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As a result of the interaction of the middle part of the chordomesoderm with the dorsal plate of the ectoderm in the embryo from the 11th day of the prenatal period, the development of the nervous system begins (Fig. 491, A). The multiplication of nerve cells in the area of \u200b\u200bthe nerve sulcus leads to its closure in the cerebral tube, which up to 4-5 weeks has holes at the ends - blastopores (Fig. 491, B). The brain tube is detached from the ectodermal layer, plunging into the thickness of the middle germ layer. Simultaneously with the formation of the cerebral tube, paired nerve strips are laid under the layer of the epidermis, from which the ganglionic plates are formed. Ganglionic plates are the ancestors of the paravertebral head and spinal nerve nodes, which are a homologue of the paired nerve chain of invertebrates. Based on phylogenetic prerequisites, the ganglionic plates should have developed in embryogenesis earlier than the brain tube, but in reality they arise after the brain tube. This circumstance indicates that the progressive development of the central nervous system and its dominant functional significance in humans are preserved in the prenatal and postnatal periods.

491. Formation of the neural groove and neural tube at the 3rd week of embryonic development (according to Bartelmetz).
A: 1 - nerve groove; 2 - ectoderm; 3 - mesenchyme; 4 - endoderm; 5 - celoma; B: - the appearance of the embryo at the 3rd week of embryonic development. The neural tube at the head and tail ends of the body is open (according to Corner).

Following the laying of the ganglionic plates and the cerebral tube, intensive growth of the anterior end of the embryo is observed, mainly due to the development of the cerebral tube and sensory organs. From the cerebral tube, five cerebral vesicles and the spinal cord are isolated.

The developmental stage of one cerebral bladder corresponds to 16-20 days of intrauterine development, when the anterior end of the open cerebral tube overtakes the anterior end of the notochord in growth. During this period, at the level of the posterior part of the cerebral bladder, the auditory placodes are laid, representing the protrusion of the ectoderm (). The stage of development of two cerebral vesicles is observed after the 21st day of intrauterine development. The head end of the notochord lags behind the anterior part of the cerebral tube, which is separated by some narrowing into the prechordal and suprachordal cerebral vesicles. The prechordal cerebral bladder is not closed and covers the mouth bay, hanging over the anlage of the heart (Fig. 492). The brain tube is bent at the anterior end.

492. Sagittal section of the embryo at 10-11 weeks of development (according to Yu. G. Shevchenko).
1 - isthmus of the brain; 2 - the cavity of the hindbrain; 3 - longitudinal posterior bundle; 4 - bridge; 5 - transverse paths to the cores of the bridge (from the cortex to the cores of the bridge); 6 - pyramidal paths; 7 - spinal cord; 8 - spinal cord; 9 - spinal column; 10 - trachea; 11 - esophagus; 12 - epiglottis; 13 - language; 14 - pituitary gland; 15 - hypothalamus; 16 - diencephalon cavity; 17 - the cavity of the telencephalon; 18 - terminal brain; 19 - midbrain.

The stage of development of three cerebral vesicles is noted at 4-5 weeks of the prenatal period. The bubbles are called: front (prosencephalon), middle (mesencephalon), rhomboid (rhombencephalon) (Fig. 492). They differ from one another in bends and narrowings that deform the cerebral tube not only outside, but also its cavity. The wall of the cerebral vesicles is formed by three layers: 1) the matrix layer, or the embryonic layer, consisting of poorly differentiated cells; 2) the intermediate layer; 3) the marginal layer with few cellular elements. In the ventral wall of the cerebral vesicles, the interstitial layer is well developed, from which numerous nuclei are subsequently formed, and the dorsal wall is almost devoid of them. The anterior neuropore is closed by a structureless endplate. In the area of \u200b\u200bthe lateral wall of the anterior cerebral bladder, in which the eye cups are laid, the matrix layer of cells doubles and expands, forming the retina. The eye vesicles are formed at the site of the division of the anterior cerebral bladder into two parts. In the same period of development, the posterior part of the cerebral tube, corresponding to the spinal cord, has an inner ependymal and outer nuclear layers, which are more compact on the ventral wall. On the ventral wall of the cerebral vesicles, a ventral cerebral fold is formed, which contributes to the narrowing of the cavity of the cerebral vesicles. In the same way, the laying of the funnel and the pituitary gland occurs on the ventral wall of the anterior cerebral bladder (Fig. 492).

At 6-7 weeks of embryonic development, the period of formation of five cerebral vesicles begins. The forebrain is divided into the telencephalon and the diencephalon. The midbrain (mesencephalon) is not divided into secondary bubbles. The rhomboid brain is divided into the hindbrain (metencephalon) and the medulla oblongata (myelencephalon). During this period, the brain tube is strongly curved and the forebrain hangs over the horny bay and the heart. In the neural tube bends are distinguished: 1) the parietal bend, which has a bulge in the dorsal direction at the level of the midbrain (Fig. 492); 2) a ventral bridge protrusion at the level of the bridge; 3) the occipital bend, in location corresponding to the level of the spinal cord and medulla oblongata.

Endbrain (telencephalon) (I brain bladder)... In a 7-8-week-old embryo in the endbrain, in the lateral and medial regions, the development of the medial and lateral tubercles is observed, which represent the nucl anlage. caudatus et putamen. From the protrusion of the ventral wall of the telencephalon, the olfactory bulb and tract are also formed. At the end of the 8th week of embryonic development, a qualitative restructuring of the endbrain is carried out: a longitudinal groove appears along the midline, dividing the brain into two thin-walled cerebral hemispheres. These bean-shaped hemispheres lie outside the massive nuclei of the diencephalon, midbrain, and hindbrain. From the 6-week period, the primary stratification of the cortex begins due to the migration of neuroblasts in the pre- and post-mitotic phase. Only from the 9-10th week of embryonic development there is a rapid growth of the cerebral hemispheres and conducting systems that establish a connection between all the nuclei of the central nervous system. After 3 months of fetal development, thickening of the cerebral cortex, isolation of cell layers and growth of individual brain lobes occur. By the 7th month, a six-layered crust is formed. The lobes of the cerebral hemispheres develop unevenly. The temporal lobes grow faster, then the frontal, occipital and parietal lobes.

Outside the hemispheres, at the junction of the frontal and temporal lobes, there is an area in the area of \u200b\u200bthe lateral fossae that is lagging behind in growth. In this place, that is, in the walls of the lateral fossae, the basal nodes of the cerebral hemispheres and the cortex of the insula are laid. The developing cerebral hemispheres cover the third cerebral bladder by the sixth month of intrauterine development, and the fourth and fifth cerebral vesicles - by the ninth month. After the 5th month of development, a more rapid increase in the mass of the white matter is noted than in the cerebral cortex. The mismatch between the growth of white matter and bark contributes to the formation of many convolutions, grooves and crevices. At the third month on the medial surface of the hemispheres, the gyri of the hippocampus are laid, on the IV - the groove of the corpus callosum, on the V-cingulate gyrus, the spur, occipito-parietal and lateral grooves. On the 6th-7th months, grooves appear on the dorsolateral surface: central, pre- and postcentral grooves, grooves of the temporal lobes, the superior and inferior grooves of the frontal lobe, inter-parietal groove. During the period of development of the nodes and thickening of the cortex, the wide cavity of the endbrain turns into a narrow slit-lateral ventricle, entering the frontal, temporal and occipital lobes. The thin wall of the brain, together with the choroid, protrudes into the cavity of the ventricles, forming the choroid plexus.

Diencephalon (II brain bladder)... Has an uneven wall thickness. The lateral walls are thickened and are the tab of the thalamus, the inner part of the nucl. lentiformis, internal and external geniculate bodies.

In the lower wall of the diencephalon, protrusions are formed: the bookmarks of the retina and optic nerve, the optic pocket, the pocket of the pituitary funnel, the intersavoid and mastoid pockets. With the funnel of the pituitary gland, epithelial cells secreted from the head intestine grow together, forming the pituitary gland. The lower wall, in addition to such pockets, has several protrusions for the formation of a gray tubercle and mastoid bodies, which grow together with the pillars of the vault (derivatives of the I cerebral bladder). The upper wall is thin and devoid of the matrix cell layer. At the junction of the II and III cerebral vesicles, a pineal gland (corpus pineale) grows from the upper wall. A posterior cerebral commissure, leashes, leash triangles are formed under it. The rest of the upper wall is transformed into the choroid plexus, which is drawn into the cavity of the third ventricle.

The anterior wall of the diencephalon is formed by a derivative of the telencephalon in the form of lamina terminalis.

Midbrain (mesencephalon) (III brain bladder)... It has a thicker ventral wall. Its cavity turns into a cerebral aqueduct, which communicates the III and IV cerebral ventricles. From the ventral wall, after the third month, the legs of the brain develop, containing ascending (dorsally) and descending (ventrally) pathways, between which the black matter, red nuclei, nuclei of the III and IV pairs of cranial nerves are laid. The anterior perforated substance is located between the legs. Initially, the lower colliculus develops from the dorsal wall, and then the upper colliculus of the midbrain. From these tubercles, bundles of fibers emerge - brachia colliculorum superius et inferius to connect with the nuclei of the III cerebral bladder and the upper legs of the cerebellum to connect with the nuclei of the cerebellum.

Hindbrain (metencephalon) (IV brain bladder) and medulla oblongata (myelencephalon) (V brain bladder) elongated along one line and do not have clear intervesical boundaries.

The human nervous system develops from the outer germ layer - ectoderm. In the dorsal parts of the body of the embryo, differentiating ectodermal cells form a medullary (neural) plate (Fig. 109). The latter initially consists of one layer of cells, which subsequently differentiate into spongioblasts (from which supporting tissue develops - neuroglia) and neuroblasts (from which nerve cells develop). Due to the fact that the intensity of cell multiplication in different parts of the medullary plate is not the same, the latter bends and gradually takes the form of a groove or groove. The growth of the lateral sections of this nerve (medullary) groove leads to the fact that its edges first approach, and then grow together. Thus, the neural groove, closing in its dorsal sections, turns into neural tube.Fusion initially occurs in the anterior section, somewhat departing from the anterior edge of the neural tube. Then the posterior, caudal, parts of it grow together. At the anterior and posterior ends of the neural tube, small ununited areas remain - neuropores. After fusion of the dorsal sections, the neural tube is detached from the ectoderm and plunges into the mesoderm.

During the formation period, the neural tube consists of three layers. From the inner layer, the ependymal lining of the cavities of the ventricles of the brain and the central canal of the spinal cord develops, from the middle ("mantle") layer - the gray matter of the brain. The outer layer, almost devoid of cells, turns into a white matter. Initially, all the walls of the neural tube are the same thickness. Subsequently, the lateral sections of the tube develop more intensively, which thicken more and more. The ventral and dorsal walls lag behind in growth and gradually sink between the intensively developing lateral sections. As a result of such immersion, the ventral and dorsal longitudinal median grooves of the future spinal cord and medulla oblongata are formed.

On the side of the tube cavity, on the inner surface of each of the side walls, shallow longitudinal border grooves are formed, which divide the lateral sections of the tube into the ventral main and dorsal wing plates.

The main plate serves as the rudiment from which the anterior columns of gray matter and the adjacent white matter are formed. The processes developing in the anterior columns of neurons emerge (germinate) from the spinal cord, form the anterior (motor) root. The posterior columns of gray matter and adjoining white matter develop from the wing plate. Even at the stage of the neural groove in the lateral parts of it, cellular cords are distinguished, which are called medullary combs. During the formation of the neural tube, two combs, growing together, form a ganglionic plate, located dorsal to the neural tube, between the latter and the ectoderm. Subsequently, the ganglion plate is divided for the second time into two symmetrical ganglionic ridges, each of which is displaced to the lateral surface of the neural tube. Then the ganglionic ridges turn into the spinal nodes corresponding to each segment of the trunk, ganglia spinatia,and sensory nodes of the cranial nerves, ganglia sensorialia nn. cranialium.The cells that have evicted from the ganglionic ridges also serve as rudiments for the development of the peripheral parts of the autonomic nervous system.

Following the separation of the ganglionic plate, the neural tube at the head end noticeably thickens. This enlarged part serves as the brain bud. The remaining sections of the neural tube are later transformed into the spinal cord. Neuroblasts located in the emerging spinal ganglion are bipolar cells. In the process of further differentiation of neuroblasts, the areas of its two processes located in the immediate vicinity of the cell body merge into one T-shaped process that then divides. Thus, the cells of the spinal nodes become pseudo-unipolar in shape. The central processes of these cells are directed to the spinal cord and form the posterior (sensory) root. Other processes of pseudo-unipolar cells grow from nodes to the periphery, where they have receptors of various types.

The stage of development of three cerebral vesicles is noted at 4-5 weeks of the prenatal period. The bubbles are called: front (prosencephalon), middle (mesencephalon), rhomboid (rhombencephalon) (Fig. 492). They differ from one another in bends and narrowings that deform the cerebral tube not only outside, but also its cavity. The wall of the cerebral vesicles is formed by three layers: 1) the matrix layer, or the embryonic layer, consisting of poorly differentiated cells; 2) the intermediate layer; 3) the marginal layer with few cellular elements. In the ventral wall of the cerebral vesicles, the interstitial layer is well developed, from which numerous nuclei are subsequently formed, and the dorsal wall is almost devoid of them. The anterior neuropore is closed by a structureless endplate. In the area of \u200b\u200bthe lateral wall of the anterior cerebral bladder, in which the eye cups are laid, the matrix layer of cells doubles and expands, forming the retina. The eye vesicles are formed at the site of the division of the anterior cerebral bladder into two parts. In the same period of development, the posterior part of the cerebral tube, corresponding to the spinal cord, has an inner ependymal and outer nuclear layers, which are more compact on the ventral wall. On the ventral wall of the cerebral vesicles, a ventral cerebral fold is formed, which contributes to the narrowing of the cavity of the cerebral vesicles. In the same way, the laying of the funnel and the pituitary gland occurs on the ventral wall of the anterior cerebral bladder (Fig. 492).
At 6-7 weeks of embryonic development, the period of formation of five cerebral vesicles begins. Front brain divided into the telencephalon and the diencephalon. The midbrain (mesencephalon) is not divided into secondary bubbles. The rhomboid brain is divided into the hindbrain (metencephalon) and the medulla oblongata (myelencephalon). During this period, the brain tube is strongly bent and the anterior brain hangs over horny bay and heart. In the neural tube bends are distinguished: 1) the parietal bend, which has a bulge in the dorsal direction at the level of the midbrain (Fig. 492); 2) a ventral bridge protrusion at the level of the bridge; 3) the occipital bend, in location corresponding to the level of the spinal cord and medulla oblongata.
Endbrain (telencephalon) (I brain bladder)... In a 7-8-week-old embryo in the endbrain in the lateral and medial regions development medial and lateral tubercles, which represent the nucl tab. caudatus et putamen. From the protrusion of the ventral wall of the telencephalon, the olfactory bulb and tract are also formed. At the end of the 8th week of embryonic development, a qualitative restructuring of the endbrain is carried out: a longitudinal groove appears along the midline, dividing the brain into two thin-walled cerebral hemispheres. These bean-shaped hemispheres lie outside the massive nuclei of the diencephalon, midbrain, and hindbrain. From the 6-week period, the primary stratification of the cortex begins due to the migration of neuroblasts in the pre- and post-mitotic phase. Only from the 9-10th week of embryonic development there is a rapid growth of the cerebral hemispheres and conducting systems that establish a connection between all the nuclei of the central nervous system. After 3 months of fetal development, thickening of the cerebral cortex, isolation of cell layers and growth of individual brain lobes occur. By the 7th month, a six-layered crust is formed. The lobes of the cerebral hemispheres develop unevenly. The temporal lobes grow faster, then the frontal, occipital and parietal lobes.
Outside the hemispheres, at the junction of the frontal and temporal lobes, there is an area in the area of \u200b\u200bthe lateral fossae that is lagging behind in growth. In this place, that is, in the walls of the lateral fossae, the basal nodes of the cerebral hemispheres and the cortex of the insula are laid. The developing hemispheres of the brain cover III brain bladder by the 6th month of intrauterine development, and the 4th and 5th cerebral vesicles - by the 9th month. After the 5th month of development, a more rapid increase in the mass of the white matter is noted than in the cerebral cortex. The mismatch between the growth of white matter and bark contributes to the formation of many convolutions, grooves and crevices. At the third month on the medial surface of the hemispheres, the gyri of the hippocampus are laid, on the IV - the groove of the corpus callosum, on the V-cingulate gyrus, the spur, occipito-parietal and lateral grooves. On the 6th-7th months, grooves appear on the dorsolateral surface: central, pre- and postcentral grooves, grooves of the temporal lobes, the superior and inferior grooves of the frontal lobe, inter-parietal groove. During the period of development of the nodes and thickening of the cortex, the wide cavity of the endbrain turns into a narrow slit-lateral ventricle, entering the frontal, temporal and occipital lobes. Thin wall the brain, together with the choroid, protrudes into the cavity of the ventricles, forming the choroid plexus.
Diencephalon (II brain bladder)... Has an uneven wall thickness. The lateral walls are thickened and are the tab of the thalamus, the inner part of the nucl. lentiformis, internal and external geniculate bodies.
In the lower wall of the diencephalon, protrusions are formed: the bookmarks of the retina and optic nerve, the optic pocket, the pocket of the pituitary funnel, the intersavoid and mastoid pockets. With the funnel of the pituitary gland, epithelial cells secreted from the head intestine grow together, forming the pituitary gland. The lower wall, in addition to similar pockets, has several protrusions for the formation of a gray tubercle and mastoid bodies, which grow together with the pillars of the vault (derivatives of the I cerebral bladder). Upper wall thin and devoid of a matrix cell layer. At the junction of the II and III cerebral vesicles, a pineal gland (corpus pineale) grows from the upper wall. A posterior cerebral commissure, leashes, leash triangles are formed under it. The rest of the upper wall is transformed into the choroid plexus, which is drawn into the cavity of the third ventricle.
The anterior wall of the diencephalon is formed by a derivative of the telencephalon in the form of lamina terminalis.
Midbrain (mesencephalon) (III brain bladder)... It has a thicker ventral wall. Its cavity turns into a cerebral aqueduct, which communicates the III and IV cerebral ventricles. From the ventral wall, after the third month, the legs of the brain develop, containing ascending (dorsally) and descending (ventrally) pathways, between which the black matter, red nuclei, nuclei of the III and IV pairs of cranial nerves are laid. The anterior perforated substance is located between the legs. Initially, the lower colliculus develops from the dorsal wall, and then the upper colliculus of the midbrain. From these tubercles, bundles of fibers emerge - brachia colliculorum superius et inferius to connect with the nuclei of the III cerebral bladder and the upper legs of the cerebellum to connect with the nuclei of the cerebellum.
Hindbrain (metencephalon) (IV brain bladder) and medulla oblongata (myelencephalon) (V brain bladder) elongated along one line and do not have clear intervesical boundaries.

4.Thoracic duct (ductus throracicus) - the main lymphatic collector that collects lymph from most of the human body and flows into the venous system. Only lymph flowing from the right half of the chest, head, neck and right upper limb passes by G. of the item - it flows into the right lymphatic duct. The duct is formed in the retroperitoneal tissue at the level of the THXII - LII vertebrae by the fusion of large lymphatic trunks. The initial part of the duct (milk cistern) is wide - 7-8 mm in diameter. The thoracic duct passes through the aortic opening of the diaphragm into the posterior mediastinum and is located between the descending aorta and the azygos vein. Then the thoracic duct deviates to the left and over the aortic arch comes out from under the left edge of the esophagus, slightly above the left clavicle bends arcuately and flows into the venous bed at the confluence of the left subclavian and internal jugular veins. In the thoracic duct, incl. at its confluence with the venous system, there are valves that prevent blood from flowing into it.