189 identified

--
 * The {fore-brain [FMA61992:Forebrain]} or {prosencephalon [FMA61992:Forebrain]} consists of: (1) the {diencephalon [FMA62001:Diencephalon]}, corresponding in a large measure to the {third ventricle [FMA78454:Third ventricle]} and the structures which bound it; and (2) the {telencephalon [FMA62000:Telencephalon]}, comprising the largest part of the {brain [FMA50801:Brain]}, viz., the {cerebral hemispheres [FMA61817:Cerebral hemisphere]}; these hemispheres are intimately connected with each other across the middle line, and each contains a large cavity, named the {lateral ventricle [FMA78448:Lateral ventricle]}. The {lateral ventricles [FMA78448:Lateral ventricle]} communicate through the {interventricular foramen [FMA75351:Interventricular foramen]} with the {third ventricle [FMA78454:Third ventricle]}, but are separated from each other by a medial septum, the {septum pellucidum [FMA61842:Septum of telencephalon; FMA61844:Septum pellucidum]}; this contains a slit-like cavity, which does not communicate with the ventricles.
 * The {Diencephalon [FMA62001:Diencephalon]}.—The {diencephalon [FMA62001:Diencephalon]} is connected above and in front with the {cerebral hemispheres [FMA61817:Cerebral hemisphere]}; behind with the {mid-brain [FMA61993:Midbrain]}. Its upper surface is concealed by the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]}, and is covered by a fold of {pia mater [FMA9590:Pia mater]}, named the {tela chorioidea of the third ventricle [FMA78463:Tela choroidea of third ventricle]}; inferiorly it reaches to the {base of the brain [FMA77700:Basal forebrain]}. 2
 * The {diencephalon [FMA62001:Diencephalon]} comprises: (1) the {thalamencephalon [FMA62007:Thalamus]}; (2) the {pars mamillaris hypothalami [FMA62029:Posterior hypothalamic region]}; and (3) the posterior part of the {third ventricle [FMA78454:Third ventricle]}. For descriptive purposes, however, it is more convenient to consider the whole of the {third ventricle [FMA78454:Third ventricle]} and its boundaries together; this necessitates the inclusion, under this heading, of the {pars optica hypothalami [FMA62027:Anterior hypothalamic region]} and the corresponding part of the {third ventricle [FMA78454:Third ventricle]}—structures which properly belong to the {telencephalon [FMA62000:Telencephalon]}. 3
 * The {Thalamencephalon [FMA62007:Thalamus]}.—The {thalamencephalon [FMA62007:Thalamus]} comprises: (1) the {thalamus [FMA62007:Thalamus]}; (2) the {metathalamus [FMA62023:Metathalamus]} or {corpora geniculata [FMA62023:Metathalamus]}; and (3) the {epithalamus [FMA62009:Epithalamus]}, consisting of the {trigonum habenulæ [FMA74868:Habenular trigone]}, the {pineal body [FMA62033:Pineal body]}, and the {posterior commissure [FMA62072:Posterior commissure]}.
 * The {Thalami [FMA62007:Thalamus]} ({optic thalamus [FMA62007:Thalamus]}) (Figs. 716, 717) are two large ovoid masses, situated one on either side of the {third ventricle [FMA78454:Third ventricle]} and reaching for some distance behind that cavity. Each measures about 4 cm. in length, and presents two extremities, an anterior and a posterior, and four surfaces, superior, inferior, medial, and lateral. 5
 * The anterior extremity is narrow; it lies close to the middle line and forms the posterior boundary of the {interventricular foramen [FMA75351:Interventricular foramen]}. 6
 * The posterior extremity is expanded, directed backward and lateralward, and overlaps the {superior colliculus [FMA62403:Superior colliculus]}. Medially it presents an angular prominence, the {pulvinar [FMA62178:Pulvinar]}, which is continued laterally into an oval swelling, the {lateral geniculate body [FMA62209:Lateral geniculate body]}, while beneath the {pulvinar [FMA62178:Pulvinar]}, but separated from it by the {superior brachium [FMA72417:Brachium of superior colliculus]}, is a second oval swelling, the {medial geniculate body [FMA62211:Medial geniculate body]}. 7
 * The superior surface is free, slightly convex, and covered by a layer of {white substance [FMA83929:White matter of neuraxis]}, termed the {stratum zonale [FMA83905:Stratum zonale of thalamus]}. It is separated laterally from the {caudate nucleus [FMA61833:Caudate nucleus]} by a white band, the {stria terminalis [FMA61974:Stria terminalis]}, and by the {terminal vein [FMA50997:Superior thalamostriate vein]}. It is divided into a medial and a lateral portion by an oblique shallow furrow which runs from behind forward and medialward and corresponds with the lateral margin of the {fornix [FMA61965:Fornix of forebrain]}; the lateral part forms a portion of the floor of the {lateral ventricle [FMA78448:Lateral ventricle]}, and is covered by the epithelial lining of this cavity; the medial part is covered by the {tela chorioidea of the third ventricle [FMA78463:Tela choroidea of third ventricle]}, and is destitute of an epithelial covering. In front, the superior is separated from the medial surface by a salient margin, the {tænia thalami [FMA78461:Tenia of thalamus]}, along which the epithelial lining of the {third ventricle [FMA78454:Third ventricle]} is reflected on to the under surface of the {tela chorioidea [FMA242849:Tela choroidea]}. Behind, it is limited medially by a groove, the {sulcus habenulæ [FMA78466:Habenular sulcus]}, which intervenes between it and a small triangular area, termed the {trigonum habenulæ [FMA74868:Habenular trigone]}. 8
 * The inferior surface rests upon and is continuous with the upward prolongation of the tegmentum ({subthalamic tegmental region [FMA62010:Subthalamus]}), in front of which it is related to the {substantia innominata of Meynert [FMA61885:Substantia innominata]}. 9
 * The medial surface constitutes the upper part of the lateral {wall of the third ventricle [FMA242776:Wall of third ventricle]}, and is connected to the corresponding surface of the opposite {thalamus [FMA62007:Thalamus]} by a flattened gray band, the {massa intermedia [FMA74869:Interthalamic adhesion]} (middle or gray commissure). This mass averages about 1 cm. in its antero-posterior diameter: it sometimes consists of two parts and occasionally is absent. It contains {nerve cells [FMA54527:Neuron]} and {nerve fibers [FMA5914:Nerve fiber]}; a few of the latter may cross the middle line, but most of them pass toward the middle line and then curve lateralward on the same side. 10
 * The lateral surface is in contact with a thick band of {white substance [FMA83929:White matter of neuraxis]} which forms {the occipital part of the internal capsule [FMA61954:Posterior limb of internal capsule]} and separates the {thalamus [FMA62007:Thalamus]} from the {lentiform nucleus [FMA77615:Lentiform nucleus]} of the {corpus striatum [FMA77616:Corpus striatum]}. 11
 * Structure.—The {thalamus [FMA62007:Thalamus]} consists chiefly of {gray substance [FMA67242:Gray matter of neuraxis]}, but its upper surface is covered by a layer of {white substance [FMA83929:White matter of neuraxis]}, named the {stratum zonale [FMA83905:Stratum zonale of thalamus]}, and its lateral surface by a similar layer termed the {lateral medullary lamina [FMA62469:Lateral medullary lamina of globus pallidus]}. Its {gray substance [FMA67242:Gray matter of neuraxis]} is incompletely subdivided into three parts—anterior, medial, and lateral—by a white layer, the {medial medullary lamina [FMA62079:Internal medullary lamina]}. The anterior part comprises the {anterior tubercle [FMA74867:Anterior tubercle of diencephalon]}, the medial part lies next the lateral {wall of the third ventricle [FMA242776:Wall of third ventricle]} while the lateral and largest part is interposed between the medullary laminæ and includes the {pulvinar [FMA62178:Pulvinar]}. The lateral part is traversed by numerous fibers which radiate from the {thalamus [FMA62007:Thalamus]} into the {internal capsule [FMA61950:Internal capsule]}, and pass through the latter to the {cerebral cortex [FMA61830:Cerebral cortex]}. These three parts are built up of numerous nuclei, the connections of many of which are imperfectly known. 12
 * Connections.—The {thalamus [FMA62007:Thalamus]} may be regarded as a large ganglionic mass in which the ascending tracts of the tegmentum and a considerable proportion of the fibers of the {optic tract [FMA62046:Optic tract]} end, and from the cells of which numerous fibers (thalamocortical) take origin, and radiate to almost every part of the {cerebral cortex [FMA61830:Cerebral cortex]}. The {lemniscus [FMA83676:Lemniscus of neuraxis]}, together with the other longitudinal strands of the tegmentum, enters its ventral part: the {thalamomammillary fasciculus [FMA83849:Mammillothalamic tract]} ({bundle of Vicq d’Azyr [FMA83849:Mammillothalamic tract]}), from the {corpus mammillare [FMA74877:Mammillary body]}, enters in its {anterior tubercle [FMA74867:Anterior tubercle of diencephalon]}, while many of the fibers of the {optic tract [FMA62046:Optic tract]} terminate in its posterior end. The {thalamus [FMA62007:Thalamus]} also receives numerous fibers (corticothalamic) from the cells of the {cerebral cortex [FMA61830:Cerebral cortex]}. The fibers that arise from the cells of the {thalamus [FMA62007:Thalamus]} form four principal groups or stalks: (a) those of the anterior stalk pass through the {frontal [FMA46757:Frontalis]} part of the {internal capsule [FMA61950:Internal capsule]} to the {frontal lobe [FMA61824:Frontal lobe]}; (b) the fibers of the posterior stalk ({optic radiations [FMA61941:Optic radiation]}) arise in the {pulvinar [FMA62178:Pulvinar]} and are conveyed through {the occipital part of the internal capsule [FMA61954:Posterior limb of internal capsule]} to the {occipital lobe [FMA67325:Occipital lobe]}; (c) the fibers of the inferior stalk leave the under and medial surfaces of the {thalamus [FMA62007:Thalamus]}, and pass beneath the {lentiform nucleus [FMA77615:Lentiform nucleus]} to the {temporal lobe [FMA61825:Temporal lobe]} and {insula [FMA67329:Insula]}; (d) those of the parietal stalk pass from the {lateral nucleus of the thalamus [FMA62174:Lateral nuclear group of thalamus]} to the {parietal lobe [FMA61826:Parietal lobe]}. Fibers also extend from the {thalamus [FMA62007:Thalamus]} into the {corpus striatum [FMA77616:Corpus striatum]}—those destined for the {caudate nucleus [FMA61833:Caudate nucleus]} leave the lateral surface, and those for the {lentiform nucleus [FMA77615:Lentiform nucleus]}, the inferior surface of the {thalamus [FMA62007:Thalamus]}.
 * The {Metathalamus [FMA62023:Metathalamus]} (Fig. 719) comprises the geniculate bodies, which are two in number—a medial and a lateral—on each side. 14
 * The {medial geniculate body [FMA62211:Medial geniculate body]} ({corpus geniculatum mediale [FMA62211:Medial geniculate body]}; internal geniculate body; postgeniculatum) lies under cover of the {pulvinar [FMA62178:Pulvinar]} of the {thalamus [FMA62007:Thalamus]} and on the lateral aspect of the {corpora quadrigemina [FMA242157:Set of colliculi]}. Oval in shape, with its long {axis [FMA12520:Axis; FMA58907:Axis of lens]} directed forward and lateralward, it is lighter in color and smaller in size than the lateral. The {inferior brachium [FMA71114:Brachium of inferior colliculus]} from the {inferior colliculus [FMA62404:Inferior colliculus]} disappears under cover of it while from its lateral extremity a strand of fibers passes to join the {optic tract [FMA62046:Optic tract]}. Entering it are many acoustic fibers from the {lateral lemniscus [FMA72502:Lateral lemniscus]}. The {medial geniculate bodies [FMA62211:Medial geniculate body]} are connected with one another by the {commissure of Gudden [FMA62052:Ventral supraoptic decussation]}, which passes through the posterior part of the {optic chiasma [FMA62045:Optic chiasm]}. 15
 * The {lateral geniculate body [FMA62209:Lateral geniculate body]} ({corpus geniculatum laterale [FMA62209:Lateral geniculate body; FMA62214:Dorsal nucleus of lateral geniculate body; FMA62215:Ventral nucleus of lateral geniculate body]}; external geniculate body; pregeniculatum) is an oval elevation on the lateral part of the posterior end of the {thalamus [FMA62007:Thalamus]}, and is connected with the {superior colliculus [FMA62403:Superior colliculus]} by the {superior brachium [FMA72417:Brachium of superior colliculus]}. It is of a dark color, and presents a laminated arrangement consisting of alternate layers of gray and {white substance [FMA83929:White matter of neuraxis]}. It receives numerous fibers from the {optic tract [FMA62046:Optic tract]}, while other fibers of this tract pass over or through it into the {pulvinar [FMA62178:Pulvinar]}. Its cells are large and pigmented; their {axons [FMA67308:Axon]} pass to the visual area in the occipital part of the {cerebral cortex [FMA61830:Cerebral cortex]}. 16
 * The {superior colliculus [FMA62403:Superior colliculus]}, the {pulvinar [FMA62178:Pulvinar]}, and the {lateral geniculate body [FMA62209:Lateral geniculate body]} receive many fibers from the {optic tracts [FMA62046:Optic tract]}, and are therefore intimately connected with sight, constituting what are termed the lower visual centers. Extirpation of the {eyes [FMA54448:Eye]} in a newly born animal entails an arrest of the development of these centers, but has no effect on the {medial geniculate bodies [FMA62211:Medial geniculate body]} or on the {inferior colliculi [FMA62404:Inferior colliculus]}. Moreover, the latter are well-developed in the mole, an animal in which the {superior colliculi [FMA62403:Superior colliculus]} are rudimentary. 17
 * The {Epithalamus [FMA62009:Epithalamus]} comprises the {trigonum habenulæ [FMA74868:Habenular trigone]}, the {pineal body [FMA62033:Pineal body]}, and the {posterior commissure [FMA62072:Posterior commissure]}. 18
 * The {trigonum habenulæ [FMA74868:Habenular trigone]} is a small depressed triangular area situated in front of the {superior colliculus [FMA62403:Superior colliculus]} and on the lateral aspect of the posterior part of the {tænia thalami [FMA78461:Tenia of thalamus]}. It contains a group of {nerve cells [FMA54527:Neuron]} termed the {ganglion [FMA5884:Ganglion]} habenulæ. Fibers enter it from the stalk of the {pineal body [FMA62033:Pineal body]}, and others, forming what is termed the {habenular commissure [FMA62048:Habenular commissure]}, pass across the middle line to the corresponding {ganglion [FMA5884:Ganglion]} of the opposite side. Most of its fibers are, however, directed downward and form a bundle, the {fasciculus retroflexus of Meynert [FMA72400:Habenulo-interpeduncular tract]}, which passes medial to the {red nucleus [FMA62407:Red nucleus]}, and, after decussating with the corresponding fasciculus of the opposite side, ends in the {interpeduncular ganglion [FMA72439:Interpeduncular nucleus]}. 19
 * The {pineal body [FMA62033:Pineal body]} ({corpus pineale [FMA62033:Pineal body]}; {epiphysis [FMA24012:Epiphysis]}) is a small, conical, reddish-gray body which lies in the depression between the {superior colliculi [FMA62403:Superior colliculus]}. It is placed beneath the {splenium of the corpus callosum [FMA61948:Splenium of corpus callosum]}, but is separated from this by the {tela chorioidea of the third ventricle [FMA78463:Tela choroidea of third ventricle]}, the lower layer of which envelops it. It measures about 8 mm. in length, and its base, directed forward, is attached by a stalk or peduncle of {white substance [FMA83929:White matter of neuraxis]}. The stalk of the {pineal body [FMA62033:Pineal body]} divides anteriorly into two laminæ, a dorsal and a ventral, separated from one another by the {pineal recess of the third ventricle [FMA78458:Pineal recess of third ventricle]}. The ventral {lamina is [FMA242259:Plexiform layer of cerebral cortex]} continuous with the {posterior commissure [FMA62072:Posterior commissure]}; the dorsal {lamina is [FMA242259:Plexiform layer of cerebral cortex]} continuous with the {habenular commissure [FMA62048:Habenular commissure]} and divides into two strands the medullary striæ, which run forward, one on either side, along the junction of the medial and upper surfaces of the {thalamus [FMA62007:Thalamus]} to blend in front with the {columns of the fornix [FMA61968:Body of fornix of forebrain]}. 20
 * The {posterior commissure [FMA62072:Posterior commissure]} is a rounded band of white fibers crossing the middle line on the dorsal aspect of the upper end of the {cerebral aqueduct [FMA78467:Cerebral aqueduct]}. Its fibers acquire their {medullary sheaths [FMA62983:Myelin sheath]} early, but their connections have not been definitely determined. Most of them have their origin in a nucleus, the {nucleus of the posterior commissure [FMA68463:Nucleus of posterior commissure]} ({nucleus of Darkschewitsch [FMA68464:Ventral nucleus of posterior commissure]}), which lies in the {central gray substance [FMA83134:Central gray substance]} of the upper end of the {cerebral aqueduct [FMA78467:Cerebral aqueduct]}, in front of the {nucleus of the oculomotor nerve [FMA54510:Oculomotor nuclear complex]}. Some are probably derived from the posterior part of the {thalamus [FMA62007:Thalamus]} and from the {superior colliculus [FMA62403:Superior colliculus]}, while others are believed to be continued downward into the {medial longitudinal fasciculus [FMA83846:Medial longitudinal fasciculus]}. 21
 * The {Hypothalamus [FMA62008:Hypothalamus]} (Fig. 720) includes the {subthalamic tegmental region [FMA62010:Subthalamus]} and the structures forming the greater part of the floor of the {third ventricle [FMA78454:Third ventricle]}, viz., the {corpora mammillaria [FMA74877:Mammillary body]}, {tuber cinereum [FMA62327:Tuber cinereum]}, {infundibulum [FMA74635:Infundibulum of neurohypophysis]}, {hypophysis [FMA13889:Pituitary gland]}, and {optic chiasma [FMA62045:Optic chiasm]}. 22
 * The {subthalamic tegmental region [FMA62010:Subthalamus]} consists of the upward continuation of the tegmentum; it lies on the {ventro [FMA9719:Muscle belly]}-lateral aspect of the {thalamus [FMA62007:Thalamus]} and separates it from the fibers of the {internal capsule [FMA61950:Internal capsule]}. The {red nucleus [FMA62407:Red nucleus]} and the {substantia nigra [FMA62907:Substantia nigra pars compacta; FMA62908:Substantia nigra pars reticulata; FMA67947:Substantia nigra]} are prolonged into its lower part; in front it is continuous with the {substantia innominata of Meynert [FMA61885:Substantia innominata]}, medially with the {gray substance [FMA67242:Gray matter of neuraxis]} of the floor of the {third ventricle [FMA78454:Third ventricle]}. 23
 * It consists from above downward of three strata: (1) stratum dorsale, directly applied to the under surface of the {thalamus [FMA62007:Thalamus]} and consisting of fine longitudinal fibers; (2) {zona incerta [FMA62038:Zona incerta]}, a continuation forward of the {formatio reticularis [FMA77719:Reticular formation]} of the tegmentum; and (3) the {corpus subthalamicum [FMA62035:Subthalamic nucleus]} ({nucleus of Luys [FMA62035:Subthalamic nucleus]}), a brownish mass presenting a lenticular shape on transverse section, and situated on the dorsal aspect of the fibers of the {base of the cerebral peduncle [FMA242166:Base of midbrain peduncle]}; it is encapsuled by a lamina of {nerve fibers [FMA5914:Nerve fiber]} and contains numerous medium-sized {nerve cells [FMA54527:Neuron]}, the connections of which are as yet not fully determined. 24
 * The {corpora mammillaria [FMA74877:Mammillary body]} ({corpus albicantia [FMA74877:Mammillary body]}) are two round white masses, each about the size of a small pea, placed side by side below the {gray substance [FMA67242:Gray matter of neuraxis]} of the floor of the {third ventricle [FMA78454:Third ventricle]} in front of the {posterior perforated substance [FMA77523:Posterior perforated substance]}. They consist of {white substance [FMA83929:White matter of neuraxis]} externally and of {gray substance [FMA67242:Gray matter of neuraxis]} internally, the cells of the latter forming two nuclei, a medial of smaller and a lateral of larger cells. The {white substance [FMA83929:White matter of neuraxis]} is mainly formed by the fibers of the {columns of the fornix [FMA61968:Body of fornix of forebrain]}, which descend to the {base of the brain [FMA77700:Basal forebrain]} and end partly in the {corpora mammillaria [FMA74877:Mammillary body]}. From the cells of the {gray substance [FMA67242:Gray matter of neuraxis]} of each {mammillary body [FMA74877:Mammillary body]} two fasciculi arise: one, the {thalamomammillary fasciculus [FMA83849:Mammillothalamic tract]} ({bundle of Vicq d’Azyr [FMA83849:Mammillothalamic tract]}), passes upward into the {anterior nucleus of the thalamus [FMA62019:Anterior nuclear group of thalamus]}; the other is directed downward into the tegmentum. {Afferent fibers [FMA76570:Set of afferent nerve fibers]} are believed to reach the {corpus mammillare [FMA74877:Mammillary body]} from the {medial lemniscus [FMA83675:Medial lemniscus]} and from the tegmentum.
 * The {tuber cinereum [FMA62327:Tuber cinereum]} is a hollow eminence of {gray substance [FMA67242:Gray matter of neuraxis]} situated between the {corpora mammillaria [FMA74877:Mammillary body]} behind, and the {optic chiasma [FMA62045:Optic chiasm]} in front. Laterally it is continuous with the {anterior perforated substances [FMA61891:Anterior perforated substance]} and anteriorly with a thin lamina, the {lamina terminalis [FMA61975:Lamina terminalis]}. From the under surface of the {tuber cinereum [FMA62327:Tuber cinereum]} a hollow conical process, the {infundibulum [FMA74635:Infundibulum of neurohypophysis]}, projects downward and forward and is attached to the posterior lobe of the {hypophysis [FMA13889:Pituitary gland]}. 26
 * In the lateral part of the {tuber cinereum [FMA62327:Tuber cinereum]} is a nucleus of {nerve cells [FMA54527:Neuron]}, the basal optic nucleus of Meynert, while close to the {cavity of the third ventricle [FMA242751:Cavity of third ventricle]} are three additional nuclei. Between the {tuber cinereum [FMA62327:Tuber cinereum]} and the {corpora mammillaria [FMA74877:Mammillary body]} a small elevation, with a corresponding depression in the {third ventricle [FMA78454:Third ventricle]}, is sometimes seen. Retzius has named it the {eminentia [FMA75432:Eminence]} saccularis, and regards it as a representative of the saccus vasculosus found in this situation in some of the lower vertebrates. 27
 * The {hypophysis [FMA13889:Pituitary gland]} ({pituitary body [FMA13889:Pituitary gland]}) (Fig. 721) is a reddish-gray, somewhat oval mass, measuring about 12.5 mm. in its transverse, and about 8 mm. in its antero-posterior diameter. It is attached to the end of the {infundibulum [FMA74635:Infundibulum of neurohypophysis]}, and is situated in the {fossa hypophyseos [FMA54721:Hypophysial fossa]} of the {sphenoidal bone [FMA52736:Sphenoid bone]}, where it is retained by a circular fold of {dura mater [FMA9592:Dura mater]}, the {diaphragma sella [FMA78540:Diaphragma sellae]}; this fold almost completely roofs in the fossa, leaving only a small central aperture through which the {infundibulum [FMA74635:Infundibulum of neurohypophysis]} passes.
 * {Optic Chiasma [FMA62045:Optic chiasm]} ({chiasma opticum [FMA62045:Optic chiasm]}; {optic commissure [FMA62045:Optic chiasm]}).—The {optic chiasma [FMA62045:Optic chiasm]} is a flattened, somewhat quadrilateral band of fibers, situated at the junction of the floor and anterior {wall of the third ventricle [FMA242776:Wall of third ventricle]}. Most of its fibers have their origins in the {retina [FMA58301:Retina]}, and reach the {chiasma [FMA62045:Optic chiasm]} through the {optic nerves [FMA50863:Optic nerve]}, which are continuous with its antero-lateral angles. In the {chiasma [FMA62045:Optic chiasm]}, they undergo a partial decussation (Fig. 722); the fibers from the nasal half of the {retina [FMA58301:Retina]} decussate and enter the {optic tract [FMA62046:Optic tract]} of the opposite side, while the fibers from the temporal half of the {retina [FMA58301:Retina]} do not undergo decussation, but pass {back [FMA24205:Surface of back]} into the {optic tract [FMA62046:Optic tract]} of the same side. Occupying the posterior part of the commissure, however, is a strand of fibers, the {commissure of Gudden [FMA62052:Ventral supraoptic decussation]}, which is not derived from the {optic nerves [FMA50863:Optic nerve]}; it forms a connecting link between the {medial geniculate bodies [FMA62211:Medial geniculate body]}. 29
 * {Optic Tracts [FMA62046:Optic tract]}.—The {optic tracts [FMA62046:Optic tract]} are continued backward and lateralward from the postero-lateral angles of the {optic chiasma [FMA62045:Optic chiasm]}. Each passes between the {anterior perforated substance [FMA61891:Anterior perforated substance]} and the {tuber cinereum [FMA62327:Tuber cinereum]}, and, winding around the ventrolateral aspect of the {cerebral peduncle [FMA62394:Peduncle of midbrain; FMA72464:Cerebral crus]}, divides into a medial and a lateral root. The former comprises the fibers of {Gudden’s commissure [FMA62052:Ventral supraoptic decussation]}. The lateral root consists mainly of {afferent fibers [FMA76570:Set of afferent nerve fibers]} which arise in the {retina [FMA58301:Retina]} and undergo partial decussation in the {optic chiasma [FMA62045:Optic chiasm]}, as described; but it also contains a few fine efferent fibers which have their origins in the {brain [FMA50801:Brain]} and their terminations in the {retina [FMA58301:Retina]}. When traced backward, the {afferent fibers [FMA76570:Set of afferent nerve fibers]} of the lateral root are found to end in the {lateral geniculate body [FMA62209:Lateral geniculate body]} and {pulvinar [FMA62178:Pulvinar]} of the {thalamus [FMA62007:Thalamus]}, and in the {superior colliculus [FMA62403:Superior colliculus]}; and these three structures constitute the lower visual centers. Fibers arise from the {nerve cells [FMA54527:Neuron]} in these centers and pass through {the occipital part of the internal capsule [FMA61954:Posterior limb of internal capsule]}, under the name of the {optic radiations [FMA61941:Optic radiation]}, to the {cortex of the occipital lobe [FMA242205:Cortex of occipital lobe]} of the {cerebrum [FMA62000:Telencephalon]}, where the higher or cortical visual center is situated. Some of the fibers of the {optic radiations [FMA61941:Optic radiation]} take an opposite course, arising from the cells of the {occipital cortex [FMA67325:Occipital lobe]} and passing to the lower visual centers. Some fibers are detached from the {optic tract [FMA62046:Optic tract]}, and pass through the {cerebral peduncle [FMA62394:Peduncle of midbrain; FMA72464:Cerebral crus]} to the {nucleus of the oculomotor nerve [FMA54510:Oculomotor nuclear complex]}. These may be regarded as the afferent branches for the Sphincter pupillæ and {Ciliaris muscles [FMA49151:Ciliary muscle]}. Other fibers have been described as reaching the {cerebellum [FMA67944:Cerebellum]} through the {superior peduncle [FMA62075:Superior thalamic peduncle]}; while others, again, are lost in the {pons [FMA67943:Pons]}. 30
 * The {Third Ventricle [FMA78454:Third ventricle]} ({ventriculus tertius [FMA78454:Third ventricle]}) (Figs. 716, 720).—The {third ventricle [FMA78454:Third ventricle]} is a median cleft between the two {thalami [FMA62007:Thalamus]}. Behind, it communicates with the {fourth ventricle [FMA78469:Fourth ventricle]} through the {cerebral aqueduct [FMA78467:Cerebral aqueduct]}, and in front with the {lateral ventricles [FMA78448:Lateral ventricle]} through the {interventricular foramen [FMA75351:Interventricular foramen]}. Somewhat triangular in shape, with the apex directed backward, it has a roof, a floor, an anterior and a posterior boundary and a pair of lateral walls.
 * The roof (Fig. 723) is formed by a layer of {epithelium [FMA9639:Portion of epithelium]}, which stretches between the upper edges of the lateral walls of the cavity and is continuous with the epithelial lining of the ventricle. It is covered by and adherent to a fold of {pia mater [FMA9590:Pia mater]}, named the {tela chorioidea of the third ventricle [FMA78463:Tela choroidea of third ventricle]}, from the under surface of which a pair of vascular fringed processes, the {choroid plexuses of the third ventricle [FMA78462:Choroid plexus of third ventricle]}, project downward, one on either side of the middle line, and invaginate the epithelial roof into the {ventricular cavity [FMA13238:Cavity of ventricle]}. 32
 * The floor slopes downward and forward and is formed mainly by the structures which constitute the {hypothalamus [FMA62008:Hypothalamus]}: from before backward these are: the {optic chiasma [FMA62045:Optic chiasm]}, the {tuber cinereum [FMA62327:Tuber cinereum]} and {infundibulum [FMA74635:Infundibulum of neurohypophysis]}, and the {corpora mammillaria [FMA74877:Mammillary body]}. Behind the last, the floor is formed by the {interpeduncular fossa [FMA83740:Interpeduncular fossa]} and the tegmenta of the {cerebral peduncles [FMA62394:Peduncle of midbrain; FMA72464:Cerebral crus]}. The ventricle is prolonged downward as a funnel-shaped recess, the {recessus infundibuli [FMA78456:Infundibular recess of third ventricle]}, into the {infundibulum [FMA74635:Infundibulum of neurohypophysis]}, and to the apex of the latter the {hypophysis [FMA13889:Pituitary gland]} is attached. 33
 * The anterior boundary is constituted below by the {lamina terminalis [FMA61975:Lamina terminalis]}, a thin layer of {gray substance [FMA67242:Gray matter of neuraxis]} stretching from the upper surface of the {optic chiasma [FMA62045:Optic chiasm]} to the {rostrum of the corpus callosum [FMA61945:Rostrum of corpus callosum; FMA61946:Genu of corpus callosum]}; above by the {columns of the fornix [FMA61968:Body of fornix of forebrain]} and the {anterior commissure [FMA61961:Anterior commissure]}. At the junction of the floor and anterior wall, immediately above the {optic chiasma [FMA62045:Optic chiasm]}, the ventricle presents a small angular recess or diverticulum, the {optic recess [FMA78455:Optic recess of third ventricle]}. Between the {columns of the fornix [FMA61968:Body of fornix of forebrain]}, and above the {anterior commissure [FMA61961:Anterior commissure]}, is a second recess termed the {vulva [FMA20462:Vulva]}. At the junction of the roof and anterior {wall of the ventricle [FMA13884:Wall of ventricle]}, and situated between the {thalami [FMA62007:Thalamus]} behind and the {columns of the fornix [FMA61968:Body of fornix of forebrain]} in front, is the {interventricular foramen [FMA75351:Interventricular foramen]} ({foramen of Monro [FMA75351:Interventricular foramen]}) through which the third communicates with the {lateral ventricles [FMA78448:Lateral ventricle]}.
 * The posterior boundary is constituted by the {pineal body [FMA62033:Pineal body]}, the {posterior commissure [FMA62072:Posterior commissure]} and the {cerebral aqueduct [FMA78467:Cerebral aqueduct]}. A small recess, the {recessus pinealis [FMA78458:Pineal recess of third ventricle]}, projects into the stalk of the {pineal body [FMA62033:Pineal body]}, while in front of and above the {pineal body [FMA62033:Pineal body]} is a second recess, the {recessus suprapinealis [FMA78457:Suprapineal recess of third ventricle]}, consisting of a diverticulum of the {epithelium [FMA9639:Portion of epithelium]} which forms the ventricular roof. 35
 * Each lateral wall consists of an upper portion formed by the medial surface of the anterior two-thirds of the {thalamus [FMA62007:Thalamus]}, and a lower consisting of an upward continuation of the {gray substance [FMA67242:Gray matter of neuraxis]} of the ventricular floor. These two parts correspond to the {alar [FMA264759:Alare]} and basal laminæ respectively of the lateral wall of the {fore-brain [FMA61992:Forebrain]} vesicle and are separated from each other by a furrow, the {sulcus [:]} of Monro, which extends from the {interventricular foramen [FMA75351:Interventricular foramen]} to the {cerebral aqueduct [FMA78467:Cerebral aqueduct]} (pages 741 and 742). The lateral wall is limited above by the {tænia thalami [FMA78461:Tenia of thalamus]}. The {columns of the fornix [FMA61968:Body of fornix of forebrain]} curve downward in front of the {interventricular foramen [FMA75351:Interventricular foramen]}, and then run in the lateral {walls of the ventricle [FMA13884:Wall of ventricle]}, where, at first, they form distinct prominences, but subsequently are lost to sight. The lateral walls are joined to each other across the {cavity of the ventricle [FMA13238:Cavity of ventricle]} by {a band [FMA67918:Anisotropic band]} of {gray matter [FMA67242:Gray matter of neuraxis]}, the {massa intermedia [FMA74869:Interthalamic adhesion]} (page 809). 36
 * {Interpeduncular Fossa [FMA83740:Interpeduncular fossa]} (Fig. 724).—This is a somewhat lozenge-shaped area of the {base of the brain [FMA77700:Basal forebrain]}, limited in front by the {optic chiasma [FMA62045:Optic chiasm]}, behind by the antero-superior surface of the {pons [FMA67943:Pons]}, antero-laterally by the converging {optic tracts [FMA62046:Optic tract]}, and postero-laterally by the diverging {cerebral peduncles [FMA62394:Peduncle of midbrain; FMA72464:Cerebral crus]}. The structures contained in it have already been described; from behind forward, they are the {posterior perforated substance [FMA77523:Posterior perforated substance]}, {corpora mamillaria [FMA74877:Mammillary body]}, {tuber cinereum [FMA62327:Tuber cinereum]}, {infundibulum [FMA74635:Infundibulum of neurohypophysis]}, and {hypophysis [FMA13889:Pituitary gland]}.
 * The {Telencephalon [FMA62000:Telencephalon]}.—The {telencephalon [FMA62000:Telencephalon]} includes: (1) the {cerebral hemispheres [FMA61817:Cerebral hemisphere]} with their {cavities [:]}, the {lateral ventricles [FMA78448:Lateral ventricle]}; and (2) the {pars optica hypothalami [FMA62027:Anterior hypothalamic region]} and the anterior portion of the {third ventricle [FMA78454:Third ventricle]} (already described under the {diencephalon [FMA62001:Diencephalon]}). As previously stated (see page 744), each {cerebral hemisphere [FMA61817:Cerebral hemisphere]} may be divided into three fundamental parts, viz., the {rhinencephalon [FMA62430:Paleocortex]}, the {corpus striatum [FMA77616:Corpus striatum]}, and the {neopallium [FMA62429:Neocortex]}. The {rhinencephalon [FMA62430:Paleocortex]}, associated with the sense of smell, is the oldest part of the {telencephalon [FMA62000:Telencephalon]}, and forms almost the whole of the hemisphere in some of the lower animals, e. g., fishes, amphibians, and reptiles. In man it is rudimentary, whereas the {neopallium [FMA62429:Neocortex]} undergoes great development and forms the chief part of the hemisphere. 38
 * The {Cerebral Hemispheres [FMA61817:Cerebral hemisphere]}.—The {cerebral hemispheres [FMA61817:Cerebral hemisphere]} constitute the largest part of the {brain [FMA50801:Brain]}, and, when viewed together from above, assume the form of an ovoid mass broader behind than in front, the greatest transverse diameter corresponding with a line connecting the two {parietal eminences [FMA57080:Parietal tuber]}. The hemispheres are separated medially by a deep cleft, named the {longitudinal cerebral fissure [FMA83727:Longitudinal fissure]}, and each possesses a central cavity, the {lateral ventricle [FMA78448:Lateral ventricle]}. 39
 * The {Longitudinal Cerebral Fissure [FMA83727:Longitudinal fissure]} ({fissura cerebri longitudinalis [FMA9712:Hand]}; {great longitudinal fissure [FMA9712:Hand]}) contains a sickle-shaped process of {dura mater [FMA9592:Dura mater]}, the {falx cerebri [FMA83967:Falx cerebri]}. It front and behind, the fissure extends from the upper to the under surfaces of the hemispheres and completely separates them, but its middle portion separates them for only about one-half of their vertical extent; for at this part they are connected across the middle line by a great central white commissure, the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]}. 40
 * In a median sagittal section (Fig. 720) the cut {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]} presents the appearance of a broad, arched band. Its thick posterior end, termed the {splenium [FMA7196:Spleen]}, overlaps the {mid-brain [FMA61993:Midbrain]}, but is separated from it by the {tela chorioidea of the third ventricle [FMA78463:Tela choroidea of third ventricle]} and the {pineal body [FMA62033:Pineal body]}. Its anterior curved end, termed the {genu [FMA24974:Knee]}, gradually tapers into a thinner portion, the rostrum, which is continued downward and backward in front of the {anterior commissure [FMA61961:Anterior commissure]} to join the {lamina terminalis [FMA61975:Lamina terminalis]}. Arching backward from immediately behind the {anterior commissure [FMA61961:Anterior commissure]} to the under surface of the {splenium [FMA7196:Spleen]} is a second white band named the {fornix [FMA61965:Fornix of forebrain]}: between this and the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]} are the laminæ and {cavity of the septum pellucidum [FMA61874:Cave of septum pellucidum]}. 41
 * {Surfaces of the Cerebral Hemispheres [FMA256259:Surface of cerebral hemisphere]}.—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 [FMA46565:Skull]}. The medial surface is flat and vertical, and is separated from that of the opposite hemisphere by the {great longitudinal fissure [FMA9712:Hand]} and the {falx cerebri [FMA83967: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 [FMA57406:Cerebral surface of orbital part of frontal bone]}, is concave, and rests on the {roof of the orbit [FMA53078:Roof of orbit]} and {nose [FMA46472:Nose]}; the middle area is convex, and consists of the under {surface of the temporal lobe [FMA256285:Surface of temporal lobe]}: it is adapted to the corresponding half of the {middle cranial fossa [FMA54369: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 [FMA83966:Tentorium cerebelli]}, which intervenes between it and the upper surface of the {cerebellum [FMA67944: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 [FMA49034:Orbitalis]} surface, is known as the {superciliary border [FMA256358:Superciliary border]}; (c) medial occipital, separating the medial and tentorial surfaces; and (d) medial {orbital [FMA49034:Orbitalis]}, separating the {orbital [FMA49034:Orbitalis]} from the medial surface. The anterior end of the hemisphere is named the {frontal pole [FMA71028:Frontal pole (FP); FMA74885:Frontal pole]}; the posterior, the {occipital pole [FMA71036:Occipital pole (OP); FMA74892:Occipital pole]}; and the anterior end of the {temporal lobe [FMA61825:Temporal lobe]}, the {temporal pole [FMA71071:Temporal pole (TP); FMA74890:Temporal pole]}. About 5 cm. in front of the {occipital pole [FMA71036:Occipital pole (OP); FMA74892:Occipital pole]} on the infero-lateral border is an indentation or {notch [FMA75036:Notch]}, named the {preoccipital notch [FMA83739: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 [FMA50801:Brain]} wall, and give rise to corresponding elevations in the interior of the ventricle. They comprise the {hippocampal fissure [FMA83747:Hippocampal sulcus]}, and parts of the calcarine and {collateral fissures [FMA83751:Collateral sulcus]}. The incomplete furrows are very numerous, and only indent the subjacent {white substance [FMA83929:White matter of neuraxis]}, without producing any corresponding elevations in the {ventricular cavity [FMA13238:Cavity of ventricle]}. 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 [FMA50801:Brain]}. The convoluted condition of the surface permits of a great increase of the {gray matter [FMA67242:Gray matter of neuraxis]} 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 [FMA83751:Collateral sulcus]}, the central and {cingulate sulci [FMA83748:Cingulate sulcus]}, and the {sulcus circularis [FMA83753:Circular sulcus of insula]}.
 * The {Lateral Cerebral Fissure [FMA77801:Lateral sulcus]} ({fissura cerebri lateralis [FMA77801:Lateral sulcus]} [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 [FMA77700:Basal forebrain]}, and commences in a depression at the lateral angle of the {anterior perforated substance [FMA61891:Anterior perforated substance]}. From this {point [FMA50596:Point]} it extends between the anterior part of the {temporal lobe [FMA61825:Temporal lobe]} and the {orbital surface of the frontal lobe [FMA57406:Cerebral surface of orbital part of frontal bone]}, 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 [FMA61860: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 [FMA61826:Parietal lobe]}. 48
 * The {Central Sulcus [FMA83752:Central sulcus]} ({sulcus centralis [FMA83752:Central sulcus]} [Rolandi]; {fissure of Rolando [FMA83752:Central sulcus]}; {central fissure [FMA83752:Central sulcus]}) (Figs. 725, 726) is situated about the middle of the lateral surface of the hemisphere, and begins in or near the {longitudinal cerebral fissure [FMA83727:Longitudinal fissure]}, a little behind its mid-{point [FMA50596:Point]}. It runs sinuously downward and forward, and ends a little above the posterior ramus of the {lateral fissure [FMA77801:Lateral sulcus]}, and about 2.5 cm. behind the anterior ascending ramus of the same fissure. It described two chief curves: a superior {genu [FMA24974:Knee]} with its concavity directed forward, and an inferior {genu [FMA24974:Knee]} with its concavity directed backward. The {central sulcus [FMA83752:Central sulcus]} forms an angle opening forward of about 70° with the {median plane [FMA49450: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 [FMA71036:Occipital pole (OP); FMA74892: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 [FMA83749:Calcarine sulcus]} below and behind the posterior end of the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]}. In most cases it contains a submerged gyrus. 52
 * The {Calcarine Fissure [FMA83749:Calcarine sulcus]} ({fissura calcarina [FMA83749:Calcarine sulcus]}) (Fig. 727) is on the medial surface of the hemisphere. It begins near the {occipital pole [FMA71036:Occipital pole (OP); FMA74892:Occipital pole]} in two converging rami, and runs forward to a {point [FMA50596:Point]} a little below the {splenium of the corpus callosum [FMA61948:Splenium of 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 [FMA78438:Calcarine spur; FMA83707:Calcar avis]} in the {posterior cornu [FMA83700:Occipital horn of lateral ventricle]} of the {lateral ventricle [FMA78448:Lateral ventricle]}. 53
 * The {Cingulate Sulcus [FMA83748:Cingulate sulcus]} ({sulcus cinguli [FMA83748:Cingulate sulcus]}; {callosomarginal fissure [FMA83748:Cingulate sulcus]}) (Fig. 727) is on the medial surface of the hemisphere; it begins below the anterior end of the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]} and runs upward and forward nearly parallel to the rostrum of this body and, curving in front of the {genu [FMA24974:Knee]}, is continued backward above the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]}, and finally ascends to the supero-medial border of the hemisphere a short distance behind the upper end of the {central sulcus [FMA83752:Central sulcus]}. It separates the superior {frontal [FMA46757:Frontalis]} from the {cingulate gyrus [FMA62434:Cingulate gyrus]}. 54
 * The {Collateral Fissure [FMA83751:Collateral sulcus]} (fissura collateralis) (Fig. 727) is on the tentorial surface of the hemisphere and extends from near the {occipital pole [FMA71036:Occipital pole (OP); FMA74892:Occipital pole]} to within a short distance of the {temporal pole [FMA71071:Temporal pole (TP); FMA74890:Temporal pole]}. Behind, it lies below and lateral to the {calcarine fissure [FMA83749:Calcarine sulcus]}, from which it is separated by the {lingual gyrus [FMA61904:Lingual gyrus]}; in front, it is situated between the {hippocampal gyrus [FMA61918:Parahippocampal gyrus]} and the anterior part of the {fusiform gyrus [FMA61908:Fusiform gyrus]}. 55
 * The {Sulcus Circularis [FMA83753:Circular sulcus of insula]} ({circuminsular fissure [FMA83753:Circular sulcus of insula]}) (Fig. 731) is on the lower and lateral surfaces of the hemisphere: it surrounds the {insula [FMA67329:Insula]} and separates it from the {frontal [FMA46757:Frontalis]}, parietal, and {temporal lobes [FMA61825:Temporal lobe]}. 56
 * {Lobes of the Hemispheres [FMA77800:Set of cerebral lobes]}.—By means of these fissures and sulci, assisted by certain arbitrary lines, each hemisphere is divided into the following lobes: the {frontal [FMA46757:Frontalis]}, the parietal, the temporal, the occipital, the limbic, and the {insula [FMA67329:Insula]}. 57
 * {Frontal Lobe [FMA61824:Frontal lobe]} ({lobus frontalis [FMA61824:Frontal lobe]}).—On the lateral surface of the hemisphere this lobe extends from the {frontal pole [FMA71028:Frontal pole (FP); FMA74885:Frontal pole]} to the {central sulcus [FMA83752:Central sulcus]}, the latter separating it from the {parietal lobe [FMA61826:Parietal lobe]}. Below, it is limited by the posterior ramus of the {lateral fissure [FMA77801:Lateral sulcus]}, which intervenes between it and the {central lobe [FMA67329:Insula]}. On the medial surface, it is separated from the {cingulate gyrus [FMA62434:Cingulate gyrus]} by the {cingulate sulcus [FMA83748:Cingulate sulcus]}; and on the inferior surface, it is bounded behind by the stem of the {lateral fissure [FMA77801:Lateral sulcus]}.
 * The lateral {surface of the frontal lobe [FMA256267:Surface of 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 [FMA46757:Frontalis]}; the gyri are the anterior central, and the superior, middle, and inferior {frontal [FMA46757:Frontalis]}. The {precentral sulcus [FMA83800:Precentral sulcus]} runs parallel to the {central sulcus [FMA83752:Central sulcus]}, and is usually divided into an upper and a lower part; between it and the {central sulcus [FMA83752:Central sulcus]} is the anterior central gyrus. From the {precentral sulcus [FMA83800:Precentral sulcus]}, the superior and {inferior frontal sulci [FMA83757:Inferior frontal sulcus]} 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 [FMA61860:Inferior frontal gyrus]}. 59
 * The anterior central gyrus ({gyrus centralis anterior [FMA61894:Precentral gyrus]}; ascending {frontal [FMA46757:Frontalis]} convolution; {precentral gyre [FMA61894:Precentral gyrus; FMA71044:Precentral gyrus (PRG)]}) is bounded in front by the {precentral sulcus [FMA83800:Precentral sulcus]}, behind by the {central sulcus [FMA83752:Central sulcus]}; it extends from the supero-medial border of the hemisphere to the posterior ramus of the {lateral fissure [FMA77801:Lateral sulcus]}. 60
 * The {superior frontal gyrus [FMA61857:Superior frontal gyrus]} ({gyrus frontalis superior [FMA61857:Superior frontal gyrus]}; superfrontal gyre) is situated above the {superior frontal sulcus [FMA83755:Superior frontal sulcus]} and is continued on to the medial surface of the hemisphere. The portion on the lateral surface of the hemisphere is usually more or {less [FMA63048:Circular muscle layer of abdominal part of esophagus]} completely subdivided into an upper and a lower part by an antero-posterior {sulcus [:]}, the paramedial {sulcus [:]}, which, however, is frequently interrupted by bridging gyri. 61
 * The {middle frontal gyrus [FMA61859:Middle frontal gyrus]} ({gyrus frontalis medius [FMA61859:Middle frontal gyrus]}; medifrontal gyre), between the superior and {inferior frontal sulci [FMA83757:Inferior frontal sulcus]}, is continuous with the {anterior orbital gyrus [FMA256196:Anterior orbital gyrus]} on the inferior surface of the hemisphere; it is frequently subdivided into two by a horizontal {sulcus [:]}, the medial {frontal [FMA46757:Frontalis]} {sulcus [:]} of Eberstaller, which ends anteriorly in a wide bifurcation. 62
 * The {inferior frontal gyrus [FMA61860:Inferior frontal gyrus]} ({gyrus frontalis inferior [FMA61860:Inferior frontal gyrus; FMA61980:Triangular part of inferior frontal gyrus; FMA61981:Opercular part of inferior frontal gyrus; FMA61982:Orbital part of inferior frontal gyrus]}; subfrontal gyre) lies below the {inferior frontal sulcus [FMA83757:Inferior frontal sulcus]}, and extends forward from the lower part of the {precentral sulcus [FMA83800:Precentral sulcus]}; it is continuous with the lateral and {posterior orbital gyri [FMA80184:Posterior orbital gyrus]} on the under surface of the lobe. It is subdivided by the anterior horizontal and ascending rami of the {lateral fissure [FMA77801:Lateral sulcus]} into three parts, viz., (1) the {orbital [FMA49034:Orbitalis]} part, below the anterior horizontal ramus of the fissure; (2) the triangular part (cap of Broca), between the ascending and horizontal rami; and (3) the basilar part, behind the anterior ascending ramus. The {left inferior frontal gyrus [FMA72658:Left inferior frontal gyrus]} is, as a rule, more highly developed than the right, and is named the gyrus of Broca, from the fact that Broca described it as the center for articulate speech. 63
 * The inferior or {orbital surface of the frontal lobe [FMA57406:Cerebral surface of orbital part of frontal bone]} is concave, and rests on the {orbital plate of the frontal bone [FMA54674:Orbital plate of frontal bone]} (Fig. 729). It is divided into four {orbital gyri [FMA72020:Set of orbital gyri]} by a well-marked H-shaped {orbital sulcus [FMA83770:Orbital sulcus]}. These are named, from their position, the medial, anterior, lateral, and {posterior orbital gyri [FMA80184:Posterior orbital gyrus]}. The {medial orbital gyrus [FMA62419:Medial orbital gyrus]} presents a well-marked antero-posterior {sulcus [:]}, the {olfactory sulcus [FMA83769:Olfactory sulcus]}, for the {olfactory tract [FMA46787:Olfactory nerve]}; the portion medial to this is named the {straight gyrus [FMA61893:Straight gyrus]}, and is continuous with the {superior frontal gyrus [FMA61857:Superior frontal gyrus]} on the medial surface. 64
 * The medial {surface of the frontal lobe [FMA256267:Surface of frontal lobe]} is occupied by the medial part of the {superior frontal gyrus [FMA61857:Superior frontal gyrus]} ({marginal gyrus [FMA61857:Superior frontal gyrus]}) (Fig. 727). It lies between the {cingulate sulcus [FMA83748:Cingulate sulcus]} and the supero-medial margin of the hemisphere. The posterior part of this gyrus is sometimes marked off by a vertical {sulcus [:]}, and is distinguished as the {paracentral lobule [FMA77534:Paracentral lobule]}, because it is continuous with the anterior and {posterior central gyri [FMA61896:Postcentral gyrus]}. 65
 * {Parietal Lobe [FMA61826:Parietal lobe]} ({lobus parietalis [FMA61826:Parietal lobe]}).—The {parietal lobe [FMA61826:Parietal lobe]} is separated from the {frontal lobe [FMA61824:Frontal lobe]} by the {central sulcus [FMA83752:Central sulcus]}, but its boundaries below and behind are not so definite. Posteriorly, it is limited by the parietoöccipital fissure, and by a line carried across the hemisphere from the end of this fissure toward the {preoccipital notch [FMA83739:Preoccipital notch]}. Below, it is separated from the {temporal lobe [FMA61825:Temporal lobe]} by the posterior ramus of the {lateral fissure [FMA77801:Lateral sulcus]}, and by a line carried backward from it to meet the line passing downward to the {preoccipital notch [FMA83739:Preoccipital notch]}.
 * The lateral {surface of the parietal lobe [FMA256279:Surface of parietal lobe]} (Fig. 726) is cleft by a well-marked furrow, the {intraparietal sulcus [FMA83772:Intraparietal sulcus]} of Turner, which consists of an oblique and a horizontal portion. The oblique part is named the {postcentral sulcus [FMA83774:Postcentral sulcus]}, and commences below, about midway between the lower end of the {central sulcus [FMA83752:Central sulcus]} and the upturned end of the {lateral fissure [FMA77801:Lateral sulcus]}. It runs upward and backward, parallel to the {central sulcus [FMA83752:Central sulcus]}, and is sometimes divided into an upper and a lower ramus. It forms the hinder limit of the {posterior central gyrus [FMA61896:Postcentral gyrus]}. 67
 * From about the middle of the {postcentral sulcus [FMA83774:Postcentral sulcus]}, or from the upper end of its inferior ramus, the horizontal portion of the {intraparietal sulcus [FMA83772:Intraparietal sulcus]} is carried backward and slightly upward on the {parietal lobe [FMA61826:Parietal lobe]}, and is prolonged, under the name of the occipital ramus, on to the {occipital lobe [FMA67325:Occipital lobe]}, where it divides into two parts, which form nearly a right angle with the main stem and constitute the {transverse occipital sulcus [FMA83786:Transverse occipital sulcus]}. The part of the {parietal lobe [FMA61826:Parietal lobe]} above the horizontal portion of the {intraparietal sulcus [FMA83772:Intraparietal sulcus]} is named the {superior parietal lobule [FMA61899:Superior parietal lobule; FMA71058:Superior parietal lobule (SPL)]}; the part below, the {inferior parietal lobule [FMA61897:Supramarginal gyrus; FMA77536:Inferior parietal lobule]}. 68
 * The {posterior central gyrus [FMA61896:Postcentral gyrus]} ({gyrus centralis posterior [FMA61896:Postcentral gyrus]}; ascending parietal convolution; {postcentral gyre [FMA61896:Postcentral gyrus; FMA71042:Postcentral gyrus (POG)]}) extends from the {longitudinal fissure [FMA83727:Longitudinal fissure]} above to the posterior ramus of the {lateral fissure [FMA77801:Lateral sulcus]} below. It lies parallel with the anterior central gyrus, with which it is connected below, and also, sometimes, above, the {central sulcus [FMA83752:Central sulcus]}. 69
 * The {superior parietal lobule [FMA61899:Superior parietal lobule; FMA71058:Superior parietal lobule (SPL)]} ({lobulus parietalis superior [FMA61899:Superior parietal lobule]}) is bounded in front by the upper part of the {postcentral sulcus [FMA83774:Postcentral sulcus]}, but is usually connected with the {posterior central gyrus [FMA61896:Postcentral gyrus]} above the end of the {sulcus [:]}; behind it is the lateral part of the parietoöccipital fissure, around the end of which it is joined to the {occipital lobe [FMA67325:Occipital lobe]} by a curved gyrus, the arcus parietoöccipitalis; below, it is separated from the {inferior parietal lobule [FMA61897:Supramarginal gyrus; FMA77536:Inferior parietal lobule]} by the horizontal portion of the {intraparietal sulcus [FMA83772:Intraparietal sulcus]}. 70
 * The {inferior parietal lobule [FMA61897:Supramarginal gyrus; FMA77536:Inferior parietal lobule]} ({lobulus parietalis inferior [FMA77536:Inferior parietal lobule]}; {subparietal district [FMA77536:Inferior parietal lobule]} or {lobule [FMA45737:Lobule]}) lies below the horizontal portion of the {intraparietal sulcus [FMA83772:Intraparietal sulcus]}, and behind the lower part of the {postcentral sulcus [FMA83774:Postcentral sulcus]}. It is divided from before backward into two gyri. One, the supramarginal, arches over the upturned end of the {lateral fissure [FMA77801:Lateral sulcus]}; it is continuous in front with the {postcentral gyrus [FMA61896:Postcentral gyrus; FMA71042:Postcentral gyrus (POG)]}, and behind with the {superior temporal gyrus [FMA61905:Superior temporal gyrus]}. The second, the angular, arches over the posterior end of the {superior temporal sulcus [FMA83783:Superior temporal sulcus]}, behind which it is continuous with the {middle temporal gyrus [FMA61906:Middle temporal gyrus]}. 71
 * The medial {surface of the parietal lobe [FMA256279:Surface of parietal lobe]} (Fig. 727) is bounded behind by the medial part of the parietoöccipital fissure; in front, by the posterior end of the {cingulate sulcus [FMA83748:Cingulate sulcus]}; and below, it is separated from the {cingulate gyrus [FMA62434:Cingulate gyrus]} by the {subparietal sulcus [FMA83777:Subparietal sulcus]}. It is of small size, and consists of a square-shaped convolution, which is termed the {precuneus [FMA61900:Precuneus]} or quadrate lobe. 72
 * {Occipital Lobe [FMA67325:Occipital lobe]} ({lobus occipitalis [FMA67325:Occipital lobe]}).—The {occipital lobe [FMA67325:Occipital lobe]} is small and {pyramidal [FMA15568:Pyramidalis]} in shape; it presents three surfaces: lateral, medial, and tentorial. 73
 * The lateral surface is limited in front by the lateral part of the parietoöccipital fissure, and by a line carried from the end of this fissure to the {preoccipital notch [FMA83739:Preoccipital notch]}; it is traversed by the transverse occipital and the {lateral occipital sulci [FMA83785:Lateral occipital sulcus]}. The {transverse occipital sulcus [FMA83786:Transverse occipital sulcus]} is continuous with the posterior end of the occipital ramus of the {intraparietal sulcus [FMA83772:Intraparietal sulcus]}, and runs across the upper part of the lobe, a short distance behind the parietoöccipital fissure. The {lateral occipital sulcus [FMA83785:Lateral occipital sulcus]} extends from behind forward, and divides the lateral {surface of the occipital lobe [FMA256273:Surface of occipital lobe]} into a superior and an inferior gyrus, which are continuous in front with the parietal and {temporal lobes [FMA61825:Temporal lobe]}. 125 74
 * The medial {surface of the occipital lobe [FMA256273:Surface of occipital lobe]} is bounded in front by the medial part of the parietoöccipital fissure, and is traversed by the {calcarine fissure [FMA83749:Calcarine sulcus]}, which subdivides it into the {cuneus [FMA61903:Cuneus]} and the {lingual gyrus [FMA61904:Lingual gyrus]}. The {cuneus [FMA61903:Cuneus]} is a wedge-shaped area between the {calcarine fissure [FMA83749:Calcarine sulcus]} and the medial part of the parietoöccipital fissure. The {lingual gyrus [FMA61904:Lingual gyrus]} lies between the {calcarine fissure [FMA83749:Calcarine sulcus]} and the posterior part of the {collateral fissure [FMA83751:Collateral sulcus]}; behind, it reaches the {occipital pole [FMA71036:Occipital pole (OP); FMA74892:Occipital pole]}; in front, it is continued on to the tentorial {surface of the temporal lobe [FMA256285:Surface of temporal lobe]}, and joins the {hippocampal gyrus [FMA61918:Parahippocampal gyrus]}. 75
 * The tentorial {surface of the occipital lobe [FMA256273:Surface of occipital lobe]} is limited in front by an imaginary transverse line through the {preoccipital notch [FMA83739:Preoccipital notch]}, and consists of the posterior part of the {fusiform gyrus [FMA61908:Fusiform gyrus]} (occipitotemporal convolution) and the lower part of the {lingual gyrus [FMA61904:Lingual gyrus]}, which are separated from each other by the posterior segment of the {collateral fissure [FMA83751:Collateral sulcus]}. 76
 * {Temporal Lobe [FMA61825:Temporal lobe]} ({lobus temporalis [FMA61825:Temporal lobe]}).—The {temporal lobe [FMA61825:Temporal lobe]} presents superior, lateral, and inferior surfaces. 77
 * The superior surface forms the lower limit of the {lateral fissure [FMA77801:Lateral sulcus]} and overlaps the {insula [FMA67329:Insula]}. On opening out the {lateral fissure [FMA77801:Lateral sulcus]}, three or four gyri will be seen springing from the depth of the hinder end of the fissure, and running obliquely forward and outward on the posterior part of the upper surface of the {superior temporal gyrus [FMA61905:Superior temporal gyrus]}; these are named the {transverse temporal gyri [FMA72016:Set of transverse temporal gyri]} (Heschl) (Fig. 730). 78
 * The lateral surface (Fig. 726) is bounded above by the posterior ramus of the {lateral fissure [FMA77801:Lateral sulcus]}, and by the imaginary line continued backward from it; below, it is limited by the infero-lateral border of the hemisphere. It is divided into superior, middle, and inferior gyri by the superior and {middle temporal sulci [FMA83784:Inferior temporal sulcus]}. The {superior temporal sulcus [FMA83783:Superior temporal sulcus]} runs from before backward across the {temporal lobe [FMA61825:Temporal lobe]}, some little distance below, but parallel with, the posterior ramus of the {lateral fissure [FMA77801:Lateral sulcus]}; and hence it is often termed the {parallel sulcus [FMA83783:Superior temporal sulcus]}. The {middle temporal sulcus [FMA83784:Inferior temporal sulcus]} takes the same direction as the superior, but is situated at a lower level, and is usually subdivided into two or more parts. The {superior temporal gyrus [FMA61905:Superior temporal gyrus]} lies between the posterior ramus of the {lateral fissure [FMA77801:Lateral sulcus]} and the {superior temporal sulcus [FMA83783:Superior temporal sulcus]}, and is continuous behind with the supramarginal and {angular gyri [FMA61898:Angular gyrus; FMA71018:Angular gyrus (AG)]}. The {middle temporal gyrus [FMA61906:Middle temporal gyrus]} is placed between the superior and {middle temporal sulci [FMA83784:Inferior temporal sulcus]}, and is joined posteriorly with the {angular gyrus [FMA61898:Angular gyrus; FMA71018:Angular gyrus (AG)]}. The {inferior temporal gyrus [FMA61907:Inferior temporal gyrus]} is placed below the {middle temporal sulcus [FMA83784:Inferior temporal sulcus]}, and is connected behind with the {inferior occipital gyrus [FMA61902:Lateral occipital gyrus]}; it also extends around the infero-lateral border on to the inferior {surface of the temporal lobe [FMA256285:Surface of temporal lobe]}, where it is limited by the inferior {sulcus [:]}.
 * The inferior surface is concave, and is continuous posteriorly with the tentorial {surface of the occipital lobe [FMA256273:Surface of occipital lobe]}. It is traversed by the {inferior temporal sulcus [FMA74518:Occipitotemporal sulcus; FMA83784:Inferior temporal sulcus]}, which extends from near the {occipital pole [FMA71036:Occipital pole (OP); FMA74892:Occipital pole]} behind, to within a short distance of the {temporal pole [FMA71071:Temporal pole (TP); FMA74890:Temporal pole]} in front, but is frequently subdivided by bridging gyri. Lateral to this fissure is the narrow tentorial part of the {inferior temporal gyrus [FMA61907:Inferior temporal gyrus]}, and medial to it the {fusiform gyrus [FMA61908:Fusiform gyrus]}, which extends from the occipital to the {temporal pole [FMA71071:Temporal pole (TP); FMA74890:Temporal pole]}; this gyrus is limited medially by the {collateral fissure [FMA83751:Collateral sulcus]}, which separates it from the {lingual gyrus [FMA61904:Lingual gyrus]} behind and from the {hippocampal gyrus [FMA61918:Parahippocampal gyrus]} in front. 80
 * 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
 * The anterior end is named the {genu [FMA24974:Knee]}, and is bent downward and backward in front of the {septum pellucidum [FMA61842:Septum of telencephalon; FMA61844:Septum pellucidum]}; diminishing rapidly in thickness, it is prolonged backward under the name of the rostrum, which is connected below with the {lamina terminalis [FMA61975:Lamina terminalis]}. The {anterior cerebral arteries [FMA50028:Anterior cerebral artery]} are in contact with the under surface of the rostrum; they then arch over the front of the {genu [FMA24974:Knee]}, and are carried backward above the {body of the corpus callosum [FMA61947:Body of corpus callosum]}. 101
 * The posterior end is termed the {splenium [FMA7196:Spleen]} and constitutes the thickest part of the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]}. It overlaps the {tela chorioidea of the third ventricle [FMA78463:Tela choroidea of third ventricle]} and the {mid-brain [FMA61993:Midbrain]}, and ends in a thick, convex, free border. A sagittal section of the {splenium [FMA7196:Spleen]} shows that the posterior end of the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]} is acutely bent forward, the upper and lower parts being applied to each other. 102
 * The superior surface is convex from before backward, and is about 2.5 cm. wide. Its medial part forms the bottom of the {longitudinal fissure [FMA83727:Longitudinal fissure]}, and is in contact posteriorly with the lower border of the {falx cerebri [FMA83967:Falx cerebri]}. Laterally it is overlapped by the {cingulate gyrus [FMA62434:Cingulate gyrus]}, but is separated from it by the slit-like callosal fissure. It is traversed by numerous transverse {ridges [FMA75035:Crest]} and furrows, and is covered by a thin layer of {gray matter [FMA67242:Gray matter of neuraxis]}, the {supracallosal gyrus [FMA61920:Supracallosal gyrus]}, which exhibits on either side of the middle line the medial and {lateral longitudinal stri [FMA62439:Lateral longitudinal stria]}æ, already described (page 827). 103
 * The inferior surface is concave, and forms on either side of the middle line the roof of the {lateral ventricle [FMA78448:Lateral ventricle]}. Medially, this surface is attached in front to the {septum pellucidum [FMA61842:Septum of telencephalon; FMA61844:Septum pellucidum]}; behind this it is fused with the upper {surface of the body [FMA61695:Body surface]} of the {fornix [FMA61965:Fornix of forebrain]}, while the {splenium [FMA7196:Spleen]} is in contact with the {tela chorioidea [FMA242849:Tela choroidea]}. 104
 * On either side, the fibers of the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]} radiate in the {white substance [FMA83929:White matter of neuraxis]} and pass to the various parts of the {cerebral cortex [FMA61830:Cerebral cortex]}; those curving forward from the {genu [FMA24974:Knee]} into the {frontal lobe [FMA61824:Frontal lobe]} constitute the forceps anterior, and those curving backward into the {occipital lobe [FMA67325:Occipital lobe]}, the forceps posterior. Between these two parts is the main body of the fibers which constitute the {tapetum [FMA77208:Tapetum]} and extend laterally on either side into the {temporal lobe [FMA61825:Temporal lobe]}, and cover in the {central part of the lateral ventricle [FMA83703:Body of lateral ventricle]}. 105
 * The {Lateral Ventricles [FMA78448:Lateral ventricle]} ({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]}) (Fig. 734).—The two {lateral ventricles [FMA78448:Lateral ventricle]} are irregular {cavities [:]} situated in the lower and medial parts of the {cerebral hemispheres [FMA61817:Cerebral hemisphere]}, one on either side of the middle line. They are separated from each other by a median vertical partition, the {septum pellucidum [FMA61842:Septum of telencephalon; FMA61844:Septum pellucidum]}, but communicate with the {third ventricle [FMA78454:Third ventricle]} and indirectly with each other through the {interventricular foramen [FMA75351:Interventricular foramen]}. They are lined by a thin, diaphanous membrane, the {ependyma [FMA242791:Ependyma of neuraxis]}, covered by ciliated {epithelium [FMA9639:Portion of epithelium]}, and contain {cerebrospinal fluid [FMA20935:Cerebrospinal fluid]}, which, even in health, may be secreted in considerable amount. Each {lateral ventricle [FMA78448:Lateral ventricle]} consists of a central part or body, and three prolongations from it, termed cornua (Figs. 735, 736). 106
 * The {central part (pars centralis ventriculi lateralis; cella) (Fig. 737) of the lateral ventricle [FMA83703:Body of lateral ventricle]} extends from the {interventricular foramen [FMA75351:Interventricular foramen]} to the {splenium of the corpus callosum [FMA61948:Splenium of corpus callosum]}. It is an irregularly curved cavity, triangular on transverse section, with a roof, a floor, and a medial wall. The roof is formed by the under surface of the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]}; the floor by the following parts, enumerated in their order of position, from before backward: the {caudate nucleus [FMA61833:Caudate nucleus]} of the {corpus striatum [FMA77616:Corpus striatum]}, the {stria terminalis [FMA61974:Stria terminalis]} and the {terminal vein [FMA50997:Superior thalamostriate vein]}, the lateral portion of the upper surface of the {thalamus [FMA62007:Thalamus]}, the {choroid plexus [FMA61934:Choroid plexus of cerebral hemisphere]}, and the lateral part of the {fornix [FMA61965:Fornix of forebrain]}; the medial wall is the posterior part of the {septum pellucidum [FMA61842:Septum of telencephalon; FMA61844:Septum pellucidum]}, which separates it from the opposite ventricle.
 * The anterior cornu ({cornu anterius [FMA74520:Frontal horn of lateral ventricle]}; anterior horn; precornu) (Fig. 736) passes forward and lateralward, with a slight inclination downward, from the {interventricular foramen [FMA75351:Interventricular foramen]} into the {frontal lobe [FMA61824:Frontal lobe]}, curving around the anterior end of the {caudate nucleus [FMA61833:Caudate nucleus]}. Its floor is formed by the upper surface of the reflected portion of the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]}, the rostrum. It is bounded medially by the anterior portion of the {septum pellucidum [FMA61842:Septum of telencephalon; FMA61844:Septum pellucidum]}, and laterally by the {head of the caudate nucleus [FMA61852:Head of caudate nucleus]}. Its apex reaches the posterior surface of the {genu of the corpus callosum [FMA61946:Genu of corpus callosum]}. 108
 * The {posterior cornu [FMA83700:Occipital horn of lateral ventricle]} ({cornu posterius [FMA83700:Occipital horn of lateral ventricle]}; postcornu) (Figs. 737, 788) passes into the {occipital lobe [FMA67325:Occipital lobe]}, its direction being backward and lateralward, and then medialward. Its roof is formed by the fibers of the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]} passing to the temporal and {occipital lobes [FMA67325:Occipital lobe]}. On its medial wall is a longitudinal eminence, the {calcar avis [FMA78438:Calcarine spur; FMA83707:Calcar avis]} ({hippocampus [FMA62493:Hippocampus; FMA74038:Hippocampal formation]} minor), which is an involution of the {ventricular wall [FMA13884:Wall of ventricle]} produced by the {calcarine fissure [FMA83749:Calcarine sulcus]}. Above this the forceps posterior of the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]}, sweeping around to enter the {occipital lobe [FMA67325:Occipital lobe]}, causes another projection, termed the {bulb of the posterior cornu [FMA83699:Bulb of occipital horn of lateral ventricle]}. The {calcar avis [FMA78438:Calcarine spur; FMA83707:Calcar avis]} and {bulb of the posterior cornu [FMA83699:Bulb of occipital horn of lateral ventricle]} are extremely variable in their degree of development; in some cases they are ill-defined, in others prominent.
 * The {inferior cornu [FMA83701:Temporal horn of lateral ventricle]} (cornu inferior; descending horn; middle horn; medicornu) (Fig. 739), the largest of the three, traverses the {temporal lobe [FMA61825:Temporal lobe]} of the {brain [FMA50801:Brain]}, forming in its course a curve around the posterior end of the {thalamus [FMA62007:Thalamus]}. It passes at first backward, lateralward, and downward, and then curves forward to within 2.5 cm. of the apex of the {temporal lobe [FMA61825:Temporal lobe]}, its direction being fairly well indicated on the {surface of the brain [FMA86594:Surface of brain]} by that of the {superior temporal sulcus [FMA83783:Superior temporal sulcus]}. Its roof is formed chiefly by the inferior surface of the {tapetum [FMA77208:Tapetum]} of the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]}, but the {tail of the caudate nucleus [FMA61854:Tail of caudate nucleus]} and the {stria terminalis [FMA61974:Stria terminalis]} also extend forward in the roof of the {inferior cornu [FMA83701:Temporal horn of lateral ventricle]} to its extremity; the {tail of the caudate nucleus [FMA61854:Tail of caudate nucleus]} joins the {putamen [FMA61834:Putamen]}. Its floor presents the following parts: the {hippocampus [FMA62493:Hippocampus; FMA74038:Hippocampal formation]}, the {fimbria hippocampi [FMA83866:Fimbria of hippocampus]}, the {collateral eminence [FMA83706:Collateral eminence]}, and the {choroid plexus [FMA61934:Choroid plexus of cerebral hemisphere]}. When the {choroid plexus [FMA61934:Choroid plexus of cerebral hemisphere]} is removed, a cleft-like opening is left along the medial wall of the {inferior cornu [FMA83701:Temporal horn of lateral ventricle]}; this cleft constitutes the lower part of the {choroidal fissure [FMA74512:Choroidal fissure]}. 110
 * The {hippocampus [FMA62493:Hippocampus; FMA74038:Hippocampal formation]} ({hippocampus major [FMA62493:Hippocampus]}) (Figs. 739, 740) is a curved eminence, about 5 cm. long, which extends throughout the entire length of the floor of the {inferior cornu [FMA83701:Temporal horn of lateral ventricle]}. Its lower end is enlarged, and presents two or three rounded elevations or digitations which give it a paw-like appearance, and hence it is named the {pes hippocampi [FMA84032:Set of hippocampal digitations]}. If a transverse section be made through the {hippocampus [FMA62493:Hippocampus; FMA74038:Hippocampal formation]}, it will be seen that this eminence is produced by the folding of the wall of the hemisphere to form the {hippocampal fissure [FMA83747:Hippocampal sulcus]}. The main mass of the {hippocampus [FMA62493:Hippocampus; FMA74038:Hippocampal formation]} consists of {gray substance [FMA67242:Gray matter of neuraxis]}, but on its ventricular surface is a thin white layer, the {alveus [FMA83867:Alveus of hippocampus]}, which is continuous with the {fimbria hippocampi [FMA83866:Fimbria of hippocampus]}. 111
 * The {collateral eminence [FMA83706:Collateral eminence]} ({eminentia collateralis [FMA83706:Collateral eminence]}) (Fig. 740) is an elongated swelling lying lateral to and parallel with the {hippocampus [FMA62493:Hippocampus; FMA74038:Hippocampal formation]}. It corresponds with the middle part of the {collateral fissure [FMA83751:Collateral sulcus]}, and its size depends on the depth and direction of this fissure. It is continuous behind with a flattened triangular area, the {trigonum collaterale [FMA83713:Collateral trigone]}, situated between the posterior and {inferior cornua [FMA83701:Temporal horn of lateral ventricle]}. 112
 * The {fimbria hippocampi [FMA83866:Fimbria of hippocampus]} is a continuation of the {crus of the fornix [FMA61969:Posterior column of fornix of forebrain]}, and will be discussed with that body; a description of the {choroid plexus [FMA61934:Choroid plexus of cerebral hemisphere]} will be found on page 840. 113
 * The {corpus striatum [FMA77616:Corpus striatum]} has received its name from the striped appearance which a section of its anterior part presents, in consequence of diverging white fibers being mixed with the {gray substance [FMA67242:Gray matter of neuraxis]} which forms its chief mass. A part of the {corpus striatum [FMA77616:Corpus striatum]} is imbedded in the {white substance [FMA83929:White matter of neuraxis]} of the hemisphere, and is therefore external to the ventricle; it is termed the extraventricular portion, or the {lentiform nucleus [FMA77615:Lentiform nucleus]}; the remainder, however, projects into the ventricle, and is named the intraventricular portion, or the {caudate nucleus [FMA61833:Caudate nucleus]} (Fig. 737). 114
 * The {caudate nucleus [FMA61833:Caudate nucleus]} ({nucleus caudatus [FMA61833:Caudate nucleus]}; {caudatum [FMA61833:Caudate nucleus]}) (Figs. 741, 742) is a pear-shaped, highly arched gray mass; its broad extremity, or {head [FMA7154:Head]}, is directed forward into the anterior cornu of the {lateral ventricle [FMA78448:Lateral ventricle]}, and is continuous with the {anterior perforated substance [FMA61891:Anterior perforated substance]} and with the anterior end of the {lentiform nucleus [FMA77615:Lentiform nucleus]}; its narrow end, or tail, is directed backward on the lateral side of the {thalamus [FMA62007:Thalamus]}, from which it is separated by the {stria terminalis [FMA61974:Stria terminalis]} and the {terminal vein [FMA50997:Superior thalamostriate vein]}. It is then continued downward into the roof of the {inferior cornu [FMA83701:Temporal horn of lateral ventricle]}, and ends in the {putamen [FMA61834:Putamen]} near the apex of the {temporal lobe [FMA61825:Temporal lobe]}. It is covered by the lining of the ventricle, and crossed by some {veins [FMA63814:Set of veins]} of considerable size. It is separated from the {lentiform nucleus [FMA77615:Lentiform nucleus]}, in the greater part of its extent, by a thick lamina of {white substance [FMA83929:White matter of neuraxis]}, called the {internal capsule [FMA61950:Internal capsule]}, but the two portions of the {corpus striatum [FMA77616:Corpus striatum]} are united in front (Figs. 743, 744).
 * The {lentiform nucleus [FMA77615:Lentiform nucleus]} ({nucleus lentiformis [FMA77615:Lentiform nucleus]}; {lenticular nucleus [FMA77615:Lentiform nucleus]}; lenticula) (Fig. 741) is lateral to the {caudate nucleus [FMA61833:Caudate nucleus]} and {thalamus [FMA62007:Thalamus]}, and is seen only in sections of the hemisphere. When divided horizontally, it exhibits, to some extent, the appearance of a biconvex {lens [FMA58241:Lens]} (Fig. 742), while a {coronal [FMA264717:Coronale]} section of its central part presents a somewhat triangular outline. It is shorter than the {caudate nucleus [FMA61833:Caudate nucleus]} and does not extend as far forward. It is bounded laterally by a lamina of {white substance [FMA83929:White matter of neuraxis]} called the {external capsule [FMA61959:External capsule]}, and lateral to this is a thin layer of {gray substance [FMA67242:Gray matter of neuraxis]} termed the {claustrum [FMA67440:Claustrum]}. Its anterior end is continuous with the lower part of the {head of the caudate nucleus [FMA61852:Head of caudate nucleus]} and with the {anterior perforated substance [FMA61891:Anterior perforated substance]}. 116
 * In a {coronal [FMA264717:Coronale]} section through the middle of the {lentiform nucleus [FMA77615:Lentiform nucleus]}, two medullary laminæ are seen dividing it into three parts. The lateral and largest part is of a reddish color, and is known as the {putamen [FMA61834:Putamen]}, while the medial and intermediate are of a yellowish tint, and together constitute the {globus pallidus [FMA61835:Globus pallidus; FMA61839:Lateral globus pallidus; FMA61840:Medial globus pallidus; FMA62469:Lateral medullary lamina of globus pallidus; FMA62470:Medial medullary lamina of globus pallidus]}; all three are marked by fine radiating white fibers, which are most distinct in the {putamen [FMA61834:Putamen]} (Fig. 744). 117
 * The {gray substance [FMA67242:Gray matter of neuraxis]} of the {corpus striatum [FMA77616:Corpus striatum]} is traversed by {nerve fibers [FMA5914:Nerve fiber]}, some of which originate in it. The cells are multipolar, both large and small; those of the {lentiform nucleus [FMA77615:Lentiform nucleus]} contain yellow pigment. The {caudate [FMA61833:Caudate nucleus]} and {lentiform nuclei [FMA84037:Set of lentiform nuclei]} are not only directly continuous with each other anteriorly, but are connected to each other by numerous fibers. The {corpus striatum [FMA77616:Corpus striatum]} is also connected: (1) to the {cerebral cortex [FMA61830:Cerebral cortex]}, by what are termed the corticostriate fibers; (2) to the {thalamus [FMA62007:Thalamus]}, by fibers which pass through the {internal capsule [FMA61950:Internal capsule]}, and by a strand named the ansa lentiformis; (3) to the {cerebral peduncle [FMA62394:Peduncle of midbrain; FMA72464:Cerebral crus]}, by fibers which leave the lower aspect of the {caudate [FMA61833:Caudate nucleus]} and {lentiform nuclei [FMA84037:Set of lentiform nuclei]}.
 * The {claustrum [FMA67440:Claustrum]} (Figs. 742, 744) is a thin layer of {gray substance [FMA67242:Gray matter of neuraxis]}, situated on the lateral surface of the {external capsule [FMA61959:External capsule]}. Its transverse section is triangular, with the apex directed upward. Its medial surface, contiguous to the {external capsule [FMA61959:External capsule]}, is smooth, but its lateral surface presents {ridges [FMA75035:Crest]} and furrows corresponding with the gyri and sulci of the {insula [FMA67329:Insula]}, with which it is in close relationship. The {claustrum [FMA67440:Claustrum]} is regarded as a detached portion of the {gray substance [FMA67242:Gray matter of neuraxis]} of the {insula [FMA67329:Insula]}, from which it is separated by a layer of white fibers, the {capsula extrema [FMA61960:Extreme capsule]} (band of Baillarger). Its cells are small and spindle-shaped, and contain yellow pigment; they are similar to those of the deepest layer of the {cortex [FMA15632:Adrenal cortex; FMA61109:Cortex]}. 119
 * The {nucleus amygdalæ [FMA61841:Amygdala]} ({amygdala [FMA61841:Amygdala]}) (Fig. 741), is an ovoid gray mass, situated at the lower end of the roof of the {inferior cornu [FMA83701:Temporal horn of lateral ventricle]}. It is merely a localized thickening of the gray {cortex [FMA15632:Adrenal cortex; FMA61109:Cortex]}, continuous with that of the {uncus [FMA74884:Uncus]}; in front it is continuous with the {putamen [FMA61834:Putamen]}, behind with the {stria terminalis [FMA61974:Stria terminalis]} and the {tail of the caudate nucleus [FMA61854:Tail of caudate nucleus]}. 120
 * 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
 * 2. The transverse or commissural fibers connect the two hemispheres. They include: (a) the transverse fibers of the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]}, (b) the {anterior commissure [FMA61961:Anterior commissure]}, (c) the {posterior commissure [FMA62072:Posterior commissure]}, and (d) the lyra or {hippocampal commissure [FMA61970:Commissure of fornix of forebrain]}; they have already been described.
 * 3. The association fibers (Fig. 751) unite different parts of the same hemisphere, and are of two kinds: (1) those connecting adjacent gyri, short association fibers; (2) those passing between more distant parts, long association fibers. 142
 * The short association fibers lie immediately beneath the {gray substance [FMA67242:Gray matter of neuraxis]} of the {cortex [FMA15632:Adrenal cortex; FMA61109:Cortex]} of the hemispheres, and connect together adjacent gyri. 143
 * The long association fibers include the following: (a) the {uncinate fasciculus [FMA77636:Uncinate fasciculus]}; (b) the {cingulum [FMA56731:Cingulum of tooth]}; (c) the {superior longitudinal fasciculus [FMA77631:Superior longitudinal fasciculus]}; (d) the {inferior longitudinal fasciculus [FMA77632:Inferior longitudinal fasciculus]}; (e) the perpendicular fasciculus; (f) the {occipitofrontal fasciculus [FMA77633:Inferior occipitofrontal fasciculus; FMA77634:Superior occipitofrontal fasciculus]}; and (g) the {fornix [FMA61965:Fornix of forebrain]}. 144
 * (a) The {uncinate fasciculus [FMA77636:Uncinate fasciculus]} passes across the bottom of the {lateral fissure [FMA77801:Lateral sulcus]}, and unites the gyri of the {frontal lobe [FMA61824:Frontal lobe]} with the anterior end of the {temporal lobe [FMA61825:Temporal lobe]}. 145
 * (b) The {cingulum [FMA56731:Cingulum of tooth]} is {a band [FMA67918:Anisotropic band]} of {white matter [FMA83929:White matter of neuraxis]} contained within the {cingulate gyrus [FMA62434:Cingulate gyrus]}. Beginning in front at the {anterior perforated substance [FMA61891:Anterior perforated substance]}, it passes forward and upward parallel with the rostrum, winds around the {genu [FMA24974:Knee]}, runs backward above the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]}, turns around the {splenium [FMA7196:Spleen]}, and ends in the {hippocampal gyrus [FMA61918:Parahippocampal gyrus]}. 146
 * (c) The {superior longitudinal fasciculus [FMA77631:Superior longitudinal fasciculus]} passes backward from the {frontal lobe [FMA61824:Frontal lobe]} above the {lentiform nucleus [FMA77615:Lentiform nucleus]} and {insula [FMA67329:Insula]}; some of its fibers end in the {occipital lobe [FMA67325:Occipital lobe]}, and others curve downward and forward into the {temporal lobe [FMA61825:Temporal lobe]}. 147
 * (d) The {inferior longitudinal fasciculus [FMA77632:Inferior longitudinal fasciculus]} connects the temporal and {occipital lobes [FMA67325:Occipital lobe]}, running along the lateral walls of the inferior and {posterior cornua [FMA83700:Occipital horn of lateral ventricle]} of the {lateral ventricle [FMA78448:Lateral ventricle]}.
 * (e) The perpendicular fasciculus runs vertically through the front part of the {occipital lobe [FMA67325:Occipital lobe]}, and connects the {inferior parietal lobule [FMA61897:Supramarginal gyrus; FMA77536:Inferior parietal lobule]} with the {fusiform gyrus [FMA61908:Fusiform gyrus]}. 149
 * (f) The {occipitofrontal fasciculus [FMA77633:Inferior occipitofrontal fasciculus; FMA77634:Superior occipitofrontal fasciculus]} passes backward from the {frontal lobe [FMA61824:Frontal lobe]}, along the lateral border of the {caudate nucleus [FMA61833:Caudate nucleus]}, and on the mesial aspect of the {corona radiata [FMA18661:Corona radiata]}; its fibers radiate in a fan-like manner and pass into the occipital and {temporal lobes [FMA61825:Temporal lobe]} lateral to the posterior and {inferior cornua [FMA83701:Temporal horn of lateral ventricle]}. Déjerine regards the fibers of the {tapetum [FMA77208:Tapetum]} as being derived from this fasciculus, and not from the {corpus callosum [FMA61946:Genu of corpus callosum; FMA61947:Body of corpus callosum; FMA86464:Corpus callosum]}. 150
 * (g) The {fornix [FMA61965:Fornix of forebrain]} connects the {hippocampal gyrus [FMA61918:Parahippocampal gyrus]} with the {corpus mammillare [FMA74877:Mammillary body]} and, by means of the {thalamomammillary fasciculus [FMA83849:Mammillothalamic tract]}, with the {thalamus [FMA62007:Thalamus]} (see page 839). Through the fibers of the {hippocampal commissure [FMA61970:Commissure of fornix of forebrain]} it probably also unites the opposite {hippocampal gyri [FMA61918:Parahippocampal gyrus]}. 151
 * The {gray substance [FMA67242:Gray matter of neuraxis]} of the hemisphere is divided into: (1) that of the {cerebral cortex [FMA61830:Cerebral cortex]}, and (2) that of the {caudate nucleus [FMA61833:Caudate nucleus]}, the {lentiform nucleus [FMA77615:Lentiform nucleus]}, the {claustrum [FMA67440:Claustrum]}, and the {nucleus amygdalæ [FMA61841:Amygdala]}. 152
 * Structure of the {Cerebral Cortex [FMA61830:Cerebral cortex]} (Fig. 754).—The {cerebral cortex [FMA61830:Cerebral cortex]} differs in thickness and structure in different parts of the hemisphere. It is thinner in the {occipital region [FMA67325:Occipital lobe]} than in the anterior and {posterior central gyri [FMA61896:Postcentral gyrus]}, and it is also much thinner at the bottom of the sulci than on the top of the gyri. Again, the minute structure of the anterior central differs from that of the {posterior central gyrus [FMA61896:Postcentral gyrus]}, and areas possessing a specialized type of {cortex [FMA15632:Adrenal cortex; FMA61109:Cortex]} can be mapped out in the {occipital lobe [FMA67325:Occipital lobe]}. 153
 * On examining a section of the {cortex [FMA15632:Adrenal cortex; FMA61109:Cortex]} with a {lens [FMA58241:Lens]}, it is seen to consist of alternating white and gray layers thus disposed from the surface inward: (1) a thin layer of {white substance [FMA83929:White matter of neuraxis]}; (2) a layer of {gray substance [FMA67242:Gray matter of neuraxis]}; (3) a second white layer (outer band of Baillarger or {band of Gennari [FMA75667:Occipital stripe of internal granular layer of neocortex]}); (4) a second gray layer; (5) a third white layer (inner band of Baillarger); (6) a third gray layer, which rests on the medullary substance of the gyrus. 154
 * The {cortex [FMA15632:Adrenal cortex; FMA61109:Cortex]} is made up of {nerve cells [FMA54527:Neuron]} of varying size and shape, and of {nerve fibers [FMA5914:Nerve fiber]} which are either medullated or naked {axis-cylinders [FMA67308:Axon]}, imbedded in a matrix of {neuroglia [FMA54541:Set of neuroglial cells]}. 155
 * {Nerve Cells [FMA54527:Neuron]}.—According to Cajal, the {nerve cells [FMA54527:Neuron]} are arranged in four layers, named from the surface inward as follows: (1) the molecular layer, (2) the layer of small {pyramidal cells [FMA84105:Pyramidal cell of cerebral cortex]}, (3) the layer of large {pyramidal cells [FMA84105:Pyramidal cell of cerebral cortex]}, (4) the layer of polymorphous cells. 156
 * The Molecular Layer.—In this layer the cells are polygonal, triangular, or fusiform in shape. Each polygonal cell gives off some four or five {dendrites [FMA67314:Dendrite]}, while its {axon [FMA67308:Axon]} may arise directly from the cell or from one of its {dendrites [FMA67314:Dendrite]}. Each triangular cell gives off two or three {dendrites [FMA67314:Dendrite]}, from one of which the {axon [FMA67308:Axon]} arises. The fusiform cells are placed with their long axes parallel to the surface and are mostly bipolar, each pole being prolonged into a {dendrite [FMA67314:Dendrite]}, which runs horizontally for some distance and furnishes ascending branches. Their {axons [FMA67308:Axon]}, two or three in number, arise from the {dendrites [FMA67314:Dendrite]}, and, like them, take a horizontal course, giving off numerous ascending collaterals. The distribution of the {axons [FMA67308:Axon]} and {dendrites [FMA67314:Dendrite]} of all three {sets of cells [FMA71954:Set of cells]} is limited to the molecular layer. 157
 * The Layer of Small and the Layer of Large {Pyramidal Cells [FMA84105:Pyramidal cell of cerebral cortex]}.—The cells in these two layers may be studied together, since, with the exception of the difference in size and the more superficial position of the smaller cells, they resemble each other. The average length of the small cells is from 10 to 15μ; that of the large cells from 20 to 30μ. The body of each cell is {pyramidal [FMA15568:Pyramidalis]} in shape, its base being directed to the deeper parts and its apex toward the surface. It contains granular pigment, and stains deeply with ordinary reagents. The nucleus is of large size, and round or oval in shape. The base of the cell gives off the {axis cylinder [FMA67308:Axon]}, and this runs into the central {white substance [FMA83929:White matter of neuraxis]}, giving off collaterals in its course, and is distributed as a projection, commissural, or association fiber. The apical and {basal parts of the cell [FMA72558:Basal part of cell]} give off {dendrites [FMA67314:Dendrite]}; the apical {dendrite [FMA67314:Dendrite]} is directed toward the surface, and ends in the molecular layer by dividing into numerous branches, all of which may be seen, when prepared by the silver or methylene-blue method, to be studded with projecting bristle-like processes. The largest {pyramidal cells [FMA84105:Pyramidal cell of cerebral cortex]} are found in the upper part of the anterior central gyrus and in the {paracentral lobule [FMA77534:Paracentral lobule]}; they are often arranged in groups or nests of from three to five, and are named the giant cells of Betz. In the former situation they may exceed 50μ in length and 40μ in breadth, while in the {paracentral lobule [FMA77534:Paracentral lobule]} they may attain a length of 65μ. 158
 * Layer of Polymorphous Cells.—The cells in this layer, as their name implies, are very irregular in contour; they may be fusiform, oval, triangular, or star-shaped. Their {dendrites [FMA67314:Dendrite]} are directed outward, but do not reach so far as the molecular layer; their {axons [FMA67308:Axon]} pass into the subjacent {white matter [FMA83929:White matter of neuraxis]}. 159
 * There are two other kinds of cells in the {cerebral cortex [FMA61830:Cerebral cortex]}. They are: (a) the cells of Golgi, the {axons [FMA67308:Axon]} of which divide immediately after their origins into a large number of branches, which are directed toward the surface of the {cortex [FMA15632:Adrenal cortex; FMA61109:Cortex]}; (b) the cells of Martinotti, which are chiefly found in the polymorphous layer; their {dendrites [FMA67314:Dendrite]} are short, and may have an ascending or descending course, while their {axons [FMA67308:Axon]} pass out into the molecular layer and form an extensive horizontal arborization.
 * {Nerve Fibers [FMA5914:Nerve fiber]}.—These fill up a large part of the intervals between the cells, and may be medullated or non-medullated—the latter comprising the {axons [FMA67308:Axon]} of the smallest {pyramidal cells [FMA84105:Pyramidal cell of cerebral cortex]} and the cells of Golgi. In their direction the fibers may be either tangential or radial. The tangential fibers run parallel to the surface of the hemisphere, intersecting the radial fibers at a right angle. They constitute several strata, of which the following are the more important: (1) a stratum of white fibers covering the superficial aspect of the molecular layer (plexus of Exner); (2) the band of Bechterew, in the outer part of the layer of small {pyramidal cells [FMA84105:Pyramidal cell of cerebral cortex]}; (3) the {band of Gennari [FMA75667:Occipital stripe of internal granular layer of neocortex]} or external band of Baillarger, running through the layer of large {pyramidal cells [FMA84105:Pyramidal cell of cerebral cortex]}; (4) the internal band of Baillarger, between the layer of large {pyramidal cells [FMA84105:Pyramidal cell of cerebral cortex]} and the polymorphous layer; (5) the deep tangential fibers, in the lower part of the polymorphous layer. The tangential fibers consist of (a) the collaterals of the {pyramidal [FMA15568:Pyramidalis]} and polymorphous cells and of the cells of Martinotti; (b) the branching {axons [FMA67308:Axon]} of Golgi’s cells; (c) the collaterals and terminal arborizations of the projection, commissural, or association fibers. The radial fibers.—Some of these, viz., the {axons [FMA67308:Axon]} of the {pyramidal [FMA15568:Pyramidalis]} and polymorphous cells, descend into the central {white matter [FMA83929:White matter of neuraxis]}, while others, the terminations of the projection, commissural, or association fibers, ascend to end in the {cortex [FMA15632:Adrenal cortex; FMA61109:Cortex]}. The {axons [FMA67308:Axon]} of the cells of Martinotti are also ascending fibers. 161
 * Special Types of {Cerebral Cortex [FMA61830:Cerebral cortex]}.—It has been already pointed out that the minute structure of the {cortex [FMA15632:Adrenal cortex; FMA61109:Cortex]} differs in different regions of the hemisphere; and A. W. Campbell 126 has endeavored to prove, as the result of an exhaustive examination of a series of human and anthropoid {brains [FMA50801:Brain]}, “that there exists a direct correlation between physiological function and histological structure.” The principal regions where the “typical” structure is departed from will now be referred to. 162
 * 1. In the {calcarine fissure [FMA83749:Calcarine sulcus]} and the gyri bounding it, the internal band of Baillarger is absent, while the {band of Gennari [FMA75667:Occipital stripe of internal granular layer of neocortex]} is of considerable thickness, and forms a characteristic feature of this region of the {cortex [FMA15632:Adrenal cortex; FMA61109:Cortex]}. If a section be examined microscopically, an additional layer of cells is seen to be interpolated between the molecular layer and the layer of small {pyramidal cells [FMA84105:Pyramidal cell of cerebral cortex]}. This extra layer consists of two or three strata of fusiform cells, the long axes of which are at right angles to the surface; each cell gives off two {dendrites [FMA67314:Dendrite]}, external and internal, from the latter of which the {axon [FMA67308:Axon]} arises and passes into the white central substance. In the layer of small {pyramidal cells [FMA84105:Pyramidal cell of cerebral cortex]}, fusiform cells, identical with the above, are seen, as well as ovoid or star-like cells with ascending {axons [FMA67308:Axon]} (cells of Martinotti). This is the visual area of the {cortex [FMA15632:Adrenal cortex; FMA61109:Cortex]}, and it has been shown by J. S. Bolton 127 that in old-standing cases of optic atrophy the thickness of Gennari’s band is reduced by nearly 50 per cent. 163
 * A. W. Campbell says: “Histologically, two distinct types of {cortex [FMA15632:Adrenal cortex; FMA61109:Cortex]} can be made out in the {occipital lobe [FMA67325:Occipital lobe]}. The first of these coats the walls and bounding convolutions of the {calcarine fissure [FMA83749:Calcarine sulcus]}, and is distinguished by the well-known {line of Gennari [FMA75667:Occipital stripe of internal granular layer of neocortex]} or Vicq d’Azyr; the second area forms an investing zone a centimetre or more broad around the first, and is characterized by a remarkable wealth of fibers, as well as by curious pyriform cells of large size richly stocked with chromophilic elements—cells which seem to have escaped the observation of Ramón y Cajal, Bolton, and others who have worked at this region. As to the functions of these two regions there is abundant evidence, anatomical, embryological, and pathological, to show that the first or calcarine area is that to which visual sensations primarily pass, and we are gradually obtaining proof to the effect that the second investing area is constituted for the interpretation and further elaboration of these sensations. These areas therefore deserve the names visuo-sensory and visuo-psychic.” 164
 * 2. The anterior central gyrus is characterized by the presence of the giant cells of Betz and by “a wealth of {nerve fibers [FMA5914:Nerve fiber]} immeasurably superior to that of any other part” (Campbell), and in these respects differs from the {posterior central gyrus [FMA61896:Postcentral gyrus]}. These two gyri, together with the {paracentral lobule [FMA77534:Paracentral lobule]}, were long regarded as constituting the “motor areas” of the hemisphere; but Sherrington and Grunbaum have shown 128 that in the chimpanzee the motor area never extends on to the free {face [FMA24728:Face]} of the {posterior central gyrus [FMA61896:Postcentral gyrus]}, but occupies the entire length of the anterior central gyrus, and in most cases the greater part or the whole of its width. It extends into the depth of the {central sulcus [FMA83752:Central sulcus]}, occupying the anterior wall, and in some places the floor, and in some extending even into the deeper part of the posterior wall of the {sulcus [:]}. 165
 * 3. In the {hippocampus [FMA62493:Hippocampus; FMA74038:Hippocampal formation]} the molecular layer is very thick and contains a large number of Golgi cells. It has been divided into three strata: (a) s. convolutum or s. granulosum, containing many tangential fibers; (b) s. lacunosum, presenting numerous vascular spaces; (c) s. radiatum, exhibiting a rich plexus of fibrils. The two layers of {pyramidal cells [FMA84105:Pyramidal cell of cerebral cortex]} are condensed into one, and the cells are mostly of large size. The {axons [FMA67308:Axon]} of the cells in the polymorphous layer may run in an ascending, a descending, or a horizontal direction. Between the polymorphous layer and the ventricular {ependyma [FMA242791:Ependyma of neuraxis]} is the {white substance [FMA83929:White matter of neuraxis]} of the {alveus [FMA83867:Alveus of hippocampus]}. 166
 * 4. In the {fascia dentata hippocampi [FMA61922:Dentate gyrus of hippocampal formation]} or {dentate gyrus [FMA61922:Dentate gyrus of hippocampal formation]} the molecular layer contains some {pyramidal cells [FMA84105:Pyramidal cell of cerebral cortex]}, while the layer of {pyramidal cells [FMA84105:Pyramidal cell of cerebral cortex]} is almost entirely represented by small ovoid cells. 167
 * 5. The {Olfactory Bulb [FMA77624:Olfactory bulb]}.—In many of the lower animals this contains a cavity which communicates through the {olfactory tract [FMA46787:Olfactory nerve]} with the {lateral ventricle [FMA78448:Lateral ventricle]}. In man the original cavity is filled up by {neuroglia [FMA54541:Set of neuroglial cells]} and its wall becomes thickened, but much more so on its ventral than on its dorsal aspect. Its dorsal part contains a small amount of gray and {white substance [FMA83929:White matter of neuraxis]}, but it is scanty and ill-defined. A section through the ventral part (Fig. 755) shows it to consist of the following layers from without inward: 16
 * 1. A layer of {olfactory nerve [FMA46787:Olfactory nerve]} fibers, which are the non-medullated {axons [FMA67308:Axon]} prolonged from the olfactory cells of the {nasal cavity [FMA54378:Nasal cavity]}, and reach the {bulb [FMA62004:Medulla oblongata]} by passing through the {cribriform plate [FMA52890:Cribriform plate]} of the {ethmoid [FMA52740:Ethmoid]} {bone [FMA71324:Set of bones]}. At first they cover the {bulb [FMA62004:Medulla oblongata]}, and then penetrate it to end by forming {synapses [FMA67408:Synapse]} with the {dendrites [FMA67314:Dendrite]} of the mitral cells, presently to be described. 169
 * 2. Glomerular Layer.—This contains numerous spheroidal reticulated enlargements, termed {glomeruli [FMA15624:Glomerulus]}, produced by the branching and arborization of the processes of the {olfactory nerve [FMA46787:Olfactory nerve]} fibres with the descending {dendrites [FMA67314:Dendrite]} of the mitral cells. 170
 * 3. Molecular Layer.—This is formed of a matrix of {neuroglia [FMA54541:Set of neuroglial cells]}, imbedded in which are the mitral cells. These cells are {pyramidal [FMA15568:Pyramidalis]} in shape, and the basal part of each gives off a thick {dendrite [FMA67314:Dendrite]} which descends into the glomerular layer, where it arborizes as indicated above, and others which interlace with similar {dendrites [FMA67314:Dendrite]} of neighboring mitral cells. The {axons [FMA67308:Axon]} pass through the next layer into the {white matter [FMA83929:White matter of neuraxis]} of the {bulb [FMA62004:Medulla oblongata]}, and after becoming bent on themselves at a right angle, are continued into the {olfactory tract [FMA46787:Olfactory nerve]}. 171
 * 4. {Nerve Fiber [FMA5914:Nerve fiber]} Layer.—This lies next the central {core [FMA7088:Heart]} of {neuroglia [FMA54541:Set of neuroglial cells]}, and its fibers consist of the {axons [FMA67308:Axon]} or afferent processes of the mitral cells passing to the {brain [FMA50801:Brain]}; some efferent fibers are, however, also present, and end in the molecular layer, but nothing is known as to their exact origin. 172
 * Weight of the {Encephalon [FMA50801:Brain]}.—The average weight of the {brain [FMA50801:Brain]}, in the adult male, is about 1380 gms.; that of the female, about 1250 gms. In the male, the maximum weight out of 278 cases was 1840 gms. and the minimum weight 964 gms. The maximum weight of the adult female {brain [FMA50801:Brain]}, out of 191 cases, was 1585 gms. and the minimum weight 879 gms. The {brain [FMA50801:Brain]} increases rapidly during the first four years of life, and reaches its maximum weight by about the twentieth year. As age advances, the {brain [FMA50801:Brain]} decreases slowly in weight; in old age the decrease takes place more rapidly, to the extent of about 28 gms. 173
 * The human {brain [FMA50801:Brain]} is heavier than that of any of the lower animals, except the elephant and whale. The {brain [FMA50801:Brain]} of the former weighs from 3.5 to 5.4 kilogm., and that of a whale, in a specimen 19 metres long, weighed rather more than 6.7 kilogm. 174
 * Cerebral Localization.—Physiological and pathological research have now gone far to prove that a considerable part of the {surface of the brain [FMA86594:Surface of brain]} may be mapped out into a series of more or {less [FMA63048:Circular muscle layer of abdominal part of esophagus]} definite areas, each of which is intimately connected with some well-defined function. 175
 * The chief areas are indicated in Figs. 756 and 757. 176
 * Motor Areas.—The motor area occupies the anterior central and {frontal [FMA46757:Frontalis]} gyri and the {paracentral lobule [FMA77534:Paracentral lobule]}. The centers for the {lower limb [FMA7184:Lower limb]} are located on the uppermost part of the anterior central gyrus and its continuation on to the {paracentral lobule [FMA77534:Paracentral lobule]}; those for the {trunk [FMA7181:Trunk]} are on the upper portion, and those for the {upper limb [FMA7183:Upper limb]} on the middle portion of the anterior central gyrus. The facial centers are situated on the lower part of the anterior central gyrus, those for the {tongue [FMA54640:Tongue]}, {larynx [FMA55097:Larynx]}, {muscles [:]} of mastication, and {pharynx [FMA46688:Pharynx]} on the {frontal operculum [FMA74886:Frontal operculum]}, while those for the {head [FMA7154:Head]} and {neck [FMA7155:Neck]} occupy the posterior end of the {middle frontal gyrus [FMA61859:Middle frontal gyrus]}. 1
 * Sensory Areas.—Tactile and temperature senses are located on the {posterior central gyrus [FMA61896:Postcentral gyrus]}, while the sense of form and solidity is on the {superior parietal lobule [FMA61899:Superior parietal lobule; FMA71058:Superior parietal lobule (SPL)]} and {precuneus [FMA61900:Precuneus]}. With regard to the special senses, the area for the sense of taste is probably related to the {uncus [FMA74884:Uncus]} and {hippocampal gyrus [FMA61918:Parahippocampal gyrus]}. The auditory area occupies the middle third of the {superior temporal gyrus [FMA61905:Superior temporal gyrus]} and the adjacent gyri in the {lateral fissure [FMA77801:Lateral sulcus]}; the visual area, the {calcarine fissure [FMA83749:Calcarine sulcus]} and {cuneus [FMA61903:Cuneus]}; the {olfactory area [FMA61882:Nucleus of diagonal band; FMA61891:Anterior perforated substance]}, the {rhinencephalon [FMA62430:Paleocortex]}. As special centers of much importance may be noted: the emissive center for speech on the left inferior {frontal [FMA46757:Frontalis]} and anterior central gyri (Broca); the auditory receptive center on the transverse and {superior temporal gyri [FMA61905:Superior temporal gyrus]}, and the visual receptive center on the {lingual gyrus [FMA61904:Lingual gyrus]} and {cuneus [FMA61903:Cuneus]}.