta vasculosa ) , produced by the escape of blood from divided bloodvessels . - If the upper part of Cerebral Hemispheres be removed , at a level about 1.25 cm . above the corpus callosum , the central white substance will be exposed as the centrum ovale minus , studded with puncta vasculosa ) , produced by the escape of blood from divided bloodvessels. If the remaining portions of Cerebral Hemispheres be slightly drawn apart a broad band of white substance, will be observed , connecting Cerebral Hemispheres at the bottom of the longitudinal fissure ; If the remaining portions of Cerebral Hemispheres be slightly drawn apart the corpus callosum, will be observed , connecting Cerebral Hemispheres at the bottom of the longitudinal fissure ; the margins of Cerebral Hemispheres which overlap the corpus callosum are called the labia cerebri. labia cerebri is part of the cingulate gyrus already described ; and the slit-like interval between labia cerebri is termed the callosal fissure and the slit-like interval between the upper surface of the corpus callosum is termed the callosal fissure If Cerebral Hemispheres be sliced off to a level with the upper surface of the corpus callosum, the white substance of corpus callosum will be seen connecting the two Cerebral Hemispheres. The large expanse of medullary matter now exposed, surrounded by the convoluted margin of gray substance , is called the centrum ovale majus. The Corpus Callosum is the great transverse commissure which unites the cerebral hemispheres. The Corpus Callosum is the great transverse commissure which roofs in the lateral ventricles. A good conception of Corpus Callosum 's position and size is obtained by examining a median sagittal section of the brain when Corpus Callosum is seen to form an arched structure about 10 cm. long. Corpus Callosum 's anterior end is about 4 cm. from the frontal pole Corpus Callosum 's posterior end about 6 cm. from the occipital pole of the cerebral hemispheres. Corpus Callosum 's anterior end is named the genu ; Corpus Callosum 's anterior end is bent downward and backward in front of the septum pellucidum ; diminishing rapidly in thickness, Corpus Callosum is prolonged backward under the name of the rostrum , the rostrum is connected below with the lamina terminalis. The anterior cerebral arteries are in contact with the under surface of the rostrum ; anterior cerebral arteries then arch over the front of the genu. anterior cerebral arteries then are carried backward above the body of the corpus callosum. The posterior end is termed the splenium. The posterior end constitutes the thickest part of the corpus callosum. splenium overlaps the tela chorioidea of the third ventricle. splenium overlaps the mid-brain. splenium ends in a thick, convex , free border. A sagittal section of the splenium shows that the posterior end of the corpus callosum is acutely bent forward, the upper and lower parts being applied to each other. Corpus Callosum 's superior surface is convex from before backward Corpus Callosum 's superior surface is about 2.5 cm. wide. Corpus Callosum 's superior surface 's medial part forms the bottom of the longitudinal fissure,. Corpus Callosum 's superior surface 's medial part is in contact posteriorly with the lower border of the falx cerebri. Laterally Corpus Callosum 's superior surface is overlapped by the cingulate gyrus. Laterally Corpus Callosum 's superior surface is separated from cingulate gyrus by the slit-like callosal fissure. Corpus Callosum 's superior surface is traversed by numerous transverse ridges and furrows , Corpus Callosum 's superior surface is covered by a thin layer of gray matter, the supracallosal gyrus , the supracallosal gyrus exhibits on either side of Corpus Callosum 's middle line the medial and lateral longitudinal striæ, already described ( page 827 ). Corpus Callosum 's inferior surface is concave. Corpus Callosum 's inferior surface forms on either side of the middle line the roof of the lateral ventricle. Medially, Corpus Callosum 's inferior surface is attached in front to the septum pellucidum ; behind septum pellucidum Corpus Callosum 's inferior surface is fused with the upper surface of the body of the fornix behind septum pellucidum the splenium is in contact with the tela chorioidea. On either side, the fibers of the corpus callosum radiate in the white substance ; On either side, the fibers of the corpus callosum pass to the various parts of the cerebral cortex ; the fibers of the corpus callosum curving forward from the genu into the frontal lobe constitute the forceps anterior,. the fibers of the corpus callosum curving backward into the occipital lobe constitute the forceps posterior. Between the forceps anterior is the main body of the fibers of the corpus callosum which constitute the tapetum. Between the forceps anterior is the main body of the fibers of the corpus callosum which extend laterally on either side into the temporal lobe. Between the forceps anterior is the main body of the fibers of the corpus callosum which cover in the central part of the lateral ventricle. The Lateral Ventricles - The two lateral ventricles are irregular cavities situated in the lower and medial parts of the cerebral hemispheres, one on either side of the middle line. The ventriculus lateralis ) - The two lateral ventricles are irregular cavities situated in the lower and medial parts of the cerebral hemispheres, one on either side of the middle line . The Lateral Ventricles are separated from each other by a median vertical partition . The Lateral Ventricles are separated from each other by the septum pellucidum . The Lateral Ventricles communicate with the third ventricle . The Lateral Ventricles communicate indirectly with each other through the interventricular foramen . The Lateral Ventricles are lined by a thin , diaphanous membrane , covered by ciliated epithelium . The Lateral Ventricles are lined by the ependyma , covered by ciliated epithelium . The Lateral Ventricles contain cerebrospinal fluid , which , even in health , may be secreted in considerable amount . Each lateral ventricle consists of a central part or body , . Each lateral ventricle consists of three prolongations from body , termed cornua.
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