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#21 Ge. Pe.

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Publicado el 23 mayo 2008 - 02:17







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Henry Gray (1821–1865). Anatomy of the Human Body. 1918.





4. The Brain or Encephalon



General Considerations and Divisions.—


The brain, is contained within the cranium, and constitutes the upper, greatly expanded part of the central nervous system. In its early embryonic condition it consists of three hollow vesicles, termed the hind-brain or rhombencephalon, the mid-brain or mesencephalon, and the fore-brain or prosencephalon; and the parts derived from each of these can be recognized in the adult (Fig. 677).

Thus in the process of development the wall of the hind-brain undergoes modification to form the medulla oblongata, the pons, and cerebellum, while its cavity is expanded to form the fourth ventricle.

The mid-brain forms only a small part of the adult brain; its cavity becomes the cerebral aqueduct (aqueduct of Sylvius), which serves as a tubular communication between the third and fourth ventricles; while its walls are thickened to form the corpora quadrigemina and cerebral peduncles.

The fore-brain undergoes great modification: its anterior part or telencephalon expands laterally in the form of two hollow vesicles, the cavities of which become the lateral ventricles, while the surrounding walls form the cerebral hemispheres and their commissures; the cavity of the posterior part or diencephalon forms the greater part of the third ventricle, and from its walls are developed most of the structures which bound that cavity.



FIG. 677




Scheme showing the connections of the several parts of the brain. (After Schwalbe.)






FIG. 678




Schematic representation of the chief ganglionic categories (I to V). (Spitzka.)





4a. The Hind-brain or Rhombencephalon


The hind-brain or rhombencephalon occupies the posterior fossa of the cranial cavity and lies below a fold of dura mater, the tentorium cerebelli.

It consists of

(a) the myelencephalon, comprising the medulla oblongata and the lower part of the fourth ventricle;

(b) the metencephalon, consisting of the pons, cerebellum, and the intermediate part of the fourth ventricle; and

© the isthmus rhombencephali, a constricted portion immediately adjoining the mid-brain and including the superior peduncles of the cerebellum, the anterior medullary velum, and the upper part of the fourth ventricle.



The Medulla Oblongata (spinal bulb).—


The medulla oblongata extends from the lower margin of the pons to a plane passing transversely below the pyramidal decussation and above the first pair of cervical nerves.



FIG. 679




Medulla oblongata and pons. Anterior surface.





FIG. 680




Decussation of pyramids.

Scheme showing passage of various fasciculi from medulla spinalis to medulla oblongata.

a. Pons.
b. Medulla oblongata.
c. Decussation of the pyramids.
d. Section of cervical part of medulla spinalis.
1. Anterior cerebrospinal fasciculus (in red).
2. Lateral cerebrospinal fasciculus (in red).
3. Sensory tract (fasciculi gracilis et cuneatus) (in blue). 3’. Gracile and cuneate nuclei.
4. Antero-lateral proper fasciculus (in dotted line).
5. Pyramid.
6. Lemniscus.
7. Medial longitudinal fasciculus.
8. Ventral spinocerebellar fasciculus (in blue).
9. Dorsal spinocerebellar fasciculus (in yellow). (Testut.)





FIG. 681




Hind- and mid-brains; postero-lateral view.




FIG. 682




Superficial dissection of brain-stem. Lateral view.






FIG. 683




Dissection of brain-stem. Lateral view.






FIG. 684




Deep dissection of brain-stem. Lateral view.






FIG. 685




Deep dissection of brain-stem. Lateral view.





FIG. 686




Upper part of medulla spinalis and hind- and mid-brains; posterior aspect, exposed in situ.



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#22 Ge. Pe.

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Publicado el 24 mayo 2008 - 07:50




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Henry Gray (1821–1865). Anatomy of the Human Body. 1918.





The Cerebrospinal Fasciculi.—



The downward course of these fasciculi from the pyramids of the medulla oblongata and their partial decussation have already been described in page 761. In crossing to reach the lateral funiculus of the opposite side, the fibers of the lateral cerebrospinal fasciculi extend backward through the anterior columns, and separate the head of each of these columns from its base (Figs. 687, 688).



FIG. 687




Section of the medulla oblongata through the lower part of the decussation of the pyramids. (Testut.)
1. Anterior median fissure.
2. Posterior median sulcus.
3. Anterior column (in red), with 3’, anterior root.
4. Posterior column (in blue), with 4’, posterior roots.
5. Lateral cerebrospinal fasciculus.
6. Posterior funiculus. The red arrow, a, a’, indicates the course the lateral cerebrospinal fasciculus takes at the level of the decussation of the pyramids; the blue arrow, b, b’, indicates the course which the sensory fibers take.





FIG. 688




Section of the medulla oblongata at the level of the decussation of the pyramids. (Testut.)

1. Anterior median fissure.
2. Posterior median sulcus.
3. Motor roots.
4. Sensory roots.
5. Base of the anterior column, from which the head (5’) has been detached by the lateral cerebrospinal fasciculus.
6. Decussation of the lateral cerebrospinal fasciculus.
7. Posterior columns (in blue).
8. Gracile nucleus.

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#23 Ge. Pe.

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Publicado el 28 mayo 2008 - 07:49






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Henry Gray (1821–1865). Anatomy of the Human Body. 1918.



4a. The Hind-brain or Rhombencephalon





FIG. 689




Superficial dissection of brain-stem. Ventral view.





FIG. 690




Deep dissection of brain-stem. Ventral view.





FIG. 691




Dissection of brain-stem. Dorsal view. The nuclear masses of the medulla are taken from model by Weed, Carnegie Publication, No. 19.




The fibers of the fasciculus gracilis and fasciculus cuneatus end by arborizing around the cells of these nuclei (Fig. 692). From the cells of the nuclei new fibers arise; some of these are continued as the posterior external arcuate fibers into the inferior peduncle, and through it to the cerebellum, but most of them pass forward through the neck of the posterior column, thus cutting off its head from its base (Fig. 693).



FIG. 692




Superior terminations of the posterior fasciculi of the medulla spinalis.

1. Posterior median sulcus.
2. Fasciculus gracilis.
3. Fasciculus cuneatus.
4. Gracile nucleus.
5. Cuneate nucleus.
6, 6’, 6’’. Sensory fibers forming the lemniscus.
7. Sensory decussation.
8. Cerebellar fibers uncrossed (in black).
9. Cerebellar fibers crossed (in black). (Testut.)





FIG. 693




Transverse section passing through the sensory decussation. (Schematic.)

1. Anterior median fissure.
2. Posterior median sulcus.
3, 3. Head and base of anterior column (in red).
4. Hypoglossal nerve.
5. Bases of posterior columns.
6. Gracile nucleus.
7. Cuneate nucleus.
8, 8. Lemniscus.
9. Sensory decussation. 1
10. Cerebrospinal fasciculus. (Testut.)



Gray Substance of the Medulla Oblongata (Figs. 694, 695).—


In addition to the gracile and cuneate nuclei, there are several other nuclei to be considered. Some of these are traceable from the gray substance of the medulla spinalis, while others are unrepresented in it.



FIG. 694




Section of the medulla oblongata at about the middle of the olive. (Schwalbe.)





FIG. 695




Transverse section of medulla oblongata below the middle of the olive.




FIG. 696




The cranial nerve nuclei schematically represented; dorsal view. Motor nuclei in red; sensory in blue. (The olfactory and optic centers are not represented.)





FIG. 697




Nuclei of origin of cranial motor nerves schematically represented; lateral view.





FIG. 698




Primary terminal nuclei of the afferent (sensory) cranial nerves schematically represented; lateral view. The olfactory and optic centers are not represented.





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#24 Ge. Pe.

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Continuación del post superior


________________________________________________


FIG. 699




Diagram showing the course of the arcuate fibers. (Testut.)

1. Medulla oblongata anterior surface.
2. Anterior median fissure.
3. Fourth ventricle.
4. Inferior olivary nucleus, with the accessory olivary nuclei.
5. Gracile nucleus.
6. Cuneate nucleus.
7. Trigeminal.
8. Inferior peduncles, seen from in front.
9. Posterior external arcuate fibers.
10. Anterior external arcuate fibers.
11. Internal arcuate fibers.
12. Peduncle of inferior olivary nucleus.
13. Nucleus arcuatus.
14. Vagus.
15. Hypoglossal.





Formatio Reticularis (Fig. 700).—


FIG. 700




The formatio reticularis of the medulla oblongata, shown by a transverse section passing through the middle of the olive. (Testut.)

1. Anterior median fissure.
2. Fourth ventricle.
3. Formatio reticularis, with 3’, its internal part (reticularis alba), and 3’’, its external part (reticularis grisea).
4. Raphé.
5. Pyramid.
6. Lemniscus.
7. Inferior olivary nucleus with the two accessory olivary nuclei.
8. Hypoglossal nerve, with 8’, its nucleus of origin.
9. Vagus nerve, with 9’, its nucleus of termination.
10. Lateral dorsal acoustic nucleus.
11. Nucleus ambiguus (nucleus of origin of motor fibers of glossopharyngeal, vagus, and cerebral portion of spinal accessory).
12. Gracile nucleus.
13. Cuneate nucleus.
14. Head of posterior column, with 14’, the lower sensory root of trigeminal nerve.
15. Fasciculus solitarius.
16. Anterior external arcuate fibers, with 16’, the nucleus arcuatus.
17. Nucleus lateralis
18. Nucleus of fasciculus teres.
19. Ligula.



This term is applied to the coarse reticulum which occupies the anterior and lateral districts of the medulla oblongata. It is situated behind the pyramid and olive, extending laterally as far as the inferior peduncles, and dorsally to within a short distance of the rhomboid fossa. The reticulum is caused by the intersection of bundles of fibers running at right angles to each other, some being longitudinal, others more or less transverse in direction. The formatio reticularis presents a different appearance in the anterior district from what it does in the lateral; in the former, there is an almost entire absence of nerve cells, and hence this part is known as the reticularis alba; whereas in the lateral district nerve cells are numerous, and as a consequence it presents a gray appearance, and is termed the reticularis grisea.


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#25 Ge. Pe.

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Henry Gray (1821–1865). Anatomy of the Human Body. 1918.


4a. The Hind-brain or Rhombencephalon



The Pons (pons Varoli).—



The pons or forepart of the hind-brain is situated in front of the cerebellum. From its superior surface the cerebral peduncles emerge, one on either side of the middle line. Curving around each peduncle, close to the upper surface of the pons, a thin white band, the tænia pontis, is frequently seen; it enters the cerebellum between the middle and superior peduncles. Behind and below, the pons is continuous with the medulla oblongata, but is separated from it in front by a furrow in which the abducent, facial, and acoustic nerves appear.


Structure (Fig. 701).

Transverse sections of the pons show it to be composed of two parts which differ in appearance and structure: thus, the basilar or ventral portion consists for the most part of fibers arranged in transverse and longitudinal bundles, together with a small amount of gray substance; while the dorsal tegmental portion is a continuation of the reticular formation of the medulla oblongata, and most of its constituents are continued into the tegmenta of the cerebral peduncles.


FIG. 701




Coronal section of the pons, at its upper part.



The Cerebellum.—


The cerebellum constitutes the largest part of the hindbrain. It lies behind the pons and medulla oblongata; between its central portion and these structures is the cavity of the fourth ventricle. It rests on the inferior occipital fossæ, while above it is the tentorium cerebelli, a fold of dura mater which separates it from the tentorial surface of the cerebrum. It is somewhat oval in form, but constricted medially and flattened from above downward, its greatest diameter being from side. Its surface is not convoluted like that of the cerebrum, but is traversed by numerous curved furrows or sulci, which vary in depth at different parts, and separate the laminæ of which it is composed. Its average weight in the male is about 150 gms. In the adult the proportion between the cerebellum and cerebrum is about 1 to 8, in the infant about 1 to 20.


The upper surface of the cerebellum (Fig. 702) is elevated in the middle and sloped toward the circumference, the hemispheres being connected together by the superior vermis, which assumes the form of a raised median ridge, most prominent in front, but not sharply defined from the hemispheres.



FIG. 702




Upper surface of the cerebellum. (Schäfer.)



The under surface of the cerebellum (Fig. 703) presents, in the middle line, the inferior vermis, buried in the vallecula, and separated from the hemisphere on either side by a deep groove, the sulcus valleculæ.




FIG. 703




Under surface of the cerebellum. (Schäfer.)






Internal Structure of the Cerebellum.—The cerebellum consists of white and gray substance.

White Substance.—If a sagittal section (Fig. 704) be made through either hemisphere, the interior will be found to consist of a central stem of white substance, in the middle of which is a gray mass, the dentate nucleus.




FIG. 704




The white substance of the cerebellum includes two sets of nerve fibers: (1) projection fibers, (2) fibræ propriæ.

Sagittal section of the cerebellum, near the junction of the vermis with the hemisphere. (Schäfer.)








The middle cerebellar peduncles (brachia pontis) (Fig. 705) are composed entirely of centripetal fibers, which arise from the cells of the nuclei pontis of the opposite side and end in the cerebellar cortex; the fibers are arranged in three fasciculi, superior, inferior, and deep.


FIG. 705




Dissection showing the projection fibers of the cerebellum. (After E. B. Jamieson.)





Gray Substance.—The gray substance of the cerebellum is found in two situations:

(1) on the surface, forming the cortex;

(2) as independent masses in the anterior.


(1) The gray substance of the cortex presents a characteristic foliated appearance, due to the series of laminæ which are given off from the central white substance; these in their turn give off secondary laminæ, which are covered by gray substance. Externally, the cortex is covered by pia mater; internally is the medullary center, consisting mainly of nerve fibers.

Microscopic Appearance of the Cortex (Fig. 706).—The cortex consists of two layers, viz., an external gray molecular layer, and an internal rust-colored nuclear layer; between these is an incomplete stratum of cells which are characteristic of the cerebellum, viz., the cells of Purkinje.


(2) The independent centers of gray substance in the cerebellum are four in number on either side: one is of large size, and is known as the nucleus dentatus; the other three, much smaller, are situated near the middle of the cerebellum, and are known as the nucleus emboliformis, nucleus globosus, and nucleus fastigii.

The internal rust-colored or nuclear layer (Fig. 706) is characterized by containing numerous small nerve cells of a reddish-brown color, together with many nerve fibrils.


FIG. 706




Transverse section of a cerebellar folium. (Diagrammatic, after Cajal and Kölliker.)



The nucleus dentatus (Fig. 707) is situated a little to the medial side of the center of the stem of the white substance of the hemisphere.



FIG. 707




Sagittal section through right cerebellar hemisphere. The right olive has also been cut sagitally.





The Fourth Ventricle (ventriculus quartus).—



The fourth ventricle, or cavity of the hind-brain, is situated in front of the cerebellum and behind the pons and upper half of the medulla oblongata. Developmentally considered, the fourth ventricle consists of three parts: a superior belonging to the isthmus rhombencephali, an intermediate, to the metencephalon, and an inferior, to the myelencephalon. It is lined by ciliated epithelium, and is continuous below with the central canal of the medulla oblongata; above, it communicates, by means of a passage termed the cerebral aqueduct, with the cavity of the third ventricle. It presents four angles, and possesses a roof or dorsal wall, a floor or ventral wall, and lateral boundaries.


Roof or Dorsal Wall (Fig. 708).—The upper portion of the roof is formed by the superior peduncle and the anterior medullary velum; the lower portion, by the posterior medullary velum, the epithelial lining of the ventricle covered by the tela chorioidea inferior, the tæniæ of the fourth ventricle, and the obex.



FIG. 708




Scheme of roof of fourth ventricle. The arrow is in the foramen of Majendie.




Rhomboid Fossa (fossa rhomboidea; “floor” of the fourth ventricle) (Fig. 709).—The anterior part of the fourth ventricle is named, from its shape, the rhomboid fossa, and its anterior wall, formed by the back of the pons and medulla oblongata, constitutes the floor of the fourth ventricle




FIG. 709




Rhomboid fossa.


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#26 Ge. Pe.

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4b. The Mid-brain or Mesencephalon



The mid-brain or mesencephalon (Fig. 681) is the short, constricted portion which connects the pons and cerebellum with the thalamencephalon and cerebral hemispheres. It is directed upward and forward, and consists of


FIG. 681




Hind- and mid-brains; postero-lateral view.



(1) a ventrolateral portion, composed of a pair of cylindrical bodies, named the cerebral peduncles;

(2) a dorsal portion, consisting of four rounded eminences, named the corpora quadrigemina; and


(3) an intervening passage or tunnel, the cerebral aqueduct, which represents the original cavity of the mid-brain and connects the third with the fourth ventricle (Fig. 710).



FIG. 710




Coronal section through mid-brain. (Schematic.) (Testut.)

1. Corpora quadrigemina.
2. Cerebral aqueduct.
3. Central gray stratum.
4. Interpeduncular space.
5. Sulcus lateralis.
6. Substantia nigra.
7. Red nucleus of tegmentum.
8. Oculomotor nerve, with 8’, its nucleus of origin. a. Lemniscus (in blue) with a’ the medial lemniscus and a" the lateral lemniscus. b. Medial longitudinal fasciculus. c. Raphé. d. Temporopontine fibers. e. Portion of medial lemniscus, which runs to the lentiform nucleus and insula. f. Cerebrospinal fibers. g. Frontopontine fibers.



The cerebral peduncles (pedunculus cerebri; crus cerebri) are two cylindrical masses situated at the base of the brain, and largely hidden by the temporal lobes of the cerebrum, which must be drawn aside or removed in order to expose them.



Structure of the Cerebral Peduncles (Figs. 711, 712).—

On transverse section, each peduncle is seen to consist of a dorsal and a ventral part, separated by a deeply pigmented lamina of gray substance, termed the substantia nigra.



FIG. 711




Transverse section of mid-brain at level of inferior colliculi.



FIG. 712




Transverse section of mid-brain at level of superior colliculi.



FIG. 713





Scheme showing the course of the fibers of the lemniscus; medial lemniscus in blue, lateral in red.




FIG. 714




Transverse section passing through the sensory decussation. Schematic. (Testut.)

1. Anterior median fissure.
2. Posterior median sulcus.
3, 3’. Head and base of anterior column (in red).
4. Hypoglossal nerve.
5. Bases of posterior column.
6. Gracile nucleus.
7. Cuneate nucleus.
8, 8. Lemniscus.
9. Sensory decussation.
10. Cerebrospinal fasciculus.


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#27 Ge. Pe.

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4c. The Fore-brain or Prosencephalon



The fore-brain or prosencephalon consists of:

(1) the diencephalon, corresponding in a large measure to the third ventricle and the structures which bound it; and

(2) the telencephalon, comprising the largest part of the brain, viz., the cerebral hemispheres; these hemispheres are intimately connected with each other across the middle line, and each contains a large cavity, named the lateral ventricle.

The lateral ventricles communicate through the interventricular foramen with the third ventricle, but are separated from each other by a medial septum, the septum pellucidum; this contains a slit-like cavity, which does not communicate with the ventricles.


FIG. 715




Mesal aspect of a brain sectioned in the median sagittal plane.




The Thalamencephalon.—


The thalamencephalon comprises:

(1) the thalamus;
(2) the metathalamus or corpora geniculata; and
(3) the epithalamus, consisting of the trigonum habenulæ, the pineal body, and the posterior commissure.


The Thalami (optic thalamus) (Figs. 716, 717) are two large ovoid masses, situated one on either side of the 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.


FIG. 716




Dissection showing the ventricles of the brain.





FIG. 717




Coronal section of brain immediately in front of pons.





FIG. 718




Coronal section of brain through intermediate mass of third ventricle.





The Metathalamus (Fig. 719) comprises the geniculate bodies, which are two in number—a medial and a lateral—on each side.



FIG. 719




Hind- and mid-brains; postero-lateral view.





The Epithalamus comprises the trigonum habenulæ, the pineal body, and the posterior commissure.




The Hypothalamus (Fig. 720)


includes the subthalamic tegmental region and the structures forming the greater part of the floor of the third ventricle, viz., the corpora mammillaria, tuber cinereum, infundibulum, hypophysis, and optic chiasma.



FIG. 720




Median sagittal section of brain. The relations of the pia mater are indicated by the red color.




The hypophysis (pituitary body) (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, and is situated in the fossa hypophyseos of the sphenoidal bone, where it is retained by a circular fold of dura mater, the diaphragma sella; this fold almost completely roofs in the fossa, leaving only a small central aperture through which the infundibulum passes.



FIG. 721




The hypophysis cerebri, in position. Shown in sagittal section.




Optic Chiasma (chiasma opticum; optic commissure).—


The optic chiasma is a flattened, somewhat quadrilateral band of fibers, situated at the junction of the floor and anterior wall of the third ventricle. Most of its fibers have their origins in the retina, and reach the chiasma through the optic nerves, which are continuous with its antero-lateral angles. In the chiasma, they undergo a partial decussation (Fig. 722)


FIG. 722




Scheme showing central connections of the optic nerves and optic tracts.




The Third Ventricle (ventriculus tertius) (Figs. 716, 720).—


The third ventricle is a median cleft between the two thalami. Behind, it communicates with the fourth ventricle through the cerebral aqueduct, and in front with the lateral ventricles through the 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, 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, named the tela chorioidea of the third ventricle, from the under surface of which a pair of vascular fringed processes, the choroid plexuses of the third ventricle, project downward, one on either side of the middle line, and invaginate the epithelial roof into the ventricular cavity.


FIG. 723




Coronal section of lateral and third ventricles. (Diagrammatic.)



Interpeduncular Fossa (Fig. 724).—


This is a somewhat lozenge-shaped area of the base of the brain, limited in front by the optic chiasma, behind by the antero-superior surface of the pons, antero-laterally by the converging optic tracts, and postero-laterally by the diverging cerebral peduncles. The structures contained in it have already been described; from behind forward, they are the posterior perforated substance, corpora mamillaria, tuber cinereum, infundibulum, and hypophysis.


FIG. 724




Base of brain.





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#28 Ge. Pe.

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4c. The Fore-brain or Prosencephalon




Surfaces of the Cerebral Hemispheres.—


Each hemisphere presents three surfaces: lateral, medial, and inferior.

The lateral surface is convex in adaptation to the concavity of the corresponding half of the vault of the cranium.

The medial surface is flat and vertical, and is separated from that of the opposite hemisphere by the great longitudinal fissure and the 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, is concave, and rests on the roof of the orbit and nose; the middle area is convex, and consists of the under surface of the temporal lobe: it is adapted to the corresponding half of the 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, which intervenes between it and the upper surface of the cerebellum.




FIG. 725




Lateral surface of left cerebral hemisphere, viewed from above.





The Lateral Cerebral Fissure (fissura cerebri lateralis [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.


FIG. 726




Lateral surface of left cerebral hemisphere, viewed from the side.




The Central Sulcus (sulcus centralis [Rolandi]; fissure of Rolando; central fissure) (Figs. 725, 726) is situated about the middle of the lateral surface of the hemisphere, and begins in or near the longitudinal cerebral fissure, a little behind its mid-point.



FIG. 725




Lateral surface of left cerebral hemisphere, viewed from above.




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.

The lateral part of the parietoöccipital fissure (Fig. 726) is situated about 5 cm. in front of the occipital pole of the hemisphere, and measures about 1.25 cm. in length.


FIG. 726




Lateral surface of left cerebral hemisphere, viewed from the side.


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 below and behind the posterior end of the corpus callosum.

The Calcarine Fissure (fissura calcarina) (Fig. 727) is on the medial surface of the hemisphere.

The Cingulate Sulcus (sulcus cinguli; callosomarginal fissure) (Fig. 727) is on the medial surface of the hemisphere

The Collateral Fissure (fissura collateralis) (Fig. 727) is on the tentorial surface of the hemisphere and extends from near the occipital pole to within a short distance of the temporal pole.


FIG. 727




Medial surface of left cerebral hemisphere.



The Sulcus Circularis (circuminsular fissure) (Fig. 731) is on the lower and lateral surfaces of the hemisphere: it surrounds the insula and separates it from the frontal, parietal, and temporal lobes.


FIG. 731




The insula of the left side, exposed by removing the opercula.



Lobes of the Hemispheres.—


By means of these fissures and sulci, assisted by certain arbitrary lines, each hemisphere is divided into the following lobes: the frontal, the parietal, the temporal, the occipital, the limbic, and the insula.


FIG. 728




Principal fissures and lobes of the cerebrum viewed laterally.




FIG. 729




Orbital surface of left frontal lobe.





FIG. 730




Section of brain showing upper surface of temporal lobe.




Rhinencephalon (Fig. 732).—


The rhinencephalon comprises the olfactory lobe, the uncus, the subcallosal and supracallosal gyri, the fascia dentata hippocampi, the septum pellucidum, the fornix, and the hippocampus.


FIG. 732




Scheme of rhinencephalon



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4c. The Fore-brain or Prosencephalon






Interior of the Cerebral Hemispheres.—


If the upper part of either hemisphere be removed, at a level about 1.25 cm. above the corpus callosum, the central white substance will be exposed as an oval-shaped area, the centrum ovale minus, surrounded by a narrow convoluted margin of gray substance, and studded with numerous minute red dots (puncta vasculosa), produced by the escape of blood from divided bloodvessels. If the remaining portions of the hemispheres be slightly drawn apart a broad band of white substance, the corpus callosum, will be observed, connecting them at the bottom of the longitudinal fissure; the margins of the hemispheres which overlap the corpus callosum are called the labia cerebri. Each labrium is part of the cingulate gyrus already described; and the slit-like interval between it and the upper surface of the corpus callosum is termed the callosal fissure (Fig. 727).


FIG. 727




Medial surface of left cerebral hemisphere.




If the hemispheres be sliced off to a level with the upper surface of the corpus callosum, the white substance 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, is called the centrum ovale majus.


The Corpus Callosum (Fig. 733, 720) is the great transverse commissure which unites the cerebral hemispheres and roofs in the lateral ventricle




FIG. 720




Median sagittal section of brain. The relations of the pia mater are indicated by the red color.





FIG. 733




Corpus callosum from above.





The Lateral Ventricles (ventriculus lateralis) (Fig. 734).—


The two lateral ventricles are irregular cavities situated in the lower and medial parts of the cerebral hemispheres, one on either side of the middle line.




FIG. 734




Scheme showing relations of the ventricles to the surface of the brain.





Each lateral ventricle consists of a central part or body, and three prolongations from it, termed cornua (Figs. 735, 736).



FIG. 735




Drawing of a cast of the ventricular cavities, viewed from above. (Retzius.)





FIG. 736




Drawing of a cast of the ventricular cavities, viewed from the side. (Retzius.)





The posterior cornu (cornu posterius; postcornu) (Figs. 737, 788) passes into the occipital lobe, its direction being backward and lateralward, and then medialward.



FIG. 737




Central part and anterior and posterior cornua of lateral ventricles exposed from above.





FIG. 738




Coronal section through posterior cornua of lateral ventricle.





The inferior cornu (cornu inferior; descending horn; middle horn; medicornu) (Fig. 739), the largest of the three, traverses the temporal lobe of the brain, forming in its course a curve around the posterior end of the thalamus.



FIG. 739




Posterior and inferior cornua of left lateral ventricle exposed from the side.





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4c. The Fore-brain or Prosencephalon






The hippocampus (hippocampus major) (Figs. 739, 740) is a curved eminence, about 5 cm. long, which extends throughout the entire length of the floor of the inferior cornu. 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. If a transverse section be made through the hippocampus, it will be seen that this eminence is produced by the folding of the wall of the hemisphere to form the hippocampal fissure. The main mass of the hippocampus consists of gray substance, but on its ventricular surface is a thin white layer, the alveus, which is continuous with the fimbria hippocampi.



FIG. 739




Posterior and inferior cornua of left lateral ventricle exposed from the side.




FIG. 740




Inferior and posterior cornua, viewed from above.





The caudate nucleus (nucleus caudatus; caudatum) (Figs. 741, 742) is a pear-shaped, highly arched gray mass;



FIG. 741




Two views of a model of the striatum: A, lateral aspect; B, mesal aspect.





FIG. 742




Horizontal section of right cerebral hemisphere.




FIG. 743




Coronal section through anterior cornua of lateral ventricles.






FIG. 744




Coronal section of brain through anterior commissure.




FIG. 745




Dissection showing the course of the cerebrospinal fibers. (E. B. Jamieson.)




FIG. 746




Diagram of the tracts in the internal capsule. Motor tract red.
The sensory tract (blue) is not direct, but formed of neurons receiving impulses from below in the thalamus and transmitting them to the cortex.
The optic radiation (occipitothalamic) is shown in violet.




The Fornix (Figs. 720, 747, 748) is a longitudinal, arch-shaped lamella of white substance, situated below the corpus callosum, and continuous with it behind, but separated from it in front by the septum pellucidum. It may be described as consisting of two symmetrical bands, one for either hemisphere.


FIG. 720




Median sagittal section of brain. The relations of the pia mater are indicated by the red color.





FIG. 747




Diagram of the fornix. (Spitzka.)




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4c. The Fore-brain or Prosencephalon



The Fornix (Figs. 720, 747, 748) is a longitudinal, arch-shaped lamella of white substance, situated below the corpus callosum, and continuous with it behind, but separated from it in front by the septum pellucidum.



FIG. 748




The fornix and corpus callosum from below. (From a specimen in the Department of Human Anatomy of the University of Oxford.)




FIG. 749




Coronal section of inferior horn of lateral ventricle. (Diagrammatic.)





The crura (crus fornicis; posterior pillars) of the fornix are prolonged backward from the body.


They are flattened bands, and at their commencement are intimately connected with the under surface of the corpus callosum. Diverging from one another, each curves around the posterior end of the thalamus, and passes downward and forward into the inferior cornu of the lateral ventricle (Fig. 750).


FIG. 750




Tela chorioidea of the third ventricle, and the choroid plexus of the left lateral ventricle, exposed from above.



Structure of the Cerebral Hemispheres.—


The cerebral hemispheres are composed of gray and white substance: the former covers their surface, and is termed the cortex; the latter occupies the interior of the hemispheres.

The white substance consists of medullated fibers, varying in size, and arranged in bundles separated by neuroglia.

They may be divided, according to their course and connections, into three distinct systems.

(1) Projection fibers connect the hemisphere with the lower parts of the brain and with the medulla spinalis.

(2) Transverse or commissural fibers unite the two hemispheres.

(3) Association fibers connect different structures in the same hemisphere; these are, in many instances, collateral branches of the projection fibers, but others are the axons of independent cells.


FIG. 751




Diagram showing principal systems of association fibers in the cerebrum.




FIG. 752




Dissection of cortex and brain-stem showing association fibers and island of Reil after removal of its superficial gray substance.




FIG. 753




Deep dissection of cortex and brain-stem.





Structure of the Cerebral Cortex (Fig. 754).—



The cerebral cortex differs in thickness and structure in different parts of the hemisphere. It is thinner in the occipital region than in the anterior and posterior central gyri, 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, and areas possessing a specialized type of cortex can be mapped out in the occipital lobe.

On examining a section of the cortex with a 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;

(2) a layer of gray substance;

(3) a second white layer (outer band of Baillarger or band of Gennari);

(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.

The cortex is made up of nerve cells of varying size and shape, and of nerve fibers which are either medullated or naked axis-cylinders, imbedded in a matrix of neuroglia.


FIG. 754




Cerebral cortex. (Poirier.) To the left, the groups of cells; to the right, the systems of fibers. Quite to the left of the figure a sensory nerve fiber is shown.




FIG. 755




Coronal section of olfactory bulb. (Schwalbe.)




Cerebral Localization.—


Physiological and pathological research have now gone far to prove that a considerable part of the surface of the brain may be mapped out into a series of more or less definite areas, each of which is intimately connected with some well-defined function.

The chief areas are indicated in Figs. 756 and 757.



FIG. 756




Areas of localization on lateral surface of hemisphere.

Motor area in red.
Area of general sensations in blue.
Auditory area in green. Visula area in yellow.
The psychic portions are in lighter tints.




FIG. 757




Areas of localization on medial surface of hemisphere.

Motor area in red.
Area of general sensations in blue.
Visual area in yellow.
Olfactory area in purple.
The psychic portions are in lighter tints.





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4d. Composition and Central Connections of the Spinal Nerves



The typical spinal nerve consists of at least four types of fibers, the somatic sensory, sympathetic afferent or sensory, somatic motor and sympathetic efferent or preganglionic. The somatic sensory fibers, afferent fibers, arise from cells in the spinal ganglia and are found in all the spinal nerves, except occasionally the first cervical, and conduct impulses of pain, touch and temperature from the surface of the body through the posterior roots to the spinal cord and impulses of muscle sense, tendon sense and joint sense from the deeper structures. The sympathetic afferent fibers, conduct sensory impulses from the viscera through the rami communicantes and posterior roots to the spinal cord. They are probably limited to the white rami connected with the spinal nerves in two groups, viz., the first thoracic to the second lumbar and the second sacral to the fourth sacral nerves. The somatic motor fibers, efferent fibers, arise from cells in the anterior column of the spinal cord and pass out through the anterior roots to the voluntary muscles. The sympathetic efferent fibers, probably arise from cells in the lateral column or the base of the anterior column and emerge through the anterior roots and white rami communicantes. These are preganglionic fibers which end in various sympathetic ganglia from which postganglionic fibers conduct the motor impulses to the smooth muscles of the viscera and vessels and secretory impulses to the glands. These fibers are also limited to two regions, the first thoracic to the second lumbar and the second sacral to the fourth sacral nerves.

The afferent fibers which pass into the spinal cord establish various types of connections, some within the cord itself for spinal reflexes, others for reflexes connected with higher centers in the brain, while still others conduct impulses of conscious sensation by a series of neurons to the cerebral cortex.



FIG. 758




Diagram of the spinal cord reflex apparatus.

Some of the connections of a single afferent neuron from the skin (d.r.2) are indicated: d.r.2, dorsal root from second spinal ganglion; m, muscles; sp.g.1 to sp.g.4, spinal ganglia; v.r.1 to v.r.4, ventral roots. (After Herrick.)




Sensory Pathways from the Spinal Cord to the Brain.—


The posterior root fibers conducting the impulses of conscious muscle sense, tendon sense and joint sense, those impulses which have to do with the coördination and adjustment of muscular movements, ascend in the fasciculus gracilis and fasciculus cuneatus to the nucleus gracilis and nucleus cuneatus in the medulla oblongata (Fig. 759).


FIG. 759




The sensory tract. (Modified from Poirier.)




4e. Composition and Central Connections of the Spinal Nerves



The cranial nerves are more varied in their composition than the spinal nerves. Some, for example, contain somatic motor fibers only, others contain the various types of fibers found in the spinal nerves, namely, somatic motor, sympathetic efferent, somatic sensory and sympathetic sensory. In addition there are included the nerves of the special senses, namely, the nerves of smell, sight, hearing, equilibration and taste.

Este es un capítulo largo y muy difícil, solo pondremos los dibujos.




FIG. 760




Terminal nuclei of the cochlear nerve, with their upper connections. (Schematic.)

The vestibular nerve with its terminal nuclei and their efferent fibers have been suppressed.

On the other hand, in order not to obscure the trapezoid body, the efferent fibers of the terminal nuclei on the right side have been resected in a considerable portion of their extent.

The trapezoid body, therefore, shows only one-half of its fibers, viz., those which come from the left.
1. Vestibular nerve, divided at its entrance into the medulla oblongata.
2. Cochlear nerve.
3. Accessory nucleus of acoustic nerve.
4. Tuberculum acusticum.
5. Efferent fibers of accessory nucleus.
6. Efferent fibers of tuberculum acusticum, forming the striae medullares, with 6’, their direct bundle going to the superior olivary nucleus of the same side; 6’’, their decussating bundles going to the superior olivary nucleus of the opposite side.
7. Superior olivary nucleus.
8. Trapezoid body.
9. Trapezoid nucleus.
10. Central acoustic tract (lateral lemniscus).
11. Raphé.
12. Cerebrospinal fasciculus.
13. Fourth ventricle.
14. Inferior peduncle. (Testut.)




FIG. 761




Terminal nuclei of the vestibular nerve, with their upper connections. (Schematic.)

1. Cochlear nerve, with its two nuclei.
2. Accessory nucleus.
3. Tuberculum acusticum.
4. Vestibular nerve.
5. Internal nucleus.
6. Nucleus of Deiters.
7. Nucleus of Bechterew.
8. Inferior or descending root of acoustic.
9. Ascending cerebellar fibers.
10. Fibers going to raphé.
11. Fibers taking an oblique course.
12. Lemniscus.
13. Inferior sensory root of trigeminal.
14. Cerebrospinal fasciculus.
15. Raphé.
16. Fourth ventricle.
17. Inferior peduncle. Origin of striæ medullares. (Testut.)





FIG. 762




Figure showing the different groups of cells, which constitute, according to Perlia, the nucleus of origin of the oculomotor nerve.

1. Posterior dorsal nucleus. 1’. Posterior ventral nucleus.
2. Anterior dorsal nucleus. 2’. Anterior ventral nucleus.
3. Central nucleus.
4. Nucleus of Edinger and Westphal.
5. Antero-internal nucleus.
6. Antero-external nucleus.
8. Crossed fibers.
9. Trochlear nerve, with 9’, its nucleus of origin, and 9", its decussation.
10. Third ventricle. M, M. Median line. (Testut.)





FIG. 763




Scheme showing central connections of the optic nerves and optic tracts.





1F. Pathways from the Brain to the Spinal Cord


The descending fasciculi which convey impulses from the higher centers to the spinal cord and located in the lateral and ventral funiculi.

The Motor Tract (Fig. 764), conveying voluntary impulses, arises from the pyramid cells situated in the motor area of the cortex, the anterior central and the posterior portions of the frontal gyri and the paracentral lobule.



FIG. 764




The motor tract. (Modified from Poirier.)



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4g. The Meninges of the Brain and Medulla Spinalis



The brain and medulla spinalis are enclosed within three membranes. These are named from without inward: the dura mater, the arachnoid, and the pia mater.

The Dura Mater


The dura mater is a thick and dense inelastic membrane. The portion which encloses the brain differs in several essential particulars from that which surrounds the medulla spinalis, and therefore it is necessary to describe them separately; but at the same time it must be distinctly understood that the two form one complete membrane, and are continuous with each other at the foramen magnum.


The falx cerebri (Fig. 765), so named from its sickle-like form, is a strong, arched process which descends vertically in the longitudinal fissure between the cerebral hemispheres.

FIG. 765




Dura mater and its processes exposed by removing part of the right half of the skull and the brain.



The tentorium cerebelli (Fig. 766) is an arched lamina, elevated in the middle, and inclining downward toward the circumference.




FIG. 766




Tentorium cerebelli seen from above.




FIG. 767




The medulla spinalis and its membranes.



The Arachnoid—


The arachnoid is a delicate membrane enveloping the brain and medulla spinalis and lying between the pia mater internally and the dura mater externally; it is separated from the pia mater by the subarachnoid cavity, which is filled with cerebrospinal fluid.



Subarachnoid Cisternæ (cisternæ subarachnoidales) (Fig. 768).—The cisterna cerebellomedullaris (cisterna magna) is triangular on sagittal section, and results from the arachnoid bridging over the interval between the medulla oblongata and the under surfaces of the hemispheres of the cerebellum; it is continuous with the subarachnoid cavity of the medulla spinalis at the level of the foramen magnum


FIG. 768




Diagram showing the positions of the three principal subarachnoid cisternæ.



The Arachnoid Villi (granulationes arachnoideales; glandulæ Pacchioni; Pacchionian bodies) (Fig. 769) are small, fleshy-looking elevations, usually collected into clusters of variable size, which are present upon the outer surface of the dura mater, in the vicinity of the superior sagittal sinus, and in some other situations.


FIG. 769




Diagrammatic representation of a section across the top of the skull, showing the membranes of the brain, etc. (Modified from Testut.)




The Pia Mater—


The pia mater is a vascular membrane, consisting of a minute plexus of bloodvessels, held together by an extremely fine areolar tissue and covered by a reflexion of the mesothelial cells from the arachnoid trabeculæ. It is an incomplete membrane, absent probably at the foramen of Majendie and the two foramina of Luschka and perforated in a peculiar manner by all the bloodvessels as they enter or leave the nervous system. In the perivascular spaces, the pia apparently enters as a mesothelial lining of the outer surface of the space; a variable distance from the exterior these cells become unrecognizable and are apparently lacking, replaced by neuroglia elements. The inner walls of these perivascular spaces seem likewise covered for a certain distance by the mesothelial cells, reflected with the vessels from the arachnoid covering of these vascular channels as they traverse the subarachnoid spaces.



The Spinal Pia Mater (pia mater spinalis; pia of the cord) (Figs. 767, 770) is thicker, firmer, and less vascular than the cranial pia mater: this is due to the fact that it consists of two layers, the outer or additional one being composed of bundles of connective-tissue fibers, arranged for the most part longitudinally.


FIG. 767




The medulla spinalis and its membranes.




FIG. 770




Diagrammatic transverse section of the medulla spinalis and its membranes.




The ligamentum denticulatum (dentate ligament) (Fig. 767) is a narrow fibrous band situated on either side of the medulla spinalis throughout its entire length, and separating the anterior from the posterior nerve roots.


FIG. 767




The medulla spinalis and its membranes.



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4h. The Cerebrospinal Fluid


The cerebrospinal fluid, for the most part elaborated by the choroid plexuses, is poured into the cerebral ventricles which are lined by smooth ependyma.


5. The Cranial Nerves

(Nervi Cerebrales; Cerebral Nerves)



There are twelve pairs of cranial nerves; they are attached to the brain and are transmitted through foramina in the base of the cranium. The different pairs are named from before backward as follows:

1st. Olfactory.

2d. Optic.

3d. Oculomotor.

4th. Trochlear.

5th. Trigeminal.

6th. Abducent.

7th. Facial.

8th. Acoustic.

9th. Glossopharyngeal.

10th. Vagus.

11th. Accessory.

12th. Hypoglossal.



5a. The Olfactory Nerves



FIG. 771




Nerves of septum of nose. Right side.




FIG. 772




Plan of olfactory neurons




5b. The Optic Nerve

(N. Opticus; Second Nerve)



The optic nerve (Fig. 773), or nerve of sight, consists mainly of fibers derived from the ganglionic cells of the retina. These axons terminate in arborizations around the cells in the lateral geniculate body, pulvinar, and superior colliculus which constitute the lower or primary visual centers.


FIG. 773




The left optic nerve and the optic tracts.




The Optic Tract (Fig. 774), passes backward and outward from the optic chiasma over the tuber cinereum and anterior perforated space to the cerebral peduncle and winds obliquely across its under surface.


FIG. 774




Scheme showing central connections of the optic nerves and optic tracts.




5c. The Oculomotor Nerve

(N. Oculomotorius; Third Nerve)


The oculomotor nerve (Figs. 775, 776, 777) supplies somatic motor fibers to all the ocular muscles, except the Obliquus superior and Rectus lateralis; it also supplies through its connections with the ciliary ganglion, sympathetic motor fibers to the Sphincter pupillæ and the Ciliaris muscles.


FIG. 775




Plan of oculomotor nerve.




5d. The Trochlear Nerve (N. Trochlearis; Fourth Nerve)

(N. Trochlearis; Fourth Nerve)



The trochlear nerve (Fig. 776), the smallest of the cranial nerves, supplies the Obliquus superior oculi.


FIG. 776




Nerves of the orbit. Seen from above.




FIG. 777




Nerves of the orbit, and the ciliary ganglion. Side view.




5e. The Trigeminal Nerve

(N. Trigeminus; Fifth Or Trifacial Nerve)



The trigeminal nerve is the largest cranial nerve and is the great sensory nerve of the head and face, and the motor nerve of the muscles of mastication.

It emerges from the side of the pons, near its upper border, by a small motor and a large sensory root—the former being situated in front of and medial to the latter.



The Maxillary Nerve (n. maxillaris; superior maxillary nerve) (Fig. 778), or second division of the trigeminal, is a sensory nerve



FIG. 778




Distribution of the maxillary and mandibular nerves, and the submaxillary ganglion.





FIG. 779




Alveolar branches of superior maxillary nerve and sphenopalatine ganglion. (Testut.)



Sphenopalatine Ganglion (ganglion of Meckel) (Fig. 780).—The sphenopalatine ganglion, the largest of the sympathetic ganglia associated with the branches of the trigeminal nerve, is deeply placed in the pterygopalatine fossa, close to the sphenopalatine foramen. It is triangular or heart-shaped, of a reddish-gray color, and is situated just below the maxillary nerve as it crosses the fossa. It receives a sensory, a motor, and a sympathetic root.


FIG. 780




The sphenopalatine ganglion and its branches.




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5. The Cranial Nerves

(Nervi Cerebrales; Cerebral Nerves)



The mandibular nerve (n. mandibularis; inferior maxillary nerve) (Figs. 778, 781) supplies the teeth and gums of the mandible, the skin of the temporal region, the auricula, the lower lip, the lower part of the face, and the muscles of mastication; it also supplies the mucous membrane of the anterior two-thirds of the tongue.


FIG. 778





Distribution of the maxillary and mandibular nerves, and the submaxillary ganglion.





FIG. 781





Mandibular division of the trifacial nerve. (Testut.)





The Inferior Alveolar Nerve (n. alveolaris inferior; inferior dental nerve)(Fig. 782) is the largest branch of the mandibular nerve.



FIG. 782





Mandibular division of trifacial nerve, seen from the middle line. The small figure is an enlarged view of the otic ganglion. (Testut.)




Otic Ganglion (ganglion oticum)(Fig. 783).—

The otic ganglion is a small, ovalshaped, flattened ganglion of a reddish-gray color, situated immediately below the foramen ovale; it lies on the medial surface of the mandibular nerve, and surrounds the origin of the nerve to the Pterygoideus internus. It is in relation, laterally, with the trunk of the mandibular nerve at the point where the motor and sensory roots join; medially, with the cartilaginous part of the auditory tube, and the origin of the Tensor veli palatini; posteriorly, with the middle meningeal artery.


FIG. 783





The otic ganglion and its branches.




FIG. 784





Sensory areas of the head, showing the general distribution of the three divisions of the fifth nerve. (Modified from Testut.)




Submaxillary Ganglion (ganglion submaxillare)(Fig. 778).—


The submaxillary ganglion is of small size and is fusiform in shape. It is situated above the deep portion of the submaxillary gland, on the hyoglossus, near the posterior border of the Mylohyoideus, and is connected by filaments with the lower border of the lingual nerve. It is suspended from the lingual nerve by two filaments which join the anterior and posterior parts of the ganglion.


FIG. 778





Distribution of the maxillary and mandibular nerves, and the submaxillary ganglion.





1F. The Abducent Nerve


(N. Abducens; Sixth Nerve)



The abducent nerve (Fig. 777) supplies the Rectus lateralis oculi.


FIG. 777





Nerves of the orbit, and the ciliary ganglion. Side view.




Its fibers arise from a small nucleus situated in the upper part of the rhomboid fossa, close to the middle line and beneath the colliculus facialis. They pass downward and forward through the pons, and emerge in the furrow between the lower border of the pons and the upper end of the pyramid of the medulla oblongata.

From the nucleus of the sixth nerve, fibers are said to pass through the medial longitudinal fasciculus to the oculomotor nerve of the opposite side, along which they are carried to the Rectus medialis. The Rectus lateralis of one eye and the Rectus medialis of the other may therefore be said to receive their nerves from the same nucleus (Fig. 785).


FIG. 785





Figure showing the mode of innervation of the Recti medialis and lateralis of the eye (after Duval and Laborde).




In the cavernous sinus (Fig. 786), the oculomotor, trochlear, and ophthalmic nerves are placed in the lateral wall of the sinus, in the order given, from above downward.



FIG. 786





Oblique section through the right cavernous sinus.




In the superior orbital fissure (Fig. 787), the trochlear nerve and the frontal and lacrimal divisions of the ophthalmic lie in this order from the medial to the lateral side upon the same plane; they enter the cavity of the orbit above the muscles.


FIG. 787





Dissection showing origins of right ocular muscles, and nerves entering by the superior orbital fissure.





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5. The Cranial Nerves


(Nervi Cerebrales; Cerebral Nerves)




5g. The Facial Nerve


(N. Facialis; Seventh Nerve)



The facial nerve (Figs. 788, 790) consists of a motor and a sensory part, the latter being frequently described under the name of the nervus intermedius (pars intermedii of Wrisberg)(Fig. 788). The two parts emerge at the lower border of the pons in the recess between the olive and the inferior peduncle, the motor part being the more medial, immediately to the lateral side of the sensory part is the acoustic nerve.


FIG. 788





Plan of the facial and intermediate nerves and their communication with other nerves.




FIG. 789





The course and connections of the facial nerve in the temporal bone.






FIG. 790





The nerves of the scalp, face, and side of neck.





5h. The Acoustic Nerve

(Eighth Nerve)



The acoustic nerve consists of two distinct sets of fibers which differ in their peripheral endings, central connections, functions, and time of medullation. It is soft in texture and devoid of neurilemma.



5i. The Glossopharyngeal Nerve

(N. Glossopharyngeus; Ninth Nerve)




The glossopharyngeal nerve (Figs. 791, 792, 793) contains both motor and sensory fibers, and is distributed, as its name implies, to the tongue and pharynx. It is the nerve of ordinary sensation to the mucous membrane of the pharynx, fauces, and palatine tonsil, and the nerve of taste to the posterior part of the tongue. It is attached by three or four filaments to the upper part of the medulla oblongata, in the groove between the olive and the inferior peduncle.

The sensory fibers arise from the cells of the superior and petrous ganglia, which are situated on the trunk of the nerve, and will be presently described. When traced into the medulla, some of the sensory fibers, probably sympathetic afferent, end by arborizing around the cells of the upper part of a nucleus which lies beneath the ala cinerea in the lower part of the rhomboid fossa. Many of the fibers, probably the taste fibers, contribute to form a strand, named the fasciculus solitarius, which descends in the medulla oblongata. Associated with this strand are numerous nerve cells, and around these the fibers of the fasciculus end. The somatic sensory fibers, few in number, are said to join the spinal tract of the trigeminal nerve.


5j. The Vagus Nerve


(N. Vagus; Tenth Nerve; Pneumogastric Nerve)



The vagus nerve (Figs. 791, 792, 793) is composed of both motor and sensory fibers, and has a more extensive course and distribution than any of the other cranial nerves, since it passes through the neck and thorax to the abdomen.



FIG. 791




Plan of upper portions of glossopharyngeal, vagus, and accessory nerves.




FIG. 792





Upper part of medulla spinalis and hind- and mid-brains; posterior aspect, exposed in situ.





FIG. 793




Course and distribution of the glossopharyngeal, vagus, and accessory nerves.





5k. The Accessory Nerve


(N. Accessorius; Eleventh Nerve; Spinal Accessory Nerve)



The accessory nerve (Figs. 792, 793, 794) consists of two parts: a cranial and a spinal.



FIG. 792




Upper part of medulla spinalis and hind- and mid-brains; posterior aspect, exposed in situ.





FIG. 793





Course and distribution of the glossopharyngeal, vagus, and accessory nerves.




FIG. 794





Hypoglossal nerve, cervical plexus, and their branches.





5l. The Hypoglossal Nerve


(N. Hypoglossus; Twelfth Nerve)



The hypoglossal nerve (Figs. 794, 795) is the motor nerve of the tongue.




FIG. 795





Plan of hypoglossal nerve.




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6. The Spinal Nerves


(Nervi Spinales)



The spinal nerves spring from the medulla spinalis, and are transmitted through the intervertebral foramina. They number thirty-one pairs, which are grouped as follows: Cervical, 8; Thoracic, 12; Lumbar, 5; Sacral, 5; Coccygeal, 1.



Structure (Fig. 638).—

The Spinal Ganglia (ganglion spinale) are collections of nerve cells on the posterior roots of the spinal nerves.

The ganglia consist chiefly of unipolar nerve cells, and from these the fibers of the posterior root take origin—the single process of each cell dividing after a short course into a central fiber which enters the medulla spinalis and a peripheral fiber which runs into the spinal nerve


FIG. 638




Transverse section of spinal ganglion of rabbit. A. Ganglion. X 30. a. Large clear nerve cell. b. Small deeply staining nerve cell. c. Nuclei of capsule. X 250. The lines in the center point to the corresponding cells in the ganglion.



FIG. 796




A portion of the spinal cord, showing its right lateral surface. The dura is opened and arranged to show the nerve roots. (Testut.)




FIG. 797




Distribution of cutaneous nerves. Ventral aspect.




FIG. 798




Distribution of cutaneous nerves. Dorsal aspect.




FIG. 799




Scheme showing structure of a typical spinal nerve.

1. Somatic efferent.

2. Somatic afferent.

3,4,5. Sympathetic efferent.

6,7. Sympathetic afferent.



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6. The Spinal Nerves




6a. The Posterior Divisions


(Rami Posteriores)[/size]



The posterior divisions are as a rule smaller than the anterior. They are directed backward, and, with the exceptions of those of the first cervical, the fourth and fifth sacral, and the coccygeal, divide into medial and lateral branches for the supply of the muscles and skin (Figs. 800, 801, 802) of the posterior part of the trunk.



FIG. 800




Posterior primary divisions of the upper three cervical nerves. (Testut.)




FIG. 801




Diagram of the distribution of the cutaneous branches of the posterior divisions of the spinal nerves




FIG. 802




Areas of distribution of the cutaneous branches of the posterior divisions of the spinal nerves. The areas of the medial branches are in black, those of the lateral in red. (H. M. Johnston.)




The Lumbar Nerves (Nn. Lumbales)—The medial branches of the posterior divisions of the lumbar nerves run close to the articular processes of the vertebræ and end in the Multifidus.


The Sacral Nerves (Nn. Sacrales)—The posterior divisions of the sacral nerves (rami posteriores)(Fig. 803) are small, and diminish in size from above downward; they emerge, except the last, through the posterior sacral foramina. The upper three are covered at their points of exit by the Multifidus, and divide into medial and lateral branches.


FIG. 803




The posterior divisions of the sacral nerves.




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6. The Spinal Nerves


6b. The Anterior Divisions

(Rami Anteriores)



The anterior divisions of the spinal nerves supply the antero-lateral parts of the trunk, and the limbs; they are for the most part larger than the posterior divisions. In the thoracic region they run independently of one another, but in the cervical, lumbar, and sacral regions they unite near their origins to form plexuses.


The Cervical Nerves (Nn. Cervicales)


The anterior divisions of the cervical nerves (rami anteriores), with the exception of the first, pass outward between the Intertransversarii anterior and posterior, lying on the grooved upper surfaces of the transverse processes of the vertebræ. The anterior division of the first or suboccipital nerve issues from the vertebral canal above the posterior arch of the atlas and runs forward around the lateral aspect of its superior articular process, medial to the vertebral artery. In most cases it descends medial to and in front of the Rectus capitis lateralis, but occasionally it pierces the muscle.

The anterior divisions of the upper four cervical nerves unite to form the cervical plexus, and each receives a gray ramus communicans from the superior cervical ganglion of the sympathetic trunk. Those of the lower four cervical, together with the greater part of the first thoracic, form the brachial plexus. They each receive a gray ramus communicans, those for the fifth and sixth being derived from the middle, and those for the seventh and eighth from the lowest, cervical ganglion of the sympathetic trunk.


The Cervical Plexus (plexus cervicalis)(Fig. 804).

—The cervical plexus is formed by the anterior divisions of the upper four cervical nerves; each nerve, except the first, divides into an upper and a lower branch, and the branches unite to form three loops. The plexus is situated oppostie the upper four cervical vertebræ, in front of the Levator scapulæ and Scalenus medius, and covered by the Sternocleidomastoideus.


FIG. 804




Plan of the cervical plexus. (Gerrish.)




Superficial Branches of the Cervical Plexus (Fig. 805).—

The Smaller Occipital Nerve (n. occipitalïs minor; small occipital nerve) arises from the second cervical nerve, sometimes also from the third; it curves around and ascends along the posterior border of the Sternocleidomastoideus


FIG. 805




The nerves of the scalp, face, and side of neck.




FIG. 806




The phrenic nerve and its relations with the vagus nerve.




The Branchial Plexus (plexus brachialis) (Fig. 807).—

The brachial plexus is formed by the union of the anterior divisions of the lower four cervical nerves and the greater part of the anterior division of the first thoracic nerve; the fourth cervical usually gives a branch to the fifth cervical, and the first thoracic frequently receives one from the second thoracic. The plexus extends from the lower part of the side of the neck to the axilla.


FIG. 807




Plan of brachial plexus.



FIG. 808




The right brachial plexus with its short branches, viewed from in front.
The Sternomastoid and Trapezius muscles have been completely, the Omohyoid and Subclavius have been partially, removed; a piece has been sawed out of the clavicle; the Pectoralis muscles have been incised and reflected. (Spalteholz.)





FIG. 809




The right brachial plexus (infraclavicular portion) in the axillary fossa; viewed from below and in front.
The Pectoralis major and minor muscles have been in large part removed; their attachments have been reflected. (Spalteholz.)




FIG. 810





Suprascapular and axillary nerves of right side, seen from behind. (Testut.)




FIG. 811




Cutaneous nerves of right upper extremity. Anterior view.




FIG. 812




Diagram of segmental distribution of the cutaneous nerves of the right upper extremity. Anterior view.




FIG. 813




Cutaneous nerves of right upper extremity. Posterior view.






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Continuación del post anterior...



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FIG. 814




Diagram of segmental distribution of the cutaneous nerves of the right upper extremity. Posterior view.




FIG. 815




Superficial palmar nerves. (Testut.)





FIG. 816




Nerves of the left upper extremity.





FIG. 817





Deep palmar nerves. (Testut.)





FIG. 818




The suprascapular, axillary, and radial nerves.




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