Brain bubbles. Formation of primary brain vesicles Brain development stage 3 and 5 brain vesicles

The neural plate grows rapidly, its edges begin to thicken and rise above the original germinal plate. After a few days, the left and right edges come together and fuse along the midline, forming the neural tube. Neural tube cells subsequently differentiate into neurons of the brain and spinal cord, as well as neuroglial cells (oligodendrocytes, astrocytes and ependymal cells).

During the folding of the neural tube, some cells of the neural plate remain outside of it, and from them the neural crest is formed. It lies between the neural tube and the skin, and subsequently neurons of the peripheral nervous system, Schwann cells, cells of the adrenal medulla and pia mater develop from the neural crest cells.

Soon after the formation of the neural tube, the end from which the head is subsequently formed closes. Then the anterior part of the neural tube begins to swell, and three swellings are formed - the so-called primary medullary vesicles ( FOOTNOTE: This stage of brain development is called the “three-brain vesicle stage.”) (Fig. 18). Simultaneously with the formation of these bubbles, two bends of the future brain are formed in the sagittal plane. The cephalic or parietal curve is formed in the area of the middle bladder.

The cervical flexure separates the brain primordium from the rest of the neural tube, from which the spinal cord will subsequently form.

From the primary brain vesicles, three main parts of the brain are formed: the anterior (prosencephalon - forebrain), middle (mesencephalon - midbrain) and posterior (rhombencephalon - hind, or rhomboid brain). This stage of brain development is called the three-brain vesicle stage. After the formation of three primary vesicles, simultaneously with the closure of the posterior end of the neural tube, optic vesicles appear on the lateral surfaces of the anterior vesicle, from which the retina and optic nerves will form.

The next stage of brain development is the parallel further formation of the bends of the brain tube and the formation of five secondary brain vesicles from the primary vesicles (the stage of five brain vesicles). First ( FOOTNOTE: In the singular, the first secondary vesicle is spoken of when one of the symmetrical halves of the developing brain is considered. In fact, there are two such bubbles; they form symmetrically on the side walls of the second secondary bubble. From their walls, the cerebral hemispheres will subsequently form, and their cavities will turn into the lateral ventricles.) and the second secondary cerebral vesicles are formed by dividing the anterior primary vesicle into two parts. From these bubbles, the telencephalon (cerebral hemispheres) and diencephalon are subsequently formed, respectively. The third secondary medullary vesicle is formed from the nondividing middle primary vesicle. The fourth and fifth cerebral vesicles are formed as a result of the division of the third (posterior) primary vesicle into upper and lower parts. Of these, the hindbrain itself (cerebellum and pons) and the medulla oblongata are subsequently formed.

As a result of the interaction of the middle part of the chordomesoderm with the dorsal plate of the ectoderm, the development of the nervous system begins in the embryo from the 11th day of the intrauterine period (Fig. 491, A). The proliferation of nerve cells in the area of the neural groove leads to its closure into the brain tube, which until 4-5 weeks has holes at the ends - blastopores (Fig. 491, B). The medullary tube is detached from the ectodermal layer, plunging into the thickness of the middle germ layer. Simultaneously with the formation of the brain tube, paired nerve strips are laid under the epidermis layer, from which ganglion plates are formed. Ganglion plates are the ancestors of the paravertebral cephalic and spinal nerve ganglia, which are a homologue of the paired nerve chain of invertebrates. Based on phylogenetic premises, the ganglion 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 in the 3rd week of embryonic development (according to Bartelmetz).
A: 1 - neural groove; 2 - ectoderm; 3 - mesenchyme; 4 - endoderm; 5 - celoma; B: - 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 Korner).

Following the laying of the ganglion plates and brain tube, intensive growth of the anterior end of the embryo is observed, mainly due to the development of the brain tube and sensory organs. Five brain vesicles and the spinal cord are separated from the brain tube.

The stage of development of one brain bladder corresponds to 16-20 days of intrauterine development, when the anterior end of the open brain tube outstrips the anterior end of the notochord in growth. During this period, at the level of the posterior part of the brain bladder, auditory placodes are formed, representing a protrusion of the ectoderm (). The stage of development of two brain vesicles is observed after the 21st day of intrauterine development. The cephalic end of the notochord lags behind the anterior part of the brain tube, which is separated by some narrowing into the prechordal and supachordal brain vesicles. The prechordal medullary vesicle is not closed and encloses the oral bay, hanging over the anlage of the heart (Fig. 492). The medullary tube bends at the anterior end.

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

The stage of development of three brain vesicles is observed in the 4-5th week of the intrauterine period. The bubbles are called: anterior (prosencephalon), middle (mesencephalon), diamond-shaped (rhombencephalon) (Fig. 492). They differ from one another in bends and narrowings that deform the brain tube not only from the outside, but also from its cavity. The wall of the brain vesicles is formed by three layers: 1) the matrix layer, or germinal layer, consisting of poorly differentiated cells; 2) intermediate layer; 3) marginal layer, which has few cellular elements. In the ventral wall of the brain vesicles there is a well-developed interstitial layer, 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 region of the lateral wall of the anterior medullary vesicle, in which the eye cups are formed, the matrix layer of cells doubles and expands, forming the retina of the eyes. The optic vesicles form at the site where the forebrain vesicle divides into two parts. During the same period of development, the posterior part of the brain tube, corresponding to the spinal cord, has an internal ependymal and outer nuclear layer, more compact on the ventral wall. A ventral medullary fold is formed on the ventral wall of the brain vesicles, which narrows the cavity of the brain vesicles. The formation of the infundibulum and pituitary gland also occurs on the ventral wall of the anterior brain bladder (Fig. 492).

At the 6-7th week of embryonic development, the period of formation of five brain vesicles begins. The forebrain is divided into the telencephalon and diencephalon. The midbrain (mesencephalon) is not divided into secondary vesicles. The rhombencephalon 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) parietal bend, which has a convexity in the dorsal direction at the level of the midbrain (Fig. 492); 2) ventral pontine projection at the level of the bridge; 3) the occipital flexure, in location corresponding to the level of the spinal cord and medulla oblongata.

Telencephalon (I brain vesicle). In a 7-8 week embryo, in the telencephalon in the lateral and medial sections, the development of the medial and lateral tubercles, which represent the nucl anlage, is observed. caudatus et putamen. The olfactory bulb and tract are also formed from the protrusion of the ventral wall of the telencephalon. At the end of the 8th week of embryonic development, a qualitative restructuring of the telencephalon occurs: 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 postmitotic phase. Only from the 9-10th week of embryonic development does the rapid growth of the cerebral hemispheres and conducting systems occur, establishing connections between all the nuclei of the central nervous system. After 3 months of fetal development, thickening of the cerebral cortex, separation of cell layers and growth of individual medullary lobes occur. By the 7th month, a six-layer bark is formed. The lobes of the cerebral hemispheres develop unevenly. The temporal, then the frontal, occipital and parietal lobes grow faster.

Outside the hemispheres, at the junction of the frontal and temporal lobes, there is an area in the region of the lateral fossae that is stunted in growth. In this place, i.e. in the walls of the lateral fossae, the basal ganglia of the cerebral hemispheres and the insular cortex are formed. The developing hemispheres of the brain cover the third brain vesicle by the sixth month of intrauterine development, and the fourth and fifth brain vesicles by the ninth month. After V months of development, there is a more rapid increase in the mass of the white matter than the cerebral cortex. The discrepancy between the growth of white matter and the cortex contributes to the formation of many convolutions, grooves and fissures. At the 3rd month, the hippocampal gyri are formed on the medial surface of the hemispheres, at the 4th month - the sulcus of the corpus callosum, on the V-cingulate gyrus, calcarine, occipito-parietal and lateral sulci. At VI-VII months, grooves appear on the dorsolateral surface: central, pre- and postcentral grooves, grooves of the temporal lobes, superior and inferior grooves of the frontal lobe, interparietal groove. During the period of development of nodes and thickening of the cortex, the wide cavity of the telencephalon turns into a narrow slit-lateral ventricle, extending into 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 vesicle). Has uneven wall thickness. The lateral walls are thickened and form the lining 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: retinal anlage and optic nerve, optic recess, pituitary infundibulum recess, intermastoid and mastoid recesses. Epithelial cells released from the head intestine fuse with the pituitary funnel, forming the pituitary gland. The lower wall, in addition to similar pockets, has several protrusions to form the gray tubercle and mastoid bodies, which grow together with the columns of the fornix (derivatives of the first medullary bladder). The upper wall is thin and lacks a matrix cell layer. At the junction of the II and III brain vesicles, the pineal gland (corpus pineale) grows from the upper wall. Under it, the posterior cerebral commissure, leashes, and triangles of leashes are formed. The remaining part of the upper wall is transformed into the choroid plexus, which is retracted 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 cerebral vesicle). It has a thicker ventral wall. Its cavity turns into the cerebral aqueduct, connecting the III and IV cerebral ventricles. From the ventral wall, after the third month, the cerebral peduncles develop, containing ascending (dorsal) and descending (ventral) pathways, between which the substantia nigra, red nuclei, and nuclei of the III and IV pairs of cranial nerves are formed. Between the legs there is an anterior perforated substance. From the dorsal wall, initially the inferior colliculus develops, and then the superior colliculus of the midbrain. From these tubercles emerge bundles of fibers - brachia colliculorum superius et inferius for connection with the nuclei of the third medullary vesicle and the superior cerebellar peduncles for connection with the cerebellar nuclei.

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

Period, during which the brain consists of three bubbles, does not last long. By the end of the fourth week, signs of the impending division of the forebrain already appear, and soon after this, differentiation of the hindbrain becomes noticeable. At the sixth week of development, we can distinguish five sections in the brain. The forebrain was divided into the telencephalon and the diencephalon, the midbrain did not change, and the hindbrain differentiated into the cerebellum metencephalon and the medulla oblongata myelencephalon.

Finite brain, telencephalon, represents the most anterior part of the brain, and its two lateral projections are called the lateral telencephalic vesicles. Its posterior border is easily determined by drawing a line from a fold in the roof of the brain, called the velum transversum, to the optic fovea, a depression in the floor of the brain at the level of the optic stalks. Because this fossa is located immediately anterior to the optic chiasm, it is often called the preoptic fossa.

Diencephalon, diencephalon, is the more posterior part of the former forebrain. Its posterior border is conventionally determined by drawing a line from the tubercle in the bottom of the neural tube, called the tuberculum posterium, to the depression in the roof of the neural tube, which already appears at this stage of development. When examining the entire embryo, it is sometimes clearly visible and sometimes invisible.

The most distinct feature of the diencephalon is the presence of lateral outgrowths that form the optic vesicles, as well as a diverticulum located in the middle of the ventral wall and forming the infundibulum. The outgrowth from the middle of the dorsal wall of the diencephalon is known as the pineal gland, which, becoming noticeable in the chick embryo on the 3-4th day, appears relatively late in the pig and in humans.
Typically, human embryos 9-11 mm long do not yet have any signs of epiphyseal protrusion, first noted in 12 mm embryos.

Midbrain mesencephalon in early embryos it remains almost unchanged. It is separated from the mezencephalon by a clearly visible narrowing of the neural tube.
At this stage observed division of the hindbrain rhombencephalon into the cerebellar anlage metencephalon and the medulla oblongata myelencephalon. The dorsal wall of the neural tube immediately caudal to the meso-rhombencephalic constriction is very thick, in contrast to the thin roof of the caudal hindbrain. The part of the neural tube where this thickening is located is the metencephalon, and the end of the hindbrain with a thin roof constitutes the myelencephalon.

Although all external signs of individual neuromeres by this time they disappear, the inner surface of the myelsencephalon wall reveals obvious traces of metamerism.

Cranial nerves

Cranial nerve connections with different structures of the head and especially the brain are very stable in all mammals. In fish we observe 10 pairs of cranial nerves. Mammals have the same 10 cranial nerves with similar relationships and functions.

Besides, brain mammals, in the process of progressive specialization, included part of the neural tube, which in primitive fish is the unchanged spinal cord. This is evidenced by the presence in mammals of 12 pairs of cranial nerves, of which the first 10 are homologues of the 10 cranial nerves of fish, and the last two pairs represent a modification of the anterior most spinal nerves of fish.

Twelve pairs of cranial nerves are identified by numbers and names. Starting from the most anterior, these are the following nerves: (I) olfactory (olfactorius); (II) visual (opticus); (III) oculomotor (oculomotorius); (IV) block (trochlearis); (V) trigeminal (trigeminus); (VI) abducens; (VII) facial (facialis); (VIII) auditory (acusticus); (IX) glossopharyngeal (glossopharyngeus); (X) wandering (vagus); (XI) additional (accessorius); (XII) sublingual (hypoglossus). In six-week embryos, all cranial nerves are clearly visible, with the exception of the olfactory and optic nerves.

Nerves carrying sensory (afferent) fibers, have ganglia near their junction with the brain. With the exception of the auditory (VIII), all nerves carrying ganglia also contain a certain amount of efferent (motor) fibers, i.e., they are mixed nerves. Those cranial nerves that are built almost exclusively from efferent fibers do not have external ganglia (nerves III, IV, VI, XII).

The human nervous system develops from the outer germ layer - the ectoderm. In the dorsal parts of the embryo's body, differentiating ectodermal cells form a medullary (nervous) 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 proliferation 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 neural (medullary) groove leads to the fact that its edges first come closer together and then grow together. Thus, the neural groove, closing in its dorsal sections, turns into neural tube. Fusion initially occurs in the anterior section, slightly away from the anterior edge of the neural tube. Then its posterior, caudal sections fuse. At the anterior and posterior ends of the neural tube, small unfused areas remain - neuropores. After fusion of the dorsal sections, the neural tube is detached from the ectoderm and plunges into the mesoderm.

During its formation, 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 subsequently develops, from the middle (“cloak”) layer - the gray matter of the brain. The outer layer, almost devoid of cells, turns into white matter. At first, all the walls of the neural tube have the same thickness. Subsequently, the lateral sections of the tube develop more intensively, becoming increasingly thicker. 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.

From the side of the tube cavity, shallow longitudinal boundary grooves are formed on the inner surface of each of the lateral walls, which subdivide the lateral sections of the tube into the ventral main and dorsal alar 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 of neurons developing in the anterior columns emerge (sprout) from the spinal cord and form the anterior (motor) root. The posterior columns of gray matter and the adjacent white matter develop from the wing plate. Even at the stage of the neural groove, cellular cords are distinguished in its lateral sections, called medullary ridges. During the formation of the neural tube, two crests fuse to form a ganglion plate located dorsal to the neural tube, between the latter and the ectoderm. Subsequently, the ganglion plate is secondarily divided into two symmetrical ganglion ridges, each of which is displaced to the lateral surface of the neural tube. Then the ganglion ridges turn into the spinal nodes corresponding to each segment of the body, ganglia spinatia and sensory ganglia of the cranial nerves, ganglia sensorialia nn. cranialium. Cells evicted from the ganglion ridges also serve as rudiments for the development of the peripheral parts of the autonomic nervous system.

Following the separation of the ganglion plate, the neural tube at the head end noticeably thickens. This expanded part serves as the rudiment of the brain. The remaining parts of the neural tube later develop into the spinal cord. Neuroblasts located in the developing spinal ganglion have the form of bipolar cells. In the process of further differentiation of neuroblasts, areas of its two processes located in close proximity to the cell body merge into one T-shaped process, which then divides. Thus, the cells of the spinal ganglia become pseudounipolar in shape. The central processes of these cells are sent to the spinal cord and form the dorsal (sensitive) root. Other processes of pseudounipolar cells grow from the nodes to the periphery, where they have receptors of various types.

The stage of development of three brain vesicles is observed in the 4-5th week of the intrauterine period. The bubbles are called: anterior (prosencephalon), middle (mesencephalon), diamond-shaped (rhombencephalon) (Fig. 492). They differ from one another in bends and narrowings that deform the brain tube not only from the outside, but also from its cavity. The wall of the brain vesicles is formed by three layers: 1) the matrix layer, or germinal layer, consisting of poorly differentiated cells; 2) intermediate layer; 3) marginal layer, which has few cellular elements. In the ventral wall of the brain vesicles there is a well-developed interstitial layer, 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 region of the lateral wall of the anterior medullary vesicle, in which the eye cups are formed, the matrix layer of cells doubles and expands, forming the retina of the eyes. The optic vesicles form at the site where the forebrain vesicle divides into two parts. During the same period of development, the posterior part of the brain tube, corresponding to the spinal cord, has an internal ependymal and outer nuclear layer, more compact on the ventral wall. A ventral medullary fold is formed on the ventral wall of the brain vesicles, which narrows the cavity of the brain vesicles. The formation of the infundibulum and pituitary gland also occurs on the ventral wall of the anterior brain bladder (Fig. 492).
At the 6-7th week of embryonic development, the period of formation of five brain vesicles begins. Front brain divided into the telencephalon and the diencephalon. The midbrain (mesencephalon) is not divided into secondary vesicles. The rhombencephalon is divided into the hindbrain (metencephalon) and the medulla oblongata (myelencephalon). During this period, the brain tube is strongly curved and the anterior brain hangs over the horny bay and heart. In the neural tube, bends are distinguished: 1) parietal bend, which has a convexity in the dorsal direction at the level of the midbrain (Fig. 492); 2) ventral pontine projection at the level of the bridge; 3) the occipital flexure, in location corresponding to the level of the spinal cord and medulla oblongata.
Telencephalon (I brain vesicle). In a 7-8 week embryo, in the telencephalon in the lateral and medial sections there is development medial and lateral tubercles, which represent the nucl. caudatus et putamen. The olfactory bulb and tract are also formed from the protrusion of the ventral wall of the telencephalon. At the end of the 8th week of embryonic development, a qualitative restructuring of the telencephalon occurs: 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 postmitotic phase. Only from the 9-10th week of embryonic development does the rapid growth of the cerebral hemispheres and conducting systems occur, establishing connections between all the nuclei of the central nervous system. After 3 months of fetal development, thickening of the cerebral cortex, separation of cell layers and growth of individual medullary lobes occur. By the 7th month, a six-layer bark is formed. The lobes of the cerebral hemispheres develop unevenly. The temporal, then the frontal, occipital and parietal lobes grow faster.
Outside the hemispheres, at the junction of the frontal and temporal lobes, there is an area in the region of the lateral fossae that is stunted in growth. In this place, i.e. in the walls of the lateral fossae, the basal ganglia of the cerebral hemispheres and the insular cortex are formed. The developing hemispheres of the brain cover III brain bubble by the VI month of intrauterine development, and the IV and V brain vesicles by the IX month. After V months of development, there is a more rapid increase in the mass of the white matter than the cerebral cortex. The discrepancy between the growth of white matter and the cortex contributes to the formation of many convolutions, grooves and fissures. At the 3rd month, the hippocampal gyri are formed on the medial surface of the hemispheres, at the 4th month - the sulcus of the corpus callosum, on the V-cingulate gyrus, calcarine, occipito-parietal and lateral sulci. At VI-VII months, grooves appear on the dorsolateral surface: central, pre- and postcentral grooves, grooves of the temporal lobes, superior and inferior grooves of the frontal lobe, interparietal groove. During the period of development of nodes and thickening of the cortex, the wide cavity of the telencephalon turns into a narrow slit-lateral ventricle, extending into 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 vesicle). Has uneven wall thickness. The lateral walls are thickened and form the lining 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: retinal anlage and optic nerve, optic recess, pituitary infundibulum recess, intermastoid and mastoid recesses. Epithelial cells released from the head intestine fuse with the pituitary funnel, forming the pituitary gland. The lower wall, in addition to similar pockets, has several protrusions to form the gray tubercle and mastoid bodies, which grow together with the columns of the fornix (derivatives of the first medullary bladder). Upper wall thin and lacking a matrix cell layer. At the junction of the II and III brain vesicles, the pineal gland (corpus pineale) grows from the upper wall. Under it, the posterior cerebral commissure, leashes, and triangles of leashes are formed. The remaining part of the upper wall is transformed into the choroid plexus, which is retracted 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 cerebral vesicle). It has a thicker ventral wall. Its cavity turns into the cerebral aqueduct, connecting the III and IV cerebral ventricles. From the ventral wall, after the third month, the cerebral peduncles develop, containing ascending (dorsal) and descending (ventral) pathways, between which the substantia nigra, red nuclei, and nuclei of the III and IV pairs of cranial nerves are formed. Between the legs there is an anterior perforated substance. From the dorsal wall, initially the inferior colliculus develops, and then the superior colliculus of the midbrain. From these tubercles emerge bundles of fibers - brachia colliculorum superius et inferius for connection with the nuclei of the third medullary vesicle and the superior cerebellar peduncles for connection with the cerebellar nuclei.
Hindbrain (metencephalon) (IV cerebral vesicle) and medulla oblongata (myelencephalon) (V cerebral vesicle) elongated along one line and do not have clear intervesical boundaries.

4. Thoracic duct(ductus throracicus) is the main lymphatic collector that collects lymph from most of the human body and flows into the venous system. Only the lymph flowing from the right half of the chest, head, neck and right upper limb bypasses the G. p. - it flows into the right lymphatic duct. The duct is formed in the retroperitoneal tissue at the level of THXII - LII vertebrae by the fusion of large lymphatic trunks. The initial part of the duct (lacteal 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 above the aortic arch it emerges from under the left edge of the esophagus, slightly above the left clavicle it bends in an arcuate manner and flows into the venous bed at the confluence of the left subclavian and internal jugular veins. In the thoracic duct, incl. at its entry into the venous system, there are valves that prevent blood from flowing into it.

Brain vesicles of human embryos

Literature

Savelyev S.B. Stages of embryonic development of the human brain. - Moscow: Vedi, 2002. - 112 p. - ISBN 5-94624-007-2

Notes

Wikimedia Foundation. 2010.

See what “Brain Bubbles” are in other dictionaries:

Extensions of the head section of the neural tube in vertebrate embryos. After the neural plate closes (at the stage of neurulation) into a tube, three microorganisms are formed in its anterior section: the primary forebrain, the midbrain, and the primary hindbrain, or... ... Biological encyclopedic dictionary

brain bubbles- ANIMAL EMBRYOLOGY BRAIN BUBBLES – at the stage of neurulation in the development of vertebrates, the formation of pocket-like protrusions from the anterior part of the neural tube. Pocket-like protrusions give rise to the cerebral hemispheres, the anterior, middle and... ... General embryology: Terminological dictionary

Expansion of the head section of the neural tube in vertebrate and human embryos. Soon after the closure of the neural tube, 3 MPs are formed: primary anterior, middle and primary posterior. Subsequently, the primary anterior and posterior MPs are divided ...

BRAIN- BRAIN, cerebrum, a unifying concept for the entire central nervous system. M. is divided into two main sections: the brain and spinal cord (see); the first is located in the cranial cavity, the second in the spinal canal; the border between them passes through... ...

Organ of vision. We will outline here briefly: 1) the structure of the human eye; 2) embryonic development of the eye and its structure in different classes of vertebrates; 3) development of the organ of vision in the animal kingdom, the invertebrate eye. THE EYE OF A HUMAN...

EMBRYO- EMBRYO, a) 3. in zoology (embryo) an animal in the period from the beginning of egg crushing until the moment it emerges from the egg membranes, resp. from the mother's body. Nutrition 3. occurs in oviparous animals due to the nutritional reserves (yolk) of the developing egg, and in ... ... Great Medical Encyclopedia

We will outline here briefly: 1) the structure of the human eye; 2) embryonic development of the eye and its structure in different classes of vertebrates; 3) development of the organ of vision in the animal kingdom, the invertebrate eye. HUMAN EYE. Eye… … Encyclopedic Dictionary F.A. Brockhaus and I.A. Efron

Genus. in 1838, in the city of Jedrzeev, Radom province, and in 1861 he completed a course at the Medical Academy in St. Petersburg. He was left with her to prepare for a professorship and devoted himself to the study of mental illness under the guidance of... ... Large biographical encyclopedia

Movements of cells and cell layers in the developing embryo of animals, leading to the formation of germ layers (See Germ layers) and organ rudiments. The most intense M. d. occur during gastrulation (See Gastrulation), ... ... Great Soviet Encyclopedia

The study of the development of the human body from the formation of a single-celled zygote, or fertilized egg, until the birth of a child. Embryonic (intrauterine) human development lasts approximately 265,270 days. During this time from... Collier's Encyclopedia